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Sample records for cool stars stellar

  1. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

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    Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

    2017-01-20

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  2. Cool WISPs for stellar cooling excesses

    Energy Technology Data Exchange (ETDEWEB)

    Giannotti, Maurizio [Physical Sciences, Barry University, 11300 NE 2nd Avenue, Miami Shores, FL 33161 (United States); Irastorza, Igor; Redondo, Javier [Departamento de Física Teórica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009, Zaragoza, España (Spain); Ringwald, Andreas, E-mail: mgiannotti@barry.edu, E-mail: igor.irastorza@cern.ch, E-mail: jredondo@unizar.es, E-mail: andreas.ringwald@desy.de [Theory group, Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg (Germany)

    2016-05-01

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC.

  3. Cool WISPs for stellar cooling excesses

    International Nuclear Information System (INIS)

    Giannotti, Maurizio; Irastorza, Igor; Redondo, Javier; Ringwald, Andreas

    2016-01-01

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC.

  4. Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

    Science.gov (United States)

    Barnes, S. A.; Spada, F.; Weingrill, J.

    2016-09-01

    Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

  5. Expanded calculation of weak-interaction-mediated neutrino cooling rates due to 56Ni in stellar matter

    International Nuclear Information System (INIS)

    Nabi, Jameel-Un

    2010-01-01

    An accurate estimate of the neutrino cooling rates is required in order to study the various stages of stellar evolution of massive stars. Neutrino losses from proto-neutron stars play a crucial role in deciding whether these stars would be crushed into black holes or explode as supernovae. Both pure leptonic and weak-interaction processes contribute to the neutrino energy losses in stellar matter. At low temperatures and densities, the characteristics of the early phase of presupernova evolution, cooling through neutrinos produced via the weak interaction, are important. Proton-neutron quasi-particle random phase approximation (pn-QRPA) theory has recently been used with success for the calculation of stellar weak-interaction rates of fp-shell nuclide. The lepton-to-baryon ratio (Y e ) during early phases of stellar evolution of massive stars changes substantially, mainly due to electron captures on 56 Ni. The stellar matter is transparent to the neutrinos produced during the presupernova evolution of massive stars. These neutrinos escape the site and assist the stellar core in maintaining a lower entropy. Here, an expanded calculation of weak-interaction-mediated neutrino and antineutrino cooling rates due to 56 Ni in stellar matter using the pn-QRPA theory is presented. This detailed scale is appropriate for interpolation purposes and is of greater utility for simulation codes. The calculated rates are compared with earlier calculations. During the relevant temperature and density regions of stellar matter the reported rates show few differences compared with the shell model rates and might contribute in fine-tuning of the lepton-to-baryon ratio during the presupernova phases of stellar evolution of massive stars.

  6. The distances of nearby cool carbon stars

    International Nuclear Information System (INIS)

    Bergeat, J.; Sibille, F.; Lunel, M.

    1978-01-01

    Distance ratios are provided for 38 cool carbon stars on the basis of a previous study (Bergeat et al., 1976 a,b,c). The validation of this distance scale is obtained through an analysis of stellar velocities. A relationship is established between proper motions and the distance scale. Luminosities and radii are derived for cool carbon stars which permit a discussion of their evolutionary status. Finally, evaluations are given for the rate of mass ejection corresponding to large graphite grains. (WL) [de

  7. Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation

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    Silich, Sergiy; Tenorio-Tagle, Guillermo

    2018-05-01

    Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds and supernova explosions, or that the enrichment of the residual gas and the formation of the second stellar generation occur so rapidly, that the negative stellar feedback is not significant. Here we continue our study of the early development of star clusters in the extreme environments and discuss the restrictions that strong radiative cooling and stellar mass segregation provide on the gas expulsion from dense star-forming clouds. A large range of physical initial conditions in star-forming clouds which include the star-forming cloud mass, compactness, gas metallicity, star formation efficiency and effects of massive stars segregation are discussed. It is shown that in sufficiently massive and compact clusters hot shocked winds around individual massive stars may cool before merging with their neighbors. This dramatically reduces the negative stellar feedback, prevents the development of the global star cluster wind and expulsion of the residual and the processed matter into the ambient interstellar medium. The critical lines which separate the gas expulsion and the gas retention regimes are obtained.

  8. The evolution of coronal activity in main sequence cool stars

    International Nuclear Information System (INIS)

    Stern, R.A.

    1984-01-01

    Stars spend most of their lifetime and show the least amount of nuclear evolution on the main sequence. However, the x-ray luminosities of cool star coronas change by orders of magnitude as a function of main sequence age. Such coronal evolution is discussed in relation to our knowledge of the solar corona, solar and stellar flares, stellar rotation and binarity. The relevance of X-ray observations to current speculations on stellar dynamos is also considered

  9. APOKASC 2.0: Asteroseismology and Spectroscopy for Cool Stars

    Science.gov (United States)

    Pinsonneault, Marc H.; Elsworth, Yvonne P.; APOKASC

    2017-01-01

    The APOGEE survey has obtained and analyzed high resolution H band spectra of more than 10,000 cool dwarfs and giants in the original Kepler fields. The APOKASC effort combines this data with asteroseismology and star spot studies, resulting in more than 7,000 stellar mass estimates for dwarfs and giants with high quality abundances, temperatures, and surface gravities. We highlight the main results from this effort so far, which include a tight correlation between surface abundances in giants and stellar mass, precise absolute gravity calibrations, and the discovery of unexpected stellar populations, such as young alpha-enhanced stars. We discuss grid modeling estimates for stellar masses and compare the absolute asteroseismic mass scale to calibrators in star clusters and the halo Directions for future efforts are discussed.

  10. Stellar winds and coronae of low-mass Population II/III stars

    Science.gov (United States)

    Suzuki, Takeru K.

    2018-06-01

    We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

  11. Stellar winds and coronae of low-mass Population II/III stars

    Science.gov (United States)

    Suzuki, Takeru K.

    2018-04-01

    We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

  12. On hot and cool stars, spectroscopic investigations in the ultraviolet

    International Nuclear Information System (INIS)

    Hucht, K.A. van der.

    1978-01-01

    Measured ultraviolet stellar spectra are compared with theoretically synthesised spectra. Three A-type and some B-type stars have been observed. The expanding outer layers of cool giants and supergiants are dealt with. K-type and M-type stars are discussed. The problem of the continuous energy distribution of Wolf-Tayet stars derived from observations is considered. (C.F.)

  13. Stellar oscillations in planet-hosting giant stars

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    Hatzes, Artie P; Zechmeister, Mathias [Thueringer Landessternwarte, Sternwarte 5, D-07778 (Germany)], E-mail: artie@tls-tautenburg.de

    2008-10-15

    Recently a number of giant extrasolar planets have been discovered around giant stars. These discoveries are important because many of these giant stars have intermediate masses in the range 1.2-3 Msun. Early-type main sequence stars of this mass range have been avoided by radial velocity planet search surveys due the difficulty of getting the requisite radial velocity precision needed for planet discoveries. Thus, giant stars can tell us about planet formation for stars more massive than the sun. However, the determination of stellar masses for giant stars is difficult due to the fact that evolutionary tracks for stars covering a wide range of masses converge to the same region of the H-R diagram. We report here on stellar oscillations in three planet-hosting giant stars: HD 13189, {beta} Gem, and {iota} Dra. Precise stellar radial velocity measurements for these stars show variations whose periods and amplitudes are consistent with solar-like p-mode oscillations. The implied stellar masses for these objects based on the characteristics of the stellar oscillations are consistent with the predictions of stellar isochrones. An investigation of stellar oscillations in planet hosting giant stars offers us the possibility of getting an independent determination of the stellar mass for these objects which is of crucial importance for extrasolar planet studies.

  14. Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star

    Science.gov (United States)

    Bourrier, Vincent; Lovis, Christophe; Beust, Hervé; Ehrenreich, David; Henry, Gregory W.; Astudillo-Defru, Nicola; Allart, Romain; Bonfils, Xavier; Ségransan, Damien; Delfosse, Xavier; Cegla, Heather M.; Wyttenbach, Aurélien; Heng, Kevin; Lavie, Baptiste; Pepe, Francesco

    2018-01-01

    The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope. Spin–orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars. Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet. We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere.

  15. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

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    Jabran Zahid, H. [Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kudritzki, Rolf-Peter; Ho, I-Ting [University of Hawaii at Manoa, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Conroy, Charlie [Department of Astronomy, Harvard University, Cambridge, MA, 02138 (United States); Andrews, Brett, E-mail: zahid@cfa.harvard.edu [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 (United States)

    2017-09-20

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  16. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

    International Nuclear Information System (INIS)

    Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting; Conroy, Charlie; Andrews, Brett

    2017-01-01

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  17. Towards new generation spectroscopic models of cool stars

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    Bergemann, Maria

    2018-06-01

    Abstract: Spectroscopy is a unique tool to determine the physical parameters of stars. Knowledge of stellar chemical abundances, masses, and ages is the key to understanding the evolution of their host populations. I will focus on the current outstanding problems in spectroscopy of cool stars, which are the most useful objects in studies of our local Galactic neighborhood but also very distant systems, like faint dwarf Spheroidal galaxies. Among the most debated issues is to what extent can we trust the techniques, which rely on the classical assumptions of local thermodynamic equilibrium and hydrostatic balance. I will summarise the ongoing efforts to improve the models of cool stars, with the emphasis on NLTE and 3D modelling. I will then discuss how these exciting observations impact our knowledge of abundances in the Milky Way and in dSph systems, and present outlook for the future studies.

  18. STELLAR ATMOSPHERES, ATMOSPHERIC EXTENSION, AND FUNDAMENTAL PARAMETERS: WEIGHING STARS USING THE STELLAR MASS INDEX

    Energy Technology Data Exchange (ETDEWEB)

    Neilson, Hilding R.; Lester, John B. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4 (Canada); Baron, Fabien; Norris, Ryan; Kloppenborg, Brian, E-mail: neilson@astro.utoronto.ca [Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States)

    2016-10-20

    One of the great challenges of understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology, and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angular diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star’s effective temperature, radius, and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.

  19. Modeling Atmospheric Activity of Cool Stars

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    Schrijver, C. J.

    2003-10-01

    This review discusses a set of simple models for cool-star activity with which we compute (1) photospheric field patterns on stars of different activity levels, (2) the associated outer-atmospheric field configurations, and (3) the soft X-ray emission that is expected to result from the ensemble of loop atmospheres in the coronae of these stars. The model is based on empirically-determined properties of solar activity. It allows us to extrapolate to stars of significantly higher and lower activity than seen on the present-day Sun through its cycle. With it, we can, for example, gain insight into stellar field patterns (including a possible formation mechanism for polar starspots), as well as in the properties of coronal heating (helpful in the identification of the quiescent coronal heating mechanism). Lacking comprehensive theoretical understanding, the model's reliance on empirical solar data means that the multitude of processes involved are approximated to be independent of rotation rate, activity level, and fundamental stellar parameters, or -- where unavoidably necessary -- assumed to simply scale with activity. An evaluation of the most important processes involved guides a discussion of the limits of the model, of the limitations in our knowledge, and of future needs. "I propose to adopt such rules as will ensure the testability of scientific statements; which is to say, their falsifiability." Karl Popper (1902-1994)

  20. Stellar signatures of AGN-jet-triggered star formation

    International Nuclear Information System (INIS)

    Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

    2014-01-01

    To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

  1. Stellar Companions of Exoplanet Host Stars in K2

    Science.gov (United States)

    Matson, Rachel; Howell, Steve; Horch, Elliott; Everett, Mark

    2018-01-01

    Stellar multiplicity has significant implications for the detection and characterization of exoplanets. A stellar companion can mimic the signal of a transiting planet or distort the true planetary radii, leading to improper density estimates and over-predicting the occurrence rates of Earth-sized planets. Determining the fraction of exoplanet host stars that are also binaries allows us to better determine planetary characteristics as well as establish the relationship between binarity and planet formation. Using high-resolution speckle imaging to obtain diffraction limited images of K2 planet candidate host stars we detect stellar companions within one arcsec and up to six magnitudes fainter than the host star. By comparing our observed companion fraction to TRILEGAL star count simulations, and using the known detection limits of speckle imaging, we find the binary fraction of K2 planet host stars to be similar to that of Kepler host stars and solar-type field stars. Accounting for stellar companions in exoplanet studies is therefore essential for deriving true stellar and planetary properties as well as maximizing the returns for TESS and future exoplanet missions.

  2. Rhapsody-G simulations I: the cool cores, hot gas and stellar content of massive galaxy clusters

    International Nuclear Information System (INIS)

    Hahn, Oliver; Martizzi, Davide; Wu, Hao-Yi

    2017-01-01

    We present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the M vir ~10 15 M ⊙ scale. These simulations include cooling and subresolution models for star formation and stellar and supermassive black hole feedback. The sample is selected to capture the whole gamut of assembly histories that produce clusters of similar final mass. We present an overview of the successes and shortcomings of such simulations in reproducing both the stellar properties of galaxies as well as properties of the hot plasma in clusters. In our simulations, a long-lived cool-core/non-cool-core dichotomy arises naturally, and the emergence of non-cool cores is related to low angular momentum major mergers. Nevertheless, the cool-core clusters exhibit a low central entropy compared to observations, which cannot be alleviated by thermal active galactic nuclei feedback. For cluster scaling relations, we find that the simulations match well the M 500 –Y 500 scaling of Planck Sunyaev–Zeldovich clusters but deviate somewhat from the observed X-ray luminosity and temperature scaling relations in the sense of being slightly too bright and too cool at fixed mass, respectively. Stars are produced at an efficiency consistent with abundance-matching constraints and central galaxies have star formation rates consistent with recent observations. In conclusion, while our simulations thus match various key properties remarkably well, we conclude that the shortcomings strongly suggest an important role for non-thermal processes (through feedback or otherwise) or thermal conduction in shaping the intracluster medium.

  3. Hot moons and cool stars

    Directory of Open Access Journals (Sweden)

    Heller René

    2013-04-01

    Full Text Available The exquisite photometric precision of the Kepler space telescope now puts the detection of extrasolar moons at the horizon. Here, we firstly review observational and analytical techniques that have recently been proposed to find exomoons. Secondly, we discuss the prospects of characterizing potentially habitable extrasolar satellites. With moons being much more numerous than planets in the solar system and with most exoplanets found in the stellar habitable zone being gas giants, habitable moons could be as abundant as habitable planets. However, satellites orbiting planets in the habitable zones of cool stars will encounter strong tidal heating and likely appear as hot moons.

  4. The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars

    Science.gov (United States)

    Rayner, John T.; Cushing, Michael C.; Vacca, William D.

    2009-12-01

    We present a 0.8-5 μm spectral library of 210 cool stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of cool stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.

  5. THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

    International Nuclear Information System (INIS)

    Pascucci, I.; Apai, D.; Luhman, K.; Henning, Th.; Bouwman, J.; Meyer, M. R.; Lahuis, F.; Natta, A.

    2009-01-01

    Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks around young Sun-like stars (K1-M5) and cool stars/brown dwarfs (M5-M9). The comparison of these two large samples of over 60 sources reveal major differences in the evolution of both the dust and gas components. We report the first detection of organic molecules in disks around brown dwarfs. The detection rate statistics and the line flux ratios of HCN and C 2 H 2 show a striking difference between the two samples, demonstrating a significant underabundance of HCN relative to C 2 H 2 in the disk surface of cool stars. We propose this to originate from the large difference in the UV irradiation around the two types of sources. The statistical comparison of the 10 μm silicate emission features also reveals a difference between the two samples. Cool stars and brown dwarfs show weaker features arising from more processed silicate grains in the disk atmosphere. These findings complement previous indications of flatter disk structures and longer disk lifetimes around cool stars. Our results highlight important differences in the chemical and physical evolution of protoplanetary disks as a function of stellar mass, temperature, and radiation field which should be taken into account in planet formation models. We note that the different chemistry of preplanetary materials in the disk may also influence the bulk composition and volatile content of the forming planets. In particular, if exogenous HCN has played a key role in the synthesis of prebiotic molecules on Earth as proposed, then prebiotic chemistry may unfold differently on planets around cool stars.

  6. Hot Jupiters and cool stars

    International Nuclear Information System (INIS)

    Villaver, Eva; Mustill, Alexander J.; Livio, Mario; Siess, Lionel

    2014-01-01

    Close-in planets are in jeopardy, as their host stars evolve off the main sequence (MS) to the subgiant and red giant phases. In this paper, we explore the influences of the stellar mass (in the range 1.5-2 M ☉ ), mass-loss prescription, planet mass (from Neptune up to 10 Jupiter masses), and eccentricity on the orbital evolution of planets as their parent stars evolve to become subgiants and red giants. We find that planet engulfment along the red giant branch is not very sensitive to the stellar mass or mass-loss rates adopted in the calculations, but quite sensitive to the planetary mass. The range of initial separations for planet engulfment increases with decreasing mass-loss rates or stellar masses and increasing planetary masses. Regarding the planet's orbital eccentricity, we find that as the star evolves into the red giant phase, stellar tides start to dominate over planetary tides. As a consequence, a transient population of moderately eccentric close-in Jovian planets is created that otherwise would have been expected to be absent from MS stars. We find that very eccentric and distant planets do not experience much eccentricity decay, and that planet engulfment is primarily determined by the pericenter distance and the maximum stellar radius.

  7. Stellar Wind Retention and Expulsion in Massive Star Clusters

    Science.gov (United States)

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2018-05-01

    Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

  8. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    International Nuclear Information System (INIS)

    Daemgen, Sebastian; Bonavita, Mariangela; Jayawardhana, Ray; Lafrenière, David; Janson, Markus

    2015-01-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M ☉ and low-mass stars at ∼0.2 M ☉ . We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M Jup . The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3 −4.9 +6.6 %. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M ☉ appear to be multiple. Higher order multiples were found in 1.8 −1.5 +4.2 % of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively

  9. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Daemgen, Sebastian [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5H 3H4 (Canada); Bonavita, Mariangela [The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Jayawardhana, Ray [Physics and Astronomy, York University, Toronto, Ontario L3T 3R1 (Canada); Lafrenière, David [Department of Physics, University of Montréal, Montréal, QC (Canada); Janson, Markus, E-mail: daemgen@astro.utoronto.ca [Department of Astronomy, Stockholm University, Stockholm (Sweden)

    2015-02-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

  10. Stellar magnetic activity – Star-Planet Interactions

    Directory of Open Access Journals (Sweden)

    Poppenhaeger, K.

    2015-01-01

    Full Text Available Stellar magnetic activity is an important factor in the formation and evolution of exoplanets. Magnetic phenomena like stellar flares, coronal mass ejections, and high-energy emission affect the exoplanetary atmosphere and its mass loss over time. One major question is whether the magnetic evolution of exoplanet host stars is the same as for stars without planets; tidal and magnetic interactions of a star and its close-in planets may play a role in this. Stellar magnetic activity also shapes our ability to detect exoplanets with different methods in the first place, and therefore we need to understand it properly to derive an accurate estimate of the existing exoplanet population. I will review recent theoretical and observational results, as well as outline some avenues for future progress.

  11. MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS

    International Nuclear Information System (INIS)

    Paxton, Bill; Cantiello, Matteo; Bildsten, Lars; Arras, Phil; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

    2013-01-01

    We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ☉ stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results

  12. Mass-loss rates of cool stars

    Science.gov (United States)

    Katrien Els Decin, Leen

    2015-08-01

    Over much of the initial mass function, stars lose a significant fraction of their mass through a stellar wind during the late stages of their evolution when being a (super)giant star. As of today, we can not yet predict the mass-loss rate during the (super)giant phase for a given star with specific stellar parameters from first principles. This uncertainty directly impacts the accuracy of current stellar evolution and population synthesis models that predict the enrichment of the interstellar medium by these stellar winds. Efforts to establish the link between the initial physical and chemical conditions at stellar birth and the mass-loss rate during the (super)giant phase have proceeded on two separate tracks: (1) more detailed studies of the chemical and morpho-kinematical structure of the stellar winds of (super)giant stars in our own Milky Way by virtue of the proximity, and (2) large scale and statistical studies of a (large) sample of stars in other galaxies (such as the LMC and SMC) and globular clusters eliminating the uncertainty on the distance estimate and providing insight into the dependence of the mass-loss rate on the metallicity. In this review, I will present recent results of both tracks, will show how recent measurements confirm (some) theoretical predictions, but also how results from the first track admonish of common misconceptions inherent in the often more simplified analysis used to analyse the large samples from track 2.

  13. THE INFRARED TELESCOPE FACILITY (IRTF) SPECTRAL LIBRARY: COOL STARS

    International Nuclear Information System (INIS)

    Rayner, John T.; Cushing, Michael C.; Vacca, William D.

    2009-01-01

    We present a 0.8-5 μm spectral library of 210 cool stars observed at a resolving power of R ≡ λ/Δλ ∼ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of cool stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.

  14. Planets, stars and stellar systems

    CERN Document Server

    Bond, Howard; McLean, Ian; Barstow, Martin; Gilmore, Gerard; Keel, William; French, Linda

    2013-01-01

    This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in...

  15. Formation of stars and stellar clusters in galactic environment

    OpenAIRE

    Smilgys, Romas

    2018-01-01

    Star and stellar cluster formation in spiral galaxies is one of the biggest questions of astrophysics. In this thesis, I study how star formation, and the formation of stellar clusters, proceeds using SPH simulations. These simulations model a region of 400 pc and 10⁷ solar masses. Star formation is modelled through the use of sink particles which represent small groups of stars. Star formation occurs in high density regions, created by galactic spiral arm passage. The spiral shock compresses...

  16. Effects of stellar evolution and ionizing radiation on the environments of massive stars

    Science.gov (United States)

    Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

    2014-09-01

    We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

  17. ESTIMATION OF DISTANCES TO STARS WITH STELLAR PARAMETERS FROM LAMOST

    Energy Technology Data Exchange (ETDEWEB)

    Carlin, Jeffrey L.; Newberg, Heidi Jo [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Liu, Chao; Deng, Licai; Li, Guangwei; Luo, A-Li; Wu, Yue; Yang, Ming; Zhang, Haotong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Beers, Timothy C. [Department of Physics and JINA: Joint Institute for Nuclear Astrophysics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Chen, Li; Hou, Jinliang; Smith, Martin C. [Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030 (China); Guhathakurta, Puragra [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Hou, Yonghui [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China); Lépine, Sébastien [Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Zheng, Zheng, E-mail: jeffreylcarlin@gmail.com [Department of Physics and Astronomy, University of Utah, UT 84112 (United States)

    2015-07-15

    We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

  18. Modeling tracers of young stellar population age in star-forming galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Levesque, Emily M. [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado 389-UCB, Boulder, CO 80309 (United States); Leitherer, Claus, E-mail: Emily.Levesque@colorado.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  19. STAR FORMATION EFFICIENCY IN THE COOL CORES OF GALAXY CLUSTERS

    International Nuclear Information System (INIS)

    McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher; Rupke, David S. N.

    2011-01-01

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and Hα (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to Hα luminosity, the UV spectral energy distribution, and the far-UV and Hα morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given Hα luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/Hα ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) ∼ 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from ∼0.05 M sun yr -1 in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to ∼5 M sun yr -1 in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, Hα, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14 +18 -8 %. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

  20. Not-so-simple stellar populations in nearby, resolved massive star clusters

    Science.gov (United States)

    de Grijs, Richard; Li, Chengyuan

    2018-02-01

    Around the turn of the last century, star clusters of all kinds were considered ‘simple’ stellar populations. Over the past decade, this situation has changed dramatically. At the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. In this review of where the field has moved to in recent years, we place particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Magellanic Cloud star clusters across the full age range. Our most recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate-age (˜1-3 Gyr old) star clusters, opening up exciting avenues for future research efforts.

  1. MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Paxton, Bill; Cantiello, Matteo; Bildsten, Lars [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States); Arras, Phil [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Brown, Edward F. [Department of Physics and Astronomy, National Superconducting Cyclotron Laboratory, and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48864 (United States); Dotter, Aaron [Research School of Astronomy and Astrophysics, The Australian National University, Weston, ACT 2611 (Australia); Mankovich, Christopher [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Montgomery, M. H. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Stello, Dennis [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Timmes, F. X. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Townsend, Richard, E-mail: matteo@kitp.ucsb.edu [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)

    2013-09-15

    We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M{sub Sun} stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star

  2. Radio stars

    International Nuclear Information System (INIS)

    Hjellming, R.M.; Gibson, D.M.

    1985-01-01

    Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

  3. Neutron stars

    International Nuclear Information System (INIS)

    Irvine, J.M.

    1978-01-01

    The subject is covered in chapters entitled: introduction (resume of stellar evolution, gross characteristics of neutron stars); pulsars (pulsar characteristics, pulsars as neutron stars); neutron star temperatures (neutron star cooling, superfluidity and superconductivity in neutron stars); the exterior of neutron stars (the magnetosphere, the neutron star 'atmosphere', pulses); neutron star structure; neutron star equations of state. (U.K.)

  4. Impacts of WIMP dark matter upon stellar evolution: main-sequence stars

    CERN Document Server

    Scott, Pat; Edsjo, Joakim

    2008-01-01

    The presence of large amounts of WIMP dark matter in stellar cores has been shown to have significant effects upon models of stellar evolution. We present a series of detailed grids of WIMP-influenced stellar models for main sequence stars, computed using the DarkStars code. We describe the changes in stellar structure and main sequence evolution which occur for masses ranging from 0.3 to 2.0 solar masses and metallicities from Z = 0.0003-0.02, as a function of the rate of energy injection by WIMPs. We then go on to show what rates of energy injection can be obtained using realistic orbital parameters for stars near supermassive black holes, including detailed considerations of dark matter halo velocity and density profiles. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits, causing WIMP annihilation to provide up to 100 times the energy of hydrogen fusion in stars at the Galactic centre.

  5. Advanced Spectral Library (ASTRAL): Atomic Fluorescence in Cool, Evolved Stars

    Science.gov (United States)

    Carpenter, Ken G.; Nielsen, Krister E.; Kober, Gladys V.; Rau, Gioia

    2018-01-01

    The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) collected a definitive set of representative, high-resolution (R~46,000 in the FUV up to ~1700 Å, R~30,000 for 1700-2150 Å, and R~114,000 >2150 Å) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and from the Univ. of Colorado (http://casa.colorado.edu/~ayres/ASTRAL/) and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we extend our study of the very rich emission-line spectra of the four evolved K-M stars in the sample, Beta Gem (K0 IIIb), Gamma Dra (K5 III), Gamma Cru (M3.4 III), and Alpha Ori (M2 Iab), to study the atomic fluorescence processes operating in their outer atmospheres. We summarize the pumping transitions and fluorescent line products known on the basis of previous work (e.g. Carpenter 1988, etc.) and newly identified in our current, on-going analysis of these extraordinary ASTRAL STIS spectra.

  6. The Role of Gender in Asking Questions at Cool Stars 18 and 19

    OpenAIRE

    Schmidt, Sarah J.; Douglas, Stephanie; Gosnell, Natalie M.; Muirhead, Philip S.; Booth, Rachel S.; Davenport, James R. A.; Mace, Gregory N.

    2017-01-01

    We examine the gender balance of the 18th and 19th meetings of the Cambridge Workshop on Cool Stellar Systems and the Sun (CS18 and CS19). The percent of female attendees at both meetings (31% at CS18 and 37% at CS19) was higher than the percent of women in the American Astronomical Society (25%) and the International Astronomical Union (18%). The representation of women in Cool Stars as SOC members, invited speakers, and contributed speakers was similar to or exceeded the percent of women at...

  7. The sun as a star: Solar phenomena and stellar applications

    International Nuclear Information System (INIS)

    Noyes, R.W.

    1981-01-01

    Our Sun is a run-of-the-mill star, having no obvious extremes of stellar properties. For this reason it is perhaps more, rather than less, interesting as an astrophysical object, for its sameness to other stars suggests that in studying the Sun, we are studying at close hand common, rather than unusual stellar phenomena. Conversely, comparative study of the Sun and other solar-type stars is an invaluable tool for solar physics, for two reasons: First, it allows us to explore how solar properties and phenomena depend on parameters we cannot vary on the Sun - most fundamentally, rotation rate and mass. Second, study of solar-like stars of different ages allows us to see how stellar and solar phenomena depend on age; study of other stars may be one of the best ways to infer the earlier history of the Sun, as well as its future history. In this review we shall concentrate on phenomena common to the Sun and solar-type (main sequence) stars with different fundamental properties such as mass, age, and rotation. (orig.)

  8. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

    Energy Technology Data Exchange (ETDEWEB)

    Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States); Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David [NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Van Belle, Gerard [Lowell Observatory, Flagstaff, AZ 86001 (United States); Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit [The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States); Muirhead, Philip S. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Lopez-Morales, Mercedes [Institut de Ciencies de L' Espai (CSIC-IEEC), E-08193 Bellaterra (Spain); Ridgway, Stephen [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States); Rojas-Ayala, Barbara [Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); and others

    2012-10-01

    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally

  9. Spiral structure and star formation. II. Stellar lifetimes and cloud kinematics

    International Nuclear Information System (INIS)

    Hausman, M.A.; Roberts, W.W. Jr.

    1984-01-01

    We present further results of our model, introduced in Paper I, of star formation and star-gas interactions in the cloud-dominated ISMs of spiral density wave galaxies. The global density distribution and velocity field of the gas clouds are virtually independent of stellar parameters and even of mean free path for the wide range of values studied, but local density variations are found which superficially resemble cloud complexes. Increasing the average life span of ''spiral tracer'' stellar associations beyond about 20 Myr washes out the spiral pattern which younger associations show. Allowing clouds to form several successive associations (sequential star formation) slightly increases the frequency of interarm, young-star spurs and substantially increases the average star formation rate. The mean velocity field of clouds shows tipped oval streamlines, similar to both continuum gas dynamical models and stellar-kinematic models of spiral density waves. These streamlines are almost ballistic orbits except close to the spiral arms. Newly formed stellar associations leave the spiral density peak with initial tangential velocitie shigher than ''postshock'' values and do not fall back into the ''preshock'' region. By varying our stellar parametes within physically reasonable limits, we may reproduce spiral galaxies with a wide range of morphological appearaces

  10. Rate of formation of neutron stars in the galaxy estimated from stellar statistics

    International Nuclear Information System (INIS)

    Endal, A.S.

    1979-01-01

    Stellar statistics and stellar evolution models can be used to estimate the rate of formation of neutron stars in the Galaxy. A recent analysis by Hills suggests that the mean interval between neutron-star births is greater than 27 years. This is incompatible with estimates based on pulsar statistics. However, a closer examination of the stellar data shows that Hill's result is incorrect. A mean interval between neutron-star births as short as 4 years is consistent with (though certainly not required by) stellar evolution theory

  11. THE RELATION BETWEEN COOL CLUSTER CORES AND HERSCHEL-DETECTED STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Rawle, T. D.; Egami, E.; Rex, M.; Fiedler, A.; Haines, C. P.; Pereira, M. J.; Portouw, J.; Walth, G. [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Edge, A. C. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Smith, G. P. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Altieri, B.; Valtchanov, I. [Herschel Science Centre, ESAC, ESA, P.O. Box 78, Villanueva de la Canada, 28691 Madrid (Spain); Perez-Gonzalez, P. G. [Departamento de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Van der Werf, P. P. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA, Leiden (Netherlands); Zemcov, M., E-mail: trawle@as.arizona.edu [Department of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2012-03-01

    We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500 {mu}m), we calculate the obscured star formation rate (SFR). 22{sup +6.2}{sub -5.3}% of the BCGs are detected in the far-infrared, with SFR = 1-150 M{sub Sun} yr{sup -1}. The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing H{alpha} emission is also correlated with obscured star formation. For all but the most luminous BCGs (L{sub TIR} > 2 Multiplication-Sign 10{sup 11} L{sub Sun }), only a small ({approx}<0.4 mag) reddening correction is required for SFR(H{alpha}) to agree with SFR{sub FIR}. The relatively low H{alpha} extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.

  12. Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars

    International Nuclear Information System (INIS)

    Barklem, Paul S

    2012-01-01

    The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H ↔ X(n'l') + H and charge transfer processes X(nl) + H ↔ X + + H − have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. [4]. Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.

  13. An improved age-activity relationship for cool stars older than a gigayear

    DEFF Research Database (Denmark)

    Booth, R. S.; Poppenhaeger, K.; Watson, C. A.

    2017-01-01

    Stars with convective envelopes display magnetic activity, which decreases over time due to the magnetic braking of the star. This age dependence of magnetic activity is well studied for younger stars, but the nature of this dependence for older stars is not well understood. This is mainly because...... absolute stellar ages for older stars are hard to measure. However, relatively accurate stellar ages have recently come into reach through asteroseismology. In this work, we present X-ray luminosities, which are a measure for magnetic activity displayed by the stellar coronae, for 24 stars with well......-determined ages older than a gigayear. We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by the stellar surface area, and age that is steeper than the relationships found for younger...

  14. Stellar winds

    International Nuclear Information System (INIS)

    Weymann, R.J.

    1978-01-01

    It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

  15. The Birth of a Galaxy: Primordial Metal Enrichment and Stellar Populations

    Science.gov (United States)

    Wise, John H.; Turk, Matthew J.; Norman, Michael L.; Abel, Tom

    2012-01-01

    By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10-6-10-3.5 Z ⊙. We present an adaptive mesh refinement radiation hydrodynamics simulation that follows the transition from Population III to Population II star formation. The maximum spatial resolution of 1 comoving parsec allows for individual molecular clouds to be well resolved and their stellar associations to be studied in detail. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5% to nearly the cosmic fraction in halos with merger histories rich in halos above 107 M ⊙. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10-3 Z ⊙ and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyα systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.

  16. FIRST ZEEMAN DOPPLER IMAGING OF A COOL STAR USING ALL FOUR STOKES PARAMETERS

    International Nuclear Information System (INIS)

    Rosén, L.; Kochukhov, O.; Wade, G. A.

    2015-01-01

    Magnetic fields are ubiquitous in active cool stars, but they are in general complex and weak. Current Zeeman Doppler imaging (ZDI) studies of cool star magnetic fields chiefly employ circular polarization observations because linear polarization is difficult to detect and requires a more sophisticated radiative transfer modeling to interpret. But it has been shown in previous theoretical studies, and in the observational analyses of magnetic Ap stars, that including linear polarization in the magnetic inversion process makes it possible to correctly recover many otherwise lost or misinterpreted magnetic features. We have obtained phase-resolved observations in all four Stokes parameters of the RS CVn star II Peg at two separate epochs. Here we present temperature and magnetic field maps reconstructed for this star using all four Stokes parameters. This is the very first such ZDI study of a cool active star. Our magnetic inversions reveal a highly structured magnetic field topology for both epochs. The strength of some surface features is doubled or even quadrupled when linear polarization is taken into account. The total magnetic energy of the reconstructed field map also becomes about 2.1–3.5 times higher. The overall complexity is also increased as the field energy is shifted toward higher harmonic modes when four Stokes parameters are used. As a consequence, the potential field extrapolation of the four Stokes parameter ZDI results indicates that magnetic field becomes weaker at a distance of several stellar radii due to a decrease of the large-scale field component

  17. Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

    Energy Technology Data Exchange (ETDEWEB)

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

    2014-06-01

    A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

  18. Stellar and wind parameters of massive stars from spectral analysis

    Science.gov (United States)

    Araya, Ignacio; Curé, Michel

    2017-11-01

    The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

  19. The DarkStars code: a publicly available dark stellar evolution package

    CERN Document Server

    Scott, Pat; Fairbairn, Malcolm

    2009-01-01

    We announce the public release of the 'dark' stellar evolution code DarkStars. The code simultaneously solves the equations of WIMP capture and annihilation in a star with those of stellar evolution assuming approximate hydrostatic equilibrium. DarkStars includes the most extensive WIMP microphysics of any dark evolution code to date. The code employs detailed treatments of the capture process from a range of WIMP velocity distributions, as well as composite WIMP distribution and conductive energy transport schemes based on the WIMP mean-free path in the star. We give a brief description of the input physics and practical usage of the code, as well as examples of its application to dark stars at the Galactic centre.

  20. A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars within 30 pc

    Energy Technology Data Exchange (ETDEWEB)

    Hinkel, Natalie R.; Somers, Garrett [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Mamajek, Eric E. [Jet Propulsion Laboratory, California Institute of Technology, M/S 321-100, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Turnbull, Margaret C. [Global Science Institute, P.O. Box 252, Antigo, WI 54409 (United States); Osby, Ella; Shkolnik, Evgenya L.; Desch, Steven J. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Smith, Graeme H. [University of California Observatories and Department of Astronomy and Astrophysics, University of California, Santa Cruz CA 95064 (United States); Klimasewski, Alexis, E-mail: natalie.hinkel@gmail.com [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627-0171 (United States)

    2017-10-10

    Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet’s mass and radius demand accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (<30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca ii H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT , XMM, and Chandra . We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate that CATSUP will be useful for discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk versus thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.

  1. A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars within 30 pc

    International Nuclear Information System (INIS)

    Hinkel, Natalie R.; Somers, Garrett; Mamajek, Eric E.; Turnbull, Margaret C.; Osby, Ella; Shkolnik, Evgenya L.; Desch, Steven J.; Smith, Graeme H.; Klimasewski, Alexis

    2017-01-01

    Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet’s mass and radius demand accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (<30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca ii H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT , XMM, and Chandra . We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate that CATSUP will be useful for discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk versus thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.

  2. Cooling of Accretion-Heated Neutron Stars

    Science.gov (United States)

    Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

    2017-09-01

    We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

  3. Old star clusters: Bench tests of low mass stellar models

    Directory of Open Access Journals (Sweden)

    Salaris M.

    2013-03-01

    Full Text Available Old star clusters in the Milky Way and external galaxies have been (and still are traditionally used to constrain the age of the universe and the timescales of galaxy formation. A parallel avenue of old star cluster research considers these objects as bench tests of low-mass stellar models. This short review will highlight some recent tests of stellar evolution models that make use of photometric and spectroscopic observations of resolved old star clusters. In some cases these tests have pointed to additional physical processes efficient in low-mass stars, that are not routinely included in model computations. Moreover, recent results from the Kepler mission about the old open cluster NGC6791 are adding new tight constraints to the models.

  4. Stellar magnetic activity

    International Nuclear Information System (INIS)

    Schrijver, C.J.

    1986-01-01

    The stellar emission in the chromospheric Ca II H+K lines is compared with the coronal soft X-ray emission, measuring the effects of non-radiative heating in the outer atmosphere at temperatures differing two orders of magnitude. The comparison of stellar flux densities in Ca II H+K and X-rays is extended to fluxes from the transition-region and the high-temperature chromosphere. The stellar magnetic field is probably generated in the differentially rotating convective envelope. The relation between rotation rate and the stellar level of activity measured in chromospheric, transition-region, and coronal radiative diagnostics is discovered. X-ray observations of the binary λ Andromedae are discussed. The departure of M-type dwarfs from the main relations, and the implications for the structure of the chromospheres of these stars are discussed. Variations of the average surface flux densities of the Sun during the 11-year activity cycle agree with flux-flux relations derived for other cool stars, suggesting that the interpretation of the stellar relations may be furthered by studying the solar analogue in more detail. (Auth.)

  5. Axisymmetric general relativistic hydrodynamics: Long-term evolution of neutron stars and stellar collapse to neutron stars and black holes

    International Nuclear Information System (INIS)

    Shibata, Masaru

    2003-01-01

    We report a new implementation for axisymmetric simulation in full general relativity. In this implementation, the Einstein equations are solved using the Nakamura-Shibata formulation with the so-called cartoon method to impose an axisymmetric boundary condition, and the general relativistic hydrodynamic equations are solved using a high-resolution shock-capturing scheme based on an approximate Riemann solver. As tests, we performed the following simulations: (i) long-term evolution of nonrotating and rapidly rotating neutron stars, (ii) long-term evolution of neutron stars of a high-amplitude damping oscillation accompanied with shock formation, (iii) collapse of unstable neutron stars to black holes, and (iv) stellar collapses to neutron stars. Tests (i)-(iii) were carried out with the Γ-law equation of state, and test (iv) with a more realistic parametric equation of state for high-density matter. We found that this new implementation works very well: It is possible to perform the simulations for stable neutron stars for more than 10 dynamical time scales, to capture strong shocks formed at stellar core collapses, and to accurately compute the mass of black holes formed after the collapse and subsequent accretion. In conclusion, this implementation is robust enough to apply to astrophysical problems such as stellar core collapse of massive stars to a neutron star, and black hole, phase transition of a neutron star to a high-density star, and accretion-induced collapse of a neutron star to a black hole. The result for the first simulation of stellar core collapse to a neutron star started from a realistic initial condition is also presented

  6. THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS

    International Nuclear Information System (INIS)

    Wise, John H.; Turk, Matthew J.; Norman, Michael L.; Abel, Tom

    2012-01-01

    By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10 –6 -10 –3.5 Z ☉ . We present an adaptive mesh refinement radiation hydrodynamics simulation that follows the transition from Population III to Population II star formation. The maximum spatial resolution of 1 comoving parsec allows for individual molecular clouds to be well resolved and their stellar associations to be studied in detail. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5% to nearly the cosmic fraction in halos with merger histories rich in halos above 10 7 M ☉ . A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10 –3 Z ☉ and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyα systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t–Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.

  7. Stellar activity for every TESS star in the Southern sky

    Science.gov (United States)

    Howard, Ward S.; Law, Nicholas; Fors, Octavi; Corbett, Henry T.; Ratzloff, Jeff; del Ser, Daniel

    2018-01-01

    Although TESS will search for Earths around more than 200,000 nearby stars, the life-impacting superflare occurrence of these stars remains poorly characterized. We monitor long-term stellar flare occurrence for every TESS star in the accessible sky at 2-minute cadence with the CTIO-based Evryscope, a combination of twenty-four telescopes, together giving instantaneous sky coverage of 8000 square degrees. In collaboration with Owens Valley Long Wavelength Array (LWA) all-sky monitoring, Evryscope also provides optical counterparts to radio flare, CME, and exoplanet-magnetosphere stellar activity searches. A Northern Evryscope will be installed at Mount Laguna Observatory, CA in collaboration with SDSU later this year, enabling stellar activity characterization for the full TESS target list and both continuous viewing zones, as well as providing 100% overlap with LWA radio activity. Targets of interest (e.g. Proxima Cen, TRAPPIST-1) are given special focus. We are currently sensitive to stellar activity down to 1% precision at g' ~ 10 and about 0.2 of a magnitude at g' ~ 15. With 2-minute cadence and a projected 5-year timeline, with 2+ years already recorded, we present preliminary results from an activity characterization of every Southern TESS target.

  8. The incidence of stellar mergers and mass gainers among massive stars

    International Nuclear Information System (INIS)

    De Mink, S. E.; Sana, H.; Langer, N.; Izzard, R. G.; Schneider, F. R. N.

    2014-01-01

    Because the majority of massive stars are born as members of close binary systems, populations of massive main-sequence stars contain stellar mergers and products of binary mass transfer. We simulate populations of massive stars accounting for all major binary evolution effects based on the most recent binary parameter statistics and extensively evaluate the effect of model uncertainties. Assuming constant star formation, we find that 8 −4 +9 % of a sample of early-type stars are the products of a merger resulting from a close binary system. In total we find that 30 −15 +10 % of massive main-sequence stars are the products of binary interaction. We show that the commonly adopted approach to minimize the effects of binaries on an observed sample by excluding systems detected as binaries through radial velocity campaigns can be counterproductive. Systems with significant radial velocity variations are mostly pre-interaction systems. Excluding them substantially enhances the relative incidence of mergers and binary products in the non-radial velocity variable sample. This poses a challenge for testing single stellar evolutionary models. It also raises the question of whether certain peculiar classes of stars, such as magnetic O stars, are the result of binary interaction and it emphasizes the need to further study the effect of binarity on the diagnostics that are used to derive the fundamental properties (star-formation history, initial mass function, mass-to-light ratio) of stellar populations nearby and at high redshift.

  9. Star-disc interaction in galactic nuclei: formation of a central stellar disc

    Science.gov (United States)

    Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

    2018-05-01

    We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

  10. Molecules in stars

    International Nuclear Information System (INIS)

    Tsuji, T.

    1986-01-01

    Recently, research related to molecules in stars has rapidly expanded because of progress in related fields. For this reason, it is almost impossible to cover all the topics related to molecules in stars. Thus, here the authors focus their attention on molecules in the atmospheres of cool stars and do not cover in any detail topics related to circumstellar molecules originating from expanding envelopes located far from the stellar surface. However, the authors do discuss molecules in quasi-static circumstellar envelopes (a recently discovered new component of circumstellar envelopes) located near the stellar surface, since molecular lines originating from such envelopes show little velocity shift relative to photospheric lines, and hence they directly affect the interpretation and analysis of stellar spectra

  11. Stellar aspects of habitability--characterizing target stars for terrestrial planet-finding missions.

    Science.gov (United States)

    Kaltenegger, Lisa; Eiroa, Carlos; Ribas, Ignasi; Paresce, Francesco; Leitzinger, Martin; Odert, Petra; Hanslmeier, Arnold; Fridlund, Malcolm; Lammer, Helmut; Beichman, Charles; Danchi, William; Henning, Thomas; Herbst, Tom; Léger, Alain; Liseau, René; Lunine, Jonathan; Penny, Alan; Quirrenbach, Andreas; Röttgering, Huub; Selsis, Frank; Schneider, Jean; Stam, Daphne; Tinetti, Giovanna; White, Glenn J

    2010-01-01

    We present and discuss the criteria for selecting potential target stars suitable for the search for Earth-like planets, with a special emphasis on the stellar aspects of habitability. Missions that search for terrestrial exoplanets will explore the presence and habitability of Earth-like exoplanets around several hundred nearby stars, mainly F, G, K, and M stars. The evaluation of the list of potential target systems is essential in order to develop mission concepts for a search for terrestrial exoplanets. Using the Darwin All Sky Star Catalogue (DASSC), we discuss the selection criteria, configuration-dependent subcatalogues, and the implication of stellar activity for habitability.

  12. Clementine Star Tracker Stellar Compass: Final report part 1

    Energy Technology Data Exchange (ETDEWEB)

    Priest, R.E.; Kordas, J.F.; Lewis, I.T. [and others

    1995-07-01

    The Clementine mission provided the first ever complete, systematic surface mapping of the moon from the ultra-violet to the near-infrared regions. More than 1.7 million images of the moon, earth and space were returned from this mission. Two star stracker stellar compasses (star tracker camera + stellar compass software) were included on the spacecraft, serving a primary function of providing angle updates to the guidance and navigation system. These cameras served a secondary function by providing a wide field of view imaging capability for lunar horizon glow and other dark-side imaging data. This 290 g camera using a 576 x 384 focal plane array and a 17 mm entrance pupil, detected and centroided stars as dim and dimmer than 4.5 m{sub v}, providing rms pointing accuracy of better than 100 {mu}rad pitch and yaw and 450 {mu}rad roll. A description of this light-weight, low power star tracker camera along with a summary of lessons learned is presented. Design goals and preliminary on-orbit performance estimates are addressed in terms of meeting the mission`s primary objective for flight qualifying the sensors for future Department of Defense flights. Documentation generated during the design, analysis, build, test and characterization of the star tracker cameras are presented. Collectively, this documentation represents a small library of information for this camera, and may be used as a framework for producing copy units by commercial enterprises, and therefore satisfies a Department of Defense and Department of Energy goal to transfer technology to industry. However, the considerable knowledge gained from the experience of the individuals involved in the system trades, design, analysis, production, testing and characterization of the star tracker stellar compass is not contained in this documentation.

  13. Formation of new stellar populations from gas accreted by massive young star clusters.

    Science.gov (United States)

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  14. A system of three transiting super-Earths in a cool dwarf star

    Science.gov (United States)

    Díez Alonso, E.; Suárez& Gómez, S. L.; González Hernández, J. I.; Suárez Mascareño, A.; González Gutiérrez, C.; Velasco, S.; Toledo-Padrón, B.; de Cos Juez, F. J.; Rebolo, R.

    2018-05-01

    We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High-resolution spectra obtained with High Accuracy Radial velocity Planet Searcher-North/Telescopio Nazionale Galileo (HARPS-N/TNG) showed that the star is a mid-late K dwarf. Using spectral synthesis models, we infer its effective temperature, surface gravity, and metallicity, and subsequently determined from evolutionary models a stellar radius of 0.58 R⊙. The planets have radii of 1.8, 2.6, and 1.9 R⊕ and orbital periods of 6.34, 13.85, and 40.72 d. High-resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 au, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky-gaseous threshold, their atmospheres, internal structure, composition, and interactions with host stars.

  15. Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

    Science.gov (United States)

    Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

    2018-01-01

    We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

  16. RECONCILING THE OBSERVED STAR-FORMING SEQUENCE WITH THE OBSERVED STELLAR MASS FUNCTION

    International Nuclear Information System (INIS)

    Leja, Joel; Van Dokkum, Pieter G.; Franx, Marijn; Whitaker, Katherine E.

    2015-01-01

    We examine the connection between the observed star-forming sequence (SFR ∝ M α ) and the observed evolution of the stellar mass function in the range 0.2 < z < 2.5. We find that the star-forming sequence cannot have a slope α ≲ 0.9 at all masses and redshifts because this would result in a much higher number density at 10 < log (M/M ☉ ) < 11 by z = 1 than is observed. We show that a transition in the slope of the star-forming sequence, such that α = 1 at log (M/M ☉ ) < 10.5 and α = 0.7-0.13z (Whitaker et al.) at log (M/M ☉ ) > 10.5, greatly improves agreement with the evolution of the stellar mass function. We then derive a star-forming sequence that reproduces the evolution of the mass function by design. This star-forming sequence is also well described by a broken power law, with a shallow slope at high masses and a steep slope at low masses. At z = 2, it is offset by ∼0.3 dex from the observed star-forming sequence, consistent with the mild disagreement between the cosmic star formation rate (SFR) and recent observations of the growth of the stellar mass density. It is unclear whether this problem stems from errors in stellar mass estimates, errors in SFRs, or other effects. We show that a mass-dependent slope is also seen in other self-consistent models of galaxy evolution, including semianalytical, hydrodynamical, and abundance-matching models. As part of the analysis, we demonstrate that neither mergers nor hidden low-mass quiescent galaxies are likely to reconcile the evolution of the mass function and the star-forming sequence. These results are supported by observations from Whitaker et al

  17. Star Classification for the Kepler Input Catalog: From Images to Stellar Parameters

    Science.gov (United States)

    Brown, T. M.; Everett, M.; Latham, D. W.; Monet, D. G.

    2005-12-01

    The Stellar Classification Project is a ground-based effort to screen stars within the Kepler field of view, to allow removal of stars with large radii (and small potential transit signals) from the target list. Important components of this process are: (1) An automated photometry pipeline estimates observed magnitudes both for target stars and for stars in several calibration fields. (2) Data from calibration fields yield extinction-corrected AB magnitudes (with g, r, i, z magnitudes transformed to the SDSS system). We merge these with 2MASS J, H, K magnitudes. (3) The Basel grid of stellar atmosphere models yields synthetic colors, which are transformed to our photometric system by calibration against observations of stars in M67. (4) We combine the r magnitude and stellar galactic latitude with a simple model of interstellar extinction to derive a relation connecting {Teff, luminosity} to distance and reddening. For models satisfying this relation, we compute a chi-squared statistic describing the match between each model and the observed colors. (5) We create a merit function based on the chi-squared statistic, and on a Bayesian prior probability distribution which gives probability as a function of Teff, luminosity, log(Z), and height above the galactic plane. The stellar parameters ascribed to a star are those of the model that maximizes this merit function. (6) Parameter estimates are merged with positional and other information from extant catalogs to yield the Kepler Input Catalog, from which targets will be chosen. Testing and validation of this procedure are underway, with encouraging initial results.

  18. StarNet: An application of deep learning in the analysis of stellar spectra

    Science.gov (United States)

    Kielty, Collin; Bialek, Spencer; Fabbro, Sebastien; Venn, Kim; O'Briain, Teaghan; Jahandar, Farbod; Monty, Stephanie

    2018-06-01

    In an era when spectroscopic surveys are capable of collecting spectra for hundreds of thousands of stars, fast and efficient analysis methods are required to maximize scientific impact. These surveys provide a homogeneous database of stellar spectra that are ideal for machine learning applications. In this poster, we present StarNet: a convolutional neural network model applied to the analysis of both SDSS-III APOGEE DR13 and synthetic stellar spectra. When trained on synthetic spectra alone, the calculated stellar parameters (temperature, surface gravity, and metallicity) are of excellent precision and accuracy for both APOGEE data and synthetic data, over a wide range of signal-to-noise ratios. While StarNet was developed using the APOGEE observed spectra and corresponding ASSeT synthetic grid, we suggest that this technique is applicable to other spectral resolutions, spectral surveys, and wavelength regimes. As a demonstration of this, we present a StarNet model trained on lower resolution, R=6000, IR synthetic spectra, describing the spectra delivered by Gemini/NIFS and the forthcoming Gemini/GIRMOS instrument (PI Sivanandam, UToronto). Preliminary results suggest that the stellar parameters determined from this low resolution StarNet model are comparable in precision to the high-resolution APOGEE results. The success of StarNet at lower resolution can be attributed to (1) a large training set of synthetic spectra (N ~200,000) with a priori stellar labels, and (2) the use of the entire spectrum in the solution rather than a few weighted windows, which are common methods in other spectral analysis tools (e.g. FERRE or The Cannon). Remaining challenges in our StarNet applications include rectification, continuum normalization, and wavelength coverage. Solutions to these problems could be used to guide decisions made in the development of future spectrographs, spectroscopic surveys, and data reduction pipelines, such as for the future MSE.

  19. Clustered star formation and the origin of stellar masses.

    Science.gov (United States)

    Pudritz, Ralph E

    2002-01-04

    Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation.

  20. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    International Nuclear Information System (INIS)

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P.; Yates, R. M.

    2013-01-01

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using ∼150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses 10 M ☉ . There is a sharp transition in the relation at a stellar mass of 10 10 M ☉ . At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10 10 M ☉ is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.

  1. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P. [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822 (United States); Yates, R. M. [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

    2013-02-15

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using {approx}150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses <10{sup 10} M {sub Sun }. There is a sharp transition in the relation at a stellar mass of 10{sup 10} M {sub Sun }. At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10{sup 10} M {sub Sun} is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.

  2. Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars

    OpenAIRE

    Frebel, Anna

    2010-01-01

    The abundance patterns of the most metal-poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, these old survivors allow us to study the nature of the first stars and supernovae, the relevant nucleosynthesis processes responsible for the formation and evolution of the elements, early star- and galaxy formation processes, as well as the assembly process of the stellar halo from dwarf galaxies a long time ago. T...

  3. Stellar C III Emissions as a New Classification Parameter for (WC) Central Stars

    Science.gov (United States)

    Feibelman, W. A.

    1999-01-01

    We report detection of stellar C III lambda 1909 emission in International Ultraviolet Explorer (IUE) echelle spectra of early-type [WC] planetary nebula central stars (CSPNs). Additionally, stellar C III emission at lambda 2297 is observed in early- and late-type [WC) CSPNS. Inclusion of these C III features for abundance determinations may resolve a conflict of underabundance of C/O for early type [WC2] - [WC4] CSPNS. A linear dependence on stellar C III lambda 2297 equivalent widths can be used to indicate a new classification of type [WCUV] central stars.

  4. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B. [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); De Mink, S. E. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); De Koter, A.; Sana, H. [Astronomical Institute " Anton Pannekoek" , Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands); Gvaramadze, V. V. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992 (Russian Federation); Liermann, A., E-mail: fschneid@astro.uni-bonn.de [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2014-01-10

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range

  5. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    International Nuclear Information System (INIS)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >De Koter, A.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >Sana, H.; Gvaramadze, V. V.; Liermann, A.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ☉ limit and observations of four stars with initial masses of 165-320 M ☉ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ☉ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ☉ .

  6. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    Science.gov (United States)

    Schneider, F. R. N.; Izzard, R. G.; de Mink, S. E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V. V.; Hußmann, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ⊙ limit and observations of four stars with initial masses of 165-320 M ⊙ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ⊙ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ⊙.

  7. Comparative Modelling of the Spectra of Cool Giants

    Science.gov (United States)

    Lebzelter, T.; Heiter, U.; Abia, C.; Eriksson, K.; Ireland, M.; Neilson, H.; Nowotny, W; Maldonado, J; Merle, T.; Peterson, R.; hide

    2012-01-01

    Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are.

  8. ASSESSMENT OF STELLAR STRATIFICATION IN THREE YOUNG STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gouliermis, Dimitrios A.; Rochau, Boyke; Mackey, Dougal; Xin Yu

    2010-01-01

    We present a comprehensive study of stellar stratification in young star clusters in the Large Magellanic Cloud (LMC). We apply our recently developed effective radius method for the assessment of stellar stratification on imaging data obtained with the Advanced Camera for Surveys of three young LMC clusters to characterize the phenomenon and develop a comparative scheme for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC 2002, and NGC 2010, are selected on the basis of their youthfulness, and their variety in appearance, structure, stellar content, and surrounding stellar ambient. Our photometry is complete for magnitudes down to m 814 ≅ 23 mag, allowing the calculation of the structural parameters of the clusters, the estimation of their ages, and the determination of their stellar content. Our study shows that each cluster in our sample demonstrates stellar stratification in a quite different manner and at different degree from the others. Specifically, NGC 1983 shows partial segregation, with the effective radius increasing with fainter magnitudes only for the faintest stars of the cluster. Our method on NGC 2002 provides evidence of strong stellar stratification for both bright and faint stars; the cluster demonstrates the phenomenon with the highest degree in the sample. Finally, NGC 2010 is not segregated, as its bright stellar content is not centrally concentrated, the relation of effective radius to magnitude for stars of intermediate brightness is rather flat, and we find no evidence of stratification for its faintest stars. For the parameterization of the phenomenon of stellar stratification and its quantitative comparison among these clusters, we propose the slope derived from the change in the effective radius over the corresponding magnitude range as indicative parameter of the degree of stratification in the clusters. A positive value of this slope indicates mass segregation in the cluster, while a negative or zero value

  9. Abundance analyses of thirty cool carbon stars

    International Nuclear Information System (INIS)

    Utsumi, Kazuhiko

    1985-01-01

    The results were previously obtained by use of the absolute gf-values and the cosmic abundance as a standard. These gf-values were found to contain large systematic errors, and as a result, the solar photospheric abundances were revised. Our previous results, therefore, must be revised by using new gf-values, and abundance analyses are extended for as many carbon stars as possible. In conclusion, in normal cool carbon stars heavy metals are overabundant by factors of 10 - 100 and rare-earth elements are overabundant by a factor of about 10, and in J-type cool carbon stars, C 12 /C 13 ratio is smaller, C 2 and CN bands and Li 6708 are stronger than in normal cool carbon stars, and the abundances of s-process elements with respect to Fe are nearly normal. (Mori, K.)

  10. The Prospect for Detecting Stellar Coronal Mass Ejections

    Science.gov (United States)

    Osten, Rachel A.; Crosley, Michael Kevin

    2018-06-01

    The astrophysical study of mass loss, both steady-state and transient, on the cool half of the HR diagram has implications bothfor the star itself and the conditions created around the star that can be hospitable or inimical to supporting life. Recent results from exoplanet studies show that planets around M dwarfs are exceedingly common, which together with the commonality of M dwarfs in our galaxy make this the dominant mode of star and planet configurations. The closeness of the exoplanets to the parent M star motivate a comprehensive understanding of habitability for these systems. Radio observations provide the most clear signature of accelerated particles and shocks in stars arising as the result of MHD processes in the stellar outer atmosphere. Stellar coronal mass ejections have not been conclusively detected, despite the ubiquity with which their radiative counterparts in an eruptive event (stellar flares) have. I will review some of the different observational methods which have been used and possibly could be used in the future in the stellar case, emphasizing some of the difficulties inherent in such attempts. I will provide a framework for interpreting potential transient stellar mass loss in light of the properties of flares known to occur on magnetically active stars. This uses a physically motivated way to connect the properties of flares and coronal mass ejections and provides a testable hypothesis for observing or constraining transient stellar mass loss. I will describe recent results using radio observations to detect stellar coronal mass ejections, and what those results imply about transient stellar mass loss. I will provide some motivation for what could be learned in this topic from space-based low frequency radio experiments.

  11. Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars. I. Classifying Low-Mass Host Stars Observed During Campaigns 1-7

    Science.gov (United States)

    Dressing, Courtney D.; Newton, Elisabeth R.; Schlieder, Joshua E.; Charbomeau, David; Krutson, Heather A.; Vanderburg, Andrew; Sinukoff, Evan

    2017-01-01

    We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3-M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 solar radius (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.

  12. Investigating stellar surface rotation using observations of starspots

    DEFF Research Database (Denmark)

    Korhonen, Heidi Helena

    2011-01-01

    Rapid rotation enhances the dynamo operating in stars, and thus also introduces significantly stronger magnetic activity than is seen in slower rotators. Many young cool stars still have the rapid, primordial rotation rates induced by the interstellar molecular cloud from which they were formed....... Also older stars in close binary systems are often rapid rotators. These types of stars can show strong magnetic activity and large starspots. In the case of large starspots which cause observable changes in the brightness of the star, and even in the shapes of the spectral line profiles, one can get...... information on the rotation of the star. At times even information on the spot rotation at different stellar latitudes can be obtained, similarly to the solar surface differential rotation measurements using magnetic features as tracers. Here, I will review investigations of stellar rotation based...

  13. Gravitational Waves from Stellar Black Hole Binaries and the Impact on Nearby Sun-like Stars

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Ilídio [Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Silk, Joseph, E-mail: ilidio.lopes@tecnico.ulisboa.pt, E-mail: silk@astro.ox.ac.uk [Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, Paris F-75014 (France)

    2017-07-20

    We investigate the impact of resonant gravitational waves on quadrupole acoustic modes of Sun-like stars located nearby stellar black hole binary systems (such as GW150914 and GW151226). We find that the stimulation of the low-overtone modes by gravitational radiation can lead to sizeable photometric amplitude variations, much larger than the predictions for amplitudes driven by turbulent convection, which in turn are consistent with the photometric amplitudes observed in most Sun-like stars. For accurate stellar evolution models, using up-to-date stellar physics, we predict photometric amplitude variations of 1–10{sup 3} ppm for a solar mass star located at a distance between 1 au and 10 au from the black hole binary and belonging to the same multi-star system. The observation of such a phenomenon will be within the reach of the Plato mission because the telescope will observe several portions of the Milky Way, many of which are regions of high stellar density with a substantial mixed population of Sun-like stars and black hole binaries.

  14. KNOW THE STAR, KNOW THE PLANET. V. CHARACTERIZATION OF THE STELLAR COMPANION TO THE EXOPLANET HOST STAR HD 177830

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Lewis C. Jr.; Beichman, Charles; Burruss, Rick; Cady, Eric; Lockhart, Thomas G. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109 (United States); Oppenheimer, Rebecca; Brenner, Douglas; Luszcz-Cook, Statia; Nilsson, Ricky [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Baranec, Christoph [Institute for Astronomy, University of Hawai‘i at Mānoa, Hilo, HI 96720-2700 (United States); Dekany, Richard; Hillenbrand, Lynne [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Hinkley, Sasha [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); King, David; Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road., Cambridge, CB3 OHA (United Kingdom); Pueyo, Laurent [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sivaramakrishnan, Anand; Soummer, Rémi [Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, SE-10691 Stockholm (Sweden); Rice, Emily L., E-mail: lewis.c.roberts@jpl.nasa.gov [Department of Engineering Science and Physics, College of Staten Island, City University of New York, Staten Island, NY 10314 (United States); and others

    2015-10-15

    HD 177830 is an evolved K0IV star with two known exoplanets. In addition to the planetary companions it has a late-type stellar companion discovered with adaptive optics imagery. We observed the binary star system with the PHARO near-IR camera and the Project 1640 coronagraph. Using the Project 1640 coronagraph and integral field spectrograph we extracted a spectrum of the stellar companion. This allowed us to determine that the spectral type of the stellar companion is a M4 ± 1 V. We used both instruments to measure the astrometry of the binary system. Combining these data with published data, we determined that the binary star has a likely period of approximately 800 years with a semimajor axis of 100–200 AU. This implies that the stellar companion has had little or no impact on the dynamics of the exoplanets. The astrometry of the system should continue to be monitored, but due to the slow nature of the system, observations can be made once every 5–10 years.

  15. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  16. STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

    Energy Technology Data Exchange (ETDEWEB)

    Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

    2015-03-01

    Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

  17. STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

    International Nuclear Information System (INIS)

    Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

    2015-01-01

    Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

  18. Dynamical evolution of stars and gas of young embedded stellar sub-clusters

    Science.gov (United States)

    Sills, Alison; Rieder, Steven; Scora, Jennifer; McCloskey, Jessica; Jaffa, Sarah

    2018-03-01

    We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution which can include a filamentary structure in addition to gas surrounding the stellar subclusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young proto-star clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

  19. Fluorine Abundances of AGB Stars in Stellar Clusters

    Science.gov (United States)

    Hren, A.; Lebzelter, T.; Aringer, B.; Hinkle, K. H.; Nowotny, W.

    2015-08-01

    We have measured the abundance of fluorine, [F/Fe], in a number of AGB stars in stellar clusters have correlated the results with their C/O ratios. This allows us to investigate the change in the fluorine abundance along the evolution on the giant branch. The target list includes primarily O-rich stars in three LMC globular clusters - NGC 1806, NGC 1846 and NGC 1978 - as well as Rup 106 and 47 Tuc in our Galaxy. The observational data were obtained with the PHOENIX spectrograph, and the COMA code was used for modelling the synthetic spectra. Within individual clusters, we find consistent [F/Fe] values at similar C/O for most of our target stars.

  20. STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

    International Nuclear Information System (INIS)

    Matzner, Christopher D.; Jumper, Peter H.

    2015-01-01

    During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive

  1. Neutrino diffusion and mass ejection in protoneutron stars

    International Nuclear Information System (INIS)

    Almeida, L. G.; Rodrigues, H.; Portes, D. Jr.; Duarte, S. B.

    2010-01-01

    We discuss the mass ejection mechanism induced by diffusion of neutrino during the early stage of the protoneutron star cooling. A dynamical calculation is employed in order to determine the amount of matter ejected and the remnant compact object mass. An equation of state considering hadronic and quark phases for the stellar dense matter was used to solve the whole time evolution of the system during the cooling phase. The initial neutrino population was obtained by considering beta equilibrium in the dense stellar matter with confined neutrinos, in the very early period of the deleptonic stage of the nascent pulsar. For specified initial configurations of the protoneutron star, we solve numerically the set of equations of motion together with neutrino diffusion through the dense stellar medium.

  2. Stellar dynamism. Activity and rotation of solar stars observed from the Kepler satellite

    International Nuclear Information System (INIS)

    Ceillier, Tugdual

    2015-01-01

    This thesis concerns the study of seismic solar-like stars' rotation and magnetic activity. We use data from the Kepler satellite to study the rotational history of these stars throughout their evolution. This allows to have a more complete picture of stellar rotation and magnetism. In the first part, we present the context of this PhD: astro-seismology, the seismic study of stars. We continue by describing the tool we developed to measure surface rotation of stars using photometric data from Kepler. We compare it to other methodologies used by the community and show that its efficiency is very high. In the second part, we apply this tool to around 500 main-sequence and sub-giant solar-like stars. We measure surface rotation periods and activity levels for 300 of them. We show that the measured periods and the ages from astro-seismology do not agree well with the standard period-age relationships and propose to modify these relationships for stars older than the Sun. We also use the surface rotation as a constraint to estimate the internal rotation of a small number of seismic targets. We demonstrate that these stars have, like the Sun, a very low differential rotation ratio. In the third part, we apply our surface rotation-measuring tool to the most extensive sample of red giants observed by Kepler, comprising more than 17,000 stars. We identify more than 360 fast rotating red giants and compare our detection rates with the ones predicted by theory to better understand the reasons for this rapid rotation. We also use stellar modelling to reproduce the internal rotation profile of a particular red giant. This allows us to emphasize how important implementing new angular momentum transport mechanisms in stellar evolution codes is. This work offers new results that are useful to a very wide community of stellar physicists. It also puts strong constraints on the evolution of solar-like stars' rotation and magnetic activity. (author) [fr

  3. THE MASSIVE STAR-FORMING REGION CYGNUS OB2. II. INTEGRATED STELLAR PROPERTIES AND THE STAR FORMATION HISTORY

    International Nuclear Information System (INIS)

    Wright, N. J.; Drake, J. J.; Drew, J. E.; Vink, J. S.

    2010-01-01

    Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 M sun (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5 +0.75 -1.0 and 5.25 +1.5 -1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = -1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 x 10 4 M sun , similar to that of many of our Galaxy's most massive SFRs.

  4. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Grasha, K.; Calzetti, D. [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States); Adamo, A.; Messa, M. [Dept. of Astronomy, The Oskar Klein Centre, Stockholm University, Stockholm (Sweden); Kim, H. [Gemini Observatory, La Serena (Chile); Elmegreen, B. G. [IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY (United States); Gouliermis, D. A. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Dale, D. A. [Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY (United States); Fumagalli, M. [Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Durham University, Durham (United Kingdom); Grebel, E. K.; Shabani, F. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Johnson, K. E. [Dept. of Astronomy, University of Virginia, Charlottesville, VA (United States); Kahre, L. [Dept. of Astronomy, New Mexico State University, Las Cruces, NM (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Cambridge (United Kingdom); Pellerin, A. [Dept. of Physics and Astronomy, State University of New York at Geneseo, Geneseo NY (United States); Ryon, J. E.; Ubeda, L. [Space Telescope Science Institute, Baltimore, MD (United States); Smith, L. J. [European Space Agency/Space Telescope Science Institute, Baltimore, MD (United States); Thilker, D., E-mail: kgrasha@astro.umass.edu [Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)

    2017-05-10

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  5. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    Science.gov (United States)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Messa, M.; Pellerin, A.; Ryon, J. E.; Smith, L. J.; Shabani, F.; Thilker, D.; Ubeda, L.

    2017-05-01

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3-15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ˜40-60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  6. The Hierarchical Distribution of the Young Stellar Clusters in Six Local Star-forming Galaxies

    International Nuclear Information System (INIS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Messa, M.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Dale, D. A.; Fumagalli, M.; Grebel, E. K.; Shabani, F.; Johnson, K. E.; Kahre, L.; Kennicutt, R. C.; Pellerin, A.; Ryon, J. E.; Ubeda, L.; Smith, L. J.; Thilker, D.

    2017-01-01

    We present a study of the hierarchical clustering of the young stellar clusters in six local (3–15 Mpc) star-forming galaxies using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). We identified 3685 likely clusters and associations, each visually classified by their morphology, and we use the angular two-point correlation function to study the clustering of these stellar systems. We find that the spatial distribution of the young clusters and associations are clustered with respect to each other, forming large, unbound hierarchical star-forming complexes that are in general very young. The strength of the clustering decreases with increasing age of the star clusters and stellar associations, becoming more homogeneously distributed after ∼40–60 Myr and on scales larger than a few hundred parsecs. In all galaxies, the associations exhibit a global behavior that is distinct and more strongly correlated from compact clusters. Thus, populations of clusters are more evolved than associations in terms of their spatial distribution, traveling significantly from their birth site within a few tens of Myr, whereas associations show evidence of disruption occurring very quickly after their formation. The clustering of the stellar systems resembles that of a turbulent interstellar medium that drives the star formation process, correlating the components in unbound star-forming complexes in a hierarchical manner, dispersing shortly after formation, suggestive of a single, continuous mode of star formation across all galaxies.

  7. Cooling of hypernuclear compact stars

    Science.gov (United States)

    Raduta, Adriana R.; Sedrakian, Armen; Weber, Fridolin

    2018-04-01

    We study the thermal evolution of hypernuclear compact stars constructed from covariant density functional theory of hypernuclear matter and parametrizations which produce sequences of stars containing two-solar-mass objects. For the input in the simulations, we solve the Bardeen-Cooper-Schrieffer gap equations in the hyperonic sector and obtain the gaps in the spectra of Λ, Ξ0, and Ξ- hyperons. For the models with masses M/M⊙ ≥ 1.5 the neutrino cooling is dominated by hyperonic direct Urca processes in general. In the low-mass stars the (Λp) plus leptons channel is the dominant direct Urca process, whereas for more massive stars the purely hyperonic channels (Σ-Λ) and (Ξ-Λ) are dominant. Hyperonic pairing strongly suppresses the processes on Ξ-s and to a lesser degree on Λs. We find that intermediate-mass 1.5 ≤ M/M⊙ ≤ 1.8 models have surface temperatures which lie within the range inferred from thermally emitting neutron stars, if the hyperonic pairing is taken into account. Most massive models with M/M⊙ ≃ 2 may cool very fast via the direct Urca process through the (Λp) channel because they develop inner cores where the S-wave pairing of Λs and proton is absent.

  8. Chemical Soups Around Cool Stars

    Science.gov (United States)

    2009-01-01

    This artist's conception shows a young, hypothetical planet around a cool star. A soupy mix of potentially life-forming chemicals can be seen pooling around the base of the jagged rocks. Observations from NASA's Spitzer Space Telescope hint that planets around cool stars the so-called M-dwarfs and brown dwarfs that are widespread throughout our galaxy might possess a different mix of life-forming, or prebiotic, chemicals than our young Earth. Life on our planet is thought to have arisen out of a pond-scum-like mix of chemicals. Some of these chemicals are thought to have come from a planet-forming disk of gas and dust that swirled around our young sun. Meteorites carrying the chemicals might have crash-landed on Earth. Astronomers don't know if these same life-generating processes are taking place around stars that are cooler than our sun, but the Spitzer observations show their disk chemistry is different. Spitzer detected a prebiotic molecule, called hydrogen cyanide, in the disks around yellow stars like our sun, but found none around cooler, less massive, reddish stars. Hydrogen cyanide is a carbon-containing, or organic compound. Five hydrogen cyanide molecules can join up to make adenine a chemical element of the DNA molecule found in all living organisms on Earth.

  9. An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

    Science.gov (United States)

    Cowie, L. L.; Barger, A. J.

    2008-10-01

    We present an integrated study of star formation and galactic stellar mass assembly from z = 0.05 to 1.5 and galactic metallicity evolution from z = 0.05 to 0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 M⊙). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24 μm sources, but after correcting for extinction, the bulk of the 24 μm sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21 +/- 0.03 dex between the local value and the value at z = 0.77 in the 1010-1011 M⊙ range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (gtrsim1011 M⊙) ceases at z Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

  10. Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library

    Science.gov (United States)

    Yee, Samuel W.; Petigura, Erik A.; von Braun, Kaspar

    2017-02-01

    Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R ≈ 60,000), high signal-to-noise ratio (S/N ≈ 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ˜M5-F1 (T eff ≈ 3000-7000 K, R ⋆ ≈ 0.1-16 R ⊙). We also present “Empirical SpecMatch” (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature (T eff), 15% in stellar radius (R ⋆), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ˜K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T eff, 10% in R ⋆, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.

  11. Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library

    Energy Technology Data Exchange (ETDEWEB)

    Yee, Samuel W.; Petigura, Erik A. [California Institute of Technology (United States); Von Braun, Kaspar, E-mail: syee@caltech.edu [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2017-02-10

    Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution ( R ≈ 60,000), high signal-to-noise ratio (S/N ≈ 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ∼M5–F1 ( T {sub eff} ≈ 3000–7000 K, R {sub ⋆} ≈ 0.1–16 R {sub ⊙}). We also present “Empirical SpecMatch” (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature ( T {sub eff}), 15% in stellar radius ( R {sub ⋆}), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ∼K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T {sub eff}, 10% in R {sub ⋆}, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.

  12. Dark stars: a new study of the first stars in the Universe

    International Nuclear Information System (INIS)

    Freese, Katherine; Bodenheimer, Peter; Gondolo, Paolo; Spolyar, Douglas

    2009-01-01

    We have proposed that the first phase of stellar evolution in the history of the Universe may be dark stars (DSs), powered by dark matter (DM) heating rather than by nuclear fusion. Weakly interacting massive particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a DS, powered by DM annihilation as long as there is DM fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright (∼10 6 L o-dot ) and cool (T surf surf > 50 000 K); hence DS should be observationally distinct from standard Pop III stars. Once the DM fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.

  13. Limits on stellar companions to exoplanet host stars with eccentric planets

    International Nuclear Information System (INIS)

    Kane, Stephen R.; Hinkel, Natalie R.; Howell, Steve B.; Horch, Elliott P.; Feng, Ying; Wright, Jason T.; Ciardi, David R.; Everett, Mark E.; Howard, Andrew W.

    2014-01-01

    Though there are now many hundreds of confirmed exoplanets known, the binarity of exoplanet host stars is not well understood. This is particularly true of host stars that harbor a giant planet in a highly eccentric orbit since these are more likely to have had a dramatic dynamical history that transferred angular momentum to the planet. Here we present observations of four exoplanet host stars that utilize the excellent resolving power of the Differential Speckle Survey Instrument on the Gemini North telescope. Two of the stars are giants and two are dwarfs. Each star is host to a giant planet with an orbital eccentricity >0.5 and whose radial velocity (RV) data contain a trend in the residuals to the Keplerian orbit fit. These observations rule out stellar companions 4-8 mag fainter than the host star at passbands of 692 nm and 880 nm. The resolution and field of view of the instrument result in exclusion radii of 0.''05-1.''4, which excludes stellar companions within several AU of the host star in most cases. We further provide new RVs for the HD 4203 system that confirm that the linear trend previously observed in the residuals is due to an additional planet. These results place dynamical constraints on the source of the planet's eccentricities, place constraints on additional planetary companions, and inform the known distribution of multiplicity amongst exoplanet host stars.

  14. A new interpretation of luminous blue stars

    International Nuclear Information System (INIS)

    Stothers, R.

    1976-01-01

    A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

  15. Constraining stellar physics from red-giant stars in binaries – stellar rotation, mixing processes and stellar activity

    Directory of Open Access Journals (Sweden)

    Beck P. G.

    2017-01-01

    Full Text Available The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

  16. StarHorse: a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars

    Science.gov (United States)

    Queiroz, A. B. A.; Anders, F.; Santiago, B. X.; Chiappini, C.; Steinmetz, M.; Dal Ponte, M.; Stassun, K. G.; da Costa, L. N.; Maia, M. A. G.; Crestani, J.; Beers, T. C.; Fernández-Trincado, J. G.; García-Hernández, D. A.; Roman-Lopes, A.; Zamora, O.

    2018-05-01

    Understanding the formation and evolution of our Galaxy requires accurate distances, ages, and chemistry for large populations of field stars. Here, we present several updates to our spectrophotometric distance code, which can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectrophotometric parameters, we calculate the posterior probability distribution over a given grid of stellar evolutionary models, using flexible Galactic stellar-population priors. The code (called StarHorse) can accommodate different observational data sets, prior options, partially missing data, and the inclusion of parallax information into the estimated probabilities. We validate the code using a variety of simulated stars as well as real stars with parameters determined from asteroseismology, eclipsing binaries, and isochrone fits to star clusters. Our main goal in this validation process is to test the applicability of the code to field stars with known Gaia-like parallaxes. The typical internal precisions (obtained from realistic simulations of an APOGEE+Gaia-like sample) are {˜eq } 8 {per cent} in distance, {˜eq } 20 {per cent} in age, {˜eq } 6 {per cent} in mass, and ≃ 0.04 mag in AV. The median external precision (derived from comparisons with earlier work for real stars) varies with the sample used, but lies in the range of {˜eq } [0,2] {per cent} for distances, {˜eq } [12,31] {per cent} for ages, {˜eq } [4,12] {per cent} for masses, and ≃ 0.07 mag for AV. We provide StarHorse distances and extinctions for the APOGEE DR14, RAVE DR5, GES DR3, and GALAH DR1 catalogues.

  17. Book Review: "Inside Stars. A Theory of the Internal Constitution of Stars, and the Sources of Stellar Energy According to General Relativity" (Letters to Progress in Physics

    Directory of Open Access Journals (Sweden)

    Millette P. A.

    2014-01-01

    Full Text Available This book provides a general relativistic theory of the internal constitution of liquid stars. It is a solid contribution to our understanding of stellar structure from a general relativistic perspective. It raises new ideas on the constitution of stars and planetary systems, and proposes a new approach to stellar structure an d stellar energy generation which is bound to help us better understand stellar astrophysics.

  18. LARGER PLANET RADII INFERRED FROM STELLAR ''FLICKER'' BRIGHTNESS VARIATIONS OF BRIGHT PLANET-HOST STARS

    International Nuclear Information System (INIS)

    Bastien, Fabienne A.; Stassun, Keivan G.; Pepper, Joshua

    2014-01-01

    Most extrasolar planets have been detected by their influence on their parent star, typically either gravitationally (the Doppler method) or by the small dip in brightness as the planet blocks a portion of the star (the transit method). Therefore, the accuracy with which we know the masses and radii of extrasolar planets depends directly on how well we know those of the stars, the latter usually determined from the measured stellar surface gravity, log g. Recent work has demonstrated that the short-timescale brightness variations ( f licker ) of stars can be used to measure log g to a high accuracy of ∼0.1-0.2 dex. Here, we use flicker measurements of 289 bright (Kepmag < 13) candidate planet-hosting stars with T eff = 4500-6650 K to re-assess the stellar parameters and determine the resulting impact on derived planet properties. This re-assessment reveals that for the brightest planet-host stars, Malmquist bias contaminates the stellar sample with evolved stars: nearly 50% of the bright planet-host stars are subgiants. As a result, the stellar radii, and hence the radii of the planets orbiting these stars, are on average 20%-30% larger than previous measurements had suggested

  19. Effect of binary stars on the dynamical evolution of stellar clusters. II. Analytic evolutionary models

    International Nuclear Information System (INIS)

    Hills, J.G.

    1975-01-01

    We use analytic models to compute the evolution of the core of a stellar system due simultaneously to stellar evaporation which causes the system (core) to contract and to its binaries which cause it to expand by progressively decreasing its binding energy. The evolution of the system is determined by two parameters: the initial number of stars in the system N 0 , and the fraction f/subb/ of its stars which are binaries. For a fixed f/subb/, stellar evaporation initially dominates the dynamical evolution if N 0 is sufficiently large due to the fact that the rate of evaporation is determined chiefly by long-range encounters which increase in importance as the number of stars in the system increases. If stellar evaporation initially dominates, the system first contracts, but as N/subc/, the number of remaining stars in the system, decreases by evaporation, the system reaches a minimum radius and a maximum density and then it expands monotonically as N/subc/ decreases further. Open clusters expand monotonically from the beginning if they have anything approaching average Population I binary frequencies. Globular clusters are highly deficient in binaries in order to have formed and retained the high-density stellar cores observed in most of them. We estimate that for these system f/subb/ < or = 0.15

  20. SECOND-GENERATION STELLAR DISKS IN DENSE STAR CLUSTERS AND CLUSTER ELLIPTICITIES

    International Nuclear Information System (INIS)

    Mastrobuono-Battisti, Alessandra; Perets, Hagai B.

    2016-01-01

    Globular clusters (GCs) and nuclear star clusters (NSCs) are typically composed of several stellar populations, characterized by different chemical compositions. Different populations show different ages in NSCs, but not necessarily in GCs. The youngest populations in NSCs appear to reside in disk-like structures as observed in our Galaxy and in M31. Gas infall followed by formation of second-generation (SG) stars in GCs may similarly form disk-like structures in the clusters nuclei. Here we explore this possibility and follow the long-term evolution of stellar disks embedded in GCs, and study their effects on the evolution of the clusters. We study disks with different masses by means of detailed N-body simulations and explore their morphological and kinematic signatures on the GC structures. We find that as a SG disk relaxes, the old, first-generation stellar population flattens and becomes more radially anisotropic, making the GC structure become more elliptical. The SG stellar population is characterized by a lower velocity dispersion and a higher rotational velocity compared with the primordial older population. The strength of these kinematic signatures depends both on the relaxation time of the system and on the fractional mass of the SG disk. We therefore conclude that SG populations formed in flattened configurations will give rise to two systematic trends: (1) a positive correlation between GC ellipticity and fraction of SG population and (2) a positive correlation between GC relaxation time and ellipticity. Therefore, GC ellipticities and rotation could be related to the formation of SG stars and their initial configuration.

  1. The Dynamical Evolution of Stellar-Mass Black Holes in Dense Star Clusters

    Science.gov (United States)

    Morscher, Maggie

    Globular clusters are gravitationally bound systems containing up to millions of stars, and are found ubiquitously in massive galaxies, including the Milky Way. With densities as high as a million stars per cubic parsec, they are one of the few places in the Universe where stars interact with one another. They therefore provide us with a unique laboratory for studying how gravitational interactions can facilitate the formation of exotic systems, such as X-ray binaries containing black holes, and merging double black hole binaries, which are produced much less efficiently in isolation. While telescopes can provide us with a snapshot of what these dense clusters look like at present, we must rely on detailed numerical simulations to learn about their evolution. These simulations are quite challenging, however, since dense star clusters are described by a complicated set of physical processes occurring on many different length and time scales, including stellar and binary evolution, weak gravitational scattering encounters, strong resonant binary interactions, and tidal stripping by the host galaxy. Until very recently, it was not possible to model the evolution of systems with millions of stars, the actual number contained in the largest clusters, including all the relevant physics required describe these systems accurately. The Northwestern Group's Henon Monte Carlo code, CMC, which has been in development for over a decade, is a powerful tool that can be used to construct detailed evolutionary models of large star clusters. With its recent parallelization, CMC is now capable of addressing a particularly interesting unsolved problem in astrophysics: the dynamical evolution of stellar black holes in dense star clusters. Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters may have formed hundreds to thousands of stellar-mass black holes, the remnants of stars with initial masses from 20 - 100

  2. Neutron star cooling constraints for color superconductivity in hybrid stars

    International Nuclear Information System (INIS)

    Popov, S.; Grigoryan, Kh.; Blaschke, D.

    2005-01-01

    We apply the recently developed LogN-LogS test of compact star cooling theories for the first time to hybrid stars with a color superconducting quark matter core. While there is not yet a microscopically founded superconducting quark matter phase which would fulfill constraints from cooling phenomenology, we explore the hypothetical 2SC+X phase and show that the magnitude and density-dependence of the X-gap can be chosen to satisfy a set of tests: temperature-age (T-t), the brightness constraint, LogN-LogS, and the mass spectrum constraint. The latter test appears as a new conjecture from the present investigation

  3. Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars

    OpenAIRE

    Paxton, Bill; Cantiello, Matteo; Arras, Phil; Bildsten, Lars; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

    2013-01-01

    We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA Star. Improvements in MESA Star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiab...

  4. Ecology of blue straggler stars

    CERN Document Server

    Carraro, Giovanni; Beccari, Giacomo

    2015-01-01

    The existence of blue straggler stars, which appear younger, hotter, and more massive than their siblings, is at odds with a simple picture of stellar evolution. Such stars should have exhausted their nuclear fuel and evolved long ago to become cooling white dwarfs. They are found to exist in globular clusters, open clusters, dwarf spheroidal galaxies of the Local Group, OB associations and as field stars. This book summarises the many advances in observational and theoretical work dedicated to blue straggler stars. Carefully edited extended contributions by well-known experts in the field cover all the relevant aspects of blue straggler stars research: Observations of blue straggler stars in their various environments; Binary stars and formation channels; Dynamics of globular clusters; Interpretation of observational data and comparison with models. The book also offers an introductory chapter on stellar evolution written by the editors of the book.

  5. The Role of Stellar Feedback on the Structure of the ISM and Star Formation in Galaxies

    Science.gov (United States)

    Grisdale, Kearn Michael

    2017-08-01

    Stellar feedback refers to the injection of energy, momentum and mass into the interstellar medium (ISM) by massive stars. This feedback owes to a combination of ionising radiation, radiation pressure, stellar winds and supernovae and is likely responsible both for the inefficiency of star formation in galaxies, and the observed super-sonic turbulence of the ISM. In this thesis, I study how stellar feedback shapes the ISM thereby regulating galaxy evolution. In particular, I focus on three key questions: (i) How does stellar feedback shape the gas density distribution of the ISM? (ii) How does feedback change or influence the distribution of the kinetic energy in the ISM? and (iii) What role does feedback play in determining the star formation efficiency of giant molecular clouds (GMCs)? To answer these questions, I run high resolution (Deltax 4.6 pc) numerical simulations of three isolated galaxies, both with and without stellar feedback. I compare these simulations to observations of six galaxies from The HI Nearby Galaxy Survey (THINGS) using power spectra, and I use clump finding techniques to identify GMCs in my simulations and calculate their properties. I find that the kinetic energy power spectra in stellar feedback- regulated galaxies, regardless of the galaxy's mass and size, show scalings in excellent agreement with supersonic turbulence on scales below the thickness of the HI layer. I show that feedback influences the gas density field, and drives gas turbulence, up to large (kiloparsec) scales. This is in stark contrast to the density fields generated by large-scale gravity-only driven turbulence (i.e. without stellar feedback). Simulations with stellar feedback are able to reproduce the internal properties of GMCs such as: mass, size and velocity dispersion. Finally, I demonstrate that my simulations naturally reproduce the observed scatter (3.5-4 dex) in the star formation efficiency per free-fall time of GMCs, despite only employing a simple Schmidt

  6. ON THE INCORPORATION OF METALLICITY DATA INTO MEASUREMENTS OF STAR FORMATION HISTORY FROM RESOLVED STELLAR POPULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Dolphin, Andrew E., E-mail: adolphin@raytheon.com [Raytheon Company, Tucson, AZ 85734 (United States)

    2016-07-10

    The combination of spectroscopic stellar metallicities and resolved star color–magnitude diagrams (CMDs) has the potential to constrain the entire star formation history (SFH) of a galaxy better than fitting CMDs alone (as is most common in SFH studies using resolved stellar populations). In this paper, two approaches to incorporating external metallicity information into CMD-fitting techniques are presented. Overall, the joint fitting of metallicity and CMD information can increase the precision of measured age–metallicity relationships (AMRs) and star formation rates by 10% over CMD fitting alone. However, systematics in stellar isochrones and mismatches between spectroscopic and photometric determinations of metallicity can reduce the accuracy of the recovered SFHs. I present a simple mitigation of these systematics that can reduce their amplitude to the level obtained from CMD fitting alone, while ensuring that the AMR is consistent with spectroscopic metallicities. As is the case in CMD-fitting analysis, improved stellar models and calibrations between spectroscopic and photometric metallicities are currently the primary impediment to gains in SFH precision from jointly fitting stellar metallicities and CMDs.

  7. ON THE INCORPORATION OF METALLICITY DATA INTO MEASUREMENTS OF STAR FORMATION HISTORY FROM RESOLVED STELLAR POPULATIONS

    International Nuclear Information System (INIS)

    Dolphin, Andrew E.

    2016-01-01

    The combination of spectroscopic stellar metallicities and resolved star color–magnitude diagrams (CMDs) has the potential to constrain the entire star formation history (SFH) of a galaxy better than fitting CMDs alone (as is most common in SFH studies using resolved stellar populations). In this paper, two approaches to incorporating external metallicity information into CMD-fitting techniques are presented. Overall, the joint fitting of metallicity and CMD information can increase the precision of measured age–metallicity relationships (AMRs) and star formation rates by 10% over CMD fitting alone. However, systematics in stellar isochrones and mismatches between spectroscopic and photometric determinations of metallicity can reduce the accuracy of the recovered SFHs. I present a simple mitigation of these systematics that can reduce their amplitude to the level obtained from CMD fitting alone, while ensuring that the AMR is consistent with spectroscopic metallicities. As is the case in CMD-fitting analysis, improved stellar models and calibrations between spectroscopic and photometric metallicities are currently the primary impediment to gains in SFH precision from jointly fitting stellar metallicities and CMDs.

  8. THE OCCURRENCE RATE OF SMALL PLANETS AROUND SMALL STARS

    International Nuclear Information System (INIS)

    Dressing, Courtney D.; Charbonneau, David

    2013-01-01

    We use the optical and near-infrared photometry from the Kepler Input Catalog to provide improved estimates of the stellar characteristics of the smallest stars in the Kepler target list. We find 3897 dwarfs with temperatures below 4000 K, including 64 planet candidate host stars orbited by 95 transiting planet candidates. We refit the transit events in the Kepler light curves for these planet candidates and combine the revised planet/star radius ratios with our improved stellar radii to revise the radii of the planet candidates orbiting the cool target stars. We then compare the number of observed planet candidates to the number of stars around which such planets could have been detected in order to estimate the planet occurrence rate around cool stars. We find that the occurrence rate of 0.5-4 R ⊕ planets with orbital periods shorter than 50 days is 0.90 +0.04 -0.03 planets per star. The occurrence rate of Earth-size (0.5-1.4 R ⊕ ) planets is constant across the temperature range of our sample at 0.51 -0.05 +0.06 Earth-size planets per star, but the occurrence of 1.4-4 R ⊕ planets decreases significantly at cooler temperatures. Our sample includes two Earth-size planet candidates in the habitable zone, allowing us to estimate that the mean number of Earth-size planets in the habitable zone is 0.15 +0.13 -0.06 planets per cool star. Our 95% confidence lower limit on the occurrence rate of Earth-size planets in the habitable zones of cool stars is 0.04 planets per star. With 95% confidence, the nearest transiting Earth-size planet in the habitable zone of a cool star is within 21 pc. Moreover, the nearest non-transiting planet in the habitable zone is within 5 pc with 95% confidence.

  9. The ATLAS3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies

    Science.gov (United States)

    McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Cappellari, Michele; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2015-04-01

    We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, R^maj_e), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ˜ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions.

  10. MEASURING Be DEPLETION IN COOL STARS WITH EXOPLANETS

    International Nuclear Information System (INIS)

    Delgado Mena, E.; Israelian, G.; Gonzalez Hernandez, J. I.; Rebolo, R.; Santos, N. C.

    2011-01-01

    We present new UVES spectra of a sample of 14 mostly cool unevolved stars with planetary companions with the aim of studying possible differences in Be abundance with respect to stars without detected planets. We determine Be abundances for these stars that show an increase in Be depletion as we move to lower temperatures. We carry out a differential analysis of spectra of analog stars with and without planets to establish a possible difference in Be content. While for hot stars no measurable difference is found in Be, for the only cool (T eff ∼ 5000 K) planet-host star with several analogs in the sample we find enhanced Be depletion by 0.25 dex. This is a first indication that the extra-depletion of Li in solar-type stars with planets may also happen for Be, but shifted toward lower temperatures (T eff < 5500 K) due to the depth of the convective envelopes. The processes that take place in the formation of planetary systems may affect the mixing of material inside their host stars and hence the abundances of light elements.

  11. STELLAR MASSES AND STAR FORMATION RATES OF LENSED, DUSTY, STAR-FORMING GALAXIES FROM THE SPT SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Jingzhe; Gonzalez, Anthony H. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Spilker, J. S.; Marrone, D. P. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Strandet, M. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69 D-53121 Bonn (Germany); Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aravena, M. [Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Béthermin, M.; Breuck, C. de; Gullberg, B. [European Southern Observatory, Karl Schwarzschild Straße 2, D-85748 Garching (Germany); Bothwell, M. S. [Cavendish Laboratory, University of Cambridge, JJ Thompson Avenue, Cambridge CB3 0HA (United Kingdom); Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Chapman, S. C. [Dalhousie University, Halifax, Nova Scotia (Canada); Fassnacht, C. D. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Greve, T. R. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Hezaveh, Y. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Malkan, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Saliwanchik, B. R., E-mail: jingzhema@ufl.edu [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); and others

    2015-10-10

    To understand cosmic mass assembly in the universe at early epochs, we primarily rely on measurements of the stellar masses and star formation rates (SFRs) of distant galaxies. In this paper, we present stellar masses and SFRs of six high-redshift (2.8 ≤ z ≤ 5.7) dusty, star-forming galaxies (DSFGs) that are strongly gravitationally lensed by foreground galaxies. These sources were first discovered by the South Pole Telescope (SPT) at millimeter wavelengths and all have spectroscopic redshifts and robust lens models derived from Atacama Large Millimeter/submillimeter Array observations. We have conducted follow-up observations to obtain multi-wavelength imaging data using the Hubble Space Telescope (HST), Spitzer, Herschel, and the Atacama Pathfinder EXperiment. We use the high-resolution HST/Wide Field Camera 3 images to disentangle the background source from the foreground lens in Spitzer/IRAC data. The detections and upper limits provide important constraints on the spectral energy distributions (SEDs) for these DSFGs, yielding stellar masses, IR luminosities, and SFRs. The SED fits of six SPT sources show that the intrinsic stellar masses span a range more than one order of magnitude with a median value ∼5 ×10{sup 10} M{sub ⊙}. The intrinsic IR luminosities range from 4 × 10{sup 12} L{sub ⊙} to 4 × 10{sup 13} L{sub ⊙}. They all have prodigious intrinsic SFRs of 510–4800 M{sub ⊙} yr{sup −1}. Compared to the star-forming main sequence (MS), these six DSFGs have specific SFRs that all lie above the MS, including two galaxies that are a factor of 10 higher than the MS. Our results suggest that we are witnessing ongoing strong starburst events that may be driven by major mergers.

  12. Cooling of Accretion-Heated Neutron Stars

    Indian Academy of Sciences (India)

    Rudy Wijnands

    2017-09-12

    Sep 12, 2017 ... the magnetic field might play an important role in the heating and cooling of the neutron stars. .... Source near Sgr A ..... marked the start of the research field that uses the cool- ... This curve is just to guide the eye for the individual sources and it is clear ..... Not all accretion-induced nuclear reactions might.

  13. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    NARCIS (Netherlands)

    Schneider, F.R.N.; Izzard, R.G.; de Mink, S.E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V.V.; Huβman, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass

  14. IN-SYNC I: Homogeneous stellar parameters from high-resolution apogee spectra for thousands of pre-main sequence stars

    International Nuclear Information System (INIS)

    Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Nidever, David L.; Stassun, Keivan G.; Foster, Jonathan B.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Skrutskie, Michael; Majewski, Steven R.; Wilson, John C.; Zasowski, Gail; Flaherty, Kevin M.; Frinchaboy, Peter M.

    2014-01-01

    Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J – H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.

  15. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    International Nuclear Information System (INIS)

    Delgado Mena, E.; Israelian, G.; González Hernández, J. I.; Rebolo, R.; Santos, N. C.

    2012-01-01

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T eff decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T eff decreases for T eff < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  16. Cooling Curve of Strange Star in Strong Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-Qin; LUO Zhi-Quan

    2008-01-01

    In this paper, firstly, we investigate the neutrino emissivity from quark Urca process in strong magnetic field. Then, we discuss the heat capacity of strange stars in strong magnetic field. Finally, we give the cooling curve in strong magnetic field. In order to make a comparison, we also give the corresponding cooling curve in the case of null magnetic field. It turns out that strange stars cool faster in strong magnetic field than that without magnetic field.

  17. A UKIDSS-based search for low-mass stars and small stellar clumps in off-cloud parts of young star-forming regions* **

    Directory of Open Access Journals (Sweden)

    Barrado y Navascués D.

    2011-07-01

    Full Text Available The form and universality of the mass function of young and nearby star-forming regions is still under debate. Its relation to the stellar density, its mass peak and the dependency on most recent models shows significant differencies for the various regions and remains unclear up to date. We aim to get a more complete census of two of such regions. We investigate yet unexplored areas of Orion and Taurus-Auriga, observed by the UKIDSS survey. In the latter, we search for low-mass stars via photometric and proper motion criteria and signs for variability. In Orion, we search for small stellar clumps via nearest-neighbor methods. Highlights in Taurus would be the finding of the missing low-mass stars and the detection of a young cluster T dwarf. In Orion, we discovered small stellar associations of its OB1b and OB1c populations. Combined with what is known in literature, we will provide by this investigations a general picture of the results of the star-forming processes in large areas of Taurus and Orion and probe the most recent models.

  18. Multiple Stellar Populations in Star Clusters

    Science.gov (United States)

    Piotto, G.

    2013-09-01

    For half a century it had been astronomical dogma that a globular cluster (GC) consists of stars born at the same time out of the same material, and this doctrine has borne rich fruits. In recent years, high resolution spectroscopy and high precision photometry (from space and ground-based observations) have shattered this paradigm, and the study of GC populations has acquired a new life that is now moving it in new directions. Evidence of multiple stellar populations have been identified in the color-magnitude diagrams of several Galactic and Magellanic Cloud GCs where they had never been imagined before.

  19. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    Science.gov (United States)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately equal to 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 dex above the redshift (z) approximately 1 stellar mass-SFR relation and 0.23 plus or minus 0.23 dex below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately equal to 100 (sup plus 310) (sub minus 75) million years which suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 94.4 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  20. Time-scales of stellar rotational variability and starspot diagnostics

    Science.gov (United States)

    Arkhypov, Oleksiy V.; Khodachenko, Maxim L.; Lammer, Helmut; Güdel, Manuel; Lüftinger, Teresa; Johnstone, Colin P.

    2018-01-01

    The difference in stability of starspot distribution on the global and hemispherical scales is studied in the rotational spot variability of 1998 main-sequence stars observed by Kepler mission. It is found that the largest patterns are much more stable than smaller ones for cool, slow rotators, whereas the difference is less pronounced for hotter stars and/or faster rotators. This distinction is interpreted in terms of two mechanisms: (1) the diffusive decay of long-living spots in activity complexes of stars with saturated magnetic dynamos, and (2) the spot emergence, which is modulated by gigantic turbulent flows in convection zones of stars with a weaker magnetism. This opens a way for investigation of stellar deep convection, which is yet inaccessible for asteroseismology. Moreover, a subdiffusion in stellar photospheres was revealed from observations for the first time. A diagnostic diagram was proposed that allows differentiation and selection of stars for more detailed studies of these phenomena.

  1. Cooling compact stars and phase transitions in dense QCD

    Energy Technology Data Exchange (ETDEWEB)

    Sedrakian, Armen [J.W. Goethe University, Institute for Theoretical Physics, Frankfurt am Main (Germany)

    2016-03-15

    We report new simulations of cooling of compact stars containing quark cores and updated fits to the Cas A fast cooling data. Our model is built on the assumption that the transient behaviour of the star in Cas A is due to a phase transition within the dense QCD matter in the core of the star. Specifically, the fast cooling is attributed to an enhancement in the neutrino emission triggered by a transition from a fully gapped, two-flavor, red-green color-superconducting quark condensate to a superconducting crystalline or an alternative gapless, color-superconducting phase. The blue-colored condensate is modeled as a Bardeen-Cooper-Schrieffer (BCS)-type color superconductor with spin-one pairing order parameter. We study the sensitivity of the fits to the phase transition temperature, the pairing gap of blue quarks and the timescale characterizing the phase transition (the latter modelled in terms of a width parameter). Relative variations in these parameter around their best-fit values larger than 10{sup -3} spoil the fit to the data. We confirm the previous finding that the cooling curves show significant variations as a function of compact star mass, which allows one to account for dispersion in the data on the surface temperatures of thermally emitting neutron stars. (orig.)

  2. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Blum, R. D. [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Srinivasan, S.; Kemper, F.; Ling, B. [Academia Sinica, Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, NTU/AS, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Volk, K. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  3. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    International Nuclear Information System (INIS)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2014-01-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  4. Be ABUNDANCES IN COOL MAIN-SEQUENCE STARS WITH EXOPLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Delgado Mena, E.; Israelian, G.; Gonzalez Hernandez, J. I.; Rebolo, R. [Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife (Spain); Santos, N. C., E-mail: edm@iac.es [Centro de Astrofisica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2012-02-10

    We present new Ultraviolet and Visual Echelle Spectrograph (UVES) spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between the two groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the Be II resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are approximately constant, with a slight fall as T{sub eff} decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as T{sub eff} decreases for T{sub eff} < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets; thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.

  5. Topics in the theory of neutron star cooling

    International Nuclear Information System (INIS)

    Duncan, R.C. Jr.

    1986-01-01

    The author calculates the neutrino emissivity of interacting, degenerate quark matter, which may make up the dense cores of neutron stars. QCD interactions between quarks are included to first order. The author shows that when massive s-quarks are present in cold quark matter, electrons are not present in equilibrium at densities above a threshold electron extinction density n/sub ex/. This results in a much lower neutrino emissivity epsilon/sub nu/ at high densities than has been previously calculated. Dependences of epsilon/sub nu/ on the strange quark mass m/sub s/ and the QCD coupling constant a/sub c/ are determined for a quark liquid in β-equilibrium. Implications of these calculations for neutron-star cooling are briefly discussed. Eventually, it is shown that neutrino momentum effects may be ignored in neutron star cooling calculations without significant error, even when high-density quark-matter cores are present. Finally considered is the very early cooling epoch, lasting up to ∼1 minutes after formation, when a neutron star is optically thick to neutrinos. It is shown that the coupled equations of neutrino and photon transport in the atmosphere of a sufficiently hot, nascent neutron star do not admit hydrostatic solutions

  6. FITspec: A New Algorithm for the Automated Fit of Synthetic Stellar Spectra for OB Stars

    Science.gov (United States)

    Fierro-Santillán, Celia R.; Zsargó, Janos; Klapp, Jaime; Díaz-Azuara, Santiago A.; Arrieta, Anabel; Arias, Lorena; Sigalotti, Leonardo Di G.

    2018-06-01

    In this paper we describe the FITspec code, a data mining tool for the automatic fitting of synthetic stellar spectra. The program uses a database of 27,000 CMFGEN models of stellar atmospheres arranged in a six-dimensional (6D) space, where each dimension corresponds to one model parameter. From these models a library of 2,835,000 synthetic spectra were generated covering the ultraviolet, optical, and infrared regions of the electromagnetic spectrum. Using FITspec we adjust the effective temperature and the surface gravity. From the 6D array we also get the luminosity, the metallicity, and three parameters for the stellar wind: the terminal velocity ({v}∞ ), the β exponent of the velocity law, and the clumping filling factor (F cl). Finally, the projected rotational velocity (v\\cdot \\sin i) can be obtained from the library of stellar spectra. Validation of the algorithm was performed by analyzing the spectra of a sample of eight O-type stars taken from the IACOB spectroscopic survey of Northern Galactic OB stars. The spectral lines used for the adjustment of the analyzed stars are reproduced with good accuracy. In particular, the effective temperatures calculated with the FITspec are in good agreement with those derived from spectral type and other calibrations for the same stars. The stellar luminosities and projected rotational velocities are also in good agreement with previous quantitative spectroscopic analyses in the literature. An important advantage of FITspec over traditional codes is that the time required for spectral analyses is reduced from months to a few hours.

  7. Infrared spectrum of an extremely cool white-dwarf star

    Science.gov (United States)

    Hodgkin; Oppenheimer; Hambly; Jameson; Smartt; Steele

    2000-01-06

    White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

  8. ChromaStarPy: A Stellar Atmosphere and Spectrum Modeling and Visualization Lab in Python

    Science.gov (United States)

    Short, C. Ian; Bayer, Jason H. T.; Burns, Lindsey M.

    2018-02-01

    We announce ChromaStarPy, an integrated general stellar atmospheric modeling and spectrum synthesis code written entirely in python V. 3. ChromaStarPy is a direct port of the ChromaStarServer (CSServ) Java modeling code described in earlier papers in this series, and many of the associated JavaScript (JS) post-processing procedures have been ported and incorporated into CSPy so that students have access to ready-made data products. A python integrated development environment (IDE) allows a student in a more advanced course to experiment with the code and to graphically visualize intermediate and final results, ad hoc, as they are running it. CSPy allows students and researchers to compare modeled to observed spectra in the same IDE in which they are processing observational data, while having complete control over the stellar parameters affecting the synthetic spectra. We also take the opportunity to describe improvements that have been made to the related codes, ChromaStar (CS), CSServ, and ChromaStarDB (CSDB), that, where relevant, have also been incorporated into CSPy. The application may be found at the home page of the OpenStars project: http://www.ap.smu.ca/OpenStars/.

  9. Kaon condensates, nuclear symmetry energy and cooling of neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Kubis, S. E-mail: kubis@alf.ifj.edu.pl; Kutschera, M

    2003-06-02

    The cooling of neutron stars by URCA processes in the kaon-condensed neutron star matter for various forms of nuclear symmetry energy is investigated. The kaon-nucleon interactions are described by a chiral Lagrangian. Nuclear matter energy is parametrized in terms of the isoscalar contribution and the nuclear symmetry energy in the isovector sector. High density behaviour of nuclear symmetry energy plays an essential role in determining the composition of the kaon-condensed neutron star matter which in turn affects the cooling properties. We find that the symmetry energy which decreases at higher densities makes the kaon-condensed neutron star matter fully protonized. This effect inhibits strongly direct URCA processes resulting in slower cooling of neutron stars as only kaon-induced URCA cycles are present. In contrast, for increasing symmetry energy direct URCA processes are allowed in the almost whole density range where the kaon condensation exists.

  10. Kaon condensates, nuclear symmetry energy and cooling of neutron stars

    International Nuclear Information System (INIS)

    Kubis, S.; Kutschera, M.

    2003-01-01

    The cooling of neutron stars by URCA processes in the kaon-condensed neutron star matter for various forms of nuclear symmetry energy is investigated. The kaon-nucleon interactions are described by a chiral Lagrangian. Nuclear matter energy is parametrized in terms of the isoscalar contribution and the nuclear symmetry energy in the isovector sector. High density behaviour of nuclear symmetry energy plays an essential role in determining the composition of the kaon-condensed neutron star matter which in turn affects the cooling properties. We find that the symmetry energy which decreases at higher densities makes the kaon-condensed neutron star matter fully protonized. This effect inhibits strongly direct URCA processes resulting in slower cooling of neutron stars as only kaon-induced URCA cycles are present. In contrast, for increasing symmetry energy direct URCA processes are allowed in the almost whole density range where the kaon condensation exists

  11. Compact Starburst Galaxies with Fast Outflows: Spatially Resolved Stellar Mass Profiles

    Science.gov (United States)

    Gottlieb, Sophia; Diamond-Stanic, Aleksandar; Lipscomb, Charles; Ohene, Senyo; Rines, Josh; Moustakas, John; Sell, Paul; Tremonti, Christy; Coil, Alison; Rudnick, Gregory; Hickox, Ryan C.; Geach, James; Kepley, Amanda

    2018-01-01

    Powerful galactic winds driven by stellar feedback and black hole accretion are thought to play an important role in regulating star formation in galaxies. In particular, strong stellar feedback from supernovae, stellar winds, radiation pressure, and cosmic rays is required by simulations of star-forming galaxies to prevent the vast majority of baryons from cooling and collapsing to form stars. However, it remains unclear whether these stellar processes play a significant role in expelling gas and shutting down star formation in massive progenitors of quiescent galaxies. What are the limits of stellar feedback? We present multi-band photometry with HST/WFC3 (F475W, F814W, F160W) for a dozen compact starburst galaxies at z~0.6 with half-light radii that suggest incredibly large central escape velocities. These massive galaxies are driving fast (>1000 km/s) outflows that have been previously attributed to stellar feedback associated with the compact (r~100 pc) starburst. But how compact is the stellar mass? In the context of the stellar feedback hypothesis, it is unclear whether these fast outflows are being driven at velocities comparable to the escape velocity of an incredibly dense stellar system (as predicted by some models of radiation-pressure winds) or at velocities that exceed the central escape velocity by large factor. Our spatially resolved measurements with HST show that the stellar mass is more extended than the light, and this requires that the physical mechanism responsible for driving the winds must be able to launch gas at velocities that are factors of 5-10 beyond the central escape velocity.

  12. Multiple stellar generations in the Large Magellanic Cloud Star Cluster NGC 1846

    Science.gov (United States)

    Milone, Antonino

    2010-09-01

    The recent discovery of multiple stellar populations in massive Galactic globular clusters poses a serious challenge for models of star cluster formation and evolution. The finding of multiple main sequences in the massive clusters NGC 2808 and omega Centauri, and multiple sub-giant-branch in NGC 1851 and many other globulars have demonstrated that star clusters are not as simple as we have imagined for decades. Surprisingly the only way to explain the main sequence splitting appears to be Helium enrichment, up to an astonishingly high Y 0.40.An unique angle on this problem can be provided by intermediate-age clusters in the Magellanic Clouds with peculiar main-sequence turn-off morphologies. Recent discoveries, based on ACS data of unparalleled photometric accuracy, have demonstrated that the CMDs of a large fraction of these clusters { 70 %} are not consistent with the simple, single stellar population hypothesis. Explanations for what conditions could give rise to multiple populations in Galactic Globular Clusters remain controversial; this is even more the case for LMC clustersTo properly constraint the multipopulation phenomenon in Magellanic Cloud star clusters, we propose deep UV/IR imaging of NGC 1846, a star cluster where multiple populations have already been identified. The proposed observation will allow us to accurately measure the age difference between the stellar populations providing fundamental clues on the formation mechanism. Our simulations of WFC3 performance suggest that we will be able to detect even the main sequence splitting caused by small He differences {Delta Y 0.02}.

  13. Extended Main-sequence Turn-offs in Intermediate-age Star Clusters: Stellar Rotation Diminishes, but Does Not Eliminate, Age Spreads

    Energy Technology Data Exchange (ETDEWEB)

    Goudfrooij, Paul; Correnti, Matteo [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Girardi, Léo, E-mail: goudfroo@stsci.edu [Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova (Italy)

    2017-09-01

    Extended main-sequence turn-off (eMSTO) regions are a common feature in color–magnitude diagrams of young- and intermediate-age star clusters in the Magellanic Clouds. The nature of eMSTOs remains debated in the literature. The currently most popular scenarios are extended star formation activity and ranges of stellar rotation rates. Here we study details of differences in main-sequence turn-off (MSTO) morphology expected from spreads in age versus spreads in rotation rates, using Monte Carlo simulations with the Geneva syclist isochrone models that include the effects of stellar rotation. We confirm a recent finding of Niederhofer et al. that a distribution of stellar rotation velocities yields an MSTO extent that is proportional to the cluster age, as observed. However, we find that stellar rotation yields MSTO crosscut widths that are generally smaller than observed ones at a given age. We compare the simulations with high-quality Hubble Space Telescope data of NGC 1987 and NGC 2249, which are the two only relatively massive star clusters with an age of ∼1 Gyr for which such data is available. We find that the distribution of stars across the eMSTOs of these clusters cannot be explained solely by a distribution of stellar rotation velocities, unless the orientations of rapidly rotating stars are heavily biased toward an equator-on configuration. Under the assumption of random viewing angles, stellar rotation can account for ∼60% and ∼40% of the observed FWHM widths of the eMSTOs of NGC 1987 and NGC 2249, respectively. In contrast, a combination of distributions of stellar rotation velocities and stellar ages fits the observed eMSTO morphologies very well.

  14. Stellar Feedback in Massive Star-Forming Regions

    Science.gov (United States)

    Baldwin, Jack; Pellegrini, Eric; Ferland, Gary; Murray, Norm; Hanson, Margaret

    2008-02-01

    Star formation rates and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study in the two nearest giant star-forming regions to nail down the physics that produces the 10-20 parsec bubbles seen to surround young massive clusters in the Milky Way. This will determine if and how the clusters disrupt their natal giant molecular clouds (GMCs). Here we request 4 nights on the Blanco telescope to obtain dense grids of optical long-slit spectra criss-crossing each nebula. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3000 different spots in each nebula. From this we can determine a number of dynamically important quantities, such as the gas density and temperature, hence pressure in and around these bubbles. These quantities can be compared to the dynamical (gravitationally induced) pressure, and the radiation pressure. All can be employed in dynamical models for the evolution of a GMC under the influence of an embedded massive star cluster. This research will elucidate the detailed workings of the star-forming regions which dominate the star formation rate in the Milky Way, and also will steadily improve our calibration and understanding of more distant, less well-resolved objects such as ULIRGS, Lyman break, and submillimeter galaxies.

  15. The Core Mass Growth and Stellar Lifetime of Thermally Pulsing Asymptotic Giant Branch Stars

    Science.gov (United States)

    Kalirai, Jason S.; Marigo, Paola; Tremblay, Pier-Emmanuel

    2014-02-01

    We establish new constraints on the intermediate-mass range of the initial-final mass relation, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). These constraints derive from newly discovered (bright) white dwarfs in the nearby Hyades and Praesepe star clusters, including a total of 18 high signal-to-noise ratio measurements with progenitor masses of M initial = 2.8-3.8 M ⊙. We also include a new analysis of existing white dwarfs in the older NGC 6819 and NGC 7789 star clusters, M initial = 1.6 and 2.0 M ⊙. Over this range of initial masses, stellar evolutionary models for metallicity Z initial = 0.02 predict the maximum growth of the core of TP-AGB stars. By comparing the newly measured remnant masses to the robust prediction of the core mass at the first thermal pulse on the AGB (i.e., from stellar interior models), we establish several findings. First, we show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with M initial = 1.6 to 2.0 M ⊙. At larger masses, the core-mass growth decreases steadily to ~10% at M initial = 3.4 M ⊙, after which there is a small hint of a upturn out to M initial = 3.8 M ⊙. These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the literature, as well as of the third dredge-up efficiency as a function of the stellar mass. Finally, we estimate the lifetime and the integrated luminosity of stars on the TP-AGB to peak at t ~ 3 Myr and E = 1.2 × 1010 L ⊙ yr for M initial ~ 2 M ⊙ (t ~ 2 Myr

  16. VERIFYING ASTEROSEISMICALLY DETERMINED PARAMETERS OF KEPLER STARS USING HIPPARCOS PARALLAXES: SELF-CONSISTENT STELLAR PROPERTIES AND DISTANCES

    Energy Technology Data Exchange (ETDEWEB)

    Silva Aguirre, V.; Chaplin, W. J.; Bedding, T. R.; Christensen-Dalsgaard, J.; Kjeldsen, H. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Campante, T. L.; Monteiro, M. J. P. F. G. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Huber, D. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Miglio, A.; Elsworth, Y.; Hekker, S. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Serenelli, A. M.; Garcia, R. A.; Mathur, S. [Kavli Institute for Theoretical Physics, Santa Barbara, CA 93106 (United States); Ballot, J. [CNRS, Institut de Recherche en Astrophysique et Planetologie, 14 avenue Edouard Belin, F-31400 Toulouse (France); Creevey, O. L. [Laboratoire Lagrange, UMR 7293, Universite de Nice Sophia-Antipolis, CNRS, Observatoire de la Cote dAzur, F-06304 Nice Cedex 4 (France); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA (United States); Metcalfe, T. S. [Space Science Institute, Boulder, CO 80301 (United States); and others

    2012-09-20

    Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution.

  17. Ageing in old degenerates: asteroseismology of white dwarf stars

    International Nuclear Information System (INIS)

    O'Donoghue, D.

    1988-01-01

    Recent results on the use of pulsations in white dwarf stars as seismic probes of their structure are reviewed. The evolution of stars to the white dwarf stage is first described, followed by a discussion of their structure as expected from the theory of stellar evolution. A summary of the salient points of stellar pulsation theory is given and then compared with observations of pulsating white dwarfs: the pulsations are non-radial 'g-mode' pulsations and occur in all white dwarfs as they cool through the temperature ranges defining each of the four 'instability strips' on the white dwarf cooling curve. The presence of only some of the possible pulsation modes in any given star suggest that a filter mechanism to select these modes is at work, possibly the chemical stratification of the star. The pulsation periods can be measured very accurately so that period changes, due to evolutionary cooling, can be detected over relatively short intervals (2 - 30 years). The detection of such period changes can be used to place interesting limits on the age of the Galaxy and ultimately the age of the Universe. 17 refs., 10 figs., 2 tabs

  18. The 12C/13C ratio in stellar atmospheres. VI. Five luminous cool stars

    International Nuclear Information System (INIS)

    Hinkle, K.H.; Lambert, D.L.; Snell, R.L.

    1976-01-01

    The isotopic abundance ratio, 12 C/ 13 C, is derived from the CO vibration rotation lines at 1.6 and 2.3 μ for five cool luminous stars by a simple curve-of-growth technique. A new analysis of CN lines at 8000 A is also described for α Sco and α Ori. Results derived independently from CO and CN are in agreement. Final results are 12 C/ 13 C=7 +- 2(α Ori), 12 +- 3(α Sco), 7 +- 3(β Peg), 25 +- 7(chi Cyg), 17 +- 4(α Her), and 7 +- 1.5(α Boo). The α Boo analysis provides a check on the CO curve-of-growth technique; the 12 C/ 13 C ratio from the 2.3 μ CO lines is in good agreement with the previously determined ratio from CN and CH lines

  19. Hypervelocity stars from young stellar clusters in the Galactic Centre

    Science.gov (United States)

    Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

    2017-05-01

    The enormous velocities of the so-called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of HVSs as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High-velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  20. Neutrino energy loss rate in a stellar plasma

    International Nuclear Information System (INIS)

    Esposito, S.; Mangano, G.; Miele, G.; Picardi, I.; Pisanti, O.

    2003-01-01

    We review the purely leptonic neutrino emission processes, contributing to the energy loss rate of the stellar plasma. We perform a complete analysis up to the first order in the electromagnetic coupling constant. In particular the radiative electromagnetic corrections, at order α, to the process e + e - →νν-bar at finite density and temperature have been computed. This process gives one of the main contributions to the cooling of stellar interior in the late stages of star evolution. As a result of the analysis we find that the corrections affect the energy loss rate, computed at tree level, by a factor (-4-1)% in the temperature and density region where the pair annihilation is the most efficient cooling mechanism

  1. Stellar systems fed by outside stars: the evolution of model galactic nuclei

    International Nuclear Information System (INIS)

    Dokuchaev, V.I.; Ozernoi, L.M.

    1985-01-01

    Through relaxation mechanisms, a dense central core surrounded by an extended, rarefied stellar system in a nonisothermal galactic nuclear region can be kept supplied with energy and mass conveyed by incoming stars. These factors may significantly influence the secular evolution of the core, competing with the conventional star-evaporation process. Under certain circumstances the outside environment will in fact dominate the core evolution, causing not collapse but expansion

  2. Star formation in N-body simulations .1. The impact of the stellar ultraviolet radiation on star formation

    NARCIS (Netherlands)

    Gerritsen, JPE; Icke, [No Value

    We present numerical simulations of isolated disk galaxies including gas dynamics and star formation. The gas is allowed to cool to 10 K, while heating of the gas is provided by the far-ultraviolet flux of all stars. Stars are allowed to form from the gas according to a Jeans instability criterion:

  3. Young stellar population and star formation history ofW4 HII region/Cluster Complex

    Science.gov (United States)

    Panwar, Neelam

    2018-04-01

    The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to thei! r immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

  4. The core mass growth and stellar lifetime of thermally pulsing asymptotic giant branch stars

    International Nuclear Information System (INIS)

    Kalirai, Jason S.; Tremblay, Pier-Emmanuel; Marigo, Paola

    2014-01-01

    We establish new constraints on the intermediate-mass range of the initial-final mass relation, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). These constraints derive from newly discovered (bright) white dwarfs in the nearby Hyades and Praesepe star clusters, including a total of 18 high signal-to-noise ratio measurements with progenitor masses of M initial = 2.8-3.8 M ☉ . We also include a new analysis of existing white dwarfs in the older NGC 6819 and NGC 7789 star clusters, M initial = 1.6 and 2.0 M ☉ . Over this range of initial masses, stellar evolutionary models for metallicity Z initial = 0.02 predict the maximum growth of the core of TP-AGB stars. By comparing the newly measured remnant masses to the robust prediction of the core mass at the first thermal pulse on the AGB (i.e., from stellar interior models), we establish several findings. First, we show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with M initial = 1.6 to 2.0 M ☉ . At larger masses, the core-mass growth decreases steadily to ∼10% at M initial = 3.4 M ☉ , after which there is a small hint of a upturn out to M initial = 3.8 M ☉ . These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the literature, as well as of the third dredge-up efficiency as a function of the stellar mass. Finally, we estimate the lifetime and the integrated luminosity of stars on the TP-AGB to peak at t ∼ 3 Myr and E = 1.2 × 10 10 L ☉ yr for M initial ∼ 2 M

  5. The core mass growth and stellar lifetime of thermally pulsing asymptotic giant branch stars

    Energy Technology Data Exchange (ETDEWEB)

    Kalirai, Jason S.; Tremblay, Pier-Emmanuel [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Marigo, Paola, E-mail: jkalirai@stsci.edu, E-mail: paola.marigo@unipd.it, E-mail: ptremblay@lsw.uni-heidelberg.de [Department of Physics and Astronomy, University of Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy)

    2014-02-10

    We establish new constraints on the intermediate-mass range of the initial-final mass relation, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). These constraints derive from newly discovered (bright) white dwarfs in the nearby Hyades and Praesepe star clusters, including a total of 18 high signal-to-noise ratio measurements with progenitor masses of M {sub initial} = 2.8-3.8 M {sub ☉}. We also include a new analysis of existing white dwarfs in the older NGC 6819 and NGC 7789 star clusters, M {sub initial} = 1.6 and 2.0 M {sub ☉}. Over this range of initial masses, stellar evolutionary models for metallicity Z {sub initial} = 0.02 predict the maximum growth of the core of TP-AGB stars. By comparing the newly measured remnant masses to the robust prediction of the core mass at the first thermal pulse on the AGB (i.e., from stellar interior models), we establish several findings. First, we show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with M {sub initial} = 1.6 to 2.0 M {sub ☉}. At larger masses, the core-mass growth decreases steadily to ∼10% at M {sub initial} = 3.4 M {sub ☉}, after which there is a small hint of a upturn out to M {sub initial} = 3.8 M {sub ☉}. These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the literature, as well as of the third dredge-up efficiency as a function of the stellar mass. Finally, we estimate the lifetime and the integrated luminosity of stars on the TP-AGB to peak at t

  6. THE ESTIMATION OF STAR FORMATION RATES AND STELLAR POPULATION AGES OF HIGH-REDSHIFT GALAXIES FROM BROADBAND PHOTOMETRY

    International Nuclear Information System (INIS)

    Lee, Seong-Kook; Ferguson, Henry C.; Somerville, Rachel S.; Wiklind, Tommy; Giavalisco, Mauro

    2010-01-01

    We explore methods to improve the estimates of star formation rates and mean stellar population ages from broadband photometry of high-redshift star-forming galaxies. We use synthetic spectral templates with a variety of simple parametric star formation histories to fit broadband spectral energy distributions. These parametric models are used to infer ages, star formation rates, and stellar masses for a mock data set drawn from a hierarchical semi-analytic model of galaxy evolution. Traditional parametric models generally assume an exponentially declining rate of star formation after an initial instantaneous rise. Our results show that star formation histories with a much more gradual rise in the star formation rate are likely to be better templates, and are likely to give better overall estimates of the age distribution and star formation rate distribution of Lyman break galaxies (LBGs). For B- and V-dropouts, we find the best simple parametric model to be one where the star formation rate increases linearly with time. The exponentially declining model overpredicts the age by 100% and 120% for B- and V-dropouts, on average, while for a linearly increasing model, the age is overpredicted by 9% and 16%, respectively. Similarly, the exponential model underpredicts star formation rates by 56% and 60%, while the linearly increasing model underpredicts by 15% and 22%, respectively. For U-dropouts, the models where the star formation rate has a peak (near z ∼ 3) provide the best match for age-overprediction is reduced from 110% to 26%-and star formation rate-underprediction is reduced from 58% to 22%. We classify different types of star formation histories in the semi-analytic models and show how the biases behave for the different classes. We also provide two-band calibration formulae for stellar mass and star formation rate estimations.

  7. 3D radiative transfer in stellar atmospheres

    International Nuclear Information System (INIS)

    Carlsson, M

    2008-01-01

    Three-dimensional (3D) radiative transfer in stellar atmospheres is reviewed with special emphasis on the atmospheres of cool stars and applications. A short review of methods in 3D radiative transfer shows that mature methods exist, both for taking into account radiation as an energy transport mechanism in 3D (magneto-) hydrodynamical simulations of stellar atmospheres and for the diagnostic problem of calculating the emergent spectrum in more detail from such models, both assuming local thermodynamic equilibrium (LTE) and in non-LTE. Such methods have been implemented in several codes, and examples of applications are given.

  8. Exterior Companions to Hot Jupiters Orbiting Cool Stars Are Coplanar

    Science.gov (United States)

    Becker, Juliette C.; Vanderburg, Andrew; Adams, Fred C.; Khain, Tali; Bryan, Marta

    2017-12-01

    The existence of hot Jupiters has challenged theories of planetary formation since the first extrasolar planets were detected. Giant planets are generally believed to form far from their host stars, where volatile materials like water exist in their solid phase, making it easier for giant planet cores to accumulate. Several mechanisms have been proposed to explain how giant planets can migrate inward from their birth sites to short-period orbits. One such mechanism, called Kozai-Lidov migration, requires the presence of distant companions in orbits inclined by more than ˜40° with respect to the plane of the hot Jupiter’s orbit. The high occurrence rate of wide companions in hot-Jupiter systems lends support to this theory for migration. However, the exact orbital inclinations of these detected planetary and stellar companions is not known, so it is not clear whether the mutual inclination of these companions is large enough for the Kozai-Lidov process to operate. This paper shows that in systems orbiting cool stars with convective outer layers, the orbits of most wide planetary companions to hot Jupiters must be well aligned with the orbits of the hot Jupiters and the spins of the host stars. For a variety of possible distributions for the inclination of the companion, the width of the distribution must be less than ˜20° to recreate the observations with good fidelity. As a result, the companion orbits are likely well aligned with those of the hot Jupiters, and the Kozai-Lidov mechanism does not enforce migration in these systems.

  9. BI VULPECULAE: A SIAMESE TWIN WITH TWO VERY SIMILAR COOL STARS IN SHALLOW CONTACT

    Energy Technology Data Exchange (ETDEWEB)

    Qian, S.-B.; Liu, N.-P.; He, J.-J.; Zhu, L.-Y.; Zhao, E. G.; Wang, J.-J.; Li, L.-J.; Jiang, L.-Q. [Yunnan Observatories, Chinese Academy of Sciences (CAS), P. O. Box 110, 650011 Kunming (China); Li, K., E-mail: qsb@ynao.ac.cn [School of Space Science and Physics, Shandong University, Weihai, 264209 Weihai (China)

    2013-11-01

    BI Vul is a cool eclipsing binary star (Sp. = K3 V) with a short period of 0.2518 days. The first charge-coupled device (CCD) light curves of the binary in the BVRI obtained on 2012 August 21 are presented and are analyzed using the Wilson-Devinney code. It is discovered that BI Vul is a marginal contact binary system (f = 8.7%) that contains two very similar cool components (q = 1.037). Both the marginal contact configuration and the extremely high mass ratio suggest that it is presently evolving into contact with little mass transfer between the components and it is at the beginning stage of contact evolution. By using all available times of minimum light, the variations in the orbital period are investigated for the first time. We find that the observed – calculated (O – C) curve of BI Vul shows a cyclic change with a period of 10.8 yr and an amplitude of 0.0057 days, while it undergoes a downward parabolic variation. The cyclic oscillation is analyzed for the light-travel time effect that arises from the gravitational influence of a possible third stellar object. The mass and orbital separation of the third body are estimated as M {sub 3} ∼ 0.30 M {sub ☉} and ∼4.9 AU, respectively. The downward parabolic change reveals a long-term period decrease at a rate of P-dot = -9.5 x 10{sup -8} days yr{sup –1}. The period decrease may be caused by angular momentum loss via magnetic stellar wind and/or it is only a part of a long-period (longer than 32 yr) cyclic variation, which may reveal the presence of another stellar companion in a wider orbit. These observational properties indicate that the formation of the Siamese twin is driven by magnetic braking and the third stellar companion should play an important role by removing angular momentum from the central binary.

  10. Tracing dust in old stellar populations : the mid-infrared spectrum of globular cluster AGB stars

    International Nuclear Information System (INIS)

    Richter, H.

    2010-01-01

    Asymptotic Giant Branch (AGB) stars are considered to be the main stellar dust producers in the universe. Their dusty circumstellar shells leave fingerprints in the mid-infrared (MIR) spectra of AGB stars and in unresolved old stellar populations. Bressan et al. (2007) showed that co-added MIR-spectra of AGB stars of known luminosity, metallicity and age (like those found in the Galactic globular cluster NGC104) can be used to model the dust excess in early-type galaxies. This work aims to improve our understanding of the MIR-spectra of old stellar populations with respect to their metallicities by studying a large sample of AGB stars in Galactic globular clusters. A sample of AGB stars (taken from Lebzelter et al. 2006 and Sloan et al. 2010) is used to produce co-added MIR-spectra of globular cluster combinations for three metallicity groups. Each group consists of several globular clusters with similar age and metallicity. Combining the clusters leads to a higher number of AGB stars with available Spitzer spectra in each group. The low metallicity group (Z=0.0038) consists of five globular clusters with 18 AGB star spectra, the intermediate (Z=0.0058) and high (Z=0.01) metallicity groups both include three clusters with eight and seven available MIR-spectra, respectively. Stars within the 90% mass radius of each globular cluster are used to generate 2MASS Color- Magnitude diagrams (CMDs) of each cluster combination. Binning the stars in the CMDs with respect to their MK-values results in Luminosity Functions (LFs) for the cluster combinations. The LFs based on 2MASS data are compared to LFs obtained using theoretical isochrones from the Padova group (Bertelli et al. 2008, Marigo et al. 2008). Using the 2MASS LFs integrated MIR-spectra of the three globular cluster combinations are derived by weighting the existing spectra with the total number of AGB stars within each MK-bin of the LFs along the upper giant branch. This relies on the assumption that stars that

  11. Structure and thermal evolution of spinning-down neutron stars

    International Nuclear Information System (INIS)

    Negreiros, R.; Schramm, S.; Weber, F.

    2011-01-01

    In this paper we address the effects of spin-down on the cooling of neutron stars. During its evolution, stellar composition and structure might be substantially altered, as a result of spin-down and the consequent density increase. Since the timescale of cooling might be comparable to to that of the spin-evolution, the modifications to the structure/composition might have important effects on the thermal evolution of the object. We show that the direct Urca process might be delayed or supressed, when spin-down is taken into account. This leads to neutron stars with slow cooling, as opposed to enhanced cooling as would be the case if a "froze-in" structure and composition were considered. In conclusion we demonstrate that the inclusion of spin-down effects on the cooling of neutron stars have far-reaching implications for the interpretation of pulsars. (author)

  12. Recovering star formation histories: Integrated-light analyses vs. stellar colour-magnitude diagrams

    Science.gov (United States)

    Ruiz-Lara, T.; Pérez, I.; Gallart, C.; Alloin, D.; Monelli, M.; Koleva, M.; Pompei, E.; Beasley, M.; Sánchez-Blázquez, P.; Florido, E.; Aparicio, A.; Fleurence, E.; Hardy, E.; Hidalgo, S.; Raimann, D.

    2015-11-01

    Context. Accurate star formation histories (SFHs) of galaxies are fundamental for understanding the build-up of their stellar content. However, the most accurate SFHs - those obtained from colour-magnitude diagrams (CMDs) of resolved stars reaching the oldest main-sequence turnoffs (oMSTO) - are presently limited to a few systems in the Local Group. It is therefore crucial to determine the reliability and range of applicability of SFHs derived from integrated light spectroscopy, as this affects our understanding of unresolved galaxies from low to high redshift. Aims: We evaluate the reliability of current full spectral fitting techniques in deriving SFHs from integrated light spectroscopy by comparing SFHs from integrated spectra to those obtained from deep CMDs of resolved stars. Methods: We have obtained a high signal-to-noise (S/N ~ 36.3 per Å) integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC) using EFOSC2 at the 3.6-metre telescope at La Silla Observatory. For this same field, resolved stellar data reaching the oMSTO are available. We have compared the star formation rate (SFR) as a function of time and the age-metallicity relation (AMR) obtained from the integrated spectrum using STECKMAP, and the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of completeness we also use and discuss other synthesis codes (STARLIGHT and ULySS) to derive the SFR and AMR from the integrated LMC spectrum. Results: We find very good agreement (average differences ~4.1%) between the SFR (t) and the AMR obtained using STECKMAP on the integrated light spectrum, and the CMD analysis. STECKMAP minimizes the impact of the age-metallicity degeneracy and has the advantage of preferring smooth solutions to recover complex SFHs by means of a penalized χ2. We find that the use of single stellar populations (SSPs) to recover the stellar content, using for instance STARLIGHT or ULySS codes, hampers the reconstruction of the SFR (t) and AMR

  13. Variable Stars in (Not Only) Dwarf Galaxies : Key Tools to Constrain Distances and Stellar Content

    NARCIS (Netherlands)

    Fiorentino, G.; Koleva, M; Prugniel, P; Vauglin,

    2011-01-01

    The important role of Cepheid and RR Lyrae variable stars and what they teach us about dwarf galaxies is discussed. Despite ever improving star formation histories of Local Group dwarf galaxies uncertainties remain, in particular in the identification and characterisation of the oldest stellar

  14. Modeling the Cloudy Atmospheres of Cool Stars, Brown Dwarfs and Hot Exoplanets

    DEFF Research Database (Denmark)

    Juncher, Diana

    M-dwarfs are very attractive targets when searching for new exoplanets. Unfortunately, they are also very difficult to model since their temperatures are low enough for dust clouds to form in their atmospheres. Because the properties of an exoplanet cannot be determined without knowing the proper......M-dwarfs are very attractive targets when searching for new exoplanets. Unfortunately, they are also very difficult to model since their temperatures are low enough for dust clouds to form in their atmospheres. Because the properties of an exoplanet cannot be determined without knowing......-consistent cloudy atmosphere models that can be used to properly determine the stellar parameters of cool stars. With this enhanced model atmosphere code I have created a grid of cool, dusty atmosphere models ranging in effective temperatures from Teff = 2000 − 3000 K. I have studied the formation and structure...... of their clouds and found that their synthetic spectra fit the observed spectra of mid to late type M-dwarfs and early type L-dwarfs well. With additional development into even cooler regimes, they could be used to characterize the atmospheres of exoplanets and aid us in our search for the kind of chemical...

  15. FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

    Energy Technology Data Exchange (ETDEWEB)

    Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Muirhead, Philip S. [Institute for Astrophysical Research, Boston University, Boston, MA (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, South Bend, IN (United States); Hinkley, Sasha [Department of Physics and Astronomy, University of Exeter, Exeter (United Kingdom); Morton, Timothy D., E-mail: dpiskorz@gps.caltech.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)

    2015-12-01

    Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits.

  16. FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

    International Nuclear Information System (INIS)

    Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin; Muirhead, Philip S.; Crepp, Justin R.; Hinkley, Sasha; Morton, Timothy D.

    2015-01-01

    Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits

  17. THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

    International Nuclear Information System (INIS)

    Salmon, Brett; Papovich, Casey; Tilvi, Vithal; Finkelstein, Steven L.; Finlator, Kristian; Behroozi, Peter; Lu, Yu; Wechsler, Risa H.; Dahlen, Tomas; Ferguson, Henry C.; Davé, Romeel; Dekel, Avishai; Dickinson, Mark; Giavalisco, Mauro; Long, James; Mobasher, Bahram; Reddy, Naveen; Somerville, Rachel S.

    2015-01-01

    Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M ⋆ a with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M ☉ yr –1 ) < 0.3-0.4 dex, for galaxies with log M * /M ☉ > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot gas ), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation

  18. Stellar formation

    CERN Document Server

    Reddish, V C

    1978-01-01

    Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

  19. Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

    NARCIS (Netherlands)

    Beck, P.G.; Montalban, J.; Kallinger, T.; De Ridder, J.; Aerts, C.; García, R.A.; Hekker, S.; Dupret, M.-A.; Mosser, B.; Eggenberger, P.; Stello, D.; Elsworth, Y.; Frandsen, S.; Carrier, F.; Hillen, M.; Gruberbauer, M.; Christensen-Dalsgaard, J.; Miglio, A.; Valentini, M.; Bedding, T.R.; Kjeldsen, H.; Girouard, F.R.; Hall, J.R.; Ibrahim, K.A.

    2012-01-01

    When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars

  20. Stellar 'Incubators' Seen Cooking up Stars

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1 [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 2Figure 3Figure 4Figure 5 This image composite compares visible-light and infrared views from NASA's Spitzer Space Telescope of the glowing Trifid Nebula, a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius. Visible-light images of the Trifid taken with NASA's Hubble Space Telescope, Baltimore, Md. (inside left, figure 1) and the National Optical Astronomy Observatory, Tucson, Ariz., (outside left, figure 1) show a murky cloud lined with dark trails of dust. Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust (outlined by yellow circles), which are 'incubators' for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside. These embryos are indicated with arrows in the false-color Spitzer picture (right, figure 1), taken by the telescope's infrared array camera. The same embryos cannot be seen in the visible-light pictures (left, figure 1). Spitzer found clusters of embryos in two of the cores and only single embryos in the other two. This is one of the first times that multiple embryos have been observed in individual cores at this early stage of stellar development.

  1. A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster

    Science.gov (United States)

    McDonald, M.; Bayliss, M.; Benson, B. A.; Foley, R. J.; Ruel, J.; Sullivan, P.; Veilleux, S.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; hide

    2012-01-01

    In the cores of some galaxy clusters the hot intracluster plasma is dense enough that it should cool radiatively in the cluster s lifetime, leading to continuous "cooling flows" of gas sinking towards the cluster center, yet no such cooling flow has been observed. The low observed star formation rates and cool gas masses for these "cool core" clusters suggest that much of the cooling must be offset by astrophysical feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical, and infrared observations of the galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an exceptionally luminous (L(sub 2-10 keV) = 8.2 10(exp 45) erg/s) galaxy cluster which hosts an extremely strong cooling flow (M(sub cool) = 3820 +/- 530 Stellar Mass/yr). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (740 +/- 160 Stellar Mass/ yr), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form via accretion of the intracluster medium, rather than the current picture of central galaxies assembling entirely via mergers.

  2. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Wuyts, Stijn; Förster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter; Guo Yicheng; Giavalisco, Mauro; Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth; Bell, Eric F.; Dekel, Avishai; Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer; Hathi, Nimish P.; Huang, Kuang-Han; Newman, Jeffrey A.

    2012-01-01

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 10 M ☉ and have specific star formation rates (SFRs) above 1/t H . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to ∼20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z ∼ 1 and z ∼ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  3. Interactions between exoplanets and the winds of young stars

    Directory of Open Access Journals (Sweden)

    Vidotto A. A.

    2014-01-01

    Full Text Available The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star, we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.

  4. Massive star populations in I Zw 18: A probe of stellar evolution in the early universe

    OpenAIRE

    Schaerer, Daniel; de Mello, Duilia; Leitherer, Claus; Heldmann, Jennifer

    1998-01-01

    We present a study of the gaseous and stellar emission in I Zw18, the most metal-poor star-forming galaxy known. Archival HST WFPC2 and FOS data have been used to analyze the spatial distribution of [OIII], Halpha, and HeII 4686. The latter is used to identify Wolf-Rayet stars found by ground-based spectroscopy and to locate nebular HeII emission. Most of the HeII emission is associated with the NW stellar cluster, displaced from the surrounding shell-like [OIII] and Halpha emission. We found...

  5. Stellar population in star formation regions of galaxies

    Science.gov (United States)

    Gusev, Alexander S.; Shimanovskaya, Elena V.; Shatsky, Nikolai I.; Sakhibov, Firouz; Piskunov, Anatoly E.; Kharchenko, Nina V.

    2018-05-01

    We developed techniques for searching young unresolved star groupings (clusters, associations, and their complexes) and of estimating their physical parameters. Our study is based on spectroscopic, spectrophotometric, and UBVRI photometric observations of 19 spiral galaxies. In the studied galaxies, we found 1510 objects younger than 10 Myr and present their catalogue. Having combined photometric and spectroscopic data, we derived extinctions, chemical abundances, sizes, ages, and masses of these groupings. We discuss separately the specific cases, when the gas extinction does not agree with the interstellar one. We assume that this is due to spatial offset of Hii clouds with respect to the related stellar population.We developed a method to estimate age of stellar population of the studied complexes using their morphology and the relation with associated H emission region. In result we obtained the estimates of chemical abundances for 80, masses for 63, and ages for 57 young objects observed in seven galaxies.

  6. Stellar Parameters and Radial Velocities of Hot Stars in the Carina Nebula

    Science.gov (United States)

    Hanes, Richard J.; McSwain, M. Virginia; Povich, Matthew S.

    2018-05-01

    The Carina Nebula is an active star-forming region in the southern sky that is of particular interest due to the presence of a large number of massive stars in a wide array of evolutionary stages. Here, we present the results of the spectroscopic analysis of 82 B-type stars and 33 O-type stars that were observed in 2013 and 2014. For 82 B-type stars without line blending, we fit model spectra from the Tlusty BSTAR2006 grid to the observed profiles of Hγ and He λλ4026, 4388, and 4471 to measure the effective temperatures, surface gravities, and projected rotational velocities. We also measure the masses, ages, radii, bolometric luminosities, and distances of these stars. From the radial velocities measured in our sample, we find 31 single lined spectroscopic binary candidates. We find a high dispersion of radial velocities among our sample stars, and we argue that the Carina Nebula stellar population has not yet relaxed and become virialized.

  7. Environmental effects on stellar populations of star clusters and dwarf galaxies

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; Fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2017-03-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of gravitationally bound systems in an external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance. The developed theoretical framework has direct applications to the cases of massive star clusters, dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  8. The rise and fall of stellar across the peak of cosmic star formation history: effects of mergers versus diffuse stellar mass acquisition

    Science.gov (United States)

    Welker, C.; Dubois, Y.; Devriendt, J.; Pichon, C.; Kaviraj, S.; Peirani, S.

    2017-02-01

    Building galaxy merger trees from a state-of-the-art cosmological hydrodynamical simulation, Horizon-AGN, we perform a statistical study of how mergers and diffuse stellar mass acquisition processes drive galaxy morphologic properties above z > 1. By diffuse mass acquisition here, we mean both accretion of stars by unresolved mergers (relative stellar mass growth smaller than 4.5 per cent) as well as in situ star formation when no resolved mergers are detected along the main progenitor branch of a galaxy. We investigate how stellar densities, galaxy sizes and galaxy morphologies (defined via shape parameters derived from the inertia tensor of the stellar density) depend on mergers of different mass ratios. We investigate how stellar densities, effective radii and shape parameters derived from the inertia tensor depend on mergers of different mass ratios. We find strong evidence that diffuse stellar accretion and in situ formation tend to flatten small galaxies over cosmic time, leading to the formation of discs. On the other hand, mergers, and not only the major ones, exhibit a propensity to puff up and destroy stellar discs, confirming the origin of elliptical galaxies. We confirm that mergers grow galaxy sizes more efficiently than diffuse processes (r_{0.5}∝ M_s^{0.85} and r_{0.5}∝ M_s^{0.1} on average, respectively) and we also find that elliptical galaxies are more susceptible to grow in size through mergers than disc galaxies with a size-mass evolution r_{0.5}∝ M_s^{1.2} instead of r_{0.5}∝ M_s^{-0.5}-M^{0.5} for discs depending on the merger mass ratio. The gas content drives the size-mass evolution due to merger with a faster size growth for gas-poor galaxies r_{0.5}∝ M_s2 than for gas-rich galaxies r0.5 ∝ Ms.

  9. HOT STARS WITH HOT JUPITERS HAVE HIGH OBLIQUITIES

    International Nuclear Information System (INIS)

    Winn, Joshua N.; Albrecht, Simon; Fabrycky, Daniel; Johnson, John Asher

    2010-01-01

    We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T eff > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged more recently from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics and that disk migration plays at most a supporting role.

  10. Gravitational waves from axisymmetric rotating stellar core collapse to a neutron star in full general relativity

    International Nuclear Information System (INIS)

    Shibata, Masaru; Sekiguchi, Yu-ichirou

    2004-01-01

    Axisymmetric numerical simulations of rotating stellar core collapse to a neutron star are performed in the framework of full general relativity. The so-called Cartoon method, in which the Einstein field equations are solved in Cartesian coordinates and the axisymmetric condition is imposed around the y=0 plane, is adopted. The hydrodynamic equations are solved in cylindrical coordinates (on the y=0 plane in Cartesian coordinates) using a high-resolution shock-capturing scheme with maximum grid size (2500,2500). A parametric equation of state is adopted to model collapsing stellar cores and neutron stars following Dimmelmeier, Font, and Mueller. It is found that the evolution of the central density during the collapse, bounce, and formation of protoneutron stars agrees well with that in the work of Dimmelmeier, Font, and Mueller in which an approximate general relativistic formulation is adopted. This indicates that such an approximation is appropriate for following axisymmetric stellar core collapses and the subsequent formation of protoneutron stars. Gravitational waves are computed using a quadrupole formula. It is found that the waveforms are qualitatively in good agreement with those by Dimmelmeier, Font, and Mueller. However, quantitatively, two waveforms do not agree well. The possible reasons for the disagreement are discussed

  11. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, Giessenbachstr., D-85741 Garching (Germany); Guo Yicheng; Giavalisco, Mauro [Astronomy Department, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Dekel, Avishai [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hathi, Nimish P. [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States); Huang, Kuang-Han [Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Newman, Jeffrey A. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); and others

    2012-07-10

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 < z < 1.5 and 326 SFGs at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10{sup 10} M{sub Sun} and have specific star formation rates (SFRs) above 1/t{sub H} . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to {approx}20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z {approx} 1 and z {approx} 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  12. Stellar parameters and H α line profile variability of Be stars in the BeSOS survey

    Science.gov (United States)

    Arcos, C.; Kanaan, S.; Chávez, J.; Vanzi, L.; Araya, I.; Curé, M.

    2018-03-01

    The Be phenomenon is present in about 20 per cent of B-type stars. Be stars show variability on a broad range of time-scales, which in most cases is related to the presence of a circumstellar disc of variable size and structure. For this reason, a time-resolved survey is highly desirable in order to understand the mechanisms of disc formation, which are still poorly understood. In addition, a complete observational sample would improve the statistical significance of the study of stellar and disc parameters. The `Be Stars Observation Survey' (BeSOS) is a survey containing reduced spectra obtained using the Pontifica Universidad Católica High Echelle Resolution Optical Spectrograph (PUCHEROS) with a spectral resolution of 17 000 in the range 4260-7300 Å. BeSOS's main objective is to offer consistent spectroscopic and time-resolved data obtained with one instrument. The user can download or plot the data and obtain stellar parameters directly from the website. We also provide a star-by-star analysis based on photometric, spectroscopic and interferometric data, as well as general information about the whole BeSOS sample. Recently, BeSOS led to the discovery of a new Be star HD 42167 and facilitated study of the V/R variation of HD 35165 and HD 120324, the steady disc of HD 110335 and the Be shell status of HD 127972. Optical spectra used in this work, as well as the stellar parameters derived, are available online at http://besos.ifa.uv.cl.

  13. Axions from cooling compact stars: pair-breaking processes

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Jochen; Sedrakian, Armen [Frankfurt Univ. (Germany). Inst. fuer Theoretische Physik

    2013-07-01

    Once formed in a supernova explosion, a neutron star cools rapidly via neutrino emission during the first 10{sup 4}-10{sup 5} years of its life-time. Here we compute the axion emission rate from baryonic components of a star at temperatures below their respective critical temperatures T{sub c} for normal-superfluid phase transition. The axion production is driven by a charge neutral weak process, associated with Cooper pair breaking and recombination. The requirement that the axion cooling does not overshadow the neutrino cooling yields a lower bound on the axion decay constant f{sub a} > 6 x 10{sup 9} T{sup -1}{sub c9} GeV, with T{sub c9} = T{sub c}/10{sup 9} K. This translates into an upper bound on the axion mass m{sub a} < 10{sup -3} T{sub c9} eV.

  14. Axions from cooling compact stars: Pair-breaking processes

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Jochen [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany); Sedrakian, Armen, E-mail: sedrakian@th.physik.uni-frankfurt.de [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany)

    2013-01-02

    Once formed in a supernova explosion, a neutron star cools rapidly via neutrino emission during the first 10{sup 4}-10{sup 5} yr of its life-time. Here we compute the axion emission rate from baryonic components of a star at temperatures below their respective critical temperatures T{sub c} for normal-superfluid phase transition. The axion production is driven by a charge neutral weak process, associated with Cooper pair breaking and recombination. The requirement that the axion cooling does not overshadow the neutrino cooling puts a lower bound on the axion decay constant f{sub a}>6 Multiplication-Sign 10{sup 9}T{sub c9}{sup -1} GeV, with T{sub c9}=T{sub c}/10{sup 9} K. This translates into an upper bound on the axion mass m{sub a}<10{sup -3}T{sub c9} eV.

  15. Hα ACTIVITY OF OLD M DWARFS: STELLAR CYCLES AND MEAN ACTIVITY LEVELS FOR 93 LOW-MASS STARS IN THE SOLAR NEIGHBORHOOD

    International Nuclear Information System (INIS)

    Robertson, Paul; Endl, Michael; Cochran, William D.; Dodson-Robinson, Sarah E.

    2013-01-01

    Through the McDonald Observatory M Dwarf Planet Search, we have acquired nearly 3000 high-resolution spectra of 93 late-type (K5-M5) stars over more than a decade using the High Resolution Spectrograph on the Hobby-Eberly Telescope. This sample provides a unique opportunity to investigate the occurrence of long-term stellar activity cycles for low-mass stars. In this paper, we examine the stellar activity of our targets as reflected in the Hα feature. We have identified periodic signals for six stars, with periods ranging from days to more than 10 years, and find long-term trends for seven others. Stellar cycles with P ≥ 1 year are present for at least 5% of our targets. Additionally, we present an analysis of the time-averaged activity levels of our sample, and search for correlations with other stellar properties. In particular, we find that more massive, earlier type (M0-M2) stars tend to be more active than later type dwarfs. Furthermore, high-metallicity stars tend to be more active at a given stellar mass. We also evaluate Hα variability as a tracer of activity-induced radial velocity (RV) variation. For the M dwarf GJ 1170, Hα variation reveals stellar activity patterns matching those seen in the RVs, mimicking the signal of a giant planet, and we find evidence that the previously identified stellar activity cycle of GJ 581 may be responsible for the recently retracted planet f in that system. In general, though, we find that Hα is not frequently correlated with RV at the precision (typically 6-7 m s –1 ) of our measurements.

  16. THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

    Energy Technology Data Exchange (ETDEWEB)

    Salmon, Brett; Papovich, Casey; Tilvi, Vithal [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy Texas A and M University, College Station, TX 77843 (United States); Finkelstein, Steven L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Finlator, Kristian [DARK fellow, Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen O (Denmark); Behroozi, Peter; Lu, Yu; Wechsler, Risa H. [Physics Department, Stanford University, Particle Astrophysics, SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology Stanford, CA 94305 (United States); Dahlen, Tomas; Ferguson, Henry C. [Space Telescope Science Institute, Baltimore, MD (United States); Davé, Romeel [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Dekel, Avishai [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Dickinson, Mark [National Optical Astronomy Observatories, Tucson, AZ (United States); Giavalisco, Mauro [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Long, James [Department of Statistics, Texas A and M University, College Station, TX 77843-3143 (United States); Mobasher, Bahram; Reddy, Naveen [Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States); Somerville, Rachel S., E-mail: bsalmon@physics.tamu.edu [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States)

    2015-02-01

    Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M{sub ⋆}{sup a} with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M {sub ☉} yr{sup –1}) < 0.3-0.4 dex, for galaxies with log M {sub *}/M {sub ☉} > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot {sub gas}), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation.

  17. COMBINED EFFECTS OF BINARIES AND STELLAR ROTATION ON THE COLOR-MAGNITUDE DIAGRAMS OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Li Zhongmu; Mao Caiyan; Chen Li; Zhang Qian

    2012-01-01

    About 70% of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turnoffs, and dual red giant clumps. The observed result seems to be at odds with the classical idea that such clusters are simple stellar populations. Although many models have been used to explain the results via factors such as prolonged star formation history, metallicity spread, differential reddening, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows 'golf club' color-magnitude diagrams with broad or multiple turnoffs, dual red clumps, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams, including extended turnoff or multiple turnoffs, can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.

  18. Stellar parameters of Be stars observed with X-shooter

    Science.gov (United States)

    Shokry, A.; Rivinius, Th.; Mehner, A.; Martayan, C.; Hummel, W.; Townsend, R. H. D.; Mérand, A.; Mota, B.; Faes, D. M.; Hamdy, M. A.; Beheary, M. M.; Gadallah, K. A. K.; Abo-Elazm, M. S.

    2018-01-01

    Aims: The X-shooter archive of several thousand telluric standard star spectra was skimmed for Be and Be shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late-type Be stars and the extension of the Be phenomenon into early A stars. Methods: An adapted version of the BCD method is used, using the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but they are only useful for determining the pure emission contribution in a subsample of Be stars owing to uncertainties in determining the photospheric contribution. Results: A total of 78, mostly late-type, Be stars, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. We confirm the general trend that late-type Be stars have more tenuous disks and are less variable than early-type Be stars. The relatively large number (48) of relatively bright (V> 8.5) additional Be stars casts some doubt on the statistics of late-type Be stars; they are more common than currently thought. The Be/B star fraction may not strongly depend on spectral subtype. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 60.A-9022, 60.A-9024, 077.D-0085, 085.A-0962, 185.D-0056, 091.B-0900, and 093.D-0415.Table 6 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A108

  19. The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones

    Science.gov (United States)

    Truitt, Amanda R.; Young, Patrick A.

    2018-01-01

    I have investigated how stars of different mass and composition evolve, and how stellar evolution impacts the location of the habitable zone around a star. Current research into habitability of exoplanets focuses mostly on the concept of a “classical” HZ, the range of distances from a star over which liquid water could exist on a planet's surface. This is determined by the host star's luminosity and spectral characteristics; in order to gauge the habitability potential of a given system, both the evolutionary history and the detailed chemical characterization of the host star must be considered. With the ever-accelerating discovery of new exoplanets, it is imperative to develop a better understanding of what factors play a role in creating “habitable” conditions of a planet. I will discuss how stellar evolution is integral to how we define the HZ, and how this work will apply to the search for Earth-like planets in the future.I have developed a catalog of stellar evolution models for Sun-like stars with variable compositions; masses range from 0.1-1.2 Msol (spectral types M4-F4) at scaled metallicities (Z) of 0.1-1.5 Zsol, and O/Fe, C/Fe, and Mg/Fe values of 0.44-2.28, 0.58-1.72, and 0.54-1.84, respectively. I use a spread in abundance values based on observations of variability in nearby stars. It is important to understand how specific elements, not just total Z, impacts stellar lifetime. Time-dependent HZ boundaries are calculated for each track. I have also created a grid of M-dwarfs, and I am currently working to estimate stellar activity vs. age for each model.This catalog is meant to characterize potential host stars of interest. I have explored how to use existing observational data (i.e. Hypatia Catalog) for a more robust comparison to my grid of theoretical models, and I will discuss a new statistical analysis of the catalog to further refine our definition of “continuous” habitability. This work is an important step to assess whether a planet

  20. Prospects of detecting baryon and quark superfluidity from cooling neutron stars

    Science.gov (United States)

    Page; Prakash; Lattimer; Steiner

    2000-09-04

    Baryon and quark superfluidity in the cooling of neutron stars are investigated. Future observations will allow us to constrain combinations of the neutron or Lambda-hyperon pairing gaps and the star's mass. However, in a hybrid star with a mixed phase of hadrons and quarks, quark gaps larger than a few tenths of an MeV render quark matter virtually invisible for cooling. If the quark gap is smaller, quark superfluidity could be important, but its effects will be nearly impossible to distinguish from those of other baryonic constituents.

  1. Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

    Energy Technology Data Exchange (ETDEWEB)

    Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Martínez-Delgado, David [Max Planck Institut fur Astronomie, D-69117 Heidelberg (Germany); D' Onghia, Elena [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Zibetti, Stefano [INAF-Osservatorio Astrofisico di Arcetri, I-50125 Firenze (Italy); Gabany, R. Jay [Black Bird II Observatory, Alder Springs, CA 93602 (United States); Blanton, Michael, E-mail: rbeaton@virginia.edu [Department of Physics, New York University, New York, NY 10003 (United States)

    2014-08-01

    We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10{sup 8} M{sub ☉}, which implies a 1:50 merger ratio, has a circular radius, R{sub circ} ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10{sup 10} M{sub ☉}. Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M{sub ☉} yr{sup –1}). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

  2. Cannibalization and rebirth in the NGC 5387 system. I. The stellar stream and star-forming region

    International Nuclear Information System (INIS)

    Beaton, Rachael L.; Majewski, Steven R.; Johnson, Kelsey E.; Verbiscer, Anne; Martínez-Delgado, David; D'Onghia, Elena; Zibetti, Stefano; Gabany, R. Jay; Blanton, Michael

    2014-01-01

    We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on, spiral galaxy NGC 5387. An optically blue overdensity coincident with the stream intersection with the NGC 5387 disk was also identified in SDSS and in the Galaxy Evolution Explorer Deep Imaging Survey contributing 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features. The stellar stream is red in color, (B – V) = 0.7, has a stellar mass of 6 × 10 8 M ☉ , which implies a 1:50 merger ratio, has a circular radius, R circ ∼ 11.7 kpc, formed in ∼240 Myr, and the progenitor had a total mass of ∼4 × 10 10 M ☉ . Spectroscopy from LBT+MODS1 was used to determine that the blue overdensity is at the same redshift as NGC 5387, consists of young stellar populations (∼10 Myr), is metal-poor (12 + log (O/H) = 8.03), and is forming stars at an enhanced rate (∼1-3 M ☉ yr –1 ). The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation. Additional exploration of these scenarios is presented in a companion paper.

  3. The Constant Average Relationship Between Dust-obscured Star Formation and Stellar Mass from z=0 to z=2.5

    Science.gov (United States)

    Whitaker, Katherine E.; Pope, Alexandra; Cybulski, Ryan; Casey, Caitlin M.; Popping, Gergo; Yun, Min; 3D-HST Collaboration

    2018-01-01

    The total star formation budget of galaxies consists of the sum of the unobscured star formation, as observed in the rest-frame ultraviolet (UV), together with the obscured component that is absorbed and re-radiated by dust grains in the infrared. We explore how the fraction of obscured star formation depends (SFR) and stellar mass for mass-complete samples of galaxies at 0 MIPS 24μm photometry in the well-studied 5 extragalactic CANDELS fields. We find a strong dependence of the fraction of obscured star formation (f_obscured=SFR_IR/SFR_UV+IR) on stellar mass, with remarkably little evolution in this fraction with redshift out to z=2.5. 50% of star formation is obscured for galaxies with log(M/M⊙)=9.4 although unobscured star formation dominates the budget at lower masses, there exists a tail of low mass extremely obscured star-forming galaxies at z > 1. For log(M/M⊙)>10.5, >90% of star formation is obscured at all redshifts. We also show that at fixed total SFR, f_obscured is lower at higher redshift. At fixed mass, high-redshift galaxies are observed to have more compact sizes and much higher star formation rates, gas fractions and hence surface densities (implying higher dust obscuration), yet we observe no redshift evolution in f_obscured with stellar mass. This poses a challenge to theoretical models to reproduce, where the observed compact sizes at high redshift seem in tension with lower dust obscuration.

  4. Stellar Archeology: What White Dwarf Stars Tell Us About the History of the Galaxy

    Directory of Open Access Journals (Sweden)

    Terry D. Oswalt

    2012-06-01

    Full Text Available White dwarf stars have played important roles in rather diverse areas of astrophysics. This paper outlines how these stellar remnants, especially those in widely separated “fragile” binaries, have provided unique leverage on difficult astrophysical problems such as the ages of stars, the structure and evolution of the Galaxy, the nature of dark matter and even the discovery of dark energy.

  5. Environmental effects on stellar populations of dwarf galaxies and star clusters

    Science.gov (United States)

    Pasetto, Stefano; Cropper, Mark; fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2015-08-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation history of gravitationally bound system in an external environment. Ram pressure, Kelvin-Helmholtz instability, Rayleigh-Taylor, and tidal forces are accounted separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment useful in observational applications as well as theoretical interpretations of numerical results.We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance.The theoretical framework developed has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  6. TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

    2013-05-21

    We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

  7. TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

    International Nuclear Information System (INIS)

    Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

    2013-01-01

    We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

  8. Close Binaries in the Orion Nebula Cluster: On the Universality of Stellar Multiplicity and the Origin of Field Stars

    Science.gov (United States)

    Duchene, Gaspard; Lacour, Sylvestre; Moraux, Estelle; Bouvier, Jerome; Goodwin, Simon

    2018-01-01

    While stellar multiplicity is an ubiquitous outcome of star formation, there is a clear dichotomy between the multiplicity properties of young (~1 Myr-old) stellar clusters, like the ONC, which host a mostly field-like population of visual binaries, and those of equally young sparse populations, like the Taurus-Auriga region, which host twice as many stellar companions. Two distinct scenarios can account for this observation: one in which different star-forming regions form different number of stars, and one in which multiplicity properties are universal at birth but where internal cluster dynamics destroy many wide binaries. To solve this ambiguity, one must probe binaries that are sufficiently close so as not to be destroyed through interactions with other cluster members. To this end, we have conducted a survey for 10-100 au binaries in the ONC using the aperture masking technique with the VLT adaptive optics system. Among our sample of the 42 ONC members, we discovered 13 companions in this range of projected separations. This is consistent with the companion frequency observed in the Taurus population and twice as high as that observed among field stars. This survey thus strongly supports the idea that stellar multiplicity is characterized by near-universal initial properties that can later be dynamically altered. On the other hand, this exacerbates the question of the origin of field stars, since only clusters much denser than the ONC can effectively destroyed binaries closer than 100 au.

  9. H{alpha} ACTIVITY OF OLD M DWARFS: STELLAR CYCLES AND MEAN ACTIVITY LEVELS FOR 93 LOW-MASS STARS IN THE SOLAR NEIGHBORHOOD

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, Paul; Endl, Michael; Cochran, William D.; Dodson-Robinson, Sarah E., E-mail: paul@astro.as.utexas.edu [Department of Astronomy and McDonald Observatory, University of Texas at Austin, Austin, TX 78712 (United States)

    2013-02-10

    Through the McDonald Observatory M Dwarf Planet Search, we have acquired nearly 3000 high-resolution spectra of 93 late-type (K5-M5) stars over more than a decade using the High Resolution Spectrograph on the Hobby-Eberly Telescope. This sample provides a unique opportunity to investigate the occurrence of long-term stellar activity cycles for low-mass stars. In this paper, we examine the stellar activity of our targets as reflected in the H{alpha} feature. We have identified periodic signals for six stars, with periods ranging from days to more than 10 years, and find long-term trends for seven others. Stellar cycles with P {>=} 1 year are present for at least 5% of our targets. Additionally, we present an analysis of the time-averaged activity levels of our sample, and search for correlations with other stellar properties. In particular, we find that more massive, earlier type (M0-M2) stars tend to be more active than later type dwarfs. Furthermore, high-metallicity stars tend to be more active at a given stellar mass. We also evaluate H{alpha} variability as a tracer of activity-induced radial velocity (RV) variation. For the M dwarf GJ 1170, H{alpha} variation reveals stellar activity patterns matching those seen in the RVs, mimicking the signal of a giant planet, and we find evidence that the previously identified stellar activity cycle of GJ 581 may be responsible for the recently retracted planet f in that system. In general, though, we find that H{alpha} is not frequently correlated with RV at the precision (typically 6-7 m s{sup -1}) of our measurements.

  10. Evolving R Coronae Borealis Stars with MESA

    Science.gov (United States)

    Clayton, Geoffrey C.; Lauer, Amber; Chatzopoulos, Emmanouil; Frank, Juhan

    2018-01-01

    R Coronae Borealis (RCB) stars form a small class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He white dwarf (WD) binary and a final helium-shell flash. We are using a combination of 3D hydrodynamics codes and the 1D MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code including nucleosynthesis to construct post-merger spherical models based on realistic merger progenitor models and on our hydrodynamical simulations, and then following the evolution into the region of the HR diagram where RCB stars are located. We are investigating nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed.Our MESA modeling consists of two steps: first mimicking the WD merger event using two different techniques, (a) by choosing a very high mass accretion rate with appropriate abundances and (b) by applying "stellar engineering" to an initial CO WD model to account for the newly merged material by applying an entropy adjusting procedure. Second, we follow the post-merger evolution using a large nuclear reaction network including the effects of convective and rotational instabilities to the mixing of material in order to match the observed RCB abundances. MESA follows the evolution of the merger product as it expands and cools to become an RCB star. We then examine the surface abundances and compare them to the observed RCB abundances. We also investigate how long fusion continues in the He shell near the core and how this processed material is mixed up to the surface of the star. We then model the later evolution of RCB stars to determine their likely lifetimes and endpoints when they have returned to

  11. The relative impact of photoionizing radiation and stellar winds on different environments

    Science.gov (United States)

    Haid, S.; Walch, S.; Seifried, D.; Wünsch, R.; Dinnbier, F.; Naab, T.

    2018-05-01

    Photoionizing radiation and stellar winds from massive stars deposit energy and momentum into the interstellar medium (ISM). They might disperse the local ISM, change its turbulent multi-phase structure, and even regulate star formation. Ionizing radiation dominates the massive stars' energy output, but the relative effect of winds might change with stellar mass and the properties of the ambient ISM. We present simulations of the interaction of stellar winds and ionizing radiation of 12, 23, and 60 M⊙ stars within a cold neutral (CNM, n0 = 100 cm-3), warm neutral (WNM, n0 = 1, 10 cm-3) or warm ionized (WIM, n0 = 0.1 cm-3) medium. The FLASH simulations adopt the novel tree-based radiation transfer algorithm TREERAY. With the On-the-Spot approximation and a temperature-dependent recombination coefficient, it is coupled to a chemical network with radiative heating and cooling. In the homogeneous CNM, the total momentum injection ranges from 1.6× 104 to 4× 105 M⊙ km s-1 and is always dominated by the expansion of the ionized HII region. In the WIM, stellar winds dominate (2× 102 to 5× 103 M⊙ km s-1), while the input from radiation is small (˜ 102 M⊙ km s-1). The WNM (n0 = 1 cm-3) is a transition regime. Energetically, stellar winds couple more efficiently to the ISM (˜ 0.1 percent of wind luminosity) than radiation (< 0.001 percent of ionizing luminosity). For estimating the impact of massive stars, the strongly mass-dependent ratios of wind to ionizing luminosity and the properties of the ambient medium have to be considered.

  12. Oscillation mode linewidths of main-sequence and subgiant stars observed by Kepler

    DEFF Research Database (Denmark)

    Appourchaux, T.; Benomar, O.; Gruberbauer, M.

    2012-01-01

    Solar-like oscillations have been observed by {{\\it Kepler}} and CoRoT in several solar-type stars. We study the variations of stellar p-mode linewidth as a function of effective temperature. Time series of 9 months of Kepler data have been used. The power spectra of 42 cool main-sequence stars a...

  13. Stellar Physics 2: Stellar Evolution and Stability

    CERN Document Server

    Bisnovatyi-Kogan, Gennady S

    2011-01-01

    "Stellar Physics" is a an outstanding book in the growing body of literature on star formation and evolution. Not only does the author, a leading expert in the field, very thoroughly present the current state of knowledge on stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 1000 entries makes this book an unparalleled reference source. "Stellar Evolution and Stability" is the second of two volumes and can be read, as can the first volume "Fundamental Concepts and Stellar Equilibrium," as a largely independent work. It traces in great detail the evolution of protostars towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to supernovae explosions, gamma-ray bursts and black hole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars. This second edition is carefully updated in the areas of pre...

  14. High-angular-resolution stellar imaging with occultations from the Cassini spacecraft - III. Mira

    Science.gov (United States)

    Stewart, Paul N.; Tuthill, Peter G.; Nicholson, Philip D.; Hedman, Matthew M.

    2016-04-01

    We present an analysis of spectral and spatial data of Mira obtained by the Cassini spacecraft, which not only observed the star's spectra over a broad range of near-infrared wavelengths, but was also able to obtain high-resolution spatial information by watching the star pass behind Saturn's rings. The observed spectral range of 1-5 microns reveals the stellar atmosphere in the crucial water-bands which are unavailable to terrestrial observers, and the simultaneous spatial sampling allows the origin of spectral features to be located in the stellar environment. Models are fitted to the data, revealing the spectral and spatial structure of molecular layers surrounding the star. High-resolution imagery is recovered revealing the layered and asymmetric nature of the stellar atmosphere. The observational data set is also used to confront the state-of-the-art cool opacity-sampling dynamic extended atmosphere models of Mira variables through a detailed spectral and spatial comparison, revealing in general a good agreement with some specific departures corresponding to particular spectral features.

  15. NITROGEN ISOTOPES IN ASYMPTOTIC GIANT BRANCH CARBON STARS AND PRESOLAR SiC GRAINS: A CHALLENGE FOR STELLAR NUCLEOSYNTHESIS

    International Nuclear Information System (INIS)

    Hedrosa, R. P.; Abia, C.; Domínguez, I.; Palmerini, S.; Busso, M.; Cristallo, S.; Straniero, O.; Plez, B.

    2013-01-01

    Isotopic ratios of C, N, Si, and trace heavy elements in presolar SiC grains from meteorites provide crucial constraints to nucleosynthesis. A long-debated issue is the origin of the so-called A+B grains, as of yet no stellar progenitor thus far has been clearly identified on observational grounds. We report the first spectroscopic measurements of 14 N/ 15 N ratios in Galactic carbon stars of different spectral types and show that J- and some SC-type stars might produce A+B grains, even for 15 N enrichments previously attributed to novae. We also show that most mainstream grains are compatible with the composition of N-type stars, but in some cases might also descend from SC stars. From a theoretical point of view, no astrophysical scenario can explain the C and N isotopic ratios of SC-, J-, and N-type carbon stars together, as well as those of many grains produced by them. This poses urgent questions to stellar physics.

  16. Chemical evolution, stellar nucleosynthesis and a variable star formation rate

    International Nuclear Information System (INIS)

    Olive, K.A.; Thielemann, F.K.; Truran, J.W.

    1986-04-01

    The effects of a decreasing star formation rate (SFR) on the galactic abundances of elements produced in massive stars (M ≥ 10 Msub solar). On the basis of a straightforward model of galactic evolution, a relation between the upper mass limit of type II supernovae (M/sub SN/) contributing to chemical evolution and the decline of the SFR (tau) is derived, when the oxygen abundance is determined only by massive stars. The additional requirement that all intermediate mass elements (Ne-Ti), which are also predominantly due to nucleosynthesis in massive stars, are produced in solar proportions leads to a unique value of M/sub SN/ and tau. The application of this method with abundance yields from Arnett (1978) and Woosley and Weaver (1986) resuults, however, in contradicting solutions: M/sub SN/ ≅ 45 Msub solar, tau = ∞, and M/sub SN/ ≅ 15 Msub solar, tau = 3 x 10 9 y. Thus, in order that this approach provide an effective probe of the SFR over the history of our galaxy it is essential that converging and more accurate predictions of the consequences of stellar and supernova nucleosynthesis will be forthcoming. 54 refs., 2 figs., 2 tabs

  17. White Dwarfs in Star Clusters: The Initial-Final Mass Relation for Stars from 0.85 to 8 M$_\\odot$

    Science.gov (United States)

    Cummings, Jeffrey; Kalirai, Jason; Tremblay, P.-E.; Ramírez-Ruiz, Enrico

    2018-01-01

    The spectroscopic study of white dwarfs provides both their mass, cooling age, and intrinsic photometric properties. For white dwarfs in the field of well-studied star clusters, this intrinsic photometry can be used to determine if they are members of that star cluster. Comparison of a member white dwarf's cooling age to its total cluster's age provides the evolutionary timescale of its progenitor star, and hence the mass. This is the initial-final mass relation (IFMR) for stars, which gives critical information on how a progenitor star evolves and loses mass throughout its lifetime, and how this changes with progenitor mass. Our work, for the first time, presents a uniform analysis of 85 white dwarf cluster members spanning from progenitor masses of 0.85 to 8 M$_\\odot$. Comparison of our work to theoretical IFMRs shows remarkable consistency in their shape but differences remain. We will discuss possible explanations for these differences, including the effects of stellar rotation.

  18. X-rays from stars

    Science.gov (United States)

    Güdel, Manuel

    2004-07-01

    Spectroscopic studies available from Chandra and XMM-Newton play a pivotal part in the understanding of the physical processes in stellar (magnetic and non-magnetic) atmospheres. It is now routinely possible to derive densities and to study the influence of ultraviolet radiation fields, both of which can be used to infer the geometry of the radiating sources. Line profiles provide important information on bulk mass motions and attenuation by neutral matter, e.g. in stellar winds. The increased sensitivity has revealed new types of X-ray sources in systems that were thought to be unlikely places for X-rays: flaring brown dwarfs, including rather old, non-accreting objects, and terminal shocks in jets of young stars are important examples. New clues concerning the role of stellar high-energy processes in the modification of the stellar environment (ionization, spallation, etc.) contribute significantly to our understanding of the "astro-ecology" in forming planetary systems. Technological limitations are evident. The spectral resolution has not reached the level where bulk mass motions in cool stars become easily measurable. Higher resolution would also be important to perform X-ray "Doppler imaging" in order to reconstruct the 3-D distribution of the X-ray sources around a rotating star. Higher sensitivity will be required to perform high-resolution spectroscopy of weak sources such as brown dwarfs or embedded pre-main-sequence sources. A new generation of satellites such as Constellation-X or XEUS should pursue these goals.

  19. Stellar model chromospheres. VI - Empirical estimates of the chromospheric radiative losses of late-type stars

    Science.gov (United States)

    Linsky, J. L.; Ayres, T. R.

    1978-01-01

    A method is developed for estimating the nonradiative heating of stellar chromospheres by measuring the net radiative losses in strong Fraunhofer line cores. This method is applied to observations of the Mg II resonance lines in a sample of 32 stars including the sun. At most a small dependence of chromospheric nonradiative heating on stellar surface gravity is found, which is contrary to the large effect predicted by recent calculations based on acoustic-heating theories.

  20. Extragalactic stellar astronomy with the brightest stars in the universe

    Energy Technology Data Exchange (ETDEWEB)

    Kudritzki, R P; Urbaneja, M A; Bresolin, F [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Przybilla, N [Dr Remeis-Sternwarte Bamberg, Erlangen University, Sternwartstr. 7, D-96049 Bamberg (Germany)], E-mail: kud@ifa.hawaii.edu

    2008-12-15

    Supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest 'normal' stars at visual light with absolute visual magnitudes up to -9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss the most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low-resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure extragalactic distances accurately based on stellar gravities and effective temperatures is presented, the flux-weighted gravity-luminosity relationship (FGLR). The FGLR is a purely spectroscopic method that overcomes the uncertainties, introduced by interstellar extinction and variations of metallicity, which plague all methods of photometric stellar distance determination. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

  1. Models of large-scale magnetic fields in stellar interiors. Application to solar and ap stars

    International Nuclear Information System (INIS)

    Duez, Vincent

    2009-01-01

    Stellar astrophysics needs today new models of large-scale magnetic fields, which are observed through spectropolarimetry at the surface of Ap/Bp stars, and thought to be an explanation for the uniform rotation of the solar radiation zone, deduced from helio seismic inversions. During my PhD, I focused on describing the possible magnetic equilibria in stellar interiors. The found configurations are mixed poloidal-toroidal, and minimize the energy for a given helicity, in analogy with Taylor states encountered in spheromaks. Taking into account the self-gravity leads us to the 'non force-free' equilibria family, that will thus influence the stellar structure. I derived all the physical quantities associated with the magnetic field; then I evaluated the perturbations they induce on gravity, thermodynamic quantities as well as energetic ones, for a solar model and an Ap star. 3D MHD simulations allowed me to show that these equilibria form a first stable states family, the generalization of such states remaining an open question. It has been shown that a large-scale magnetic field confined in the solar radiation zone can induce an oblateness comparable to a high core rotation law. I also studied the secular interaction between the magnetic field, the differential rotation and the meridional circulation in the aim of implementing their effects in a next generation stellar evolution code. The influence of the magnetism on convection has also been studied. Finally, hydrodynamic processes responsible for the mixing have been compared with diffusion and a change of convection's efficiency in the case of a CoRoT star target. (author) [fr

  2. Introduction to stellar astrophysics. V. 1

    International Nuclear Information System (INIS)

    Boehm-Vitense, E.

    1989-01-01

    This textbook introduces basic elements of fundamental astronomy and astrophysics which serve as a foundation for understanding the structure, evolution, and observed properties of stars. The first half of the book explains how stellar motions, distances, luminosities, colours, radii, masses and temperatures are measured or derived. The author then shows how data of these sorts can be arranged to classify stars through their spectra. Stellar rotation and stellar magnetic fields are introduced. Stars with peculiar spectra and pulsating stars also merit special attention. The endpoints of stellar evolutions are briefly described. There is a separate chapter on the Sun and a final one on interstellar absorption. (author)

  3. The Galactic stellar disc

    International Nuclear Information System (INIS)

    Feltzing, S; Bensby, T

    2008-01-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies.

  4. Stellar structure and evolution

    International Nuclear Information System (INIS)

    Kippernhahn, R.; Weigert, A.

    1990-01-01

    This book introduces the theory of the internal structure of stars and their evolution in time. It presents the basic physics of stellar interiors, methods for solving the underlying equations, and the most important results necessary for understanding the wide variety of stellar types and phenomena. The evolution of stars is discussed from their birth through normal evolution to possibly spectacular final stages. Chapters on stellar oscillations and rotation are included

  5. PHAT+MaNGA: Using resolved stellar populations to improve the recovery of star formation histories from galaxy spectra

    Science.gov (United States)

    Byler, Nell

    2017-08-01

    Stellar Population Synthesis (SPS) models are routinely used to interpret extragalactic observations at all redshifts. Currently, the dominant source of uncertainty in SPS modeling lies in the degeneracies associated with synthesizing and fitting complex stellar populations to observed galaxy spectra. To remedy this, we propose an empirical calibration of SPS models using resolved stellar population observations from Hubble Space Telescope (HST) to constrain the stellar masses, ages, and star formation histories (SFHs) in regions matched to 2D spectroscopic observations from MaNGA. We will take advantage of the state of the art observations from the Panchromatic Hubble Andromeda Treasury (PHAT), which maps the dust content, history of chemical enrichment, and history of star formation across the disk of M31 in exquisite detail. Recently, we have coupled these observations with an unprecedented, spatially-resolved suite of IFU observations from MaNGA. With these two comprehensive data sets we can use the true underlying stellar properties from PHAT to properly interpret the aperture-matched integrated spectra from MaNGA. Our MaNGA observations target 20 regions within the PHAT footprint that fully sample the available range in metallicity, SFR, dust content, and stellar density. This transformative dataset will establish a comprehensive link between resolved stellar populations and the inferred properties of unresolved stellar populations across astrophysically important environments. The net data product will be a library of galaxy spectra matched to the true underlying stellar properties, a comparison set that has lasting legacy value for the extragalactic community.

  6. Variable accretion of stellar winds onto Sgr A*

    Science.gov (United States)

    Cuadra, Jorge; Nayakshin, Sergei

    2006-12-01

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

  7. Variable accretion of stellar winds onto Sgr A*

    Energy Technology Data Exchange (ETDEWEB)

    Cuadra, Jorge [Max-Planck-Institut fuer Astrophysik, D-85741 Garching (Germany); Nayakshin, Sergei [Department of Physics and Astronomy, University of Leicester, LEI 7RH (United Kingdom)

    2006-12-15

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

  8. Variable accretion of stellar winds onto Sgr A*

    International Nuclear Information System (INIS)

    Cuadra, Jorge; Nayakshin, Sergei

    2006-01-01

    We report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We frst show the strong inflience of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and frid that the slow winds shock and rapidly cool, forming cold gas clumps and flaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion fbw physics not resolved here, making Sgr A* an important energy source for the Galactic centre

  9. Looking for imprints of the first stellar generations in metal-poor bulge field stars

    Science.gov (United States)

    Siqueira-Mello, C.; Chiappini, C.; Barbuy, B.; Freeman, K.; Ness, M.; Depagne, E.; Cantelli, E.; Pignatari, M.; Hirschi, R.; Frischknecht, U.; Meynet, G.; Maeder, A.

    2016-09-01

    Context. Efforts to look for signatures of the first stars have concentrated on metal-poor halo objects. However, the low end of the bulge metallicity distribution has been shown to host some of the oldest objects in the Milky Way and hence this Galactic component potentially offers interesting targets to look at imprints of the first stellar generations. As a pilot project, we selected bulge field stars already identified in the ARGOS survey as having [Fe/H] ≈-1 and oversolar [α/Fe] ratios, and we used FLAMES-UVES to obtain detailed abundances of key elements that are believed to reveal imprints of the first stellar generations. Aims: The main purpose of this study is to analyse selected ARGOS stars using new high-resolution (R ~ 45 000) and high-signal-to-noise (S/N> 100) spectra. We aim to derive their stellar parameters and elemental ratios, in particular the abundances of C, N, the α-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Zr, La, and Ba, and the r-element Eu. Methods: High-resolution spectra of five field giant stars were obtained at the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. Spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe I and Fe II. The abundance analysis was performed with a MARCS LTE spherical model atmosphere grid and the Turbospectrum spectrum synthesis code. Results: We confirm that the analysed stars are moderately metal-poor (-1.04 ≤ [Fe/H] ≤-0.43), non-carbon-enhanced (non-CEMP) with [C/Fe] ≤ + 0.2, and α-enhanced. We find that our three most metal-poor stars are nitrogen enhanced. The α-enhancement suggests that these stars were formed from a gas enriched by core-collapse supernovae, and that the values are in agreement with results in the literature for bulge stars in the same metallicity range. No abundance anomalies (Na - O, Al - O, Al - Mg anti-correlations) were

  10. On the temperatures, colours, and ages of metal-poor stars predicted by stellar models

    International Nuclear Information System (INIS)

    Van den Berg, D A

    2008-01-01

    Most (but not all) of the investigations that have derived the effective temperatures of metal-poor, solar-neighbourhood field stars, from analyses of their spectra or from the infrared flux method, favour a T eff scale that is ∼100-120 K cooler than that given by stellar evolutionary models. This seems to be at odds with photometric results, given that the application of current colour-T eff relations to the observed subdwarf colours suggests a preference for hotter temperatures. Moreover, the predicted temperatures for main-sequence stars at the lowest metallicities ([Fe/H] eff for them unless some fundamental modification is made to the adopted physics. No such problems are found if the temperatures of metal-poor field stars are ∼100-120 K warmer than most determinations. In this case, stellar models would appear to provide consistent interpretations of both field and globular cluster (GC) stars of low metallicity. However, this would imply, e.g. that M 92 has an [Fe/H] value of approximately - 2.2, which is obtained from analyses of Fe I lines, instead of approximately equal to - 2.4, as derived from Fe II lines (and favoured by studies of three-dimensional model atmospheres). Finally, the age of the local, Population II subgiant HD 140283 (and GCs having similar metal abundances) is estimated to be ∼13 Gyr, if diffusive processes are taken into account.

  11. (abstract) Realization of a Faster, Cheaper, Better Mission and Its New Paradigm Star Tracker, the Advanced Stellar Compass

    Science.gov (United States)

    Eisenman, Allan Read; Liebe, Carl Christian; Joergensen, John Lief; Jensen, Gunnar Bent

    1997-01-01

    The first Danish satellite, rsted, will be launched in August of 1997. The scientific objective of sted is to perform a precision mapping of the Earth's magnetic field. Attitude data for the payload and the satellite are provided by the Advanced Stellar Compass (ASC) star tracker. The ASC consists of a CCD star camera and a capable microprocessor which operates by comparing the star image frames taken by the camera to its internal star catalogs.

  12. New Fe i Level Energies and Line Identifications from Stellar Spectra. II. Initial Results from New Ultraviolet Spectra of Metal-poor Stars

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, Ruth C. [SETI Institute and Astrophysical Advances, 607 Marion Place, Palo Alto, CA 94301 (United States); Kurucz, Robert L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ayres, Thomas R., E-mail: peterson@ucolick.org [Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309-0389 (United States)

    2017-04-01

    The Fe i spectrum is critical to many areas of astrophysics, yet many of the high-lying levels remain uncharacterized. To remedy this deficiency, Peterson and Kurucz identified Fe i lines in archival ultraviolet and optical spectra of metal-poor stars, whose warm temperatures favor moderate Fe i excitation. Sixty-five new levels were recovered, with 1500 detectable lines, including several bound levels in the ionization continuum of Fe i. Here, we extend the previous work by identifying 59 additional levels, with 1400 detectable lines, by incorporating new high-resolution UV spectra of warm metal-poor stars recently obtained by the Hubble Space Telescope Imaging Spectrograph. We provide gf values for these transitions, both computed as well as adjusted to fit the stellar spectra. We also expand our spectral calculations to the infrared, confirming three levels by matching high-quality spectra of the Sun and two cool stars in the H -band. The predicted gf values suggest that an additional 3700 Fe i lines should be detectable in existing solar infrared spectra. Extending the empirical line identification work to the infrared would help confirm additional Fe i levels, as would new high-resolution UV spectra of metal-poor turnoff stars below 1900 Å.

  13. The Resolved Stellar Populations Early Release Science Program

    Science.gov (United States)

    Gilbert, Karoline; Weisz, Daniel; Resolved Stellar Populations ERS Program Team

    2018-06-01

    The Resolved Stellar Populations Early Release Science Program (PI D. Weisz) will observe Local Group targets covering a range of stellar density and star formation histories, including a globular cluster, and ultra-faint dwarf galaxy, and a star-forming dwarf galaxy. Using observations of these diverse targets we will explore a broad science program: we will measure star formation histories, the sub-solar stellar initial mass function, and proper motions, perform studies of evolved stars, and map extinction in the target fields. Our observations will be of high archival value for other science such as calibrating stellar evolution models, studying variable stars, and searching for metal-poor stars. We will determine optimal observational setups and develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will also design, test, and release point spread function (PSF) fitting software specific to NIRCam and NIRISS, required for the crowded stellar regime. Prior to the Cycle 2 Call for Proposals, we will release PSF fitting software, matched HST and JWST catalogs, and clear documentation and step-by-step tutorials (such as Jupyter notebooks) for reducing crowded stellar field data and producing resolved stellar photometry catalogs, as well as for specific resolved stellar photometry science applications.

  14. Stellar Populations and the Star Formation Histories of LSB Galaxies—Part I: Optical and Hα Imaging

    Directory of Open Access Journals (Sweden)

    James Schombert

    2011-01-01

    Full Text Available This paper presents optical and Hα imaging for a large sample of LSB galaxies selected from the PSS-II catalogs (Schombert et al., 1992. As noted in previous work, LSB galaxies span a range of luminosities (−10>>−20 and sizes (0.3kpc<25<10kpc, although they are consistent in their irregular morphology. Their Hα luminosities (L(Hα range from 1036 to 1041 ergs s−1 (corresponding to a range in star formation, using canonical prescriptions, from 10−5 to 1 ⨀ yr−1. Although their optical colors are at the extreme blue edge for galaxies, they are similar to the colors of dwarf galaxies (Van Zee, 2001 and gas-rich irregulars (Hunter and Elmegreen, 2006. However, their star formation rates per unit stellar mass are a factor of ten less than other galaxies of the same baryonic mass, indicating that they are not simply quiescent versions of more active star-forming galaxies. This paper presents the data, reduction techniques, and new philosophy of data storage and presentation. Later papers in this series will explore the stellar population and star formation history of LSB galaxies using this dataset.

  15. INVERTING COLOR-MAGNITUDE DIAGRAMS TO ACCESS PRECISE STAR CLUSTER PARAMETERS: A NEW WHITE DWARF AGE FOR THE HYADES

    International Nuclear Information System (INIS)

    DeGennaro, Steven; Von Hippel, Ted; Jefferys, William H.; Stein, Nathan; Jeffery, Elizabeth; Van Dyk, David

    2009-01-01

    We have extended our Bayesian modeling of stellar clusters-which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres-to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 ± 45 Myr, consistent with the best prior analysis of the cluster main-sequence turnoff (MSTO) age by Perryman et al. Since the faintest WDs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's WD age. Our result demonstrates the power of the bright WD technique for deriving ages and further demonstrates complete age consistency between WD cooling and MSTO ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr.

  16. The evolution of the global stellar mass function of star clusters: an analytic description

    NARCIS (Netherlands)

    Lamers, H.J.G.L.M.; Baumgardt, H.; Gieles, M.

    2013-01-01

    The evolution of the global stellar mass function of star clusters is studied based on a large set of N-body simulations of clusters with a range of initial masses, initial concentrations, in circular or elliptical orbits in different tidal environments. Models with and without initial mass

  17. YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Hora, J. L.; Willis, S. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Gutermuth, R. A. [University of Massachusetts, Department of Astronomy, Amherst, MA 01003 (United States); Saygac, A. T., E-mail: gsaral@cfa.harvard.edu [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

  18. The fundamentals of stellar astrophysics

    International Nuclear Information System (INIS)

    Collins, G.W. II.

    1989-01-01

    A broad overview of theoretical stellar astrophysics is presented in a textbook intended for graduate students. Chapters are devoted to fundamental principles, assumptions, theorems, and polytropes; energy sources and sinks; the flow of energy through the star and the construction of stellar models; the theory of stellar evolution; relativistic stellar structure; the structure of distorted stars; stellar pulsation and oscillation. Also discussed are the flow of radiation through the stellar atmosphere, the solution of the radiative-transfer equation, the environment of the radiation field, the construction of a stellar model atmosphere, the formation and shape of spectral lines, LTE breakdown, illuminated and extended stellar atmospheres, and the transfer of polarized radiation. Diagrams, graphs, and sample problems are provided. 164 refs

  19. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji [Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Porto de Mello, Gustavo F.; Ferreira, Leticia D. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lactea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Agol, Eric, E-mail: jpaty@mail.ustc.edu.cn [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); and others

    2013-09-15

    We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

  20. Local stellar kinematics from RAVE data—VIII. Effects of the Galactic disc perturbations on stellar orbits of red clump stars

    Science.gov (United States)

    Önal Taş, Ö.; Bilir, S.; Plevne, O.

    2018-02-01

    We aim to probe the dynamic structure of the extended Solar neighborhood by calculating the radial metallicity gradients from orbit properties, which are obtained for axisymmetric and non-axisymmetric potential models, of red clump (RC) stars selected from the RAdial Velocity Experiment's Fourth Data Release. Distances are obtained by assuming a single absolute magnitude value in near-infrared, i.e. M_{Ks}=-1.54±0.04 mag, for each RC star. Stellar orbit parameters are calculated by using the potential functions: (i) for the MWPotential2014 potential, (ii) for the same potential with perturbation functions of the Galactic bar and transient spiral arms. The stellar age is calculated with a method based on Bayesian statistics. The radial metallicity gradients are evaluated based on the maximum vertical distance (z_{max}) from the Galactic plane and the planar eccentricity (ep) of RC stars for both of the potential models. The largest radial metallicity gradient in the 01 kpc, the radial metallicity gradients have zero or positive values and they do not depend on ep subsamples. There is a large radial metallicity gradient for thin disc, but no radial gradient found for thick disc. Moreover, the largest radial metallicity gradients are obtained where the outer Lindblad resonance region is effective. We claim that this apparent change in radial metallicity gradients in the thin disc is a result of orbital perturbation originating from the existing resonance regions.

  1. The stellar content of NGC 346 - A plethora of O stars in the SMC

    International Nuclear Information System (INIS)

    Massey, P.; Parker, J.W.; Garmany, C.D.

    1989-01-01

    The stellar content of NGC 346, the largest and brightest H II region in the SMC, was investigated using the results of CCD UBV photometry and spectroscopy. Spectra of 42 blue stars were classified, showing that 33 are of the O type, of which 11 are of type O6.5 or earlier, which is as many early-type O stars known in the rest of the SMC. The results identify 25-30 NGC 346 stars more massive than 25 solar masses, and six stars more massive than 40 solar masses, indicating that the upper-mass cutoff to the IMF is not lower in the SMC than in the Galaxy or the LMC. The presence of evolved 15 solar-mass stars in the NGC 346 indicates that some massive stars formed 15 million yr ago. The results of spatial distribution suggest that star formation began at the southwest side of the association and has spread to where the central cluster lies now, providing an example of sequential star formation in the SMC. 69 refs

  2. Solving the relativistic inverse stellar problem through gravitational waves observation of binary neutron stars

    Science.gov (United States)

    Abdelsalhin, Tiziano; Maselli, Andrea; Ferrari, Valeria

    2018-04-01

    The LIGO/Virgo Collaboration has recently announced the direct detection of gravitational waves emitted in the coalescence of a neutron star binary. This discovery allows, for the first time, to set new constraints on the behavior of matter at supranuclear density, complementary with those coming from astrophysical observations in the electromagnetic band. In this paper we demonstrate the feasibility of using gravitational signals to solve the relativistic inverse stellar problem, i.e., to reconstruct the parameters of the equation of state (EoS) from measurements of the stellar mass and tidal Love number. We perform Bayesian inference of mock data, based on different models of the star internal composition, modeled through piecewise polytropes. Our analysis shows that the detection of a small number of sources by a network of advanced interferometers would allow to put accurate bounds on the EoS parameters, and to perform a model selection among the realistic equations of state proposed in the literature.

  3. Improved methods for the measurement and analysis of stellar magnetic fields

    Science.gov (United States)

    Saar, Steven H.

    1988-01-01

    The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

  4. Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars

    OpenAIRE

    Bensby, T.; Johnson, J. A.; Cohen, J.; Feltzing, S.; Udalski, A.; Gould, A.; Huang, W.; Thompson, I.; Simmerer, J.; Adén, D.

    2009-01-01

    Aims. Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spe...

  5. CONTINUED NEUTRON STAR CRUST COOLING OF THE 11 Hz X-RAY PULSAR IN TERZAN 5: A CHALLENGE TO HEATING AND COOLING MODELS?

    Energy Technology Data Exchange (ETDEWEB)

    Degenaar, N.; Miller, J. M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Wijnands, R.; Altamirano, D.; Fridriksson, J. [Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands); Brown, E. F. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Cackett, E. M. [Department of Physics and Astronomy, Wayne State University, 666 W. Hancock St, Detroit, MI 48201 (United States); Homan, J. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Heinke, C. O.; Sivakoff, G. R. [Department of Physics, University of Alberta, 4-183 CCIS, Edmonton, AB T6G 2E1 (Canada); Pooley, D., E-mail: degenaar@umich.edu [Department of Physics, Sam Houston State University, Huntsville, TX (United States)

    2013-09-20

    The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR J17480-2446 in the globular cluster Terzan 5 exhibited an 11 week accretion outburst in 2010. Chandra observations performed within five months after the end of the outburst revealed evidence that the crust of the neutron star became substantially heated during the accretion episode and was subsequently cooling in quiescence. This provides the rare opportunity to probe the structure and composition of the crust. Here, we report on new Chandra observations of Terzan 5 that extend the monitoring to ≅2.2 yr into quiescence. We find that the thermal flux and neutron star temperature have continued to decrease, but remain significantly above the values that were measured before the 2010 accretion phase. This suggests that the crust has not thermally relaxed yet, and may continue to cool. Such behavior is difficult to explain within our current understanding of heating and cooling of transiently accreting neutron stars. Alternatively, the quiescent emission may have settled at a higher observed equilibrium level (for the same interior temperature), in which case the neutron star crust may have fully cooled.

  6. Ultraviolet radiation from stellar flares and the coronal X-ray emission for dwarf-Me stars

    Energy Technology Data Exchange (ETDEWEB)

    Doyle, J.G.; Butler, C.J. (Armagh Observatory, Northern Ireland (UK))

    1985-01-31

    The authors correlate Einstein observations of the X-ray flux of quiescent dMe stars with the time-averaged energy emitted by flares in the Johnson-U band, showing that the X-ray energy emitted by the coronae of these stars is about an order of magnitude greater than the U-band flare energy. From the estimate of the ratio of the total radiation emitted to the U-band flux, it is possible that, if a similar amount of energy were dissipated in the stellar atmosphere, then the observed flare events could heat the coronae of these stars.

  7. Radio emission from symbiotic stars: a binary model

    International Nuclear Information System (INIS)

    Taylor, A.R.; Seaquist, E.R.

    1985-01-01

    The authors examine a binary model for symbiotic stars to account for their radio properties. The system is comprised of a cool, mass-losing star and a hot companion. Radio emission arises in the portion of the stellar wind photo-ionized by the hot star. Computer simulations for the case of uniform mass loss at constant velocity show that when less than half the wind is ionized, optically thick spectral indices greater than +0.6 are produced. Model fits to radio spectra allow the binary separation, wind density and ionizing photon luminosity to be calculated. They apply the model to the symbiotic star H1-36. (orig.)

  8. EXPLORING SYSTEMATIC EFFECTS IN THE RELATION BETWEEN STELLAR MASS, GAS PHASE METALLICITY, AND STAR FORMATION RATE

    International Nuclear Information System (INIS)

    Telford, O. Grace; Dalcanton, Julianne J.; Skillman, Evan D.; Conroy, Charlie

    2016-01-01

    There is evidence that the well-established mass–metallicity relation in galaxies is correlated with a third parameter: star formation rate (SFR). The strength of this correlation may be used to disentangle the relative importance of different physical processes (e.g., infall of pristine gas, metal-enriched outflows) in governing chemical evolution. However, all three parameters are susceptible to biases that might affect the observed strength of the relation between them. We analyze possible sources of systematic error, including sample bias, application of signal-to-noise ratio cuts on emission lines, choice of metallicity calibration, uncertainty in stellar mass determination, aperture effects, and dust. We present the first analysis of the relation between stellar mass, gas phase metallicity, and SFR using strong line abundance diagnostics from Dopita et al. for ∼130,000 star-forming galaxies in the Sloan Digital Sky Survey and provide a detailed comparison of these diagnostics in an appendix. Using these new abundance diagnostics yields a 30%–55% weaker anti-correlation between metallicity and SFR at fixed stellar mass than that reported by Mannucci et al. We find that, for all abundance diagnostics, the anti-correlation with SFR is stronger for the relatively few galaxies whose current SFRs are elevated above their past average SFRs. This is also true for the new abundance diagnostic of Dopita et al., which gives anti-correlation between Z and SFR only in the high specific star formation rate (sSFR) regime, in contrast to the recent results of Kashino et al. The poorly constrained strength of the relation between stellar mass, metallicity, and SFR must be carefully accounted for in theoretical studies of chemical evolution.

  9. Runaways and weathervanes: The shape of stellar bow shocks

    Science.gov (United States)

    Henney, W. J.; Tarango-Yong, J. A.

    2017-11-01

    Stellar bow shocks are the result of the supersonic interaction between a stellar wind and its environment. Some of these are "runaways": high-velocity stars that have been ejected from a star cluster. Others are "weather vanes", where it is the local interstellar medium itself that is moving, perhaps as the result of a champagne flow of ionized gas from a nearby HII region. We propose a new two-dimensional classification scheme for bow shapes, which is based on dimensionless geometric ratios that can be estimated from observational images. The two ratios are related to the flatness of the bow’s apex, which we term "planitude" and the openness of its wings, which we term "alatude". We calculate the inclination-dependent tracks on the planitude-alatude plane that are predicted by simple models for the bow shock shape. We also measure the shapes of bow shocks from three different observational datasets: mid-infrared arcs around hot main-sequence stars, far-infrared arcs around luminous cool stars, and emission-line arcs around proplyds and other young stars in the Orion Nebula. Clear differences are found between the different datasets in their distributions on the planitude-alatude plane, which can be used to constrain the physics of the bow shock interaction and emission mechanisms in the different classes of object.

  10. Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling, and star formation in dwarf galaxies at high redshift

    Science.gov (United States)

    Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2018-06-01

    We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling, and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose three modifications to SAMs that will provide more accurate high-redshift simulations. These include (1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; (2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and (3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

  11. Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshift

    Science.gov (United States)

    Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2018-03-01

    We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose 3 modifications to SAMs that will provide more accurate high-redshift simulations. These include 1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; 2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and 3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

  12. Teetering Stars: Resonant Excitation of Stellar Obliquities by Hot and Warm Jupiters with External Companions

    Science.gov (United States)

    Anderson, Kassandra; Lai, Dong

    2018-04-01

    Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have been extensively probed in recent years thanks to Rossiter-McLaughlin observations. Such obliquities may reveal clues about hot Jupiter dynamical and migration histories. Common explanations for generating stellar obliquities include high-eccentricity migration, or primordial disk misalignment. This talk investigates another mechanism for producing stellar spin-orbit misalignments in systems hosting a close-in giant planet with an external, inclined planetary companion. Spin-orbit misalignment may be excited due to a secular resonance, occurring when the precession rate of the stellar spin axis (due to the inner orbit) becomes comparable to the precession rate of the inner orbital axis (due to the outer companion). Due to the spin-down of the host star via magnetic braking, this resonance may be achieved at some point during the star's main sequence lifetime for a wide range of giant planet masses and orbital architectures. We focus on both hot Jupiters (with orbital periods less than ten days) and warm Jupiters (with orbital periods around tens of days), and identify the outer perburber properties needed to generate substantial obliquities via resonant excitation, in terms of mass, separation, and inclination. For hot Jupiters, the stellar spin axis is strongly coupled to the orbital axis, and resonant excitation of obliquity requires a close perturber, located within 1-2 AU. For warm Jupiters, the spin and orbital axes are more weakly coupled, and the resonance may be achieved for more distant perturbers (at several to tens of AU). Resonant excitation of the stellar obliquity is accompanied by a decrease in the planets' mutual orbital inclination, and can thus erase high mutual inclinations in two-planet systems. Since many warm Jupiters are known to have outer planetary companions at several AU or beyond, stellar obliquities in warm Jupiter systems may be common, regardless of the

  13. Self-consistent atmosphere modeling with cloud formation for low-mass stars and exoplanets

    Science.gov (United States)

    Juncher, Diana; Jørgensen, Uffe G.; Helling, Christiane

    2017-12-01

    Context. Low-mass stars and extrasolar planets have ultra-cool atmospheres where a rich chemistry occurs and clouds form. The increasing amount of spectroscopic observations for extrasolar planets requires self-consistent model atmosphere simulations to consistently include the formation processes that determine cloud formation and their feedback onto the atmosphere. Aims: Our aim is to complement the MARCS model atmosphere suit with simulations applicable to low-mass stars and exoplanets in preparation of E-ELT, JWST, PLATO and other upcoming facilities. Methods: The MARCS code calculates stellar atmosphere models, providing self-consistent solutions of the radiative transfer and the atmospheric structure and chemistry. We combine MARCS with a kinetic model that describes cloud formation in ultra-cool atmospheres (seed formation, growth/evaporation, gravitational settling, convective mixing, element depletion). Results: We present a small grid of self-consistently calculated atmosphere models for Teff = 2000-3000 K with solar initial abundances and log (g) = 4.5. Cloud formation in stellar and sub-stellar atmospheres appears for Teff day-night energy transport and no temperature inversion.

  14. Peculiar early-type galaxies with central star formation

    International Nuclear Information System (INIS)

    Ge Chong; Gu Qiusheng

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies. Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought. Widespread recent star formation, cool gas and dust have been detected in a substantial fraction of ETGs. We make use of the radial profiles of g — r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores. By analyzing the photometric and spectroscopic data, we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus. From the results of stellar population synthesis, we find that the stellar population of the blue cores is relatively young, spreading from several Myr to less than one Gyr. In 14 galaxies with H I observations, we find that the average gas fraction of these galaxies is about 0.55. The bluer galaxies show a higher gas fraction, and the total star formation rate (SFR) correlates very well with the H I gas mass. The star formation history of these ETGs is affected by the environment, e.g. in the denser environment the H I gas is less and the total SFR is lower. We also discuss the origin of the central star formation of these early-type galaxies.

  15. Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

    Science.gov (United States)

    Martínez-Núñez, Silvia; Kretschmar, Peter; Bozzo, Enrico; Oskinova, Lidia M.; Puls, Joachim; Sidoli, Lara; Sundqvist, Jon Olof; Blay, Pere; Falanga, Maurizio; Fürst, Felix; Gímenez-García, Angel; Kreykenbohm, Ingo; Kühnel, Matthias; Sander, Andreas; Torrejón, José Miguel; Wilms, Jörn

    2017-10-01

    Massive stars, at least ˜10 times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. Supergiant high mass X-ray binaries (SgXBs) are among the brightest X

  16. Role of strangeness to the neutron star mass and cooling

    Science.gov (United States)

    Lee, Chang-Hwan; Lim, Yeunhwan; Hyun, Chang Ho; Kwak, Kyujin

    2018-01-01

    Neutron star provides unique environments for the investigation of the physics of extreme dense matter beyond normal nuclear saturation density. In such high density environments, hadrons with strange quarks are expected to play very important role in stabilizing the system. Kaons and hyperons are the lowest mass states with strangeness among meson and bayron families, respectively. In this work, we investigate the role of kaons and hyperons to the neutron star mass, and discuss their role in the neutron star cooling.

  17. Stellar magnetic activity and exoplanets

    Directory of Open Access Journals (Sweden)

    Vidotto A.A.

    2017-01-01

    Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

  18. Comments on stellar boundary cooling and the reality of supermetallicity

    Science.gov (United States)

    Deming, D.

    1980-01-01

    The paper discusses the 'super-metal-rich' (SMR) stars and reexamines Peterson's analysis of the SMR prototype mu Leo (1978) with regard to a postulated error in continuum error. Model atmospheres are used to compute theoretical equivalent widths and to explore the sensitivity of these widths to metallicity, temperature, surface gravity, and microturbulence. It is shown that Peterson's results are sensitive to continuum placement, and that her data does not indicate that the temperature gradient is steeper in mu Leo than in normal giants. It is concluded that the SMR stars are very metal rich and are also somewhat boundary cooled, possibly due to high metallicity.

  19. Energy balance in solar and stellar chromospheres

    Science.gov (United States)

    Avrett, E. H.

    1981-01-01

    Net radiative cooling rates for quiet and active regions of the solar chromosphere and for two stellar chromospheres are calculated from corresponding atmospheric models. Models of chromospheric temperature and microvelocity distributions are derived from observed spectra of a dark point within a cell, the average sun and a very bright network element on the quiet sun, a solar plage and flare, and the stars Alpha Boo and Lambda And. Net radiative cooling rates due to the transitions of various atoms and ions are then calculated from the models as a function of depth. Large values of the net radiative cooling rate are found at the base of the chromosphere-corona transition region which are due primarily to Lyman alpha emission, and a temperature plateau is obtained in the transition region itself. In the chromospheric regions, the calculated cooling rate is equal to the mechanical energy input as a function of height and thus provides a direct constraint on theories of chromospheric heating.

  20. Role of strangeness to the neutron star mass and cooling

    Directory of Open Access Journals (Sweden)

    Lee Chang-Hwan

    2018-01-01

    Full Text Available Neutron star provides unique environments for the investigation of the physics of extreme dense matter beyond normal nuclear saturation density. In such high density environments, hadrons with strange quarks are expected to play very important role in stabilizing the system. Kaons and hyperons are the lowest mass states with strangeness among meson and bayron families, respectively. In this work, we investigate the role of kaons and hyperons to the neutron star mass, and discuss their role in the neutron star cooling.

  1. EVIDENCE FOR NON-STELLAR REST-FRAME NEAR-IR EMISSION ASSOCIATED WITH INCREASED STAR FORMATION IN GALAXIES AT z ∼ 1

    International Nuclear Information System (INIS)

    Lange, Johannes U.; Van Dokkum, Pieter G.; Momcheva, Ivelina G.; Nelson, Erica J.; Leja, Joel; Brammer, Gabriel; Whitaker, Katherine E.; Franx, Marijn

    2016-01-01

    We explore the presence of non-stellar rest-frame near-IR (2–5 μm) emission in galaxies at z ∼ 1. Previous studies identified this excess in relatively small samples and suggested that such non-stellar emission, which could be linked to the 3.3 μm polycyclic aromatic hydrocarbons feature or hot dust emission, is associated with an increased star formation rate (SFR). In this Letter, we confirm and quantify the presence of an IR excess in a significant fraction of galaxies in the 3D-HST GOODS catalogs. By constructing a matched sample of galaxies with and without strong non-stellar near-IR emission, we find that galaxies with such emission are predominantly star-forming galaxies. Moreover, star-forming galaxies with an excess show increased mid- and far-IR and Hα emission compared to other star-forming galaxies without. While galaxies with a near-IR excess show a larger fraction of individually detected X-ray active galactic nuclei (AGNs), an X-ray stacking analysis, together with the IR-colors and Hα profiles, shows that AGNs are unlikely to be the dominant source of excess in the majority of galaxies. Our results suggest that non-stellar near-IR emission is linked to increased SFRs and is ubiquitous among star-forming galaxies. As such, the near-IR emission might be a powerful tool to measure SFRs in the era of the James Webb Space Telescope

  2. GAS REGULATION OF GALAXIES: THE EVOLUTION OF THE COSMIC SPECIFIC STAR FORMATION RATE, THE METALLICITY-MASS-STAR-FORMATION RATE RELATION, AND THE STELLAR CONTENT OF HALOS

    Energy Technology Data Exchange (ETDEWEB)

    Lilly, Simon J.; Carollo, C. Marcella; Pipino, Antonio; Peng Yingjie [Institute for Astronomy, Department of Physics, ETH Zurich, CH-8093 Zurich (Switzerland); Renzini, Alvio [Department of Physics and Astronomy Galileo Galilei, Universita degli Studi di Padova, via Marzolo 8, I-35131 Padova (Italy)

    2013-08-01

    A very simple physical model of galaxies is one in which the formation of stars is instantaneously regulated by the mass of gas in a reservoir with mass loss scaling with the star-formation rate (SFR). This model links together three different aspects of the evolving galaxy population: (1) the cosmic time evolution of the specific star-formation rate (sSFR) relative to the growth of halos, (2) the gas-phase metallicities across the galaxy population and over cosmic time, and (3) the ratio of the stellar to dark matter mass of halos. The gas regulator is defined by the gas consumption timescale ({epsilon}{sup -1}) and the mass loading {lambda} of the wind outflow {lambda}{center_dot}SFR. The simplest regulator, in which {epsilon} and {lambda} are constant, sets the sSFR equal to exactly the specific accretion rate of the galaxy; more realistic situations lead to an sSFR that is perturbed from this precise relation. Because the gas consumption timescale is shorter than the timescale on which the system evolves, the metallicity Z is set primarily by the instantaneous operation of the regulator system rather than by the past history of the system. The metallicity of the gas reservoir depends on {epsilon}, {lambda}, and sSFR, and the regulator system therefore naturally produces a Z(m{sub star}, SFR) relation if {epsilon} and {lambda} depend on the stellar mass m{sub star}. Furthermore, this relation will be the same at all epochs unless the parameters {epsilon} and {lambda} themselves change with time. A so-called fundamental metallicity relation is naturally produced by these conditions. The overall mass-metallicity relation Z(m{sub star}) directly provides the fraction f{sub star}(m{sub star}) of incoming baryons that are being transformed into stars. The observed Z(m{sub star}) relation of Sloan Digital Sky Survey (SDSS) galaxies implies a strong dependence of stellar mass on halo mass that reconciles the different faint-end slopes of the stellar and halo mass

  3. The progenitors of local ultra-massive galaxies across cosmic time: from dusty star-bursting to quiescent stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Marchesini, Danilo; Marsan, Cemile Z. [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Muzzin, Adam; Franx, Marijn [Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden (Netherlands); Stefanon, Mauro [Physics and Astronomy Department, University of Missouri, Columbia, MO 65211 (United States); Brammer, Gabriel G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Vulcani, Benedetta [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8582 (Japan); Fynbo, J. P. U.; Milvang-Jensen, Bo [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Dunlop, James S.; Buitrago, Fernando [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom)

    2014-10-10

    Using the UltraVISTA catalogs, we investigate the evolution in the 11.4 Gyr since z = 3 of the progenitors of local ultra-massive galaxies (log (M {sub star}/M {sub ☉}) ≈ 11.8; UMGs), providing a complete and consistent picture of how the most massive galaxies at z = 0 have assembled. By selecting the progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56{sub −0.25}{sup +0.35} dex, 0.45{sub −0.20}{sup +0.16} dex, and 0.27{sub −0.12}{sup +0.08} dex from z = 3, z = 2, and z = 1, respectively, to z = 0. At z < 1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At z > 1, the contribution from star-forming galaxies progressively increases, with the progenitors at 2 < z < 3 being dominated by massive (M {sub star} ≈ 2 × 10{sup 11} M {sub ☉}), dusty (A {sub V} ∼ 1-2.2 mag), star-forming (SFR ∼ 100-400 M {sub ☉} yr{sup –1}) galaxies with a large range in stellar ages. At z = 2.75, ∼15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that at least half of the stellar content of local UMGs was assembled at z > 1, whereas the remaining was assembled via merging from z ∼ 1 to the present. Most of the quenching of the star-forming progenitors happened between z = 2.75 and z = 1.25, in good agreement with the typical formation redshift and scatter in age of z = 0 UMGs as derived from their fossil records. The progenitors of local UMGs, including the star-forming ones, never lived on the blue cloud since z = 3. We propose an alternative path for the formation of local UMGs that refines previously proposed pictures and that is fully consistent with our findings.

  4. Winds of AGB stars: does size matter?

    International Nuclear Information System (INIS)

    Hoefner, S

    2008-01-01

    Asymptotic giant branch (AGB) stars are showing clear signs of significant mass loss through cool stellar winds. These outflows are attributed to the combined effects of pulsation-induced shocks and radiation pressure on dust grains formed in the outer atmospheric layers. This paper gives an overview of the current status of radiation-hydrodynamical modelling of these processes, and presents a toy model that allows analysis of certain features of detailed models, such as the influence of grain size dependent opacities and basic differences in winds of C- and M-type AGB stars.

  5. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. I. A LOW-MASS RATIO STELLAR COMPANION TO TYC 4110-01037-1 IN A 79 DAY ORBIT

    International Nuclear Information System (INIS)

    Wisniewski, John P.; Agol, Eric; Barnes, Rory; Ge, Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Chang, Liang; Crepp, Justin R.; Eastman, Jason; Gaudi, B. Scott; Esposito, Massimiliano; Gonzalez Hernandez, Jonay I.; Prieto, Carlos Allende; Ghezzi, Luan; Da Costa, Luiz N.; Porto De Mello, G. F.; Stassun, Keivan G.; Cargile, Phillip; Bizyaev, Dmitry

    2012-01-01

    TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T eff ∼ ☉ and radius of 0.99 ± 0.18 R ☉ . We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of ∼2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 ± 0.012 days, an eccentricity of 0.1095 ± 0.0023, and a semi-amplitude of 4199 ± 11 m s –1 . We determine the minimum companion mass (if sin i = 1) to be 97.7 ± 5.8 M Jup . The system's companion to host star mass ratio, ≥0.087 ± 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T eff ∼< 6000 K) stars. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be comoving, we estimate it would be a dM4 star. We present these results in the context of our larger-scale effort to constrain the statistics of low-mass stellar and brown dwarf companions to FGK-type stars via the MARVELS survey.

  6. The Productivity of Oxygenic Photosynthesis around Cool, M Dwarf Stars

    Science.gov (United States)

    Lehmer, Owen R.; Catling, David C.; Parenteau, Mary N.; Hoehler, Tori M.

    2018-06-01

    In the search for life around cool stars, the presence of atmospheric oxygen is a prominent biosignature, as it may indicate oxygenic photosynthesis (OP) on the planetary surface. On Earth, most oxygenic photosynthesizing organisms (OPOs) use photons between 400 and 750 nm, which have sufficient energy to drive the photosynthetic reaction that generates O2 from H2O and CO2. OPOs around cool stars may evolve similar biological machinery capable of producing oxygen from water. However, in the habitable zones (HZs) of the coolest M dwarf stars, the flux of 400–750 nm photons may be just a few percent that of Earth’s. We show that the reduced flux of 400–750 nm photons around M dwarf stars could result in Earth-like planets being growth limited by light, unlike the terrestrial biosphere, which is limited by nutrient availability. We consider stars with photospheric temperatures between 2300 and 4200 K and show that such light-limited worlds could occur at the outer edge of the HZ around TRAPPIST-1-like stars. We find that even if OP can use photons longer than 750 nm, there would still be insufficient energy to sustain the Earth’s extant biosphere throughout the HZ of the coolest stars. This is because such stars emit largely in the infrared and near-infrared, which provide sufficient energy to make the planet habitable, but limits the energy available for OP. TRAPPIST-1f and g may fall into this category. Biospheres on such planets, potentially limited by photon availability, may generate small biogenic signals, which could be difficult for future observations to detect.

  7. YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

    Energy Technology Data Exchange (ETDEWEB)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Kuhn, Michael A. [Millennium Institute of Astrophysics, Camino El Observatorio 1515, Las Condes, Santiago (Chile); Povich, Matthew S., E-mail: edf@astro.psu.edu [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Ave., Pomona, CA 91768 (United States)

    2016-12-20

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  8. YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

    International Nuclear Information System (INIS)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Povich, Matthew S.

    2016-01-01

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra -based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  9. Cosmic abundances: The impact of stellar duplicity

    OpenAIRE

    Jorissen, A.; Van Eck, S.

    2004-01-01

    The mass-transfer scenario links chemical peculiarities with stellar duplicity for an increasing number of stellar classes (classical and dwarf barium stars, subgiant and giant CH stars, S stars without technetium, yellow symbiotic stars, WIRRING stars, Abell-35-like nuclei of planetary nebulae...). Despite these successes, the mass-transfer scenario still faces several problems: What is the mass-transfer mode? Why orbital elements of dwarf barium stars do not fully match those of the classic...

  10. The Radio-X-ray Relation in Cool Stars: Are We Headed Toward a Divorce?

    Science.gov (United States)

    Forbrich, J.; Wolk, S. J.; Güdel, M.; Benz, A.; Osten, R.; Linsky, J. L.; McLean, M.; Loinard, L.; Berger, E.

    2011-12-01

    This splinter session was devoted to reviewing our current knowledge of correlated X-ray and radio emission from cool stars in order to prepare for new large radio observatories such as the EVLA. A key interest was to discuss why the X-ray and radio luminosities of some cool stars are in clear breach of a correlation that holds for other active stars, the so-called Güdel-Benz relation. This article summarizes the contributions whereas the actual presentations can be accessed on the splinter website.

  11. Stellar axion models

    Energy Technology Data Exchange (ETDEWEB)

    Nowakowski, Daniel; Kuster, Markus; Meister, Claudia V.; Fuelbert, Florian; Hoffmann, Dieter H.H. [TU Darmstadt (Germany). Institut fuer Kernphysik; Weiss, Achim [Max-Planck-Institut fuer Astrophysik, Garching (Germany)

    2010-07-01

    An axion helioscope is typically operated to observe the sun as an axion source. Additional pointings at celestial sources, e.g. stars in other galaxies, result in possible detections of axions from distant galactic objects. For the observation of supplementary axion sources we therefore calculate the thereotical axion flux from distant stars by extending axionic flux models for the axion Primakoff effect in the sun to other main sequence stars. The main sequence star models used for our calculations are based on full stellar structure calculations. To deduce the effective axion flux of stellar objects incident on the Earth the All-Sky catalogue was used to obtain the spectral class and distance of the stars treated. Our calculations of the axion flux in the galactic plane show that for a zero age main sequence star an maximum axion flux of {phi}{sub a}=303.43 cm{sup -2}s{sup -1} could be expected. Furthermore we present estimates of axion fluxes from time-evolved stars.

  12. Stellar parametrization from Gaia RVS spectra

    Science.gov (United States)

    Recio-Blanco, A.; de Laverny, P.; Allende Prieto, C.; Fustes, D.; Manteiga, M.; Arcay, B.; Bijaoui, A.; Dafonte, C.; Ordenovic, C.; Ordoñez Blanco, D.

    2016-01-01

    Context. Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as GRVS~ 16. A specific stellar parametrization will be performed on most of these RVS spectra, I.e. those with enough high signal-to-noise ratio (S/N), which should correspond to single stars that have a magnitude in the RVS band brighter than ~14.5. Some individual chemical abundances will also be estimated for the brightest targets. Aims: We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-Spec working group of the analysis consortium. The tested codes are based on optimisation (FERRE and GAUGUIN), projection (MATISSE), or pattern-recognition methods (Artificial Neural Networks). We present and discuss each of their expected performances in the recovered stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) for B- to K-type stars. The performances for determining of [α/Fe] ratios are also presented for cool stars. Methods: Each code has been homogeneously tested with a large grid of RVS simulated synthetic spectra of BAFGK-spectral types (dwarfs and giants), with metallicities varying from 10-2.5 to 10+ 0.5 the solar metallicity, and taking variations of ±0.4 dex in the composition of the α-elements into consideration. The tests were performed for S/N ranging from ten to 350. Results: For all the stellar types we considered, stars brighter than GRVS~ 12.5 are very efficiently parametrized by the GSP-Spec pipeline, including reliable estimations of [α/Fe]. Typical internal errors for FGK metal-rich and metal-intermediate stars are around 40 K in Teff, 0.10 dex in log(g), 0.04 dex in [M/H], and 0.03 dex in [α/Fe] at GRVS = 10.3. They degrade to 155 K in Teff, 0.15 dex in log(g), 0.10 dex in [M/H], and 0.1 dex in [α/Fe] at GRVS~ 12. Similar accuracies in Teff and [M/H] are

  13. Evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the Orion Nebula Cluster

    Science.gov (United States)

    Kroupa, Pavel; Jeřábková, Tereza; Dinnbier, František; Beccari, Giacomo; Yan, Zhiqiang

    2018-04-01

    A scenario for the formation of multiple co-eval populations separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10 Myr) and with masses in the range 600-20 000 M⊙ is outlined. It rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. The associated just-formed O stars ionise the inflow and suppress star formation in the embedded cluster. However, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. The inflow of molecular gas can then resume forming a second population. This sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 Myr), but is not likely to be possible in VYCs with mass <300 M⊙, because such populations are not likely to contain an O star. Stellar populations heavier than about 2000 M⊙ are likely to have too many O stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. VYCs with masses in the range 600-2000 M⊙ are likely to have such multi-age populations, while VYCs with masses in the range 2000-20 000 M⊙ can also be composed solely of co-eval, mono-age populations. More massive VYCs are not likely to host sub-populations with age differences of about 1 Myr. This model is applied to the Orion Nebula Cluster (ONC), in which three well-separated pre-main sequences in the colour-magnitude diagram of the cluster have recently been discovered. The mass-inflow history is constrained using this model and the number of OB stars ejected from each population are estimated for verification using Gaia data. As a further consequence of the proposed model, the three runaway O star systems, AE Aur, μ Col and ι Ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the ONC. Evidence for stellar

  14. The Evolution of Low-Metallicity Massive Stars

    Science.gov (United States)

    Szécsi, Dorottya

    2016-07-01

    Massive star evolution taking place in astrophysical environments consisting almost entirely of hydrogen and helium - in other words, low-metallicity environments - is responsible for some of the most intriguing and energetic cosmic phenomena, including supernovae, gamma-ray bursts and gravitational waves. This thesis aims to investigate the life and death of metal-poor massive stars, using theoretical simulations of the stellar structure and evolution. Evolutionary models of rotating, massive stars (9-600 Msun) with an initial metal composition appropriate for the low-metallicity dwarf galaxy I Zwicky 18 are presented and analyzed. We find that the fast rotating models (300 km/s) become a particular type of objects predicted only at low-metallicity: the so-called Transparent Wind Ultraviolet INtense (TWUIN) stars. TWUIN stars are fast rotating massive stars that are extremely hot (90 kK), very bright and as compact as Wolf-Rayet stars. However, as opposed to Wolf-Rayet stars, their stellar winds are optically thin. As these hot objects emit intense UV radiation, we show that they can explain the unusually high number of ionizing photons of the dwarf galaxy I Zwicky 18, an observational quantity that cannot be understood solely based on the normal stellar population of this galaxy. On the other hand, we find that the most massive, slowly rotating models become another special type of object predicted only at low-metallicity: core-hydrogen-burning cool supergiant stars. Having a slow but strong stellar wind, these supergiants may be important contributors in the chemical evolution of young galactic globular clusters. In particular, we suggest that the low mass stars observed today could form in a dense, massive and cool shell around these, now dead, supergiants. This scenario is shown to explain the anomalous surface abundances observed in these low mass stars, since the shell itself, having been made of the mass ejected by the supergiant’s wind, contains nuclear

  15. Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes

    Science.gov (United States)

    Thilker, David

    At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF

  16. Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

    Science.gov (United States)

    Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

    2013-05-01

    Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

  17. Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions

    Directory of Open Access Journals (Sweden)

    Douglas Rubin

    2011-01-01

    Full Text Available The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates >10-5M⨀yr−1 in the vicinity of ~1″. For present-day mass functions of the form, dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass ≲7M⨀ and a power-law slope ≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

  18. The Taiwanese-American occultation survey project stellar variability. III. Detection of 58 new variable stars

    Energy Technology Data Exchange (ETDEWEB)

    Ishioka, R.; Wang, S.-Y.; Zhang, Z.-W.; Lehner, M. J.; Cook, K. H.; King, S.-K.; Lee, T.; Marshall, S. L.; Schwamb, M. E.; Wang, J.-H.; Wen, C.-Y. [Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Alcock, C.; Protopapas, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Axelrod, T. [Steward Observatory, 933 North Cherry Avenue, Room N204, Tucson, AZ 85721 (United States); Bianco, F. B. [Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Byun, Y.-I. [Department of Astronomy and University Observatory, Yonsei University, 134 Shinchon, Seoul 120-749 (Korea, Republic of); Chen, W. P.; Ngeow, C.-C. [Institute of Astronomy, National Central University, No. 300, Jhongda Road, Jhongli City, Taoyuan County 320, Taiwan (China); Kim, D.-W. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Rice, J. A., E-mail: ishioka@asiaa.sinica.edu.tw [Department of Statistics, University of California Berkeley, 367 Evans Hall, Berkeley, CA 94720 (United States)

    2014-04-01

    The Taiwanese-American Occultation Survey project is designed for the detection of stellar occultations by small-size Kuiper Belt Objects, and it has monitored selected fields along the ecliptic plane by using four telescopes with a 3 deg{sup 2} field of view on the sky since 2005. We have analyzed data accumulated during 2005-2012 to detect variable stars. Sixteen fields with observations of more than 100 epochs were examined. We recovered 85 variables among a total of 158 known variable stars in these 16 fields. Most of the unrecovered variables are located in the fields observed less frequently. We also detected 58 variable stars which are not listed in the International Variable Star Index of the American Association of Variable Star Observers. These variable stars are classified as 3 RR Lyrae, 4 Cepheid, 1 δ Scuti, 5 Mira, 15 semi-regular, and 27 eclipsing binaries based on the periodicity and the profile of the light curves.

  19. Suppression of cooling by strong magnetic fields in white dwarf stars.

    Science.gov (United States)

    Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

    2014-11-06

    Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

  20. O stars and Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

  1. O stars and Wolf-Rayet stars

    Science.gov (United States)

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  2. Chromospheric activity of periodic variable stars (including eclipsing binaries) observed in DR2 LAMOST stellar spectral survey

    Science.gov (United States)

    Zhang, Liyun; Lu, Hongpeng; Han, Xianming L.; Jiang, Linyan; Li, Zhongmu; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang

    2018-05-01

    The LAMOST spectral survey provides a rich databases for studying stellar spectroscopic properties and chromospheric activity. We cross-matched a total of 105,287 periodic variable stars from several photometric surveys and databases (CSS, LINEAR, Kepler, a recently updated eclipsing star catalogue, ASAS, NSVS, some part of SuperWASP survey, variable stars from the Tsinghua University-NAOC Transient Survey, and other objects from some new references) with four million stellar spectra published in the LAMOST data release 2 (DR2). We found 15,955 spectra for 11,469 stars (including 5398 eclipsing binaries). We calculated their equivalent widths (EWs) of their Hα, Hβ, Hγ, Hδ and Caii H lines. Using the Hα line EW, we found 447 spectra with emission above continuum for a total of 316 stars (178 eclipsing binaries). We identified 86 active stars (including 44 eclipsing binaries) with repeated LAMOST spectra. A total of 68 stars (including 34 eclipsing binaries) show chromospheric activity variability. We also found LAMOST spectra of 12 cataclysmic variables, five of which show chromospheric activity variability. We also made photometric follow-up studies of three short period targets (DY CVn, HAT-192-0001481, and LAMOST J164933.24+141255.0) using the Xinglong 60-cm telescope and the SARA 90-cm and 1-m telescopes, and obtained new BVRI CCD light curves. We analyzed these light curves and obtained orbital and starspot parameters. We detected the first flare event with a huge brightness increase of more than about 1.5 magnitudes in R filter in LAMOST J164933.24+141255.0.

  3. The range of variation of the mass of the most massive star in stellar clusters derived from 35 million Monte Carlo simulations

    International Nuclear Information System (INIS)

    Popescu, Bogdan; Hanson, M. M.

    2014-01-01

    A growing fraction of simple stellar population models, in an aim to create more realistic simulations capable of including stochastic variation in their outputs, begin their simulations with a distribution of discrete stars following a power-law function of masses. Careful attention is needed to create a correctly sampled initial mass function (IMF), and here we provide a solid mathematical method, called MASSCLEAN IMF Sampling, for doing so. We use our method to perform 10 million MASSCLEAN Monte Carlo stellar cluster simulations to determine the most massive star in a mass distribution as a function of the total mass of the cluster. We find that a maximum mass range is predicted, not a single maximum mass. This range is (1) dependent on the total mass of the cluster and (2) independent of an upper stellar mass limit, M limit , for unsaturated clusters and emerges naturally from our IMF sampling method. We then turn our analysis around, starting with our new database of 25 million simulated clusters, to constrain the highest mass star from the observed integrated colors of a sample of 40 low-mass Large Magellanic Cloud stellar clusters of known age and mass. Finally, we present an analytical description of the maximum mass range of the most massive star as a function of the cluster's total mass and present a new M max -M cluster relation.

  4. Radio continuum emission from winds, chromospheres, and coronae of cool giants and supergiants

    International Nuclear Information System (INIS)

    Drake, S.A.; Linsky, J.L.

    1986-01-01

    In this paper we present the results of a sensitive VLA radio continuum survey at 6 cm of 39 of the nearest, single cool giants and supergiants with spectral types in the range G0--M5. We discuss our findings in the context of the various mechanisms that might be producing radio emission in these cool stars. We have definitely detected four K and M giants (α 1 Her, α Boo, rho Per, and μ Gem) and probably detected a fifth ( β UMi) at flux levels of 0.1--1.0 mJy. We believe that in all five of these cases the radio emission is thermal emission from cool stellar winds. We have made additional 2 cm observations of several stars, including the four stars definitely detected at 6 cm. We have derived spectral indices for α Boo, α 1 Her, and rho Per of 0.80, 0.84, and 0.95, respectively, that are close to the 0.6 value predicted by standard stellar wind models in the optically thick regime. An additional cool giant (α Tau) was detected only at 2 cm, implying a spectral index of > or =0.87. None of the coronal or hybrid-chromosphere giants observed were detected in this study, with the exception of α Aur, a 0.2 mJy radio source at 6 cm, which is in fact a widely separated, long-period (P/sub orb/approx.104/sup d/) RS CVn system containing two cool giant stars. In this case, we believe that the 6 cm radio emission is optically thin, thermal emission from the corona(e) of one or both of the components, since the radio-emission measure is consistent with that of the observed x-ray emission

  5. Radiative Hydrodynamic Simulations of In Situ Star Formation in the Galactic Center

    Science.gov (United States)

    Frazer, Chris; Heitsch, Fabian

    2018-01-01

    Many stars observed in the Galactic Center (GC) orbit the supermassive black hole (SMBH), Sagittarius A*, in a region where the extreme gravitational field is expected to inhibit star formation. Yet, many of these stars are young which favors an in situ formation scenario. Previous numerical work on this topic has focused on two possible solutions. First, the tidal capture of a > 10^4 Msun infalling molecular cloud by an SMBH may result in the formation of a surrounding gas disk which then rapidly cools and forms stars. This process results in stellar populations that are consistent with the observed stellar disk in the GC. Second, dense gas clumps of approximately 100 Msun on highly eccentric orbits about an SMBH can experience sparks of star formation via orbital compressions occurring during pericenter passage. In my dissertation, I build upon these models using a series of grid-based radiative hydrodynamic simulations, including the effects of both ionizing ultraviolet light from existing stars as well as X-ray radiation emanating from the central black hole. Radiation is treated with an adaptive ray-tracing routine, including appropriate heating and cooling for both neutral and ionized gas. These models show that ultraviolet radiation is sufficiently strong to heat low mass gas clouds, thus suppressing star formation from clump compression. Gas disks that form from cloud capture become sufficiently dense to provide shielding from the radiation of existing central stars, thus allowing star formation to continue. Conversely, X-rays easily penetrate and heat the potentially star forming gas. For sufficiently high radiation fields, this provides a mechanism to disrupt star formation for both scenarios considered above.

  6. Ultraviolet photometry of stellar populations in galaxies

    International Nuclear Information System (INIS)

    Deharveng, J.M.

    1981-01-01

    The UV flux of stellar populations, which is essentially emitted by young stars, conveys information on the process of star formation and its recent history. However, the evaluation of the flux arising from the young stellar component may be difficult. In the case of late type galaxies it is hampered by the extinction and the effect of scattered stellar radiation. In the case of early type galaxies, the star formation, if any, has to be disentangled from the contribution of hot evolved stars and of a possible 'active' phenomenon. A review of observations and results relevant two cases is presented [fr

  7. Star formation: study of the collapse of pre-stellar dense cores

    International Nuclear Information System (INIS)

    Commercon, Benoit

    2009-01-01

    One of the priorities of contemporary astrophysics remains to understand the mechanisms which lead to star formation. In the dense cores where star formation occurs, temperature, pressure, etc... are such that it is impossible to reproduce them in the laboratory. Numerical calculations remain the only mean to study physical phenomena that are involved in the star formation process. The focus of this thesis has been on the numerical methods that are used in the star formation context to describe highly non-linear and multi-scale phenomena. In particular, I have concentrated my work on the first stages of the pre-stellar dense cores collapse. This work is divided in 4 linked part. In a first study, I use a 1D Lagrangian code in spherical symmetry (Audit et al. 2002) to compare three models that incorporate radiative transfer and matter-radiation interactions. This comparison was based on simple gravitational collapse calculations which lead to the first Larson core formation. It was found that the Flux Limited Diffusion model is appropriate for star formation calculations. I also took benefit from this first work to study the properties of the accretion shock on the first Larson core. We developed a semi-analytic model based on well-known assumptions, which reproduces the jump properties at the shock. The second study consisted in implementing the Flux Limited Diffusion model with the radiation-hydrodynamics equations in the RAMSES code (Teyssier 2002). After a first step of numerical tests that validate the scheme, we used RAMSES to perform the first multidimensional collapse calculations that combine magnetic field and radiative transfer effects at small scales with a high numerical resolution. Our results show that the radiative transfer has a significant impact on the fragmentation in the collapse of pre-stellar dense cores. I also present a comparison we made between the RAMSES code (Eulerian approach) and the SPH code DRAGON (Goodwin 2004, Lagrangian approach

  8. sunstardb: A Database for the Study of Stellar Magnetism and the Solar-stellar Connection

    Science.gov (United States)

    Egeland, Ricky

    2018-05-01

    The “solar-stellar connection” began as a relatively small field of research focused on understanding the processes that generate magnetic fields in stars and sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time-series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g., luminosity, differential rotation, and the depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time-series keyed by individual named stars. The organization of the data eliminates the need for the problematic catalog cross-matching operations inherent when building an analysis data set from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

  9. Models of hot stellar systems

    International Nuclear Information System (INIS)

    Van Albada, T.S.

    1986-01-01

    Elliptical galaxies consist almost entirely of stars. Sites of recent star formation are rare, and most stars are believed to be several billion years old, perhaps as old as the Universe itself (--10/sup 10/ yrs). Stellar motions in ellipticals show a modest amount of circulation about the center of the system, but most support against the force of gravity is provided by random motions; for this reason ellipticals are called 'hot' stellar systems. Spiral galaxies usually also contain an appreciable amount of gas (--10%, mainly atomic hydrogen) and new stars are continually being formed out of this gas, especially in the spiral arms. In contrast to ellipticals, support against gravity in spiral galaxies comes almost entirely from rotation; random motions of the stars with respect to rotation are small. Consequently, spiral galaxies are called 'cold' stellar systems. Other than in hot systems, in cold systems the collective response of stars to variations in the force field is an essential part of the dynamics. The present overview is limited to mathematical models of hot systems. Computational methods are also discussed

  10. Hyperon-meson and delta-meson coupling to protoneutron stars structure using the nonlinear Walecka model

    International Nuclear Information System (INIS)

    Souto, W A; Oliveira, J C T; Rodrigues, H; Duarte, S B; Chiapparini, M

    2015-01-01

    In this work we determine the equation of state and the population of baryons and leptons and discuss the effects of the hyperon-meson coupling constants to the formation of delta resonances in the stellar medium. We also discuss the structure of the protoneutron stars including the delta matter in their composition, and compared the results of a cooled neutron star, after escape of neutrinos. For protoneutron stars structure and composition, the neutrinos are considered trapped. (paper)

  11. FUNDAMENTAL PROPERTIES OF KEPLER PLANET-CANDIDATE HOST STARS USING ASTEROSEISMOLOGY

    Energy Technology Data Exchange (ETDEWEB)

    Huber, Daniel; Lissauer, Jack J.; Rowe, Jason F. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Chaplin, William J. [School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Christensen-Dalsgaard, Jorgen; Kjeldsen, Hans; Handberg, Rasmus; Karoff, Christoffer; Lund, Mikkel N.; Lundkvist, Mia [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Gilliland, Ronald L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Buchhave, Lars A. [Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark); Fischer, Debra A.; Basu, Sarbani [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Sanchis-Ojeda, Roberto [Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 (United States); Hekker, Saskia [Astronomical Institute ' ' Anton Pannekoek' ' , University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Howard, Andrew W. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Isaacson, Howard; Marcy, Geoffrey W. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Latham, David W., E-mail: daniel.huber@nasa.gov [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); and others

    2013-04-20

    We have used asteroseismology to determine fundamental properties for 66 Kepler planet-candidate host stars, with typical uncertainties of 3% and 7% in radius and mass, respectively. The results include new asteroseismic solutions for four host stars with confirmed planets (Kepler-4, Kepler-14, Kepler-23 and Kepler-25) and increase the total number of Kepler host stars with asteroseismic solutions to 77. A comparison with stellar properties in the planet-candidate catalog by Batalha et al. shows that radii for subgiants and giants obtained from spectroscopic follow-up are systematically too low by up to a factor of 1.5, while the properties for unevolved stars are in good agreement. We furthermore apply asteroseismology to confirm that a large majority of cool main-sequence hosts are indeed dwarfs and not misclassified giants. Using the revised stellar properties, we recalculate the radii for 107 planet candidates in our sample, and comment on candidates for which the radii change from a previously giant-planet/brown-dwarf/stellar regime to a sub-Jupiter size or vice versa. A comparison of stellar densities from asteroseismology with densities derived from transit models in Batalha et al. assuming circular orbits shows significant disagreement for more than half of the sample due to systematics in the modeled impact parameters or due to planet candidates that may be in eccentric orbits. Finally, we investigate tentative correlations between host-star masses and planet-candidate radii, orbital periods, and multiplicity, but caution that these results may be influenced by the small sample size and detection biases.

  12. AN UNDERSTANDING OF THE SHOULDER OF GIANTS: JOVIAN PLANETS AROUND LATE K DWARF STARS AND THE TREND WITH STELLAR MASS

    Energy Technology Data Exchange (ETDEWEB)

    Gaidos, Eric [Department of Geology and Geophysics, University of Hawai' i at Manoa, Honolulu, HI 96822 (United States); Fischer, Debra A. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Mann, Andrew W.; Howard, Andrew W., E-mail: gaidos@hawaii.edu [Institute for Astronomy, University of Hawai' i at Manoa, Honolulu, HI 96822 (United States)

    2013-07-01

    Analyses of exoplanet statistics suggest a trend of giant planet occurrence with host star mass, a clue to how planets like Jupiter form. One missing piece of the puzzle is the occurrence around late K dwarf stars (masses of 0.5-0.75 M{sub Sun} and effective temperatures of 3900-4800 K). We analyzed four years of Doppler radial velocity (RVs) data for 110 late K dwarfs, one of which hosts two previously reported giant planets. We estimate that 4.0% {+-} 2.3% of these stars have Saturn-mass or larger planets with orbital periods <245 days, depending on the planet mass distribution and RV variability of stars without giant planets. We also estimate that 0.7% {+-} 0.5% of similar stars observed by Kepler have giant planets. This Kepler rate is significantly (99% confidence) lower than that derived from our Doppler survey, but the difference vanishes if only the single Doppler system (HIP 57274) with completely resolved orbits is considered. The difference could also be explained by the exclusion of close binaries (without giant planets) from the Doppler but not Kepler surveys, the effect of long-period companions and stellar noise on the Doppler data, or an intrinsic difference between the two populations. Our estimates for late K dwarfs bridge those for solar-type stars and M dwarfs, and support a positive trend with stellar mass. Small sample size precludes statements about finer structure, e.g., a ''shoulder'' in the distribution of giant planets with stellar mass. Future surveys such as the Next Generation Transit Survey and the Transiting Exoplanet Satellite Survey will ameliorate this deficiency.

  13. AN UNDERSTANDING OF THE SHOULDER OF GIANTS: JOVIAN PLANETS AROUND LATE K DWARF STARS AND THE TREND WITH STELLAR MASS

    International Nuclear Information System (INIS)

    Gaidos, Eric; Fischer, Debra A.; Mann, Andrew W.; Howard, Andrew W.

    2013-01-01

    Analyses of exoplanet statistics suggest a trend of giant planet occurrence with host star mass, a clue to how planets like Jupiter form. One missing piece of the puzzle is the occurrence around late K dwarf stars (masses of 0.5-0.75 M ☉ and effective temperatures of 3900-4800 K). We analyzed four years of Doppler radial velocity (RVs) data for 110 late K dwarfs, one of which hosts two previously reported giant planets. We estimate that 4.0% ± 2.3% of these stars have Saturn-mass or larger planets with orbital periods <245 days, depending on the planet mass distribution and RV variability of stars without giant planets. We also estimate that 0.7% ± 0.5% of similar stars observed by Kepler have giant planets. This Kepler rate is significantly (99% confidence) lower than that derived from our Doppler survey, but the difference vanishes if only the single Doppler system (HIP 57274) with completely resolved orbits is considered. The difference could also be explained by the exclusion of close binaries (without giant planets) from the Doppler but not Kepler surveys, the effect of long-period companions and stellar noise on the Doppler data, or an intrinsic difference between the two populations. Our estimates for late K dwarfs bridge those for solar-type stars and M dwarfs, and support a positive trend with stellar mass. Small sample size precludes statements about finer structure, e.g., a ''shoulder'' in the distribution of giant planets with stellar mass. Future surveys such as the Next Generation Transit Survey and the Transiting Exoplanet Satellite Survey will ameliorate this deficiency.

  14. Research in nuclear astrophysics: stellar collapse and supernovae. Progress report

    International Nuclear Information System (INIS)

    Burrows, A.; Lattimer, J.M.; Yahil, A.

    1986-01-01

    The interaction between nuclear theory and some outstanding problems in astrophysics is examined. The chief emphasis of our program is on stellar collapse, supernovae and neutron star formation. Central to these topics are the parallel development of both an equation of state of hot, dense matter and a novel type of hydrodynamical code. The LLPR compressible liquid drop model is the basis of the former. We are refining it to include both curvature corrections to the surface energy nuclear force parameters which are in better agreement with recently determined experimental quantities. Our study of the equation of state has the added bonus that our results can be used to analyze intermediate energy heavy ion collisions, which, in turn, may illuminate the nucleon-nucleon force. The hydrodynamical code includes a fast, but accurate, approximation to the complete LLPR equation of state. We model not only the stellar collapse leading up to a supernova, but also the quasi-static deleptonization and cooling stages of the nascent neutron star. Our detailed studies of the role of neutrinos in stellar collapse and neutron star formation concentrate on their detectability and signatures. Complementary studies include modelling both mass accretion in the nuclei of galaxies and investigating both galaxy clustering and the large scale structure of the universe. These studies are intended to shed light on the early history of the universe, in which both nuclear and elementary particle physics play a crucial role

  15. Research in nuclear astrophysics: stellar collapse and supernovae. Progress report

    International Nuclear Information System (INIS)

    Burrows, A.; Lattimer, J.M.; Yahil, A.

    1984-01-01

    The interaction between nuclear theory and some outstanding problems in astrophysics is examined. The chief emphasis of our program is on stellar collapse, supernovae and neutron star formation. Central to these topics are the parallel development of the equation of state of hot, dense matter and a novel type of hydrodynamical code. The LLPR compressible liquid drop model forms the basis for the former, and we propose to further refine it by including curvature corrections to the surface energy and by considering other nuclear force parameters which are in better agreement with experimentally determined quantities. The development of the equation of state has another bonus - it can be used to analyze intermediate energy heavy ion collisions, which, in turn, may illuminate the nucleon-nucleon force. The hydrodynamical code includes detailed neutrino transport and a fast, but accurate, approximation to the complete LLPR equation of state, which is necessary for numerical use. We propose to model not only the stellar collapse leading up to a supernova, but also the quasi-static deleptonization and cooling stages of the nascent neutron star. Our detailed studies of the role of neutrinos in stellar collapse and neutron star formation concentrate on their detectability and signatures - after all, neutrinos are the only direct method of observationally checking supernova theory. Complementary studies include modelling both mass accretion in the nuclei of galaxies (which is probably responsible for the quasar phenomenon) and investigations of galaxy clustering and the large scale structure of the universe

  16. CHARACTERIZING THE COOL KOIs. VI. H- AND K-BAND SPECTRA OF KEPLER M DWARF PLANET-CANDIDATE HOSTS

    Energy Technology Data Exchange (ETDEWEB)

    Muirhead, Philip S. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Becker, Juliette; Price, Ellen M.; Thorp, Rachel; Riddle, Reed [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Rojas-Ayala, Bárbara [Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Oporto (Portugal); Vanderburg, Andrew; Johnson, John Asher [Harvard College Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Law, Nicholas M. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Baranec, Christoph [Institute for Astronomy, University of Hawai' i at Mānoa, Hilo, HI 96720-2700 (United States); Hamren, Katherine [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Schlawin, Everett; Lloyd, James P. [Department of Astronomy, Cornell University, Ithaca, NY 14583 (United States); Covey, Kevin R., E-mail: philipm@bu.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2014-07-01

    We present H- and K-band spectra for late-type Kepler Objects of Interest (the {sup C}ool KOIs{sup )}: low-mass stars with transiting-planet candidates discovered by NASA's Kepler Mission that are listed on the NASA Exoplanet Archive. We acquired spectra of 103 Cool KOIs and used the indices and calibrations of Rojas-Ayala et al. to determine their spectral types, stellar effective temperatures, and metallicities, significantly augmenting previously published values. We interpolate our measured effective temperatures and metallicities onto evolutionary isochrones to determine stellar masses, radii, luminosities, and distances, assuming the stars have settled onto the main sequence. As a choice of isochrones, we use a new suite of Dartmouth predictions that reliably include mid-to-late M dwarf stars. We identify five M4V stars: KOI-961 (confirmed as Kepler 42), KOI-2704, KOI-2842, KOI-4290, and the secondary component to visual binary KOI-1725, which we call KOI-1725 B. We also identify a peculiar star, KOI-3497, which has Na and Ca lines consistent with a dwarf star but CO lines consistent with a giant. Visible-wavelength adaptive optics imaging reveals two objects within a 1 arcsec diameter; however, the objects' colors are peculiar. The spectra and properties presented in this paper serve as a resource for prioritizing follow-up observations and planet validation efforts for the Cool KOIs and are all available for download online using the ''data behind the figure'' feature.

  17. SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). II. COOL EVOLVED STARS

    International Nuclear Information System (INIS)

    Boyer, Martha L.; Meixner, Margaret; Gordon, Karl D.; Shiao, Bernie; Srinivasan, Sundar; Van Loon, Jacco Th.; McDonald, Iain; Kemper, F.; Zaritsky, Dennis; Block, Miwa; Engelbracht, Charles W.; Misselt, Karl; Babler, Brian; Bracker, Steve; Meade, Marilyn; Whitney, Barbara; Hora, Joe; Robitaille, Thomas; Indebetouw, Remy; Sewilo, Marta

    2011-01-01

    We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled 'Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC', or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 μm). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ∼20% of the global SMC flux (extended + point-source) at 3.6 μm, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] - [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.

  18. The range of variation of the mass of the most massive star in stellar clusters derived from 35 million Monte Carlo simulations

    Energy Technology Data Exchange (ETDEWEB)

    Popescu, Bogdan; Hanson, M. M., E-mail: bogdan.popescu@uc.edu, E-mail: margaret.hanson@uc.edu [Department of Physics, University of Cincinnati, P.O. Box 210011, Cincinnati, OH 45221-0011 (United States)

    2014-01-01

    A growing fraction of simple stellar population models, in an aim to create more realistic simulations capable of including stochastic variation in their outputs, begin their simulations with a distribution of discrete stars following a power-law function of masses. Careful attention is needed to create a correctly sampled initial mass function (IMF), and here we provide a solid mathematical method, called MASSCLEAN IMF Sampling, for doing so. We use our method to perform 10 million MASSCLEAN Monte Carlo stellar cluster simulations to determine the most massive star in a mass distribution as a function of the total mass of the cluster. We find that a maximum mass range is predicted, not a single maximum mass. This range is (1) dependent on the total mass of the cluster and (2) independent of an upper stellar mass limit, M{sub limit} , for unsaturated clusters and emerges naturally from our IMF sampling method. We then turn our analysis around, starting with our new database of 25 million simulated clusters, to constrain the highest mass star from the observed integrated colors of a sample of 40 low-mass Large Magellanic Cloud stellar clusters of known age and mass. Finally, we present an analytical description of the maximum mass range of the most massive star as a function of the cluster's total mass and present a new M{sub max} -M{sub cluster} relation.

  19. The Star–Planet Connection. I. Using Stellar Composition to Observationally Constrain Planetary Mineralogy for the 10 Closest Stars

    Science.gov (United States)

    Hinkel, Natalie R.; Unterborn, Cayman T.

    2018-01-01

    The compositions of stars and planets are connected, but the definition of “habitability” and the “habitable zone” only take into account the physical relationship between the star and planet. Planets, however, are made truly habitable by both chemical and physical processes that regulate climatic and geochemical cycling between atmosphere, surface, and interior reservoirs. Despite this, an “Earth-like” planet is often defined as a planet made of a mixture of rock and Fe that is roughly 1 Earth-density. To understand the interior of a terrestrial planet, the stellar abundances of planet-building elements (e.g., Mg, Si, and Fe) can be used as a proxy for the planet’s composition. We explore the planetary mineralogy and structure for fictive planets around the 10 stars closest to the Sun using stellar abundances from the Hypatia Catalog. Although our sample contains stars that are both sub- and super-solar in their abundances, we find that the mineralogies are very similar for all 10 planets—since the error or spread in the stellar abundances create significant degeneracy in the models. We show that abundance uncertainties need to be on the order of [Fe/H] < 0.02 dex, [Si/H] < 0.01 dex, [Al/H] < 0.002 dex, while [Mg/H] and [Ca/H] < 0.001 dex in order to distinguish two unique planetary populations in our sample of 10 stars. While these precisions are high, we believe that they are possible given certain abundance techniques, in addition to methodological transparency, that have recently been demonstrated in the literature. However, without these precisions, the uncertainty in planetary structures will be so high that we will be unable to confidently state that a planet is like the Earth, or unlike anything we have ever seen. We made some cuts and ruled out a number of stars, but these 10 are still rather nearby.

  20. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    Energy Technology Data Exchange (ETDEWEB)

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, S.; Deheuvels, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Brandao, I. M.; Cunha, M. S.; Sousa, S. G. [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Dogan, G. [High Altitude Observatory, NCAR, P.O. Box 3000, Boulder, CO 80307 (United States); Metcalfe, T. S. [Space Science Institute, Boulder, CO 80301 (United States); Serenelli, A. M.; Garcia, R. A. [Kavli Institute for Theoretical Physics, Santa Barbara, CA 93106 (United States); Ballot, J. [Institut de Recherche en Astrophysique et Planetologie, CNRS, 14 avenue Edouard Belin, F-31400 Toulouse (France); Weiss, A. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85748 Garching bei Muenchen (Germany); Appourchaux, T. [Institut d' Astrophysique Spatiale, Universite Paris Sud-CNRS (UMR8617) Batiment 121, F-91405 Orsay Cedex (France); Casagrande, L. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611 (Australia); Cassisi, S. [INAF-Astronomical Observatory of Teramo, Via M. Maggini sn, I-64100 Teramo (Italy); Creevey, O. L. [Laboratoire Lagrange, Universite de Nice Sophia-Antipolis, CNRS, I-06300 Nice, France. (France); Lebreton, Y. [Observatoire de Paris, GEPI, CNRS UMR 8111, F-92195 Meudon (France); Noels, A. [Institute of Astrophysics and Geophysics, University of Liege, B-4000 Liege (Belgium); and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  1. Evaluation of parameters of Black Hole, stellar cluster and dark matter distribution from bright star orbits in the Galactic Center

    Science.gov (United States)

    Zakharov, Alexander

    It is well-known that one can evaluate black hole (BH) parameters (including spin) analyz-ing trajectories of stars around BH. A bulk distribution of matter (dark matter (DM)+stellar cluster) inside stellar orbits modifies trajectories of stars, namely, generally there is a apoas-tron shift in direction which opposite to GR one, even now one could put constraints on DM distribution and BH parameters and constraints will more stringent in the future. Therefore, an analyze of bright star trajectories provides a relativistic test in a weak gravitational field approximation, but in the future one can test a strong gravitational field near the BH at the Galactic Center with the same technique due to a rapid progress in observational facilities. References A. Zakharov et al., Phys. Rev. D76, 062001 (2007). A.F. Zakharov et al., Space Sci. Rev. 148, 301313(2009).

  2. Formation of the First Star Clusters and Massive Star Binaries by Fragmentation of Filamentary Primordial Gas Clouds

    Science.gov (United States)

    Hirano, Shingo; Yoshida, Naoki; Sakurai, Yuya; Fujii, Michiko S.

    2018-03-01

    We perform a set of cosmological simulations of early structure formation incorporating baryonic streaming motions. We present a case where a significantly elongated gas cloud with ∼104 solar mass (M ⊙) is formed in a pre-galactic (∼107 M ⊙) dark halo. The gas streaming into the halo compresses and heats the massive filamentary cloud to a temperature of ∼10,000 Kelvin. The gas cloud cools rapidly by atomic hydrogen cooling, and then by molecular hydrogen cooling down to ∼400 Kelvin. The rapid decrease of the temperature and hence of the Jeans mass triggers fragmentation of the filament to yield multiple gas clumps with a few hundred solar masses. We estimate the mass of the primordial star formed in each fragment by adopting an analytic model based on a large set of radiation hydrodynamics simulations of protostellar evolution. The resulting stellar masses are in the range of ∼50–120 M ⊙. The massive stars gravitationally attract each other and form a compact star cluster. We follow the dynamics of the star cluster using a hybrid N-body simulation. We show that massive star binaries are formed in a few million years through multi-body interactions at the cluster center. The eventual formation of the remnant black holes will leave a massive black hole binary, which can be a progenitor of strong gravitational wave sources similar to those recently detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

  3. On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

    Science.gov (United States)

    Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

    2018-02-01

    We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

  4. The relation between stellar evolution and cosmology

    International Nuclear Information System (INIS)

    Tayler, R.J.

    1984-01-01

    Observations of star clusters combined with the theory of stellar evolution enable us to estimate the ages of stars while cosmological observations and theories give us a value for the age of the Universe. This is the most important interaction between cosmology and stellar evolution because it is clearly necessary that stars are younger than the Universe. Stellar evolution also plays an important role in relating the present chemical composition of the Universe to its original composition. The author restricts the review to a discussion of the relation between stellar evolution and the big bang cosmological theory because there is such a good qualitative agreement between the hot big bang theory and observations. (Auth.)

  5. HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Oskinova, L. M.; Hamann, W.-R. [Institute for Physics and Astronomy, University Potsdam, 14476 Potsdam (Germany); Gayley, K. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States); Huenemoerder, D. P. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA 02139 (United States); Ignace, R. [Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37663 (United States); Pollock, A. M. T., E-mail: lida@astro.physik.uni-potsdam.de [European Space Agency XMM-Newton Science Operations Centre, European Space Astronomy Centre, Apartado 78, Villanueva de la Canada, 28691 Madrid (Spain)

    2012-03-10

    We present the first high-resolution X-ray spectrum of a putatively single Wolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, 'cool' stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at Almost-Equal-To 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow 'sticky clumps' that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds.

  6. Grain formation in cool stellar envelopes

    International Nuclear Information System (INIS)

    Deguchi, S.

    1980-01-01

    The nucleation and growth of dust grains in the stellar envelope are investigated for the case of oxygen-rich stars, where the mass loss occurs as a result of the radiation pressure on the dust grains. The number density of grains, the final grain sizes, and the final amount of metals remaining in gaseous states are calculated based on the grain-nucleation theory proposed by Yamamoto and Hasegawa and Draine and Salpeter. It is shown that, even if we base our calculations on the Lothe-Pound nucleation rate equation instead of the classical, homogeneous nucleation rate equation, the proposed theory gives a number density of grains quite similar to that based on the classical rate equation. The approximate solution of the flow, in this paper, brings physical insight to the problem of how the formation of grains couples the flow passing the sonic point. The metals in the outer envelope remain in gaseous state by the amount of 1--10% of the initial content for the mass-loss rate of 10 -5 M/sub sun/ yr -1 and by less than 1% for the massloss are less than 3 x 10 -6 M/sub sun/ yr -1 . Species of metals condensed onto the grains are also discussed

  7. A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

    International Nuclear Information System (INIS)

    Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Jörg-Uwe; Müller, André; Bonnefoy, Mickaël; Henning, Thomas; Lacour, Sylvestre; Thebault, Philippe; Juhász, Attila; Sicilia-Aguilar, Aurora; Tuthill, Peter; Crida, Aurelien

    2012-01-01

    With the uniquely high contrast within 0.''1 (Δmag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 ± 5 mas (12.8 ± 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 ± 0.007, 0.012 ± 0.008, and 0.0086 ± 0.0011, respectively (3σ errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion with an estimated mass of ∼0.1-0.4 M ☉ . HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.

  8. Stellar neutron sources and s-process in massive stars

    Science.gov (United States)

    Talwar, Rashi

    The s-process or the slow neutron capture process is a nucleosynthesis process taking place at relatively low neutron densities in stars. It runs along the valley of beta stability since the neutron capture rate is much slower compared to the beta decay rate. The s-process occurs mainly during core helium burning and shell carbon burning phase in massive stars and during thermally pulsing helium burning phase in asymptotic giant-branch stars. The potential stellar neutron source for the s-process is associated with alpha-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the build-up of22Ne neutron source during the heliumburning phase in these stars. The low energy 26Mg resonances at stellar energies below 800 keV are predicted to have a critical influence on the alpha-capture rates on 22Ne. Some of these resonances may also correspond to pronounced alpha cluster structure near the alpha-threshold. However, these resonances have remained elusive during direct alpha capture measurements owing to the high Coulomb barrier and background from cosmic rays and beam induced reactions. Hence, in the present work, alpha-inelastic scattering and alpha- transfer measurements have been performed to probe the level structure of 26Mg nucleus in order to determine the 22Ne+alpha-capture rates. Both experiments have been performed using the high-resolution Grand Raiden Spectrometer at the Research Center for Nuclear Physics (RCNP), Osaka, Japan. For the alpha-inelastic scattering measurement, a self-supporting solid 26Mg target was used and for the alpha-transfer study via the (6Li,d) reaction, 22Ne gas enclosed in a gas cell with Aramid windows was used. The reaction products were momentum analysed by the spectrometer and detected at the focal plane equipped with two multi-wire drift chambers and two plastic-scintillation detectors. The focal plane detection system provided information on the position, the angle, the time of flight and

  9. Flare stars

    International Nuclear Information System (INIS)

    Nicastro, A.J.

    1981-01-01

    The least massive, but possibly most numerous, stars in a galaxy are the dwarf M stars. It has been observed that some of these dwarfs are characterized by a short increase in brightness. These stars are called flare stars. These flare stars release a lot of energy in a short amount of time. The process producing the eruption must be energetic. The increase in light intensity can be explained by a small area rising to a much higher temperature. Solar flares are looked at to help understand the phenomenon of stellar flares. Dwarfs that flare are observed to have strong magnetic fields. Those dwarf without the strong magnetic field do not seem to flare. It is believed that these regions of strong magnetic fields are associated with star spots. Theories on the energy that power the flares are given. Astrophysicists theorize that the driving force of a stellar flare is the detachment and collapse of a loop of magnetic flux. The mass loss due to stellar flares is discussed. It is believed that stellar flares are a significant contributor to the mass of interstellar medium in the Milky Way

  10. Stellar evolution

    CERN Document Server

    Meadows, A J

    2013-01-01

    Stellar Evolution, Second Edition covers the significant advances in the understanding of birth, life, and death of stars.This book is divided into nine chapters and begins with a description of the characteristics of stars according to their brightness, distance, size, mass, age, and chemical composition. The next chapters deal with the families, structure, and birth of stars. These topics are followed by discussions of the chemical composition and the evolution of main-sequence stars. A chapter focuses on the unique features of the sun as a star, including its evolution, magnetic fields, act

  11. THE 100 Myr STAR FORMATION HISTORY OF NGC 5471 FROM CLUSTER AND RESOLVED STELLAR PHOTOMETRY

    International Nuclear Information System (INIS)

    Garcia-Benito, Ruben; Perez, Enrique; Maiz Apellaniz, Jesus; Cervino, Miguel; Diaz, Angeles I.

    2011-01-01

    We show that star formation in the giant H II region NGC 5471 has been ongoing during the past 100 Myr. Using Hubble Space Telescope/Wide-Field Planetary Camera 2 F547M and F675W, ground-based JHK s , and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history (SFH) in the massive giant extragalactic H II region NGC 5471 in M101. We perform a photometric study of the color-magnitude diagram (CMD) of the resolved stars and an integrated analysis of the main individual star-forming clusters and of NGC 5471 as a whole. The integrated UV-optical-NIR photometry for the whole region provides two different reference ages, 8 Myr and 60 Myr, revealing a complex SFH, clearly confirmed by the CMD-resolved stellar photometry analysis. The spatial distribution of the stars shows that the star formation in NGC 5471 has proceeded along the whole region during, at least, the last 100 Myr. The current ionizing clusters are enclosed within a large bubble, which is likely to have been produced by the stars that formed in a major event ∼20 Myr ago.

  12. Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions

    OpenAIRE

    Paxton, Bill; Schwab, Josiah; Bauer, Evan B.; Bildsten, Lars; Blinnikov, Sergei; Duffell, Paul; Farmer, R.; Goldberg, Jared A.; Marchant, Pablo; Sorokina, Elena; Thoul, Anne; Townsend, Richard H. D.; Timmes, F. X.

    2017-01-01

    We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective core mass during both hydrogen and helium burning phases. Stars with $M

  13. On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

    Science.gov (United States)

    Windhorst, Rogier A.; Wyithe, Stuart; Alpaslan, Mehmet; Timmes, F. X.; Andrews, Stephen K.; Kim, Duho; Kelly, Patrick; Coe, Dan A.; Diego, Jose M.; Driver, Simon P.; Dijkstra, Mark

    2018-06-01

    We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-IR surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z=7-17.We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z>7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions.We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be 10^4-10^5x, with rise times of hours and decline times of z~Economia y Competitividad of Spain Consolider Project CSD2010-00064.

  14. VizieR Online Data Catalog: Stellar activity and kinematics of FGK stars (Murgas+, 2013)

    Science.gov (United States)

    Murgas, F.; Jenkins, J. S.; Rojo, P.; Jones, H. R. A.; Pinfield, D. J.

    2013-02-01

    We present a compilation of stellar activity catalogs combined with galactic velocity information of 2529 F, G, and K stars. The stellar activity catalogs use in this work are: Jenkins et al. 2011 (Cat. J/A+A/531/A8); Gray et al. 2003 (Cat. J/AJ/126/2048), 2006 (Cat. J/AJ/132/161); Henry et al 1996 (Cat. J/A+A/111/439); Wright et al. 2004 (Cat. J/ApJS/152/261); Duncan et al. (1991ApJS...76..383D, Cat. III/159). The galactic velocities are taken from the Jenkins et al. 2011 (Cat. J/A+A/531/A8) and the Geneva-Copenhaguen Survey (GCS) Nordstrom et al. (2004A&A...418..989N, Cat. V/117). (1 data file).

  15. Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter

    International Nuclear Information System (INIS)

    Page, Dany; Prakash, Madappa; Lattimer, James M.; Steiner, Andrew W.

    2011-01-01

    We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the 3 P 2 channel. We find that the critical temperature for this superfluid transition is ≅0.5x10 9 K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star.

  16. An Earth-sized planet in the habitable zone of a cool star.

    Science.gov (United States)

    Quintana, Elisa V; Barclay, Thomas; Raymond, Sean N; Rowe, Jason F; Bolmont, Emeline; Caldwell, Douglas A; Howell, Steve B; Kane, Stephen R; Huber, Daniel; Crepp, Justin R; Lissauer, Jack J; Ciardi, David R; Coughlin, Jeffrey L; Everett, Mark E; Henze, Christopher E; Horch, Elliott; Isaacson, Howard; Ford, Eric B; Adams, Fred C; Still, Martin; Hunter, Roger C; Quarles, Billy; Selsis, Franck

    2014-04-18

    The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

  17. Clustering in the stellar abundance space

    Science.gov (United States)

    Boesso, R.; Rocha-Pinto, H. J.

    2018-03-01

    We have studied the chemical enrichment history of the interstellar medium through an analysis of the n-dimensional stellar abundance space. This work is a non-parametric analysis of the stellar chemical abundance space. The main goal is to study the stars from their organization within this abundance space. Within this space, we seek to find clusters (in a statistical sense), that is, stars likely to share similar chemo-evolutionary history, using two methods: the hierarchical clustering and the principal component analysis. We analysed some selected abundance surveys available in the literature. For each sample, we labelled the group of stars according to its average abundance curve. In all samples, we identify the existence of a main enrichment pattern of the stars, which we call chemical enrichment flow. This flow is set by the structured and well-defined mean rate at which the abundances of the interstellar medium increase, resulting from the mixture of the material ejected from the stars and stellar mass-loss and interstellar medium gas. One of the main results of our analysis is the identification of subgroups of stars with peculiar chemistry. These stars are situated in regions outside of the enrichment flow in the abundance space. These peculiar stars show a mismatch in the enrichment rate of a few elements, such as Mg, Si, Sc and V, when compared to the mean enrichment rate of the other elements of the same stars. We believe that the existence of these groups of stars with peculiar chemistry may be related to the accretion of planetary material on to stellar surfaces or may be due to production of the same chemical element by different nucleosynthetic sites.

  18. The evolution of the stellar mass functions of star-forming and quiescent galaxies to z = 4 from the COSMOS/ultraVISTA survey

    DEFF Research Database (Denmark)

    Muzzin, Adam; Marchesini, Danilo; Stefano, Mauro

    2013-01-01

    We present measurements of the stellar mass functions (SMFs) of star-forming and quiescent galaxies to z = 4 using a sample of 95,675 Ks -selected galaxies in the COSMOS/UltraVISTA field. The SMFs of the combined population are in good agreement with previous measurements and show that the stellar...

  19. A Dynamic Precision Evaluation Method for the Star Sensor in the Stellar-Inertial Navigation System.

    Science.gov (United States)

    Lu, Jiazhen; Lei, Chaohua; Yang, Yanqiang

    2017-06-28

    Integrating the advantages of INS (inertial navigation system) and the star sensor, the stellar-inertial navigation system has been used for a wide variety of applications. The star sensor is a high-precision attitude measurement instrument; therefore, determining how to validate its accuracy is critical in guaranteeing its practical precision. The dynamic precision evaluation of the star sensor is more difficult than a static precision evaluation because of dynamic reference values and other impacts. This paper proposes a dynamic precision verification method of star sensor with the aid of inertial navigation device to realize real-time attitude accuracy measurement. Based on the gold-standard reference generated by the star simulator, the altitude and azimuth angle errors of the star sensor are calculated for evaluation criteria. With the goal of diminishing the impacts of factors such as the sensors' drift and devices, the innovative aspect of this method is to employ static accuracy for comparison. If the dynamic results are as good as the static results, which have accuracy comparable to the single star sensor's precision, the practical precision of the star sensor is sufficiently high to meet the requirements of the system specification. The experiments demonstrate the feasibility and effectiveness of the proposed method.

  20. Relations between stellar mass and electron temperature-based metallicity for star-forming galaxies in a wide mass range

    International Nuclear Information System (INIS)

    Shi Wei-Bin; Zhao Gang; Ruan Gui-Ping; Zhou Li; Liang Yan-Chun; Shao Xu; Liu Xiao-Wei; Hammer Francois; Flores Hector; Zhang Yong

    2014-01-01

    We select 947 star-forming galaxies from SDSS-DR7 with [O III]λ4363 emission lines detected at a signal-to-noise ratio larger than 5σ. Their electron temperatures and direct oxygen abundances are then determined. We compare the results from different methods. t 2 , the electron temperature in the low ionization region, estimated from t 3 , that in the high ionization region, is compared using three analysis relations between t 2 – t 3 . These show obvious differences, which result in some different ionic oxygen abundances. The results of t 3 , t 2 , O ++ /H + and O + /H + derived by using methods from IRAF and literature are also compared. The ionic abundances O ++ /H + are higher than O + /H + for most cases. The different oxygen abundances derived from T e and the strong-line ratios show a clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio R 23 . The sample of galaxies from SDSS with detected [O III]λ4363 have lower metallicites and higher star formation rates, so they may not be typical representatives of the whole population of galaxies. Adopting data objects from Andrews and Martini, Liang et al. and Lee et al. data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from 10 6 M ⊙ to 10 11 M ⊙ . (research papers)

  1. The Diversity of Neutron Stars

    Science.gov (United States)

    Kaplan, David L.

    2004-12-01

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the >1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby, isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population---distances, ages, and magnetic fields---the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 1e6 year-old cooling neutron stars with magnetic fields above 1e13 Gauss. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication of central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  2. Stellar CME candidates: towards a stellar CME-flare relation

    Science.gov (United States)

    Paraskevi Moschou, Sofia; Drake, Jeremy J.; Cohen, Ofer; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

    2018-06-01

    For decades the Sun has been the only star that allowed for direct CME observations. Recently, with the discovery of multiple extrasolar systems, it has become imperative that the role of stellar CMEs be assessed in the context of exoplanetary habitability. Solar CMEs and flares show a higher association with increasing flaring energy, with strong flares corresponding to large and fast CMEs. As argued in earlier studies, extrasolar environments around active stars are potentially dominated by CMEs, as a result of their extreme flaring activity. This has strong implications for the energy budget of the system and the atmospheric erosion of orbiting planets.Nevertheless, with current instrumentation we are unable to directly observe CMEs in even the closest stars, and thus we have to look for indirect techniques and observational evidence and signatures for the eruption of stellar CMEs. There are three major observational techniques for tracing CME signatures in other stellar systems, namely measuring Type II radio bursts, Doppler shifts in UV/optical lines or transient absorption in the X-ray spectrum. We present observations of the most probable stellar CME candidates captured so far and examine the different observational techniques used together with their levels of uncertainty. Assuming that they were CMEs, we try to asses their kinematic and energetic characteristics and place them in an extension of the well-established solar CME-flare energy scaling law. We finish by discussing future observations for direct measurements.

  3. The formation of secondary stellar generations in massive young star clusters from rapidly cooling shocked stellar winds

    Czech Academy of Sciences Publication Activity Database

    Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Ehlerová, Soňa

    2017-01-01

    Roč. 835, č. 1 (2017), 60/1-60/15 ISSN 0004-637X R&D Projects: GA ČR GA15-06012S Grant - others:Ga MŠk(CZ) LM2015070 Institutional support: RVO:67985815 Keywords : galaxies * ISM * star clusters Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.533, year: 2016

  4. Modeling for Stellar Feedback in Galaxy Formation Simulations

    Science.gov (United States)

    Núñez, Alejandro; Ostriker, Jeremiah P.; Naab, Thorsten; Oser, Ludwig; Hu, Chia-Yu; Choi, Ena

    2017-02-01

    Various heuristic approaches to model unresolved supernova (SN) feedback in galaxy formation simulations exist to reproduce the formation of spiral galaxies and the overall inefficient conversion of gas into stars. Some models, however, require resolution-dependent scalings. We present a subresolution model representing the three major phases of supernova blast wave evolution—free expansion, energy-conserving Sedov-Taylor, and momentum-conserving snowplow—with energy scalings adopted from high-resolution interstellar-medium simulations in both uniform and multiphase media. We allow for the effects of significantly enhanced SN remnant propagation in a multiphase medium with the cooling radius scaling with the hot volume fraction, {f}{hot}, as {(1-{f}{hot})}-4/5. We also include winds from young massive stars and AGB stars, Strömgren sphere gas heating by massive stars, and a mechanism that limits gas cooling that is driven by radiative recombination of dense H II regions. We present initial tests for isolated Milky Way-like systems simulated with the Gadget-based code SPHgal with improved SPH prescription. Compared to pure thermal SN input, the model significantly suppresses star formation at early epochs, with star formation extended both in time and space in better accord with observations. Compared to models with pure thermal SN feedback, the age at which half the stellar mass is assembled increases by a factor of 2.4, and the mass-loading parameter and gas outflow rate from the galactic disk increase by a factor of 2. Simulation results are converged for a variation of two orders of magnitude in particle mass in the range (1.3-130) × 104 solar masses.

  5. The chromospheric structure of cool carbon stars

    International Nuclear Information System (INIS)

    Luttermoser, D.G.

    1988-01-01

    The temperature-density structure of the outer atmospheres of the N-type carbon stars are investigated through computer generated synthetic spectra from model atmospheres. The synthetic spectra are compared to spectra obtained with the International Ultraviolet Explorer (IUE) spacecraft and ground-based photometry. The nature of the severe violet flux falloff seen in cool carbon stars is investigated through photospheric synthetic flux calculations with the assumption of local thermodynamic equilibrium (LTE). A new candidate for the unknown opacity source that causes this flux falloff is proposed-a preponderance of neutral metal bound-bound and bound-free transitions from low energy states. The chromospheric structure of these stars is also investigated through a semi-empirical modeling technique. Such a technique involves attaching a chromospheric temperature rise to a radiative equilibrium model photosphere and generating a synthetic spectrum of chromospheric spectral lines using non-LTE radiative transfer. The chromospheric temperature-density structure is then altered until the synthetic spectrum matches the IUE observations of the singly ionized magnesium resonance lines and the intercombination lines of singly ionized carbon. Through the above mentioned non-LTE analysis of the atmospheric structure of these stars, the excitation and ionization equilibria are investigated. The excited levels of H I, C I, Na I, Mg I, and Ca I are over-populated with respect to LTE in the middle and upper photosphere of these stars, and all are over-ionized with respect to LTE. Photons from the chromosphere greatly influence the excitation and ionization of H I, C I, and Mg I

  6. Do All O Stars Form in Star Clusters?

    Science.gov (United States)

    Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

  7. Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions

    Science.gov (United States)

    Paxton, Bill; Schwab, Josiah; Bauer, Evan B.; Bildsten, Lars; Blinnikov, Sergei; Duffell, Paul; Farmer, R.; Goldberg, Jared A.; Marchant, Pablo; Sorokina, Elena; Thoul, Anne; Townsend, Richard H. D.; Timmes, F. X.

    2018-02-01

    We update the capabilities of the software instrument Modules for Experiments in Stellar Astrophysics (MESA) and enhance its ease of use and availability. Our new approach to locating convective boundaries is consistent with the physics of convection, and yields reliable values of the convective-core mass during both hydrogen- and helium-burning phases. Stars with Meffects of Rayleigh-Taylor instabilities that, in combination with the coupling to a public version of the STELLA radiation transfer instrument, creates new avenues for exploring Type II supernova properties. These capabilities are exhibited with exploratory models of pair-instability supernovae, pulsational pair-instability supernovae, and the formation of stellar-mass black holes. The applicability of MESA is now widened by the capability to import multidimensional hydrodynamic models into MESA. We close by introducing software modules for handling floating point exceptions and stellar model optimization, as well as four new software tools - MESA-Web, MESA-Docker, pyMESA, and mesastar.org - to enhance MESA's education and research impact.

  8. Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

    Science.gov (United States)

    Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

    2017-04-01

    The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

  9. TRAPPIST-UCDTS: A prototype search for habitable planets transiting ultra-cool stars

    Directory of Open Access Journals (Sweden)

    Magain P.

    2013-04-01

    Full Text Available The ∼1000 nearest ultra-cool stars (spectral type M6 and latter represent a unique opportunity for the search for life outside solar system. Due to their small luminosity, their habitable zone is 30–100 times closer than for the Sun, the corresponding orbital periods ranging from one to a few days. Thanks to this proximity, the transits of a habitable planet are much more probable and frequent than for an Earth-Sun analog, while their tiny size (∼1 Jupiter radius leads to transits deep enough for a ground-based detection, even for sub-Earth size planets. Furthermore, a habitable planet transiting one of these nearby ultra-cool star would be amenable for a thorough atmospheric characterization, including the detection of possible biosignatures, notably with the near-to-come JWST. Motivated by these reasons, we have set up the concept of a ground-based survey optimized for detecting planets of Earth-size and below transiting the nearest Southern ultra-cool stars. To assess thoroughly the actual potential of this future survey, we are currently conducting a prototype mini-survey using the TRAPPIST robotic 60cm telescope located at La Silla ESO Observatory (Chile. We summarize here the preliminary results of this mini-survey that fully validate our concept.

  10. Effects of neutrino emissivity on the cooling of neutron stars in the presence of a strong magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Coelho, Eduardo Lenho, E-mail: eduardo.coelho@uva.br [Universidade Veiga de Almeida, 108 Ibituruna St., 20271-020, Rio de Janeiro (Brazil); Chiapparini, Marcelo [Instituto de Física, Universidade do Estado do Rio de Janeiro, 524 São Francisco Xavier St., 20271-020, Rio de Janeiro (Brazil); Negreiros, Rodrigo Picanço [Instituto de Física, Universidade Federal Fluminense, Gal. Milton Tavares de Souza Ave., 24210-346, Rio de Janeiro (Brazil)

    2015-12-17

    One of the most interesting kind of neutron stars are the pulsars, which are highly magnetized neutron stars with fields up to 10{sup 14} G at the surface. The strength of magnetic field in the center of a neutron star remains unknown. According to the scalar virial theorem, magnetic field in the core could be as large as 10{sup 18} G. In this work we study the influence of strong magnetic fields on the cooling of neutron stars coming from direct Urca process. Direct Urca process is an extremely efficient mechanism for cooling a neutron star after its formation. The matter is described using a relativistic mean-field model at zero temperature with eight baryons (baryon octet), electrons and muons. We obtain the relative population of each species of particles as function of baryon density for different magnetic fields. We calculate numerically the cooling of neutron stars for a parametrized magnetic field and compare the results for the case without a magnetic field.

  11. Search for white dwarf companions of cool stars with peculiar element abundances

    Energy Technology Data Exchange (ETDEWEB)

    Boehm-Vitense, E.

    1984-01-01

    A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars.

  12. Search for white dwarf companions of cool stars with peculiar element abundances

    International Nuclear Information System (INIS)

    Boehm-Vitense, E.

    1984-01-01

    A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars

  13. The Resolved Stellar Populations Early Release Science Program

    Science.gov (United States)

    Weisz, Daniel; Anderson, J.; Boyer, M.; Cole, A.; Dolphin, A.; Geha, M.; Kalirai, J.; Kallivayalil, N.; McQuinn, K.; Sandstrom, K.; Williams, B.

    2017-11-01

    We propose to obtain deep multi-band NIRCam and NIRISS imaging of three resolved stellar systems within 1 Mpc (NOI 104). We will use this broad science program to optimize observational setups and to develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will combine our expertise in HST resolved star studies with these observations to design, test, and release point spread function (PSF) fitting software specific to JWST. PSF photometry is at the heart of resolved stellar populations studies, but is not part of the standard JWST reduction pipeline. Our program will establish JWST-optimized methodologies in six scientific areas: star formation histories, measurement of the sub-Solar mass stellar IMF, extinction maps, evolved stars, proper motions, and globular clusters, all of which will be common pursuits for JWST in the local Universe. Our observations of globular cluster M92, ultra-faint dwarf Draco II, and star-forming dwarf WLM, will be of high archival value for other science such as calibrating stellar evolution models, measuring properties of variable stars, and searching for metal-poor stars. We will release the results of our program, including PSF fitting software, matched HST and JWST catalogs, clear documentation, and step-by-step tutorials (e.g., Jupyter notebooks) for data reduction and science application, to the community prior to the Cycle 2 Call for Proposals. We will host a workshop to help community members plan their Cycle 2 observations of resolved stars. Our program will provide blueprints for the community to efficiently reduce and analyze JWST observations of resolved stellar populations.

  14. Stellar wind theory

    International Nuclear Information System (INIS)

    Summers, D.

    1980-01-01

    The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

  15. The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

    Science.gov (United States)

    Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

    2018-01-01

    Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

  16. Grain formation in the expanding gas flow around cool luminous stars

    International Nuclear Information System (INIS)

    Hasegawa, H.

    1984-01-01

    The existence of solid particles in interstellar space has been revealed by the extinction of starlight in UV, visible and IR. The important sources of interstellar grains are considered to be cool luminous mass loss stars. (author)

  17. Recent advances in modeling stellar interiors (u)

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  18. X-ray sources associated with young stellar objects in the star formation region CMa R1

    Science.gov (United States)

    Santos-Silva, Thais; Gregorio-Hetem, Jane; Montmerle, Thierry

    2013-07-01

    In previous works we studied the star formation scenario in the molecular cloud Canis Major R1 (CMa R1), derived from the existence of young stellar population groups near the Be stars Z CMa and GU CMa. Using data from the ROSAT X-ray satellite, having a field-of-view of ~ 1° in diameter, Gregorio-Hetem et al. (2009) discovered in this region young stellar objects mainly grouped in two clusters of different ages, with others located in between. In order to investigate the nature of these objects and to test a possible scenario of sequential star formation in this region, four fields (each 30 arcmin diameter, with some overlap) have been observed with the XMM-Newton satellite, with a sensitivity about 10 times better than ROSAT. The XMM-Newton data are currently under analysis. Preliminary results indicate the presence of about 324 sources, most of them apparently having one or more near-infrared counterparts showing typical colors of young stars. The youth of the X-ray sources was also confirmed by X-ray hardness ratio diagrams (XHRD), in different energy bands, giving an estimate of their Lx/Lbol ratios. In addition to these results, we present a detailed study of the XMM field covering the cluster near Z CMa. Several of these sources were classified as T Tauri and Herbig Ae/Be stars, using optical spectroscopy obtained with Gemini telescopes, in order to validate the use of XHRD applied to the entire sample. This classification is also used to confirm the relation between the luminosities in the near-infrared and X-ray bands expected for the T Tauri stars in CMa R1. In the present work we show the results of the study based on the spectra of about 90 sources found nearby Z CMa. We checked that the X-ray spectra (0.3 to 10 keV) of young objects is different from that observed in field stars and extragalactic objects. Some of the candidates also have light curve showing flares that are typical of T Tauri stars, which confirms the young nature of these X

  19. DARK STARS: A NEW LOOK AT THE FIRST STARS IN THE UNIVERSE

    International Nuclear Information System (INIS)

    Spolyar, Douglas; Bodenheimer, Peter; Freese, Katherine; Gondolo, Paolo

    2009-01-01

    We have proposed that the first phase of stellar evolution in the history of the universe may be dark (matter powered) stars (DSs), luminous objects powered by dark matter (DM) heating rather than by nuclear fusion, and in this paper we examine the history of these DSs. The power source is annihilation of weakly interacting massive particles (WIMPs) which are their own antiparticles. These WIMPs are the best motivated DM candidates and may be discovered by ongoing direct or indirect detection searches (e.g., Fermi/GLAST) or at the Large Hadron Collider at CERN. A new stellar phase results, powered by DM annihilation as long as there is a DM fuel, from millions to billions of years. We build up the DSs from the time DM heating becomes the dominant power source, accreting more and more matter onto them. We have included many new effects in the current study, including a variety of particle masses and accretion rates, nuclear burning, feedback mechanisms, and possible repopulation of DM density due to capture. Remarkably, we find that in all these cases, we obtain the same result: the first stars are very large, 500-1000 times as massive as the Sun; as well as puffy (radii 1-10 AU), bright (10 6 -10 7 L sun ), and cool (T surf sun and the temperatures are much hotter (T surf > 50,000 K). Hence DSs should be observationally distinct from standard Pop III stars. In addition, DSs avoid the (unobserved) element enrichment produced by the standard first stars. Once the DM fuel is exhausted, the DS becomes a heavy main-sequence star; these stars eventually collapse to form massive black holes that may provide seeds for the supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate-mass black holes.

  20. On origin of stellar clusters

    International Nuclear Information System (INIS)

    Tovmasyan, G.M.

    1977-01-01

    The ratios of the gas component of the mass of young stellar clusters to their stellar mass are considered. They change by more than four orders from one cluster to another. The results are in direct contradiction with the hypothesis of formation of cluster stars from a preliminarily existing gas cloud by its condensation, and they favour the Ambartsumian hypothesis of the joint origin of stars and gas clouds from superdense protostellar matter

  1. A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES

    International Nuclear Information System (INIS)

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

    2015-01-01

    The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R ⊕ ) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ∼10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters

  2. Instability and star evolution

    International Nuclear Information System (INIS)

    Mirzoyan, L.V.

    1981-01-01

    The observational data are discussed which testify that the phenomena of dynamical instability of stars and stellar systems are definite manifestations of their evolution. The study of these phenomena has shown that the instability is a regular phase of stellar evolution. It has resulted in the recognition of the most important regularities of the process of star formation concerning its nature. This became possible due to the discovery in 1947 of stellar associations in our Galaxy. The results of the study of the dynamical instability of stellar associations contradict the predictions of classical hypothesis of stellar condensation. These data supplied a basis for a new hypothesis on the formation of stars and nebulae by the decay of superdense protostars [ru

  3. NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin A. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

    2013-04-15

    We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

  4. THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7

    International Nuclear Information System (INIS)

    Gonzalez, Valentino; Bouwens, Rychard J.; Illingworth, Garth; Labbe, Ivo; Franx, Marijn; Kriek, Mariska; Brammer, Gabriel B.

    2010-01-01

    We use a robust sample of 11 z ∼ 7 galaxies (z 850 dropouts) to estimate the stellar mass density (SMD) of the universe when it was only ∼750 Myr old. We combine the very deep optical to near-infrared photometry from the Hubble Space Telescope Advanced Camera for Surveys and NICMOS cameras with mid-infrared Spitzer Infrared Array Camera (IRAC) imaging available through the GOODS program. After carefully removing the flux from contaminating foreground sources, we have obtained reliable photometry in the 3.6 μm and 4.5 μm IRAC channels. The spectral shapes of these sources, including their rest-frame optical colors, strongly support their being at z ∼ 7 with a mean photometric redshift of (z) = 7.2 ± 0.5. We use Bruzual and Charlot synthetic stellar population models to constrain their stellar masses and star formation histories. We find stellar masses that range over (0.1-12) x 10 9 M sun and average ages from 20 Myr to 425 Myr with a mean of ∼300 Myr, suggesting that in some of these galaxies most of the stars were formed at z > 8 (and probably at z ∼> 10). The best fits to the observed SEDs are consistent with little or no dust extinction, in agreement with recent results at z ∼ 4-8. The star formation rates (SFRs) are in the range from 5 to 20 M sun yr -1 . From this sample, we measure an SMD of 6.6 +5.4 -3.3 x 10 5 M sun Mpc -3 to a limit of M UV,AB z=3 ). Combined with a fiducial lower limit for their ages (80 Myr), this implies a maximum SFR density of 0.008 M sun yr -1 Mpc -3 . This is well below the critical level needed to reionize the universe at z ∼ 8 using standard assumptions. However, this result is based on luminous sources (>L*) and does not include the dominant contribution of the fainter galaxies. Strikingly, we find that the specific SFR is constant from z ∼ 7 to z ∼ 2 but drops substantially at more recent times.

  5. The influence of H2O line blanketing on the spectra of cool dwarf stars

    Science.gov (United States)

    Allard, F.; Hauschildt, P. H.; Miller, S.; Tennyson, J.

    1994-01-01

    We present our initial results of model atmosphere calculations for cool M dwarfs using an opacity sampling method and a new list of H2O lines. We obtain significantly improved fits to the infrared spectrum of the M dwarf VB10 when compared to earlier models. H2O is by far the dominant opacity source in cool stars. To illustrate this, we show the Rosseland mean of the total extinction under various assumptions. Our calculations demonstrate the importance of a good treatment of the water opacities in cool stars and the improvements possible by using up-to-date data for the water line absorption.

  6. ON THE RELIABILITY OF STELLAR AGES AND AGE SPREADS INFERRED FROM PRE-MAIN-SEQUENCE EVOLUTIONARY MODELS

    International Nuclear Information System (INIS)

    Hosokawa, Takashi; Offner, Stella S. R.; Krumholz, Mark R.

    2011-01-01

    We revisit the problem of low-mass pre-main-sequence stellar evolution and its observational consequences for where stars fall on the Hertzsprung-Russell diagram (HRD). In contrast to most previous work, our models follow stars as they grow from small masses via accretion, and we perform a systematic study of how the stars' HRD evolution is influenced by their initial radius, by the radiative properties of the accretion flow, and by the accretion history, using both simple idealized accretion histories and histories taken from numerical simulations of star cluster formation. We compare our numerical results to both non-accreting isochrones and to the positions of observed stars in the HRD, with a goal of determining whether both the absolute ages and the age dispersions inferred from non-accreting isochrones are reliable. We show that non-accreting isochrones can sometimes overestimate stellar ages for more massive stars (those with effective temperatures above ∼3500 K), thereby explaining why non-accreting isochrones often suggest a systematic age difference between more and less massive stars in the same cluster. However, we also find the only way to produce a similar overestimate for the ages of cooler stars is if these stars grow from ∼0.01 M sun seed protostars that are an order of magnitude smaller than predicted by current theoretical models, and if the size of the seed protostar correlates systematically with the final stellar mass at the end of accretion. We therefore conclude that, unless both of these conditions are met, inferred ages and age spreads for cool stars are reliable, at least to the extent that the observed bolometric luminosities and temperatures are accurate. Finally, we note that the time dependence of the mass accretion rate has remarkably little effect on low-mass stars' evolution on the HRD, and that such time dependence may be neglected for all stars except those with effective temperatures above ∼4000 K.

  7. DISCOVERY OF TWIN WOLF-RAYET STARS POWERING DOUBLE RING NEBULAE

    International Nuclear Information System (INIS)

    Mauerhan, Jon C.; Wachter, Stefanie; Van Dyk, Schuyler D.; Hoard, D. W.; Morris, Patrick W.

    2010-01-01

    We have spectroscopically discovered a pair of twin, nitrogen-type, hydrogen-rich, Wolf-Rayet stars (WN8-9h) that are both surrounded by circular, mid-infrared-bright nebulae detected with the Spitzer Space Telescope and MIPS instrument. The emission is probably dominated by a thermal continuum from cool dust, but also may contain contributions from atomic line emission. There is no counterpart at shorter Spitzer/IRAC wavelengths, indicating a lack of emission from warm dust. The two nebulae are probably wind-swept stellar ejecta released by the central stars during a prior evolutionary phase. The nebulae partially overlap on the sky and we speculate on the possibility that they are in the early stage of a collision. Two other evolved massive stars have also been identified within the area subtended by the nebulae, including a carbon-type Wolf-Rayet star (WC8) and an O7-8 III-I star, the latter of which appears to be embedded in one of the larger WN8-9h nebulae. The derived distances to these stars imply that they are coeval members of an association lying 4.9 ± 1.2 kpc from Earth, near the intersection of the Galaxy's Long Bar and the Scutum-Centaurus spiral arm. This new association represents an unprecedented display of complex interactions between multiple stellar winds, outflows, and the radiation fields of evolved massive stars.

  8. Stellar mass black holes in star clusters: gravitational wave emission and detection rates

    OpenAIRE

    Banerjee, Sambaran

    2011-01-01

    We investigate the dynamics of stellar-mass black holes (BH) in star clusters focusing on the dynamical formation of BH-BH binaries, which are very important sources of gravitational waves (GW). We examine the properties of these BH-BH binaries through direct N-body computations of Plummer clusters, having initially N(0) = 5 X 10^4, typically a few of them dynamically harden to the extent that they can merge via GW emission within the cluster. Also, for each of such clusters, there are a few ...

  9. Final phases of stellar evolution and the supernova phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Gallino, R [Torino, Universita, Turin, Italy; Masani, A [CNR, Laboratorio di Cosmo-geofisica, Turin, Italy

    1977-12-01

    Various theoretical aspects of the final stages of stellar evolution are reviewed in the framework of gravitational collapse and thermonuclear reactions (C-12 and O-16) in degenerate electron conditions. Attention is given to the evolution of supermassive stars, massive stars, and low-mass stars and to such topics as neutrino emission in intermediate-mass stars, white-dwarf supernovae, rotational instability, and stellar collisions and eclipsing binary systems.

  10. THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

    NARCIS (Netherlands)

    Pascucci, I.; Apai, D.; Luhman, K.; Henning, Th.; Bouwman, J.; Meyer, M. R.; Lahuis, F.; Natta, A.

    2009-01-01

    Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks

  11. Mining the HST Treasury: The ASTRAL Reference Spectra for Evolved M Stars

    Science.gov (United States)

    Carpenter, K. G.; Ayres, T.; Harper, G.; Kober, G.; Wahlgren, G. M.

    2012-01-01

    The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program designed to collect a definitive set of representative, high-resolution (R greater than 100,000) and high signal/noise (S/N greater than 100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu/ayres/ASTRAL/) portal and will enable investigations of a broad range of problems -- stellar, interstellar. and beyond -- for many years. In this current paper, we concentrate on producing a roadrnap to the very rich spectra of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis (GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse) and illustrate the huge increase in coverage and quality that these spectra provide over that previously available from IUE and earlier HST observations. These roadmaps will facilitate the study of the spectra, outer atmospheres, and winds of not only these stars. but also numerous other cool, low-gravity stars and make a very interesting comparison to the already-available atlases of the K2III giant Arcturus.

  12. Stellar Abundances for Galactic Archaeology Database. IV. Compilation of stars in dwarf galaxies

    Science.gov (United States)

    Suda, Takuma; Hidaka, Jun; Aoki, Wako; Katsuta, Yutaka; Yamada, Shimako; Fujimoto, Masayuki Y.; Ohtani, Yukari; Masuyama, Miyu; Noda, Kazuhiro; Wada, Kentaro

    2017-10-01

    We have constructed a database of stars in Local Group galaxies using the extended version of the SAGA (Stellar Abundances for Galactic Archaeology) database that contains stars in 24 dwarf spheroidal galaxies and ultra-faint dwarfs. The new version of the database includes more than 4500 stars in the Milky Way, by removing the previous metallicity criterion of [Fe/H] ≤ -2.5, and more than 6000 stars in the Local Group galaxies. We examined the validity of using a combined data set for elemental abundances. We also checked the consistency between the derived distances to individual stars and those to galaxies as given in the literature. Using the updated database, the characteristics of stars in dwarf galaxies are discussed. Our statistical analyses of α-element abundances show that the change of the slope of the [α/Fe] relative to [Fe/H] (so-called "knee") occurs at [Fe/H] = -1.0 ± 0.1 for the Milky Way. The knee positions for selected galaxies are derived by applying the same method. The star formation history of individual galaxies is explored using the slope of the cumulative metallicity distribution function. Radial gradients along the four directions are inspected in six galaxies where we find no direction-dependence of metallicity gradients along the major and minor axes. The compilation of all the available data shows a lack of CEMP-s population in dwarf galaxies, while there may be some CEMP-no stars at [Fe/H] ≲ -3 even in the very small sample. The inspection of the relationship between Eu and Ba abundances confirms an anomalously Ba-rich population in Fornax, which indicates a pre-enrichment of interstellar gas with r-process elements. We do not find any evidence of anti-correlations in O-Na and Mg-Al abundances, which characterizes the abundance trends in the Galactic globular clusters.

  13. An Observational Study of Blended Young Stellar Clusters in the Galactic Plane - Do Massive Stars form First?

    Science.gov (United States)

    Martínez-Galarza, Rafael; Protopapas, Pavlos; Smith, Howard A.; Morales, Esteban

    2018-01-01

    From an observational point of view, the early life of massive stars is difficult to understand partly because star formation occurs in crowded clusters where individual stars often appear blended together in the beams of infrared telescopes. This renders the characterization of the physical properties of young embedded clusters via spectral energy distribution (SED) fitting a challenging task. Of particular relevance for the testing of star formation models is the question of whether the claimed universality of the IMF (references) is reflected in an equally universal integrated galactic initial mass function (IGIMF) of stars. In other words, is the set of all stellar masses in the galaxy sampled from a single universal IMF, or does the distribution of masses depend on the environment, making the IGIMF different from the canonical IMF? If the latter is true, how different are the two? We present a infrared SED analysis of ~70 Spitzer-selected, low mass ($facilities.

  14. Mass loss of stars on the asymptotic giant branch. Mechanisms, models and measurements

    Science.gov (United States)

    Höfner, Susanne; Olofsson, Hans

    2018-01-01

    As low- and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newly-formed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angular-resolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their wind-forming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angular-resolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building realistic models of wind acceleration and developing a predictive theory of mass loss for AGB stars, which is a crucial ingredient of stellar and galactic chemical evolution models. At present, it is still not fully possible to model all these phenomena from first principles, and to predict the mass-loss rate based on fundamental stellar parameters only. However, much progress has been made

  15. Estimating precise metallicity and stellar mass evolution of galaxies

    Science.gov (United States)

    Mosby, Gregory

    2018-01-01

    The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

  16. ON THE CARBON-TO-OXYGEN RATIO MEASUREMENT IN NEARBY SUN-LIKE STARS: IMPLICATIONS FOR PLANET FORMATION AND THE DETERMINATION OF STELLAR ABUNDANCES

    International Nuclear Information System (INIS)

    Fortney, Jonathan J.

    2012-01-01

    Recent high-resolution spectroscopic analysis of nearby FGK stars suggests that a high C/O ratio of greater than 0.8, or even 1.0, is relatively common. Two published catalogs find C/O > 0.8 in 25%-30% of systems, and C/O > 1.0 in ∼6%-10%. It has been suggested that in protoplanetary disks with C/O > 0.8 that the condensation pathways to refractory solids will differ from what occurred in our solar system, where C/O = 0.55. The carbon-rich disks are calculated to make carbon-dominated rocky planets, rather than oxygen-dominated ones. Here we suggest that the derived stellar C/O ratios are overestimated. One constraint on the frequency of high C/O is the relative paucity of carbon dwarf stars (10 –3 -10 –5 ) found in large samples of low-mass stars. We suggest reasons for this overestimation, including a high C/O ratio for the solar atmosphere model used for differential abundance analysis, the treatment of a Ni blend that affects the O abundance, and limitations of one-dimensional LTE stellar atmosphere models. Furthermore, from the estimated errors on the measured stellar C/O ratios, we find that the significance of the high C/O tail is weakened, with a true measured fraction of C/O > 0.8 in 10%-15% of stars, and C/O > 1.0 in 1%-5%, although these are still likely overestimates. We suggest that infrared T-dwarf spectra could show how common high C/O is in the stellar neighborhood, as the chemistry and spectra of such objects would differ compared to those with solar-like abundances. While possible at C/O > 0.8, we expect that carbon-dominated rocky planets are rarer than others have suggested.

  17. Introduction to stellar structure

    CERN Document Server

    Maciel, Walter J

    2016-01-01

    In the first part of this book, the author presents the basic properties of the stellar interior and describes them thoroughly, along with deriving the main stellar structure equations of temperature, density, pressure and luminosity, among others. The process and application of solving these equations is explained, as well as linking these results with actual observations.  The second part of the text describes what happens to a star over time, and how to determine this by solving the same equations at different points during a star’s lifetime. The fate of various stars is quite different depending on their masses, and this is described in the final parts of the book. This text can be used for an upper level undergraduate course or an introductory graduate course on stellar physics.

  18. The Contribution of Stellar Winds to Cosmic Ray Production

    Science.gov (United States)

    Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

    2018-04-01

    Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

  19. AGB stars as tracers to IC 1613 evolution.

    Science.gov (United States)

    Hashemi, S. A.; Javadi, A.; van Loon, J. Th.

    We are going to apply AGB stars to find star formation history for IC 1613 galaxy; this a new and simple method that works well for nearby galaxies. IC 1613 is a Local Group dwarf irregular galaxy that is located at distance of 750 kpc, a gas rich and isolated dwarf galaxy that has a low foreground extinction. We use the long period variable stars (LPVs) that represent the very final stage of evolution of stars with low and intermediate mass at the AGB phase and are very luminous and cool so that they emit maximum brightness in near-infrared bands. Thus near-infrared photometry with using stellar evolutionary models help us to convert brightness to birth mass and age and from this drive star formation history of the galaxy. We will use the luminosity distribution of the LPVs to reconstruct the star formation history-a method we have successfully applied in other Local Group galaxies. Our analysis shows that the IC 1613 has had a nearly constant star formation rate, without any dominant star formation episode.

  20. H α AS A LUMINOSITY CLASS DIAGNOSTIC FOR K- AND M-TYPE STARS

    International Nuclear Information System (INIS)

    Jennings, Jeff; Levesque, Emily M.

    2016-01-01

    We have identified the H α absorption feature as a new spectroscopic diagnostic of luminosity class in K- and M-type stars. From high-resolution spectra of 19 stars with well-determined physical properties (including effective temperatures and stellar radii), we measured equivalent widths for H α and the Ca ii triplet and examined their dependence on both luminosity class and stellar radius. H α shows a strong relation with both luminosity class and radius that extends down to late M spectral types. This behavior in H α has been predicted as a result of the density-dependent overpopulation of the metastable 2s level in hydrogen, an effect that should become dominant for Balmer line formation in non-LTE conditions. We conclude that this new metallicity-insensitive diagnostic of luminosity class in cool stars could serve as an effective means of discerning between populations such as Milky Way giants and supergiant members of background galaxies.

  1. H α AS A LUMINOSITY CLASS DIAGNOSTIC FOR K- AND M-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Jennings, Jeff [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Levesque, Emily M., E-mail: emsque@uw.edu [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)

    2016-04-20

    We have identified the H α absorption feature as a new spectroscopic diagnostic of luminosity class in K- and M-type stars. From high-resolution spectra of 19 stars with well-determined physical properties (including effective temperatures and stellar radii), we measured equivalent widths for H α and the Ca ii triplet and examined their dependence on both luminosity class and stellar radius. H α shows a strong relation with both luminosity class and radius that extends down to late M spectral types. This behavior in H α has been predicted as a result of the density-dependent overpopulation of the metastable 2s level in hydrogen, an effect that should become dominant for Balmer line formation in non-LTE conditions. We conclude that this new metallicity-insensitive diagnostic of luminosity class in cool stars could serve as an effective means of discerning between populations such as Milky Way giants and supergiant members of background galaxies.

  2. Science with Synthetic Stellar Surveys

    Science.gov (United States)

    Sanderson, Robyn Ellyn

    2018-04-01

    A new generation of observational projects is poised to revolutionize our understanding of the resolved stellar populations of Milky-Way-like galaxies at an unprecedented level of detail, ushering in an era of precision studies of galaxy formation. In the Milky Way itself, astrometric, spectroscopic and photometric surveys will measure three-dimensional positions and velocities and numerous chemical abundances for stars from the disk to the halo, as well as for many satellite dwarf galaxies. In the Local Group and beyond, HST, JWST and eventually WFIRST will deliver pristine views of resolved stars. The groundbreaking scale and dimensionality of this new view of resolved stellar populations in galaxies challenge us to develop new theoretical tools to robustly compare these surveys to simulated galaxies, in order to take full advantage of our new ability to make detailed predictions for stellar populations within a cosmological context. I will describe a framework for generating realistic synthetic star catalogs and mock surveys from state-of-the-art cosmological-hydrodynamical simulations, and present several early scientific results from, and predictions for, resolved stellar surveys of our Galaxy and its neighbors.

  3. The diversity of neutron stars: Nearby thermally emitting neutron stars and the compact central objects in supernova remnants

    Science.gov (United States)

    Kaplan, David L.

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the > 1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population -- instances, ages, and magnetic fields -- the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 10^6 year-old cooling neutron stars with magnetic fields above 10^13 G. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  4. Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions.

    Science.gov (United States)

    Driscoll, P E; Barnes, R

    2015-09-01

    The internal thermal and magnetic evolution of rocky exoplanets is critical to their habitability. We focus on the thermal-orbital evolution of Earth-mass planets around low-mass M stars whose radiative habitable zone overlaps with the "tidal zone," where tidal dissipation is expected to be a significant heat source in the interior. We develop a thermal-orbital evolution model calibrated to Earth that couples tidal dissipation, with a temperature-dependent Maxwell rheology, to orbital circularization and migration. We illustrate thermal-orbital steady states where surface heat flow is balanced by tidal dissipation and cooling can be stalled for billions of years until circularization occurs. Orbital energy dissipated as tidal heat in the interior drives both inward migration and circularization, with a circularization time that is inversely proportional to the dissipation rate. We identify a peak in the internal dissipation rate as the mantle passes through a viscoelastic state at mantle temperatures near 1800 K. Planets orbiting a 0.1 solar-mass star within 0.07 AU circularize before 10 Gyr, independent of initial eccentricity. Once circular, these planets cool monotonically and maintain dynamos similar to that of Earth. Planets forced into eccentric orbits can experience a super-cooling of the core and rapid core solidification, inhibiting dynamo action for planets in the habitable zone. We find that tidal heating is insignificant in the habitable zone around 0.45 (or larger) solar-mass stars because tidal dissipation is a stronger function of orbital distance than stellar mass, and the habitable zone is farther from larger stars. Suppression of the planetary magnetic field exposes the atmosphere to stellar wind erosion and the surface to harmful radiation. In addition to weak magnetic fields, massive melt eruption rates and prolonged magma oceans may render eccentric planets in the habitable zone of low-mass stars inhospitable for life.

  5. ON THE ORIGIN OF STELLAR MASSES

    International Nuclear Information System (INIS)

    Krumholz, Mark R.

    2011-01-01

    It has been a longstanding problem to determine, as far as possible, the characteristic masses of stars in terms of fundamental constants; the almost complete invariance of this mass as a function of the star-forming environment suggests that this should be possible. Here I provide such a calculation. The typical stellar mass is set by the characteristic fragment mass in a star-forming cloud, which depends on the cloud's density and temperature structure. Except in the very early universe, the latter is determined mainly by the radiation released as matter falls onto seed protostars. The energy yield from this process is ultimately set by the properties of deuterium burning in protostellar cores, which determines the stars' radii. I show that it is possible to combine these considerations to compute a characteristic stellar mass almost entirely in terms of fundamental constants, with an extremely weak residual dependence on the interstellar pressure and metallicity. This result not only explains the invariance of stellar masses, it resolves a second mystery: why fragmentation of a cold, low-density interstellar cloud, a process with no obvious dependence on the properties of nuclear reactions, happens to select a stellar mass scale such that stellar cores can ignite hydrogen. Finally, the weak residual dependence on the interstellar pressure and metallicity may explain recent observational hints of a smaller characteristic mass in the high-pressure, high-metallicity cores of giant elliptical galaxies.

  6. Supernovae from massive AGB stars

    NARCIS (Netherlands)

    Poelarends, A.J.T.; Izzard, R.G.; Herwig, F.; Langer, N.; Heger, A.

    2006-01-01

    We present new computations of the final fate of massive AGB-stars. These stars form ONeMg cores after a phase of carbon burning and are called Super AGB stars (SAGB). Detailed stellar evolutionary models until the thermally pulsing AGB were computed using three di erent stellar evolution codes. The

  7. Closed and open magnetic fields in stellar winds

    Science.gov (United States)

    Mullan, D. J.; Steinolfson, R. S.

    1983-01-01

    A numerical study of the interaction between a thermal wind and a global dipole field in the sun and in a giant star is reported. In order for closed field lines to persist near the equator (where a helmet-streamer-like configuration appears), the coronal temperature must be less than a critical value Tc, which scales as M/R. This condition is found to be equivalent to the following: for a static helmet streamer to persist, the sonic point above the helmet must not approach closer to the star than 2.2-2.6 stellar radii. Implications for rapid mass loss and X-ray emission from cool giants are pointed out. The results strengthen the case for identifying empirical dividing lines in the H-R diagram with a magnetic topology transition locus (MTTL). Support for the MTTL concept is also provided by considerations of the breakdown of magnetostatic equilibrium.

  8. The Influence of Atomic Diffusion on Stellar Ages and Chemical Tagging

    Energy Technology Data Exchange (ETDEWEB)

    Dotter, Aaron; Conroy, Charlie; Cargile, Phillip [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Asplund, Martin, E-mail: aaron.dotter@gmail.com [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT (Australia)

    2017-05-10

    In the era of large stellar spectroscopic surveys, there is an emphasis on deriving not only stellar abundances but also the ages for millions of stars. In the context of Galactic archeology, stellar ages provide a direct probe of the formation history of the Galaxy. We use the stellar evolution code MESA to compute models with atomic diffusion—with and without radiative acceleration—and extra mixing in the surface layers. The extra mixing consists of both density-dependent turbulent mixing and envelope overshoot mixing. Based on these models we argue that it is important to distinguish between initial, bulk abundances (parameters) and current, surface abundances (variables) in the analysis of individual stellar ages. In stars that maintain radiative regions on evolutionary timescales, atomic diffusion modifies the surface abundances. We show that when initial, bulk metallicity is equated with current, surface metallicity in isochrone age analysis, the resulting stellar ages can be systematically overestimated by up to 20%. The change of surface abundances with evolutionary phase also complicates chemical tagging, which is the concept that dispersed star clusters can be identified through unique, high-dimensional chemical signatures. Stars from the same cluster, but in different evolutionary phases, will show different surface abundances. We speculate that calibration of stellar models may allow us to estimate not only stellar ages but also initial abundances for individual stars. In the meantime, analyzing the chemical properties of stars in similar evolutionary phases is essential to minimize the effects of atomic diffusion in the context of chemical tagging.

  9. Warm gas towards young stellar objects in Corona Australis

    DEFF Research Database (Denmark)

    Lindberg, Johan; Jørgensen, Jes Kristian; D. Green, Joel

    2014-01-01

    The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an interm......The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated...... by an intermediate-mass young star. We study the effects on the warm gas and dust in a group of low-mass young stellar objects from the irradiation by the young luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented...... Be star R CrA. Our results show that a nearby luminous star does not increase the molecular excitation temperatures in the warm gas around a young stellar object (YSO). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated...

  10. KELT-19Ab: A P ∼ 4.6-day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion

    Science.gov (United States)

    Siverd, Robert J.; Collins, Karen A.; Zhou, George; Quinn, Samuel N.; Gaudi, B. Scott; Stassun, Keivan G.; Johnson, Marshall C.; Bieryla, Allyson; Latham, David W.; Ciardi, David R.; Rodriguez, Joseph E.; Penev, Kaloyan; Pinsonneault, Marc; Pepper, Joshua; Eastman, Jason D.; Relles, Howard; Kielkopf, John F.; Gregorio, Joao; Oberst, Thomas E.; Aldi, Giulio Francesco; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Dressing, Courtney D.; Patel, Rahul; Stevens, Daniel J.; Beatty, Thomas G.; Lund, Michael B.; Labadie-Bartz, Jonathan; Kuhn, Rudolf B.; Colón, Knicole D.; James, David; Yao, Xinyu; Johnson, John A.; Wright, Jason T.; McCrady, Nate; Wittenmyer, Robert A.; Johnson, Samson A.; Sliski, David H.; Jensen, Eric L. N.; Cohen, David H.; McLeod, Kim K.; Penny, Matthew T.; Joner, Michael D.; Stephens, Denise C.; Villanueva, Steven, Jr.; Zambelli, Roberto; Stockdale, Christopher; Evans, Phil; Tan, Thiam-Guan; Curtis, Ivan A.; Reed, Phillip A.; Trueblood, Mark; Trueblood, Patricia

    2018-01-01

    We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V∼ 9.9) A8V star TYC 764-1494-1 with an orbital period of 4.61 days. We confirm the planetary nature of the companion via a combination of radial velocities, which limit the mass to ≲ 4.1 {M}{{J}} (3σ ), and a clear Doppler tomography signal, which indicates a retrograde projected spin–orbit misalignment of λ =-{179.7}-3.8+3.7 degrees. Global modeling indicates that the {T}{eff}=7500+/- 110 K host star has {M}\\star ={1.62}-0.20+0.25 {M}ȯ and {R}\\star =1.83+/- 0.10 {R}ȯ . The planet has a radius of {R}P=1.91+/- 0.11 {R}{{J}} and receives a stellar insolation flux of ∼ 3.2× {10}9 {erg} {{{s}}}-1 {{cm}}-2, leading to an inferred equilibrium temperature of {T}{eq}∼ 1935 K assuming zero albedo and complete heat redistribution. With a v\\sin {I}* =84.8+/- 2.0 {km} {{{s}}}-1, the host is relatively slowly rotating compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic elements but deficient in calcium, suggesting that it is likely an Am star. KELT-19A would be the first detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late-G9V/early-K1V spectral type at a projected separation of ≈ 160 {au}. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary. However, it may have emplaced the transiting planetary companion via the Kozai–Lidov mechanism.

  11. Stellar parameters for the central star of the planetary nebula PRTM 1 using the German Astrophysical Virtual Observatory service TheoSSA

    Science.gov (United States)

    Rauch, T.; Demleitner, M.; Hoyer, D.; Werner, K.

    2018-04-01

    The German Astrophysical Virtual Observatory (GAVO) developed the registered service TheoSSA (theoretical stellar spectra access) and the supporting registered VO tool TMAW (Tübingen Model-Atmosphere WWW interface). These allow individual spectral analyses of hot, compact stars with state-of-the-art non-local thermodynamical equilibrium (NLTE) stellar-atmosphere models that presently consider opacities of the elements H, He, C, N, O, Ne, Na, and Mg, without requiring detailed knowledge about the involved background codes and procedures. Presently, TheoSSA provides easy access to about 150 000 pre-calculated stellar spectral energy distributions (SEDs) and is intended to ingest SEDs calculated by any model-atmosphere code. In the case of the exciting star of PN PRTM 1, we demonstrate the easy way to calculate individual NLTE stellar model-atmospheres to reproduce an observed optical spectrum. We measured T_eff = 98 000± 5 000 K, log (g / cm/s^2) = 5.0^{+0.3}_{-0.2}, and photospheric mass fractions of H =7.5 × 10-1 (1.02 times solar), He =2.4 × 10-1 (0.96), C =2.0 × 10-3 (0.84), N =3.2 × 10-4 (0.46), and O =8.5 × 10-3 (1.48) with uncertainties of ±0.2 dex. We determined the stellar mass and luminosity of 0.73^{+0.16}_{-0.15} M_{⊙} and log (L/L⊙) = 4.2 ± 0.4, respectively.

  12. Sating a Voracious Appetite: The Tidal Interaction of Close-in Planets with their Host Stars

    Science.gov (United States)

    Matsakos, Titos; Königl, Arieh

    2015-12-01

    Transit observations of the apparent angle between the stellar spin and the vector normal to the planetary orbital plane suggest that cool stars are preferably aligned systems even as hot stars exhibit a large range of obliquities. In addition, as was demonstrated recently by Mazeh et al., the distribution of planet periods as a function of mass exhibits a dearth of sub-Jupiter--mass planets at 1 Gyr) times and become circularized at radii of a few times the Roche limit.

  13. The Pan-STARRS1 medium-deep survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to z ∼ 0.8

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Lihwai; Chen, Chin-Wei; Coupon, Jean; Hsieh, Bau-Ching [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan, R.O.C. (China); Jian, Hung-Yu [Department of Physics, National Taiwan University, Taipei 106, Taiwan, R.O.C. (China); Foucaud, Sebastien [Department of Earth Sciences, National Taiwan Normal University, N°88, Tingzhou Road, Sec. 4, Taipei 11677, Taiwan, R.O.C. (China); Norberg, Peder; Bower, R. G.; Cole, Shaun; Arnalte-Mur, Pablo; Draper, P. [Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Heinis, Sebastien [Department of Astronomy, University of Maryland, MD 20742 (United States); Phleps, Stefanie [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, D-85748 Garching (Germany); Chen, Wen-Ping [Graduate Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan, R.O.C. (China); Lee, Chien-Hsiu [University Observatory Munich, Scheinerstrasse 1, D-81679 Munich (Germany); Burgett, William; Chambers, K. C.; Denneau, L.; Flewelling, H.; Hodapp, K. W., E-mail: lihwailin@asiaa.sinica.edu.tw [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); and others

    2014-02-10

    Using a large optically selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR)—stellar mass (M {sub *}) relation, as well as the quiescent fraction versus M {sub *} relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10{sup 14} M {sub ☉}), we find a global reduction in the SSFR of the star-forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass—the mass quenching plays a dominant role in producing quiescent

  14. The Pan-STARRS1 medium-deep survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to z ∼ 0.8

    International Nuclear Information System (INIS)

    Lin, Lihwai; Chen, Chin-Wei; Coupon, Jean; Hsieh, Bau-Ching; Jian, Hung-Yu; Foucaud, Sebastien; Norberg, Peder; Bower, R. G.; Cole, Shaun; Arnalte-Mur, Pablo; Draper, P.; Heinis, Sebastien; Phleps, Stefanie; Chen, Wen-Ping; Lee, Chien-Hsiu; Burgett, William; Chambers, K. C.; Denneau, L.; Flewelling, H.; Hodapp, K. W.

    2014-01-01

    Using a large optically selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR)—stellar mass (M * ) relation, as well as the quiescent fraction versus M * relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10 14 M ☉ ), we find a global reduction in the SSFR of the star-forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass—the mass quenching plays a dominant role in producing quiescent galaxies for more

  15. VO-compliant libraries of high resolution spectra of cool stars

    Science.gov (United States)

    Montes, D.

    2008-10-01

    In this contribution we describe a Virtual Observatory (VO) compliant version of the libraries of high resolution spectra of cool stars described by Montes et al. (1997; 1998; and 1999). Since their publication the fully reduced spectra in FITS format have been available via ftp and in the World Wide Web. However, in the VO all the spectra will be accessible using a common web interface following the standards of the International Virtual Observatory Alliance (IVOA). These libraries include F, G, K and M field stars, from dwarfs to giants. The spectral coverage is from 3800 to 10000 Å, with spectral resolution ranging from 0.09 to 3.0 Å.

  16. Metal enrichment signatures of the first stars on high-z DLAs

    Science.gov (United States)

    Ma, Q.; Maio, U.; Ciardi, B.; Salvaterra, R.

    2017-12-01

    We use numerical N-body hydrodynamical simulations with varying PopIII stellar models to investigate the possibility of detecting first star signatures with observations of high-redshift damped Lyα absorbers (DLAs). The simulations include atomic and molecular cooling, star formation, energy feedback and metal spreading due to the evolution of stars with a range of masses and metallicities. Different initial mass functions (IMFs) and corresponding metal-dependent yields and lifetimes are adopted to model primordial stellar populations. The DLAs in the simulations are selected according to either the local gas temperature (temperature selected) or the host mass (mass selected). We find that 3 per cent (40 per cent) of mass (temperature)-selected high-z (z ≥ 5.5) DLAs retain signatures of pollution from PopIII stars, independent of the first star model. Such DLAs have low halo mass ( Z⊙) and star formation rate ( generation and to constrain the first star mass ranges. Comparing the abundance ratios derived from our simulations to those observed in DLAs at z ≥ 5, we find that most of these DLAs are consistent within errors with PopII star dominated enrichment and strongly disfavour the pollution pattern of very massive first stars (i.e. 100-500 M⊙). However, some of them could still result from the pollution of first stars in the mass range [0.1, 100] M⊙. In particular, we find that the abundance ratios from SDSS J1202+3235 are consistent with those expected from PopIII enrichment dominated by massive (but not extreme) first stars.

  17. Asteroseismology of white dwarf stars

    OpenAIRE

    Córsico, A. H.

    2014-01-01

    Most of low- and intermediate-mass stars that populate the Universe will end their lives as white dwarf stars. These ancient stellar remnants have encrypted inside a precious record of the evolutionary history of the progenitor stars, providing a wealth of information about the evolution of stars, star formation, and the age of a variety of stellar populations, such as our Galaxy and open and globular clusters. While some information like surface chemical composition, temperature and gravity ...

  18. Rotational stellar structures based on the Lagrangian variational principle

    International Nuclear Information System (INIS)

    Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

    2017-01-01

    A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc. (paper)

  19. Rotational stellar structures based on the Lagrangian variational principle

    Science.gov (United States)

    Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

    2017-06-01

    A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc.

  20. An overview of white dwarf stars

    Directory of Open Access Journals (Sweden)

    Charpinet S.

    2013-03-01

    Full Text Available We present a brief summary of what is currently known about white dwarf stars, with an emphasis on their evolutionary and internal properties. As is well known, white dwarfs represent the end products of stellar evolution for the vast majority of stars and, as such, bear the signatures of past events (such as mass loss, mixing phases, loss and redistribution of angular momentum, and thermonuclear burning that are of essential importance in the evolution of stars in general. In addition, white dwarf stars represent ideal testbeds for our understanding of matter under extreme conditions, and work on their constitutive physics (neutrino production rates, conductive and radiative opacities, interior liquid/solid equations of state, partially ionized and partially degenerate envelope equations of state, diffusion coefficients, line broadening mechanisms is still being actively pursued. Given a set of constitutive physics, cooling white dwarfs can be used advantageously as cosmochronometers. Moreover, the field has been blessed by the existence of four distinct families of pulsating white dwarfs, each mapping a different evolutionary phase, and this allows the application of the asteroseismological method to probe and test their internal structure and evolutionary state. We set the stage for the reviews that follow on cooling white dwarfs as cosmochronometers and physics laboratories, as well as on the properties of pulsating white dwarfs and the asteroseismological results that can be inferred.

  1. Influence of stellar multiplicity on planet formation. I. Evidence of suppressed planet formation due to stellar companions within 20 au and validation of four planets from the Kepler multiple planet candidates

    International Nuclear Information System (INIS)

    Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei; Barclay, Thomas

    2014-01-01

    The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (K P < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamical stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study.

  2. Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

    Science.gov (United States)

    Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

    2018-06-01

    The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

  3. The Solar Twin Planet Search. III. The [Y/Mg] clock: estimating stellar ages of solar-type stars

    Science.gov (United States)

    Tucci Maia, M.; Ramírez, I.; Meléndez, J.; Bedell, M.; Bean, J. L.; Asplund, M.

    2016-05-01

    Context. Solar twins are stars with similar stellar (surface) parameters to the Sun that can have a wide range of ages. This provides an opportunity to analyze the variation of their chemical abundances with age. Nissen (2015, A&A, 579, A52) recently suggested that the abundances of the s-process element Y and the α-element Mg could be used to estimate stellar ages. Aims: This paper aims to determine with high precision the Y, Mg, and Fe abundances for a sample of 88 solar twins that span a broad age range (0.3-10.0 Gyr) and investigate their use for estimating ages. Methods: We obtained high-quality Magellan Inamori Kyocera Echelle (MIKE) spectra and determined Y and Mg abundances using equivalent widths and a line-by-line differential method within a 1D LTE framework. Stellar parameters and iron abundances were measured in Paper I of this series for all stars, but a few (three) required a small revision. Results: The [Y/Mg] ratio shows a strong correlation with age. It has a slope of -0.041 ± 0.001 dex/Gyr and a significance of 41σ. This is in excellent agreement with the relation first proposed by Nissen (2015). We found some outliers that turned out to be binaries where mass transfer may have enhanced the yttrium abundance. Given a precise measurement of [Y/Mg] with typical error of 0.02 dex in solar twins, our formula can be used to determine a stellar age with ~0.8 Gyr precision in the 0 to 10 Gyr range. Based on observations obtained at the Clay Magellan Telescopes at Las Campanas Observatory, Chile and at the 3.6 m Telescope at the La Silla ESO Observatory, Chile (program ID 188.C-0265).

  4. Intracluster age gradients in numerous young stellar clusters

    Science.gov (United States)

    Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Bate, M. R.; Broos, P. S.; Garmire, G. P.

    2018-05-01

    The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t ≲ 3 Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5 Myr pc-1. The empirical finding reported in the present study - late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions - has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vázquez-Semadeni et al.

  5. Stellar astrophysics

    International Nuclear Information System (INIS)

    1988-01-01

    Enhanced mass loss occurs at critical stages in the evolution of stars over a wide range of stellar mass. Observationally, these stages are difficult to identify because of their short duration and because the star is often obscured by dust which condenses in the ejecta. A study of a G-type star, of which only the outer envelope was directly visible, was undertaken by the South African Astronomical Observatory (SAAO). The star itself was obscured by dust clouds and its light was only feebly seen by reflection from some of these clouds. Other studies of the galaxy undertaken by the SAAO include observations of the following: the extreme carbon star IRAS 15194-5115; RV Tauri and T Tauri stars; pre-main sequence stars; the properties of circumstellar dust; rotational modulation and flares on RS CVn and BY Dra stars; heavy-element stars; hydrogen-deficient stars; the open cluster NGC6192; stars in Omega Centauri, and lunar occulations of stars. Simultaneous x-ray, radio and optical data of the flare star YZ CMi were also obtained. 1 fig

  6. Near-infrared spectroscopic observations of massive young stellar object candidates in the central molecular zone

    Science.gov (United States)

    Nandakumar, G.; Schultheis, M.; Feldmeier-Krause, A.; Schödel, R.; Neumayer, N.; Matteucci, F.; Ryde, N.; Rojas-Arriagada, A.; Tej, A.

    2018-01-01

    Context. The central molecular zone (CMZ) is a 200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims: We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods: We obtained KMOS low-resolution near-infrared spectra (R 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-to-noise ratio. We separated YSOs from cool late-type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results: Using the spectroscopically identified YSOs in our sample, we confirm that existing colour-colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-type stars. In addition, we define a new colour-colour criterion that separates YSOs from cool late-type stars in the H-KS vs. H -[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| rate than predicted by various star forming models. Based on observations collected at the European Southern Observatory, Chile, programme number 097.C-0208(A).

  7. Flares on dMe stars: IUE and optical observations of At Mic, and comparison of far-ultraviolet stellar and solar flares

    International Nuclear Information System (INIS)

    Bromage, G.E.; Phillips, K.J.H.; Dufton, P.L.; Kingston, A.E.

    1986-01-01

    The paper concerns observations of a large flare event on the dMe star At Mic, detected by the International Ultraviolet Explorer. The far-ultraviolet spectra of the flare is compared with those of other stellar flares, and also with a large solar flare recorded by the Skylab mission in 1973. The quiescent-phase optical and ultraviolet spectrum of the same dMe flare star is discussed. (U.K.)

  8. Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

    Energy Technology Data Exchange (ETDEWEB)

    Janowiecki, Steven [International Center for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009 (Australia); Salzer, John J.; Zee, Liese van [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Rosenberg, Jessica L. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030 (United States); Skillman, Evan, E-mail: steven.janowiecki@uwa.edu.au [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street, SE Minneapolis, MN, 55455 (United States)

    2017-02-10

    We discuss and test possible evolutionary connections between blue compact dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low-mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today’s BCDs are distinctive objects in a state of extreme star formation that is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

  9. Young stellar population and ongoing star formation in the H II complex Sh2-252

    Science.gov (United States)

    Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.

    2013-07-01

    In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it

  10. Stellar photometry and polarimetry

    International Nuclear Information System (INIS)

    Golay, M.; Serkowski, K.

    1976-01-01

    A critical review of progress made in stellar photometry and polarimetry over the period 1973-1975 is presented. Reports of photometric measurements from various observatories throughout the world are summarized. The summary of work on stellar polarimetry lists the review papers, the catalogues and lists of standard stars, and descriptions of new observing techniques. (B.R.H.)

  11. The Dark Energy Survey: Prospects for resolved stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  12. Local Stellar Kinematics from RAVE data - V. Kinematic Investigation of the Galaxy with Red Clump Stars

    Science.gov (United States)

    Karaali, S.; Bilir, S.; Ak, S.; Gökçe, E. Yaz; Önal, Ö.; Ak, T.

    2014-02-01

    We investigated the space velocity components of 6 610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (V lsr) shows a smooth variation relative to the mean Galactocentric radial distance (Rm ), while it attains its maximum at the Galactic plane. The space velocity components in the direction to the Galactic centre (U lsr) and in the vertical direction (W lsr) show almost flat distributions relative to Rm , with small changes in their trends at Rm ~ 7.5 kpc. U lsr values estimated for the RC stars in quadrant 180° RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180° RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

  13. The Destructive Birth of Massive Stars and Massive Star Clusters

    Science.gov (United States)

    Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

    2017-01-01

    Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is

  14. Star formation properties of galaxy cluster A1767

    International Nuclear Information System (INIS)

    Yan, Peng-Fei; Li, Feng; Yuan, Qi-Rong

    2015-01-01

    Abell 1767 is a dynamically relaxed, cD cluster of galaxies with a redshift of 0.0703. Among 250 spectroscopically confirmed member galaxies within a projected radius of 2.5r 200 , 243 galaxies (∼ 97%) are spectroscopically covered by the Sloan Digital Sky Survey. Based on this homogeneous spectral sample, the stellar evolutionary synthesis code STARLIGHT is applied to investigate the stellar populations and star formation histories of galaxies in this cluster. The star formation properties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates, are presented as functions of local galaxy density. A strong environmental effect is found such that massive galaxies in the high-density core region of the cluster tend to have higher metallicities, older mean stellar ages, and lower specific star formation rates (SSFRs), and their recent star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and SSFR with stellar mass are confirmed. (paper)

  15. PRECIPITATION-REGULATED STAR FORMATION IN GALAXIES

    International Nuclear Information System (INIS)

    Voit, G. Mark; O’Shea, Brian W.; Donahue, Megan; Bryan, Greg L.

    2015-01-01

    Galaxy growth depends critically on the interplay between radiative cooling of cosmic gas and the resulting energetic feedback that cooling triggers. This interplay has proven exceedingly difficult to model, even with large supercomputer simulations, because of its complexity. Nevertheless, real galaxies are observed to obey simple scaling relations among their primary observable characteristics. Here we show that a generic emergent property of the interplay between cooling and feedback can explain the observed scaling relationships between a galaxy's stellar mass, its total mass, and its chemical enrichment level, as well as the relationship between the average orbital velocity of its stars and the mass of its central black hole. These relationships naturally result from any feedback mechanism that strongly heats a galaxy's circumgalactic gas in response to precipitation of colder clouds out of that gas, because feedback then suspends the gas in a marginally precipitating state

  16. An application of deep learning in the analysis of stellar spectra

    Science.gov (United States)

    Fabbro, S.; Venn, K. A.; O'Briain, T.; Bialek, S.; Kielty, C. L.; Jahandar, F.; Monty, S.

    2018-04-01

    Spectroscopic surveys require fast and efficient analysis methods to maximize their scientific impact. Here, we apply a deep neural network architecture to analyse both SDSS-III APOGEE DR13 and synthetic stellar spectra. When our convolutional neural network model (StarNet) is trained on APOGEE spectra, we show that the stellar parameters (temperature, gravity, and metallicity) are determined with similar precision and accuracy as the APOGEE pipeline. StarNet can also predict stellar parameters when trained on synthetic data, with excellent precision and accuracy for both APOGEE data and synthetic data, over a wide range of signal-to-noise ratios. In addition, the statistical uncertainties in the stellar parameter determinations are comparable to the differences between the APOGEE pipeline results and those determined independently from optical spectra. We compare StarNet to other data-driven methods; for example, StarNet and the Cannon 2 show similar behaviour when trained with the same data sets; however, StarNet performs poorly on small training sets like those used by the original Cannon. The influence of the spectral features on the stellar parameters is examined via partial derivatives of the StarNet model results with respect to the input spectra. While StarNet was developed using the APOGEE observed spectra and corresponding ASSET synthetic data, we suggest that this technique is applicable to other wavelength ranges and other spectral surveys.

  17. Stellar evolution as seen by mixed modes

    Directory of Open Access Journals (Sweden)

    Mosser Benoît

    2015-01-01

    Full Text Available The detection of mixed modes in subgiants and red giants allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. Quantified asteroseismic definitions that characterize the change in the evolutionary stages have been defined. This seismic information can now be used for stellar modelling, especially for studying the energy transport in the helium burning core or for specifying the inner properties of stars all along their evolution. Modelling will also allow us to study stars identified in the helium subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage.

  18. The Stellar Imager (SI) Mission Concept

    Science.gov (United States)

    Carpenter, Kenneth G.; Schrijver, Carolus J.; Lyon, Richard G.; Mundy, Lee G.; Allen, Ronald J.; Armstrong, Thomas; Danchi, William C.; Karovska, Margarita; Marzouk, Joe; Mazzuca, Lisa M.; hide

    2002-01-01

    The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5 km. It is designed to image stars and binaries with sufficient resolution to enable long-term studies of stellar magnetic activity patterns, for comparison with those on the sun. It will also support asteroseismology (acoustic imaging) to probe stellar internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of the magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars. The ultimate goal of the mission is to achieve the best-possible forecasting of solar activity as a driver of climate and space weather on time scales ranging from months up to decades, and an understanding of the impact of stellar magnetic activity on life in the Universe. In this paper we describe the scientific goals of the mission, the performance requirements needed to address these goals, the "enabling technology" development efforts being pursued, and the design concepts now under study for the full mission and a possible pathfinder mission.

  19. Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low-Mass White Dwarfs

    Science.gov (United States)

    Kalirai, Jasonjot S.; Bergeron, P.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.

    2007-12-01

    We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, =0.43+/-0.06 Msolar, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ~3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact >~7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained at the

  20. The Effects of Single and Close Binary Evolution on the Stellar Mass Function

    Science.gov (United States)

    Schneider, R. N. F.; Izzard, G. R.; de Mink, S.; Langer, N., Stolte, A., de Koter, A.; Gvaramadze, V. V.; Hussmann, B.; Liermann, A.; Sana, H.

    2013-06-01

    Massive stars are almost exclusively born in star clusters, where stars in a cluster are expected to be born quasi-simultaneously and with the same chemical composition. The distribution of their birth masses favors lower over higher stellar masses, such that the most massive stars are rare, and the existence of an stellar upper mass limit is still debated. The majority of massive stars are born as members of close binary systems and most of them will exchange mass with a close companion during their lifetime. We explore the influence of single and binary star evolution on the high mass end of the stellar mass function using a rapid binary evolution code. We apply our results to two massive Galactic star clusters and show how the shape of their mass functions can be used to determine cluster ages and comment on the stellar upper mass limit in view of our new findings.

  1. Operations of a non-stellar object tracker in space

    DEFF Research Database (Denmark)

    Riis, Troels; Jørgensen, John Leif; Betto, Maurizio

    1999-01-01

    The ability to detect and track non-stellar objects by utilizing a star tracker may seem rather straight forward, as any bright object, not recognized as a star by the system is a non stellar object. However, several pitfalls and errors exist, if a reliable and robust detection is required. To te...

  2. Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars

    Science.gov (United States)

    Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

    2015-04-01

    Nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. Large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low conductivity pasta layer by increasing an impurity parameter Qimp. Predictions of light curves for the low mass X-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). This research was supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

  3. On the theory of group generation of stars

    Science.gov (United States)

    Zhilyayev, B. Y.; Porfiryev, V. V.; Shulman, L. M.

    1973-01-01

    The hypothesis proposed is that topology of a rotating gaseous cloud can be variable in the contraction process. Due to rotation an originally spherical cloud is transformed into a toroidal body. The contraction of a thin torus is considered with different suppositions on cooling the gas. In the determined time the torus will become gravitationally unstable. The excitation of Jeans' waves is shown to result in the disintegration of the torus into fragments. The number of the fragments and their mass distributions are calculated. The proposed hypothesis on toroidal stages in stellar evolution can remove some difficulties in the theory of structure and evolution of stars, such as absence of limitary stars, distribution of rotation velocities of early-type stars, origin of poloidal magnetic fields and decline rotators with the magnetic axis orthogonal to the axis of rotation.

  4. How Very Massive Metal-Free Stars Start Cosmological Reionization

    Science.gov (United States)

    Wise, John H.; Abel, Tom

    2008-01-01

    The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include nonequilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the case B approximation using adaptively ray-traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of approx.10(exp 6). These first sources of reionization are highly intermittent and anisotropic and first photoionize the small-scale voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf-sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies, making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately five ionizing photons are needed per sustained ionization when star formation in 10(exp 6) stellar Mass halos is dominant in the calculation. As the halos become larger than approx.10(exp 7) Stellar Mass, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Radiative feedback decreases clumping factors by 25% when compared to simulations without star formation and increases the average temperature of ionized gas to values between 3000 and 10,000 K.

  5. PRIMUS: CONSTRAINTS ON STAR FORMATION QUENCHING AND GALAXY MERGING, AND THE EVOLUTION OF THE STELLAR MASS FUNCTION FROM z = 0-1

    Energy Technology Data Exchange (ETDEWEB)

    Moustakas, John [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States); Coil, Alison L.; Mendez, Alexander J. [Center for Astrophysics and Space Sciences, Department of Physics, University of California, 9500 Gilman Dr., La Jolla, CA 92093 (United States); Aird, James [Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Blanton, Michael R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Cool, Richard J. [MMT Observatory, University of Arizona, 1540 E Second Street, Tucson, AZ 85721 (United States); Eisenstein, Daniel J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Wong, Kenneth C. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Zhu, Guangtun [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Arnouts, Stephane, E-mail: jmoustakas@siena.edu [Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743 (United States)

    2013-04-10

    We measure the evolution of the stellar mass function (SMF) from z = 0-1 using multi-wavelength imaging and spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS) and the Sloan Digital Sky Survey (SDSS). From PRIMUS we construct an i < 23 flux-limited sample of {approx}40, 000 galaxies at z = 0.2-1.0 over five fields totaling Almost-Equal-To 5.5 deg{sup 2}, and from the SDSS we select {approx}170, 000 galaxies at z = 0.01-0.2 that we analyze consistently with respect to PRIMUS to minimize systematic errors in our evolutionary measurements. We find that the SMF of all galaxies evolves relatively little since z = 1, although we do find evidence for mass assembly downsizing; we measure a Almost-Equal-To 30% increase in the number density of {approx}10{sup 10} M{sub sun} galaxies since z Almost-Equal-To 0.6, and a {approx}< 10% change in the number density of all {approx}> 10{sup 11} M{sub sun} galaxies since z Almost-Equal-To 1. Dividing the sample into star-forming and quiescent using an evolving cut in specific star formation rate, we find that the number density of {approx}10{sup 10} M{sub sun} star-forming galaxies stays relatively constant since z Almost-Equal-To 0.6, whereas the space density of {approx}> 10{sup 11} M{sub sun} star-forming galaxies decreases by Almost-Equal-To 50% between z Almost-Equal-To 1 and z Almost-Equal-To 0. Meanwhile, the number density of {approx}10{sup 10} M{sub sun} quiescent galaxies increases steeply toward low redshift, by a factor of {approx}2-3 since z Almost-Equal-To 0.6, while the number of massive quiescent galaxies remains approximately constant since z Almost-Equal-To 1. These results suggest that the rate at which star-forming galaxies are quenched increases with decreasing stellar mass, but that the bulk of the stellar mass buildup within the quiescent population occurs around {approx}10{sup 10.8} M{sub sun}. In addition, we conclude that mergers do not appear to be a dominant channel for the stellar mass

  6. Spectra of late type dwarf stars of known abundance for stellar population models

    Science.gov (United States)

    Oconnell, R. W.

    1990-01-01

    The project consisted of two parts. The first was to obtain new low-dispersion, long-wavelength, high S/N IUE spectra of F-G-K dwarf stars with previously determined abundances, temperatures, and gravities. To insure high quality, the spectra are either trailed, or multiple exposures are taken within the large aperture. Second, the spectra are assembled into a library which combines the new data with existing IUE Archive data to yield mean spectral energy distributions for each important type of star. My principal responsibility is the construction and maintenance of this UV spectral library. It covers the spectral range 1200-3200A and is maintained in two parts: a version including complete wavelength coverage at the full spectral resolution of the Low Resolution cameras; and a selected bandpass version, consisting of the mean flux in pre-selected 20A bands. These bands are centered on spectral features or continuum regions of special utility - e.g. the C IV lambda 1550 or Mg II lambda 2800 feature. In the middle-UV region, special emphasis is given to those features (including continuum 'breaks') which are most useful in the study of F-G-K star spectra in the integrated light of old stellar populations.

  7. The Role Of Gender In Asking Questions At Cool Stars 18 And 19

    Science.gov (United States)

    Schmidt, Sarah J.; Douglas, Stephanie; Gosnell, Natalie M.; Muirhead, Philip S.; Booth, Rachel S.; Davenport, James R. A.; Mace, Gregory N.

    2016-12-01

    We examine the gender balance of the 18th and 19th meetings of the Cambridge Workshop on Cool Stellar Systems and the Sun (CS18 and CS19). The percent of female attendees at both meetings (31% at CS18 and 37% at CS19) was higher than the percent of women in the American Astronomical Society (25%) and the International Astronomical Union (18%). The representation of women in Cool Stars as SOC members, invited speakers, and contributed speakers was similar to or exceeded the percent of women attending the meetings. We requested that conference attendees assist in a project to collect data on the gender of astronomers asking questions after talks. Using this data, we found that men were over-represented (and women were under-represented) in the question sessions after each talk. Men asked 79% of the questions at CS18 and 75% of the questions at CS19, but were 69% and 63% of the attendees respectively. Contrary to findings from previous conferences, we did not find that the gender balance of questions was strongly affected by the session chair gender, the speaker gender, or the length of the question period. We also found that female and male speakers were asked a comparable number of questions after each talk. The contrast of these results from previous incarnations of the gender questions survey indicate that more data would be useful in understanding the factors that contribute to the gender balance of question askers. We include a preliminary set of recommendations based on this and other work on related topics, but also advocate for additional research on the demographics of conference participants. Additional data on the intersection of gender with race, seniority, sexual orientation, ability and other marginalized identities is necessary to fully address the role of gender in asking questions at conferences.

  8. A STELLAR MASS THRESHOLD FOR QUENCHING OF FIELD GALAXIES

    International Nuclear Information System (INIS)

    Geha, M.; Blanton, M. R.; Yan, R.; Tinker, J. L.

    2012-01-01

    We demonstrate that dwarf galaxies (10 7 stellar 9 M ☉ , –12 > M r > –18) with no active star formation are extremely rare ( Hα stellar 9 M ☉ below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1σ upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0 × 10 9 M ☉ , ending star formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.

  9. Activity indicators and stellar parameters of the Kepler targets. An application of the ROTFIT pipeline to LAMOST-Kepler stellar spectra

    Science.gov (United States)

    Frasca, A.; Molenda-Żakowicz, J.; De Cat, P.; Catanzaro, G.; Fu, J. N.; Ren, A. B.; Luo, A. L.; Shi, J. R.; Wu, Y.; Zhang, H. T.

    2016-10-01

    Aims: A comprehensive and homogeneous determination of stellar parameters for the stars observed by the Kepler space telescope is necessary for statistical studies of their properties. As a result of the large number of stars monitored by Kepler, the largest and more complete databases of stellar parameters published to date are multiband photometric surveys. The LAMOST-Kepler survey, whose spectra are analyzed in the present paper, was the first large spectroscopic project, which started in 2011 and aimed at filling that gap. In this work we present the results of our analysis, which is focused on selecting spectra with emission lines and chromospherically active stars by means of the spectral subtraction of inactive templates. The spectroscopic determination of the atmospheric parameters for a large number of stars is a by-product of our analysis. Methods: We have used a purposely developed version of the code ROTFIT for the determination of the stellar parameters by exploiting a wide and homogeneous collection of real star spectra, namely the Indo US library. We provide a catalog with the atmospheric parameters (Teff, log g, and [Fe/H]), radial velocity (RV), and an estimate of the projected rotation velocity (vsini). For cool stars (Teff≤ 6000 K), we also calculated the Hα and Ca II-IRT fluxes, which are important proxies of chromospheric activity. Results: We have derived the RV and atmospheric parameters for 61 753 spectra of 51 385 stars. The average uncertainties, which we estimate from the stars observed more than once, are about 12 km s-1, 1.3%, 0.05 dex, and 0.06 dex for RV, Teff, log g, and [Fe/H], respectively, although they are larger for the spectra with a very low signal-to-noise ratio. Literature data for a few hundred stars (mainly from high-resolution spectroscopy) were used to peform quality control of our results. The final accuracy of the RV is about 14 km s-1. The accuracy of the Teff, log g, and [Fe/H] measurements is about 3.5%, 0.3 dex

  10. Stellar remnants

    CERN Document Server

    Kawaler, S D; Srinivasan, G

    1997-01-01

    This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

  11. A COMPARISON OF STELLAR ELEMENTAL ABUNDANCE TECHNIQUES AND MEASUREMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Hinkel, Natalie R.; Young, Patrick A.; Pagano, Michael D.; Desch, Steven J.; Anbar, Ariel D. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Adibekyan, Vardan; Mena, Elisa Delgado; Sousa, Sergio G.; Santos, Nuno C. [Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto (Portugal); Blanco-Cuaresma, Sergi [Observatoire de Genève, Université de Genève, CH-1290 Versoix (Switzerland); Carlberg, Joleen K. [NASA Goddard Space Flight Center, Code 667, Greenbelt MD 20771 (United States); Liu, Fan [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia); Nordlander, Thomas; Korn, Andreas; Gruyters, Pieter; Heiter, Ulrike [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Jofré, Paula [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Soubiran, Caroline, E-mail: natalie.hinkel@gmail.com [CNRS/Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac (France)

    2016-09-01

    Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond the quoted error for the same elements within the same stars. The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and the United States) to calculate 10 element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD 361, HD 10700, HD 121504, and HD 202206). Each group produced measurements for each star using (1) their own autonomous techniques, (2) standardized stellar parameters, (3) a standardized line list, and (4) both standardized parameters and a line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies the homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise.

  12. Stellar Evolution with Rotation: Mixing Processes in AGB Stars

    Science.gov (United States)

    Driebe, T.; Blöcker, T.

    We included diffusive angular momentum transport and rotationally induced mixing processes in our stellar evolution code and studied the influence of rotation on the evolution of intermediate mass stars (M*=2dots6 Msolar) towards and along the asymptotic giant branch (AGB). The calculations start in the fully convective pre-main sequence phase and the initial angular momentu m was adjusted such that on the zero-age main sequence vrot=200 km/ s is achieved. The diffusion coefficients for the five rotational instabilities considered (dynamical shear, secular shear, Eddington-Sweet (ES) circulation, Solberg-Høiland-instability and Goldreich-Schubert-Fricke (GSF) instability) were adopted from Heger et al. (2000, ApJ 528, 368). Mixing efficiency and sensitivity of these processes against molecular weight gradients have been determined by calibration of the main sequence width. In this study we focus on the abundance evolution of carbon. On the one hand, the surface abundance ratios of 12C/13C a nd 12C/16O at the base of the AGB were found to be ≈ 7dots 10 and ≈ 0.1, resp., being a factor of two lower than in non-rotating models. This results from the slow but continuously operating rotationally induced mixing due to the ES-circulation and the GSF-instability during the long main sequence phase. On the other hand, 13C serves as neutron source for interior s-process nucleosynthesis in AGB stars vi a 13C(α,n)16O. Herwig et al. (1997, A&A 324, L81) found that a 13C pocket is forme d in the intershell region of 3 Msolar AGB star if diffusive overshoot is considered. Our calculations show, that mixing processes due to rotation open an alternative channel for the formation of a 13C pocket as found by Langer et al. (1999, A&A 346, L37). Again, ES-circulation and GSF-instability are the predominant rotational mixing processes.

  13. Evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1984-01-01

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  14. Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

    Energy Technology Data Exchange (ETDEWEB)

    Miceli, A; Rest, A; Stubbs, C W; Hawley, S L; Cook, K H; Magnier, E A; Krisciunas, K; Bowell, E; Koehn, B

    2007-02-23

    We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg{sup 2} and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles ({rho}{sub OoI} {approx} R{sup -2.26{+-}0.07} and {rho}{sub OoII} {approx} R{sup -2.88{+-}0.11}). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.

  15. Astrobiological Effects of Stellar Radiation in Circumstellar Environments

    Science.gov (United States)

    Cuntz, Manfred; Gurdemir, Levent; Guinan, Edward F.; Kurucz, Robert L.

    2006-10-01

    The centerpiece of all life on Earth is carbon-based biochemistry. Previous scientific research has suggested that biochemistry based on carbon may also play a decisive role in extraterrestrial life forms, i.e., alien life outside of Earth, if existent. In the following, we explore if carbon-based macromolecules (such as DNA) in the environments of stars other than the Sun are able to survive the effects of energetic stellar radiation, such as UV-C in the wavelength band between 200 and 290 nm. We focus on main-sequence stars akin to the Sun, but of hotter (F-type stars) and cooler (K- and M-type stars) surface temperature. Emphasis is placed on investigating the radiative environment in stellar habitable zones (HZs). Stellar habitable zones have an important relevance in astrobiology because they constitute circumstellar regions in which a planet of suitable size can have surface temperatures for water to exist in liquid form.

  16. When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    El-Badry, Kareem; Quataert, Eliot [Department of Astronomy, University of California, Berkeley, CA (United States); Wetzel, Andrew R.; Hopkins, Philip F. [TAPIR, California Institute of Technology, Pasadena, CA (United States); Geha, Marla [Department of Astronomy, Yale University, New Haven, CT (United States); Kereš, Dusan; Chan, T. K. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla (United States); Faucher-Giguère, Claude-André, E-mail: kelbadry@berkeley.edu [Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL (United States)

    2017-02-01

    In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

  17. When the Jeans Do Not Fit: How Stellar Feedback Drives Stellar Kinematics and Complicates Dynamical Modeling in Low-mass Galaxies

    International Nuclear Information System (INIS)

    El-Badry, Kareem; Quataert, Eliot; Wetzel, Andrew R.; Hopkins, Philip F.; Geha, Marla; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André

    2017-01-01

    In low-mass galaxies, stellar feedback can drive gas outflows that generate non-equilibrium fluctuations in the gravitational potential. Using cosmological zoom-in baryonic simulations from the Feedback in Realistic Environments project, we investigate how these fluctuations affect stellar kinematics and the reliability of Jeans dynamical modeling in low-mass galaxies. We find that stellar velocity dispersion and anisotropy profiles fluctuate significantly over the course of galaxies’ starburst cycles. We therefore predict an observable correlation between star formation rate and stellar kinematics: dwarf galaxies with higher recent star formation rates should have systemically higher stellar velocity dispersions. This prediction provides an observational test of the role of stellar feedback in regulating both stellar and dark-matter densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies as virialized systems in dynamical equilibrium, overestimates a galaxy’s dynamical mass during periods of post-starburst gas outflow and underestimates it during periods of net inflow. Short-timescale potential fluctuations lead to typical errors of ∼20% in dynamical mass estimates, even if full three-dimensional stellar kinematics—including the orbital anisotropy—are known exactly. When orbital anisotropy is not known a priori, typical mass errors arising from non-equilibrium fluctuations in the potential are larger than those arising from the mass-anisotropy degeneracy. However, Jeans modeling alone cannot reliably constrain the orbital anisotropy, and problematically, it often favors anisotropy models that do not reflect the true profile. If galaxies completely lose their gas and cease forming stars, fluctuations in the potential subside, and Jeans modeling becomes much more reliable.

  18. Third dredge-up in cluster AGB stars : observational constraints and improved opacity data for models

    International Nuclear Information System (INIS)

    Lederer, M. T.

    2009-01-01

    evolution calculations with our findings. The second part of the thesis deals with a new set of low-temperature mean opacity coefficients. Until recently, the change in chemistry due to the TDU in the cool layers of the star, where molecules are the dominant opacity source, has been neglected in almost all stellar evolution models. I show that already within a certain chemistry regime (i. e. an oxygen-rich or carbon-rich metal mixture) an alteration of the carbon abundance causes, due to the special role of the CO molecule, considerable changes in the Rosseland opacity which has distinct consequences for the stellar structure and evolution. In the stellar evolution models, the most pronounced effect can be expected when the TDU turns the initially oxygen-rich object into a carbon star. The new opacity database contains (beside a variation of the 12 C mass fraction) also tables with a varied abundance of 14 N. After describing the database as well as the tools and the data used for its computation, I point out the implications of the new opacity data for stellar evolution models. (author) [de

  19. Influence of a stellar wind on the evolution of a star of 30 M/sub sun/

    International Nuclear Information System (INIS)

    Stothers, R.; Chin, C.

    1980-01-01

    A coarse grid of theoretical evolutionary tracks has been computed for a star of 30 M/sub sun/, in an attempt to delineate the role of mass loss in the star's evolution during core helium burning. For all of the tracks, Cox-Stewart opacities have been adopted, and the free parameters have included the rate of mass loss, criterion for convection, and initial chemical composition. With the use of the Schwarzschild criterion, the star suffers little mass loss during core helium burning and remains almost to the end, a blue supergiant, well separated from main-sequence stars on the H-R diagram. With the use of the Ledoux criterion, the same consequences are obtained only in the case of a relatively low initial hydrogen or initial metals abundance. Otherwise, the star evolves, first, into a red supergiant, whereupon rapid mass loss must be assumed to take place, if the observed paucity of very bright red supergiants is to be accounted for. The stellar remnant then consists of little more than the original helium core, and may appear, for a time, bluer than equally luminous main-sequence stars, provided that the the initial hydrogen and metals abundances are normal. Thus, a wide variety of possible evolutionary tracks can be obtained for an initial mass of 30 M/sub sun/ with reasonable choices of the free parameters

  20. A Unified Equation of State on a Microscopic Basis : Implications for Neutron Stars Structure and Cooling

    Science.gov (United States)

    Burgio, G. F.

    2018-03-01

    We discuss the structure of Neutron Stars by modelling the homogeneous nuclear matter of the core by a suitable microscopic Equation of State, based on the Brueckner-Hartree-Fock many-body theory, and the crust, including the pasta phase, by the BCPM energy density functional which is based on the same Equation of State. This allows for a uni ed description of the Neutron Star matter over a wide density range. A comparison with other uni ed approaches is discussed. With the same Equation of State, which features strong direct Urca processes and using consistent nuclear pairing gaps as well as effective masses, we model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A. We nd that several scenarios are possible to explain the features of Cas A, but only large and extended proton 1 S 0 gaps and small neutron 3 PF 2 gaps can accommodate also the major part of the complete current cooling data.

  1. Direct Urca Processes Involving Proton 1 S 0 Superfluidity in Neutron Star Cooling

    Science.gov (United States)

    Xu, Yan; Yu, Zi; Zhang, Xiao-Jun; Fan, Cun-Bo; Liu, Guang-Zhou; Zhao, En-Guang; Huang, Xiu-Lin; Liu, Cheng-Zhi

    2018-04-01

    A detailed description of the baryon direct Urca processes A: n\\to p+e+{\\bar{ν }}e, B: Λ \\to p+e+{\\bar{ν }}e and C: {\\Xi }-\\to Λ +e+{\\bar{ν }}e related to the neutron star cooling is given in the relativistic mean field approximation. The contributions of the reactions B and C on the neutrino luminosity are calculated by means of the relativistic expressions of the neutrino energy losses. Our results show that the total neutrino luminosities of the reactions A, B and C within the mass range (1.603–2.067) M⊙ ((1.515–1.840) M⊙ for TM1 model) for GM1 model are larger than the corresponding values for neutron star without hyperons. Furthermore, although the neutrino emissivity of the reaction A is suppressed with the appearance of the proton 1 S 0 superfluid, the contribution of the reactions B and C can still quicken a massive neutron star cooling. In particular, the reaction C in PSR J1614-2230 and J0348+0432 is not suppressed by the proton 1 S 0 superfluid due to the higher threshold density of the reaction C, which will further speed up the two pulsars cooling. Supported by the National Natural Science Foundation of China under Grant Nos. 11447165, 11373047, 11404336 and U1731240, Youth Innovation Promotion Association, CAS under Grant No. 2016056, and the Development Project of Science and Technology of Jilin Province under Grant No. 20180520077JH

  2. KINEMATICS OF CLASSICAL CEPHEIDS IN THE NUCLEAR STELLAR DISK

    International Nuclear Information System (INIS)

    Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Kobayashi, Naoto; Hamano, Satoshi; Inno, Laura; Genovali, Katia; Bono, Giuseppe; Baba, Junichi; Fujii, Michiko S.; Aoki, Wako; Tsujimoto, Takuji; Kondo, Sohei; Ikeda, Yuji; Nishiyama, Shogo; Nagata, Tetsuya

    2015-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic center, three of which were reported in 2011 and a fourth being reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the nuclear stellar disk, a group of stars and interstellar matter occupying a region of ∼200 pc around the center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the nuclear stellar disk like younger stars and stellar clusters therein

  3. Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chengyuan; De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai, E-mail: joshuali@pku.edu.cn, E-mail: grijs@pku.edu.cn [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

    2014-04-01

    Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of the clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.

  4. Compact stellar object: the formation and structure

    Energy Technology Data Exchange (ETDEWEB)

    Duarte, S.B. [Centro Brasileiro de Pesquisas Fisicas (CBPF/MCT), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    Full text: The formation of compact objects is viewed at the final stages of stellar evolution. The supernova explosion events are then focalized to explain the formation of pulsars, hybrid neutron star and the limit case of the latter, the quark stars. We discuss the stability and structure of these objects in connection with the properties of the hadron and quark-gluon plasma equation of state. The hadron-quark phase transition in deep interior of these objects is discussed taking into account the implications on the density distribution of matter along the radial direction. The role of neutrinos confinement in the ultradense stellar medium in the early stages of pulsar formation is another interesting aspect to be mentioned in this presentation. Recent results for maximum mass of compact stellar objects for different forms of equations of state will be shown, presenting some theoretical predictions for maximum mass of neutron stars allowed by different equations of state assigned to dense stellar medium. Although a density greater than few times the nuclear equilibrium density appears in deep interior of the core, at the crust the density decreases by several orders of magnitude where a variety of hadronic states appears, the 'pasta'-states of hadrons. More externally, a lattice of nuclei can be formed permeated not only by electrons but also by a large amount of free neutrons and protons. These are possible structure of neutron star crust to have the density and pressures with null values at the neutron star surface. The ultimate goal of this talk is to give a short view of the compact star area for students and those who are introducing in this subject. (author)

  5. Stellar Obliquity and Magnetic Activity of Planet-hosting Stars and Eclipsing Binaries Based on Transit Chord Correlation

    Science.gov (United States)

    Dai, Fei; Winn, Joshua N.; Berta-Thompson, Zachory; Sanchis-Ojeda, Roberto; Albrecht, Simon

    2018-04-01

    The light curve of an eclipsing system shows anomalies whenever the eclipsing body passes in front of active regions on the eclipsed star. In some cases, the pattern of anomalies can be used to determine the obliquity Ψ of the eclipsed star. Here we present a method for detecting and analyzing these patterns, based on a statistical test for correlations between the anomalies observed in a sequence of eclipses. Compared to previous methods, ours makes fewer assumptions and is easier to automate. We apply it to a sample of 64 stars with transiting planets and 24 eclipsing binaries for which precise space-based data are available, and for which there was either some indication of flux anomalies or a previously reported obliquity measurement. We were able to determine obliquities for 10 stars with hot Jupiters. In particular we found Ψ ≲ 10° for Kepler-45, which is only the second M dwarf with a measured obliquity. The other eight cases are G and K stars with low obliquities. Among the eclipsing binaries, we were able to determine obliquities in eight cases, all of which are consistent with zero. Our results also reveal some common patterns of stellar activity for magnetically active G and K stars, including persistently active longitudes.

  6. The origin of stellar winds: Subatmospheric nonthermal storage modes versus radiation pressure

    International Nuclear Information System (INIS)

    Cannon, C.J.; Thomas, R.N.

    1977-01-01

    Most current models of matter-flux in hot stars place its origin in radiation pressure, and then model the flow explicitly to produce no chromosphere-corona. Our model of the stellar atmosphere as a transition zone between stellar interior and interstellar medium places the origin of matter-flux, chromosphere-corona, and spectral ''emission classes'' in subatmospheric nonthermal kinetic energy storage, equally for all stars, hot or cold. Current observations of both hot and cold stars suggest chromospheres to be a universal phenomenon, correlated with matter-fluxes, and enhanced in ''emission-class'' stars. To clarify the difference between the two kinds of models above, we reformulate the wind-tunnel analogy to stellar winds, suggesting that stars satisfy and ''imperfect,'' such model;i.e., transsonic shocks occur before the throat, corresponding to an imposed outward velocity in the storage section, or subatmosphere. We then investigate the stability of an arbitrary stellar atmosphere, hot or cold, to suggest a cause for such an outward subatmospheric velocity

  7. The Life of Stars The Controversial Inception and Emergence of the Theory of Stellar Structure

    CERN Document Server

    Shaviv, Giora

    2009-01-01

    This beautifully illustrated book describes the birth and evolution of the theory of stellar structure through the vehement controversy between biology (as presented by Darwin) and physics (as presented by Kelvin) about the age of the Earth, which culminated with Rutherford suggesting radioactive dating. Shaviv analyzes critically many proclaimed scientific results, showing how and why they were wrong, and explains why it took decades to find the now accepted scientific answers - where there are such - and why there remains much more to be done before we can say we fully understand what happens up there in the heavens. The Life of the Stars provides fascinating reading for all those interested in the stars, in the history of astronomy and in what their story tells us about how science progresses. Moreover, it will bring readers up-to-date on current problems in astrophysics.

  8. Galaxy Zoo: the dependence of the star formation-stellar mass relation on spiral disc morphology

    Science.gov (United States)

    Willett, Kyle W.; Schawinski, Kevin; Simmons, Brooke D.; Masters, Karen L.; Skibba, Ramin A.; Kaviraj, Sugata; Melvin, Thomas; Wong, O. Ivy; Nichol, Robert C.; Cheung, Edmond; Lintott, Chris J.; Fortson, Lucy

    2015-05-01

    We measure the stellar mass-star formation rate (SFR) relation in star-forming disc galaxies at z ≤ 0.085, using Galaxy Zoo morphologies to examine different populations of spirals as classified by their kiloparsec-scale structure. We examine the number of spiral arms, their relative pitch angle, and the presence of a galactic bar in the disc, and show that both the slope and dispersion of the M⋆-SFR relation is constant when varying all the above parameters. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by ˜0.3 dex; this is significantly smaller than the increase seen in merging systems at z > 1. Of the galaxies lying significantly above the M⋆-SFR relation in the local Universe, more than 50 per cent are mergers. We interpret this as evidence that the spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms or are completely overwhelmed by the combination of outflows and feedback. The arrangement of the star formation can be changed, but the system as a whole regulates itself even in the presence of strong dynamical forcing.

  9. THE COOLING OF THE CASSIOPEIA A NEUTRON STAR AS A PROBE OF THE NUCLEAR SYMMETRY ENERGY AND NUCLEAR PASTA

    Energy Technology Data Exchange (ETDEWEB)

    Newton, William G.; Hooker, Joshua; Li, Bao-An [Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, TX 75429-3011 (United States); Murphy, Kyleah [Umpqua Community College, Roseburg, OR 97470 (United States)

    2013-12-10

    X-ray observations of the neutron star (NS) in the Cas A supernova remnant over the past decade suggest the star is undergoing a rapid drop in surface temperature of ≈2%-5.5%. One explanation suggests the rapid cooling is triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). Using consistent NS crust and core equations of state (EOSs) and compositions, we explore the sensitivity of this interpretation to the density dependence of the symmetry energy L of the EOS used, and to the presence of enhanced neutrino cooling in the bubble phases of crustal ''nuclear pasta''. Modeling cooling over a conservative range of NS masses and envelope compositions, we find L ≲ 70 MeV, competitive with terrestrial experimental constraints and other astrophysical observations. For masses near the most likely mass of M ≳ 1.65 M {sub ☉}, the constraint becomes more restrictive 35 ≲ L ≲ 55 MeV. The inclusion of the bubble cooling processes decreases the cooling rate of the star during the PBF phase, matching the observed rate only when L ≲ 45 MeV, taking all masses into consideration, corresponding to NS radii ≲ 11 km.

  10. Stellar chemical signatures and hierarchical galaxy formation

    NARCIS (Netherlands)

    Venn, KA; Irwin, M; Shetrone, MD; Tout, CA; Hill, [No Value; Tolstoy, E

    To compare the chemistries of stars in the Milky Way dwarf spheroidal (dSph) satellite galaxies with stars in the Galaxy, we have compiled a large sample of Galactic stellar abundances from the literature. When kinematic information is available, we have assigned the stars to standard Galactic

  11. THE STELLAR HALOS OF MASSIVE ELLIPTICAL GALAXIES. II. DETAILED ABUNDANCE RATIOS AT LARGE RADIUS

    Energy Technology Data Exchange (ETDEWEB)

    Greene, Jenny E.; Murphy, Jeremy D.; Graves, Genevieve J.; Gunn, James E.; Raskutti, Sudhir [Department of Astrophysics, Princeton University, Princeton, NJ 08540 (United States); Comerford, Julia M.; Gebhardt, Karl [Department of Astronomy, UT Austin, 1 University Station C1400, Austin, TX 71712 (United States)

    2013-10-20

    We study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions σ{sub *} ∼> 150 km s{sup –1}. We measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, the typical star at 2R{sub e} is old (∼10 Gyr), relatively metal-poor ([Fe/H] ≈ –0.5), and α-enhanced ([Mg/Fe] ≈ 0.3). The stars were made rapidly at z ≈ 1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid star formation timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to average Milky Way thick disk stars. Our observations are thus consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose star formation is truncated early (z ≈ 1.5-2)

  12. AGB stellar evolution and symbiotic stars

    International Nuclear Information System (INIS)

    Schild, H.

    1989-01-01

    Published data on the mass loss rates and periods of Miras and OH/IR stars have been compiled. There is a good correlation between mass loss rate and period and a smooth transition from Miras to OH/IR sources. At periods below 600 d. the mass loss increases exponentially but at longer periods it remains constant. As a Mira evolves from short to longer periods, its mass loss rate increases dramatically. Phenomenologically, the object evolves from a classical Mira into a variable OH/IR source. Symbiotic stars cluster in the transition zone where Miras transform into OH/IR stars and mass loss increase is at its steepest. The red star in these symbiotic systems is in the same evolutionary status as short periodic OH/IR stars. (author)

  13. Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

    Science.gov (United States)

    Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

    2014-02-01

    The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

  14. The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys-Davidson limit revisited

    Science.gov (United States)

    Davies, Ben; Crowther, Paul A.; Beasor, Emma R.

    2018-05-01

    The empirical upper luminosity boundary Lmax of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of Lmax by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble samples of cool SGs in each galaxy which are highly-complete above log L/L⊙=5.0, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases Lmax appears to be lower than previously quoted, and is in the region of log L/L⊙=5.5. There is no evidence for Lmax being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that Lmax aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.

  15. SDSS-IV MaNGA: Star Formation Cessation in Low-redshift Galaxies. I. Dependence on Stellar Mass and Structural Properties

    Science.gov (United States)

    Wang, Enci; Li, Cheng; Xiao, Ting; Lin, Lin; Bershady, Matthew; Law, David R.; Merrifield, Michael; Sanchez, Sebastian F.; Riffel, Rogemar A.; Riffel, Rogerio; Yan, Renbin

    2018-04-01

    We investigate radial gradients in the recent star formation history (SFH) of 1917 galaxies with 0.01 < z < 0.14 from the Mapping Nearby Galaxies at Apache Point Observatory project. For each galaxy, we obtain two-dimensional maps and radial profiles for three spectroscopically measured parameters that are sensitive to the recent SFH: D n (4000) (the 4000 Å break), EW(Hδ A ), and EW(Hα) (the equivalent width of the Hδ absorption and the Hα emission line). The majority of the spaxels are consistent with models of a continuously declining star formation rate, indicating that starbursts occur rarely in local galaxies with regular morphologies. We classify the galaxies into three classes: fully star-forming (SF), partly quenched (PQ), and totally quenched (TQ). The galaxies that are less massive than 1010 M ⊙ present at most weak radial gradients in the diagnostic parameters. In contrast, massive galaxies with a stellar mass above 1010 M ⊙ present significant gradients in the three diagnostic parameters if they are classified as SF or PQ but show weak gradients in D n (4000) and EW(Hδ A ) and no gradients in EW(Hα) if they are in the TQ class. This implies the existence of a critical stellar mass (∼1010 M ⊙) above which the star formation in a galaxy is shut down from the inside out. Galaxies tend to evolve synchronously from the inner to the outer regions before their mass reaches the critical value. We have further divided the sample at a fixed mass by both bulge-to-total luminosity ratio and morphological type, finding that our conclusions hold regardless of these factors; it appears that the presence of a central dense object is not a driving parameter but rather a by-product of the star formation cessation process.

  16. Recent advances in non-LTE stellar atmosphere models

    Science.gov (United States)

    Sander, Andreas A. C.

    2017-11-01

    In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

  17. LOW-METALLICITY PROTOSTARS AND THE MAXIMUM STELLAR MASS RESULTING FROM RADIATIVE FEEDBACK: SPHERICALLY SYMMETRIC CALCULATIONS

    International Nuclear Information System (INIS)

    Hosokawa, Takashi; Omukai, Kazuyuki

    2009-01-01

    The final mass of a newborn star is set at the epoch when the mass accretion onto the star is terminated. We study the evolution of accreting protostars and the limits of accretion in low-metallicity environments under spherical symmetry. Accretion rates onto protostars are estimated via the temperature evolution of prestellar cores with different metallicities. The derived rates increase with decreasing metallicity, from M-dot≅10 -6 M odot yr -1 at Z = Z sun to 10 -3 M sun yr -1 at Z = 0. With the derived accretion rates, the protostellar evolution is numerically calculated. We find that, at lower metallicity, the protostar has a larger radius and reaches the zero-age main sequence (ZAMS) at higher stellar mass. Using this protostellar evolution, we evaluate the upper stellar mass limit where the mass accretion is hindered by radiative feedback. We consider the effects of radiation pressure exerted on the accreting envelope, and expansion of an H II region. The mass accretion is finally terminated by radiation pressure on dust grains in the envelope for Z ∼> 10 -3 Z sun and by the expanding H II region for lower metallicity. The mass limit from these effects increases with decreasing metallicity from M * ≅ 10 M sun at Z = Z sun to ≅300 M sun at Z = 10 -6 Z sun . The termination of accretion occurs after the central star arrives at the ZAMS at all metallicities, which allows us to neglect protostellar evolution effects in discussing the upper mass limit by stellar feedback. The fragmentation induced by line cooling in low-metallicity clouds yields prestellar cores with masses large enough that the final stellar mass is set by the feedback effects. Although relaxing the assumption of spherical symmetry will alter feedback effects, our results will be a benchmark for more realistic evolution to be explored in future studies.

  18. The ZZ Ceti stars and the rate of evolution of white dwarfs

    International Nuclear Information System (INIS)

    Robinson, E.L.; Kepler, S.O.

    1980-01-01

    The importance of the ZZ Ceti stars, and indeed the importance of all pulsating stars, derives from the fact that stellar pulsations probe the interiors of stars, and thus they test directly our models of stellar interiors and stellar evolution. The relative value of stellar pulsations as such a probe depends on, among other factors, the number of pulsation modes simultaneously excited in a star, as each additional mode depends on and constrains the properties of the star in a different way. Judged by this criterion, the pulsations of the ZZ Ceti stars should be unusually valuable because all ZZ Ceti stars are multi-mode variables. (orig./WL)

  19. Giants of eclipse the ζ [Zeta] Aurigae stars and other binary systems

    CERN Document Server

    Griffin, Elizabeth

    2015-01-01

    The zeta Aurigae stars are the rare but illustrious sub-group of binary stars that undergo the dramatic phenomenon of "chromospheric eclipse". This book provides detailed descriptions of the ten known systems, illustrates them richly with examples of new spectra, and places them in the context of stellar structure and evolution. Comprised of a large cool giant plus a small hot dwarf, these key eclipsing binaries reveal fascinating changes in their spectra very close to total eclipse, when the hot star shines through differing heights of the "chromosphere", or outer atmosphere, of the giant star. The phenomenon provides astrophysics with the means of analyzing the outer atmosphere of a giant star and how that material is shed into space. The physics of these critical events can be explained qualitatively, but it is more challenging to extract hard facts from the observations, and tough to model the chromosphere in any detail. The book offers current thinking on mechanisms for heating a star's chromosphere an...

  20. Which of Kepler's Stars Flare?

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

  1. New Light on Dark Stars Red Dwarfs, Low-Mass Stars, Brown Dwarfs

    CERN Document Server

    Reid, I. Neill

    2005-01-01

    There has been very considerable progress in research into low-mass stars, brown dwarfs and extrasolar planets during the past few years, particularly since the fist edtion of this book was published in 2000. In this new edtion the authors present a comprehensive review of both the astrophysical nature of individual red dwarf and brown dwarf stars and their collective statistical properties as an important Galactic stellar population. Chapters dealing with the observational properies of low-mass dwarfs, the stellar mass function and extrasolar planets have been completely revised. Other chapters have been significantly revised and updated as appropriate, including important new material on observational techniques, stellar acivity, the Galactic halo and field star surveys. The authors detail the many discoveries of new brown dwarfs and extrasolar planets made since publication of the first edition of the book and provide a state-of-the-art review of our current knowledge of very low-mass stars, brown dwarfs a...

  2. Classification of extremely metal-poor stars: absent region in A(C)-[Fe/H] plane and the role of dust cooling

    Science.gov (United States)

    Chiaki, Gen; Tominaga, Nozomu; Nozawa, Takaya

    2017-11-01

    Extremely metal-poor (EMP) stars are the living fossils with records of chemical enrichment history at the early epoch of galaxy formation. By the recent large observation campaigns, statistical samples of EMP stars have been obtained. This motivates us to reconsider their classification and formation conditions. From the observed lower limits of carbon and iron abundances of Acr(C) ∼ 6 and [Fe/H]cr ∼ -5 for C-enhanced EMP (CE-EMP) and C-normal EMP (CN-EMP) stars, we confirm that gas cooling by dust thermal emission is indispensable for the fragmentation of their parent clouds to form such low mass, i.e. long-lived stars, and that the dominant grain species are carbon and silicate, respectively. We constrain the grain radius r_i^cool of a species i and condensation efficiency fij of a key element j as r_C^cool / f_C,C = 10 {μ m} and r_Sil^cool / f_Sil,Mg = 0.1 {μ m} to reproduce Acr(C) and [Fe/H]cr, which give a universal condition 10[C/H] - 2.30 + 10[Fe/H] > 10-5.07 for the formation of every EMP star. Instead of the conventional boundary [C/Fe] = 0.7 between CE-EMP and CN-EMP stars, this condition suggests a physically meaningful boundary [C/Fe]b = 2.30 above and below which carbon and silicate grains are dominant coolants, respectively.

  3. Stellar evolution and the triple-α reactions

    International Nuclear Information System (INIS)

    Suda, Takuma

    2014-01-01

    Nuclear reaction rates play a crucial role in the evolution of stars. For low-mass stars, the triple-α reaction controls the helium burning stars in the red giant and asymptotic giant branch (AGB) phase. More importantly, the cross section of the triple-α reaction has a great impact on the helium ignition at the center of the electron degenerate helium core of red giants and on the helium shell flashes of AGB stars. It is to be noted that stellar evolution models are influenced not only by the value of the cross section, but also by the temperature dependence of the reaction rate. In this paper, I present the impact of the triple-α reaction rates on the evolution of low-mass metal-free stars and intermediate-mass AGB stars. According to the previous study, the constraint on the triple-α reaction rate is derived based on stellar evolution theory. It is found that the recent revisions of the rate proposed by nuclear physics calculations satisfy the condition for the ignition of the helium core flash in low-mass stars

  4. SEMI-EMPIRICAL WHITE DWARF INITIAL-FINAL MASS RELATIONSHIPS: A THOROUGH ANALYSIS OF SYSTEMATIC UNCERTAINTIES DUE TO STELLAR EVOLUTION MODELS

    International Nuclear Information System (INIS)

    Salaris, Maurizio; Serenelli, Aldo; Weiss, Achim; Miller Bertolami, Marcelo

    2009-01-01

    Using the most recent results about white dwarfs (WDs) in ten open clusters, we revisit semiempirical estimates of the initial-final mass relation (IFMR) in star clusters, with emphasis on the use of stellar evolution models. We discuss the influence of these models on each step of the derivation. One intention of our work is to use consistent sets of calculations both for the isochrones and the WD cooling tracks. The second one is to derive the range of systematic errors arising from stellar evolution theory. This is achieved by using different sources for the stellar models and by varying physical assumptions and input data. We find that systematic errors, including the determination of the cluster age, are dominating the initial mass values, while observational uncertainties influence the final mass primarily. After having determined the systematic errors, the initial-final mass relation allows us finally to draw conclusions about the physics of the stellar models, in particular about convective overshooting.

  5. YOUNG, ULTRAVIOLET-BRIGHT STARS DOMINATE DUST HEATING IN STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Law, Ka-Hei; Gordon, Karl D.; Misselt, K. A.

    2011-01-01

    In star-forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAHs), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region-the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the IR emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star-forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.

  6. EVOLUTION OF SUPER STAR CLUSTER WINDS WITH STRONG COOLING

    International Nuclear Information System (INIS)

    Wuensch, Richard; Palous, Jan; Silich, Sergiy; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana

    2011-01-01

    We study the evolution of super star cluster winds driven by stellar winds and supernova explosions. Time-dependent rates at which mass and energy are deposited into the cluster volume, as well as the time-dependent chemical composition of the re-inserted gas, are obtained from the population synthesis code Starburst99. These results are used as input for a semi-analytic code which determines the hydrodynamic properties of the cluster wind as a function of cluster age. Two types of winds are detected in the calculations. For the quasi-adiabatic solution, all of the inserted gas leaves the cluster in the form of a stationary wind. For the bimodal solution, some of the inserted gas becomes thermally unstable and forms dense warm clumps which accumulate inside the cluster. We calculate the evolution of the wind velocity and energy flux and integrate the amount of accumulated mass for clusters of different mass, radius, and initial metallicity. We also consider conditions with low heating efficiency of the re-inserted gas or mass loading of the hot thermalized plasma with the gas left over from star formation. We find that the bimodal regime and the related mass accumulation occur if at least one of the two conditions above is fulfilled.

  7. Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

    Science.gov (United States)

    Bergemann, Maria; Sesar, Branimir; Cohen, Judith G; Serenelli, Aldo M; Sheffield, Allyson; Li, Ting S; Casagrande, Luca; Johnston, Kathryn V; Laporte, Chervin F P; Price-Whelan, Adrian M; Schönrich, Ralph; Gould, Andrew

    2018-03-15

    Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

  8. Evidence for halo kinematics among cool carbon-rich dwarfs

    Science.gov (United States)

    Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

    2018-04-01

    This paper reports preliminary yet compelling kinematical inferences for N ≳ 600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogs based on Gaia DR1 astrometry to generate estimates of their 3-D space velocities. The fraction of stars with halo-like kinematics is roughly 30% for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disk, but close to 60% of the sample lie below an old, metal-poor disk isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favors low-mass stars as in the Galactic disk, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

  9. GALAXY FORMATION WITH COLD GAS ACCRETION AND EVOLVING STELLAR INITIAL MASS FUNCTION

    International Nuclear Information System (INIS)

    Kang Xi; Lin, W. P.; Skibba, Ramin; Chen, D. N.

    2010-01-01

    The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the ΛCDM model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models (SAMs) of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0. In addition, there is a strong correlation between star formation rate (SFR) and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using an SAM that includes (1) cold gas accretion in massive halos at high redshift; (2) tidal stripping of stellar mass from satellite galaxies; and (3) an evolving stellar initial mass function (IMF; bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from (1) and (2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, while the combined effects of (1) and (3) can reproduce the correlation between SFR and stellar mass for star-forming galaxies across a wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.

  10. Observational tests for the evolution of massive stars in nearby galaxies

    International Nuclear Information System (INIS)

    Leitherer, C.

    1990-01-01

    Population synthesis calculations applicable to the massive stellar content in nearby galaxies are presented. Stellar evolution calculations are combined with mass loss, model atmospheres with line blanketing, and a spectral type calibration to compute observable parameters of massive stars as a function of the star formation rate and the initial mass function slope. The number of O stars of given spectral types, the number of W-R stars, supernova rates, and fluxes of ionizing photons are predicted. Important constraints for the theories of stellar atmospheres and stellar evolution can be derived from observations if stellar number counts and ionizing flux data are available. 94 refs

  11. Rapid mass segregation in small stellar clusters

    Science.gov (United States)

    Spera, Mario; Capuzzo-Dolcetta, Roberto

    2017-12-01

    In this paper we focus our attention on small-to-intermediate N-body systems that are, initially, distributed uniformly in space and dynamically `cool' (virial ratios Q=2T/|Ω| below ˜0.3). In this work, we study the mass segregation that emerges after the initial violent dynamical evolution. At this scope, we ran a set of high precision N-body simulations of isolated clusters by means of HiGPUs, our direct summation N-body code. After the collapse, the system shows a clear mass segregation. This (quick) mass segregation occurs in two phases: the first shows up in clumps originated by sub-fragmentation before the deep overall collapse; this segregation is partly erased during the deep collapse to re-emerge, abruptly, during the second phase, that follows the first bounce of the system. In this second stage, the proper clock to measure the rate of segregation is the dynamical time after virialization, which (for cold and cool systems) may be significantly different from the crossing time evaluated from initial conditions. This result is obtained for isolated clusters composed of stars of two different masses (in the ratio mh/ml=2), at varying their number ratio, and is confirmed also in presence of a massive central object (simulating a black hole of stellar size). Actually, in stellar systems starting their dynamical evolution from cool conditions, the fast mass segregation adds to the following, slow, secular segregation which is collisionally induced. The violent mass segregation is an effect persistent over the whole range of N (128 ≤ N ≤1,024) investigated, and is an interesting feature on the astronomical-observational side, too. The semi-steady state reached after virialization corresponds to a mass segregated distribution function rather than that of equipartition of kinetic energy per unit mass as it should result from violent relaxation.

  12. Research in astrophysics: Stellar collapse and supernovae: Termination report, August 1, 1980-November 30, 1986

    International Nuclear Information System (INIS)

    Burrows, A.; Lattimer, J.M.; Mazurek, T.J.; Yahil, A.

    1987-01-01

    The interaction between nuclear theory and some outstanding problems in astrophysics has been examined. The chief emphasis of the program was on stellar collapse, Type II supernovae and neutron star formation. Central to these topics are the development of an equation of state of hot, dense matter and numerical simulations of gravitational collapse and neutron star birth. The LLPR compressible liquid drop model is the basis of the former. It has been refined to include curvature corrections to the surface energy and nuclear force parameters which are in better agreement with experimental quantities. Numerically optimized versions were used in supernova simulations. Such studies of the equation of state can also be used to analyze intermediate energy heavy ion collisions, which, in turn, may illuminate the nucleon-nucleon force. A novel hydrodynamical code in which shocks are treated via Riemann resolution rather than with artificial viscosity was developed. We modeled not only the stellar collapse leading up to a supernova, but also the quasi-static deleptonization and cooling of the nascent neutron star. For the latter evolution we also used a hydrostatic code with detailed neutrino transport. Our studies of neutrinos in stellar collapse and neutron star formation concentrated on their detectability and signatures, as neutrinos are the only direct probe of collapse and early supernova dynamics. The neutrino signatures seen from SN1987a are in complete accord with the predictions our group has been making since 1982. Complementary studies included modeling nucleosynthesis and the accretion process in quasars, and investigating the influence of galaxy clustering on the large scale structure of the universe. The last study might impose constraints on high energy theories, such as those of inflation and GUT, which can now only be tested astrophysically. 38 refs

  13. STAR FORMATION RATES AND STELLAR MASSES OF z = 7-8 GALAXIES FROM IRAC OBSERVATIONS OF THE WFC3/IR EARLY RELEASE SCIENCE AND THE HUDF FIELDS

    International Nuclear Information System (INIS)

    Labbe, I.; Gonzalez, V.; Bouwens, R. J.; Illingworth, G. D.; Magee, D.; Franx, M.; Trenti, M.; Oesch, P. A.; Carollo, C. M.; Van Dokkum, P. G.; Stiavelli, M.; Kriek, M.

    2010-01-01

    We investigate the Spitzer/IRAC properties of 36 z ∼ 7 z 850 -dropout galaxies and three z ∼ 8 Y 098 galaxies derived from deep/wide-area WFC3/IR data of the Early Release Science, the ultradeep HUDF09, and wide-area NICMOS data. We fit stellar population synthesis models to the spectral energy distributions to derive mean redshifts, stellar masses, and ages. The z ∼ 7 galaxies are best characterized by substantial ages (>100 Myr) and M/L V ∼ 0.2. The main trend with decreasing luminosity is that of bluing of the far-UV slope from β ∼ -2.0 to β ∼ -3.0. This can be explained by decreasing metallicity, except for the lowest luminosity galaxies (0.1L* z =3 ), where low metallicity and smooth star formation histories (SFHs) fail to match the blue far-UV and moderately red H - [3.6] color. Such colors may require episodic SFHs with short periods of activity and quiescence ('on-off' cycles) and/or a contribution from emission lines. The stellar mass of our sample of z ∼ 7 star-forming galaxies correlates with star formation rate (SFR) according to log M* = 8.70(±0.09) + 1.06(±0.10)log SFR, implying that star formation may have commenced at z > 10. No galaxies are found with SFRs much higher or lower than the past averaged SFR suggesting that the typical star formation timescales are probably a substantial fraction of the Hubble time. We report the first IRAC detection of Y 098 -dropout galaxies at z ∼ 8. The average rest-frame U - V ∼ 0.3 (AB) of the three galaxies are similar to faint z ∼ 7 galaxies, implying similar M/L. The stellar mass density to M UV,AB +0.7 -1.0 x 10 6 M sun Mpc -3 , following log ρ*(z) = 10.6(±0.6) - 4.4(±0.7) log(1 + z) [M sun Mpc -3 ] over 3 < z < 8.

  14. M Stars in the TW Hydra Association: A Chandra Large Program Survey

    Science.gov (United States)

    Punzi, Kristina; Kastner, Joel; Principe, David; Stelzer, Beate; Gorti, Uma; Pascucci, Illaria; Argiroffi, Costanza

    2018-01-01

    We have conducted a Cycle 18 Chandra Large Program survey of very cool members of the $\\sim$ 8 Myr-old TW Hydra Association (TWA) to extend our previous study of the potential connections between M star disks and X-rays (Kastner et al. 2016, AJ, 152, 3) to the extreme low-mass end of the stellar initial mass function. The spectral types of our targets extend down to the M/L borderline. Thus we can further investigate the potential connection between the intense X-ray emission from young, low-mass stars and the lifetimes of their circumstellar planet-forming discs, as well as better constrain the age at which coronal activity declines for stellar masses approaching the H-burning limit of $\\sim$ 0.08 M$_{\\odot}$. We present preliminary results from the Cycle 18 survey, including X-ray detection statistics and measurements of relative X-ray luminosities and coronal (X-ray) temperatures for those TWA stars detected by Chandra. This research is supported by SAO/CXC grant GO7-18002A and NASA Astrophysics Data Analysis program grants NNX12AH37G and NNX16AG13G to RIT.

  15. Stellar compass for the Clementine Mission

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, B. [Lawrence Livermore National Lab., CA (United States)

    1994-11-15

    A CCD sensor with 42 x 28 degrees FOV and 576 x 384 pixels was built by the Advanced Technology Program (ATP) in the Physics Department at LLNL. That sensor, called the StarTracker camera, is used on the Clementine Lunar Mapping mission between January and May, 1994. Together with the Stellar Compass software, the StarTracker camera provided a way of identifying its orientation to within about 150 microradians in camera body pitch and yaw. This presentation will be an overview of basically how the Stellar Compass software works, along with showing some of its performance results.

  16. Starquakes, Heating Anomalies, and Nuclear Reactions in the Neutron Star Crust

    Science.gov (United States)

    Deibel, Alex Thomas

    When the most massive stars perish, their cores may remain intact in the form of extremely dense and compact stars. These stellar remnants, called neutron stars, are on the cusp of becoming black holes and reach mass densities greater than an atomic nucleus in their centers. Although the interiors of neutron stars were difficult to investigate at the time of their discovery, the advent of modern space-based telescopes (e.g., Chandra X-ray Observatory) has pushed our understanding of the neutron star interior into exciting new realms. It has been shown that the neutron star interior spans an enormous range of densities and contains many phases of matter, and further theoretical progress must rely on numerical calculations of neutron star phenomena built with detailed nuclear physics input. To further investigate the properties of the neutron star interior, this dissertation constructs numerical models of neutron stars, applies models to various observations of neutron star high-energy phenomena, and draws new conclusions about the neutron star interior from these analyses. In particular, we model the neutron star's outermost ? 1 km that encompasses the neutron star's envelope, ocean, and crust. The model must implement detailed nuclear physics to properly simulate the hydrostatic and thermal structure of the neutron star. We then apply our model to phenomena that occur in these layers, such as: thermonuclear bursts in the envelope, g-modes in the ocean, torsional oscillations of the crust, and crust cooling of neutron star transients. A comparison of models to observations provides new insights on the properties of dense matter that are often difficult to probe through terrestrial experiments. For example, models of the quiescent cooling of neutron stars, such as the accreting transient MAXI J0556-332, at late times into quiescence probe the thermal transport properties of the deep neutron star crust. This modeling provides independent data from astronomical

  17. AN EMPIRICAL CALIBRATION TO ESTIMATE COOL DWARF FUNDAMENTAL PARAMETERS FROM H-BAND SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Newton, Elisabeth R.; Charbonneau, David; Irwin, Jonathan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Mann, Andrew W., E-mail: enewton@cfa.harvard.edu [Astronomy Department, University of Texas at Austin, Austin, TX 78712 (United States)

    2015-02-20

    Interferometric radius measurements provide a direct probe of the fundamental parameters of M dwarfs. However, interferometry is within reach for only a limited sample of nearby, bright stars. We use interferometrically measured radii, bolometric luminosities, and effective temperatures to develop new empirical calibrations based on low-resolution, near-infrared spectra. We find that H-band Mg and Al spectral features are good tracers of stellar properties, and derive functions that relate effective temperature, radius, and log luminosity to these features. The standard deviations in the residuals of our best fits are, respectively, 73 K, 0.027 R {sub ☉}, and 0.049 dex (an 11% error on luminosity). Our calibrations are valid from mid K to mid M dwarf stars, roughly corresponding to temperatures between 3100 and 4800 K. We apply our H-band relationships to M dwarfs targeted by the MEarth transiting planet survey and to the cool Kepler Objects of Interest (KOIs). We present spectral measurements and estimated stellar parameters for these stars. Parallaxes are also available for many of the MEarth targets, allowing us to independently validate our calibrations by demonstrating a clear relationship between our inferred parameters and the stars' absolute K magnitudes. We identify objects with magnitudes that are too bright for their inferred luminosities as candidate multiple systems. We also use our estimated luminosities to address the applicability of near-infrared metallicity calibrations to mid and late M dwarfs. The temperatures we infer for the KOIs agree remarkably well with those from the literature; however, our stellar radii are systematically larger than those presented in previous works that derive radii from model isochrones. This results in a mean planet radius that is 15% larger than one would infer using the stellar properties from recent catalogs. Our results confirm the derived parameters from previous in-depth studies of KOIs 961 (Kepler

  18. STELLAR ACTIVITY AND ITS IMPLICATIONS FOR EXOPLANET DETECTION ON GJ 176

    International Nuclear Information System (INIS)

    Robertson, Paul; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Henry, Gregory W.; Williamson, Michael H.

    2015-01-01

    We present an in-depth analysis of stellar activity and its effects on radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 yr from the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are supplemented with spectra from previous observations with the HIRES and HARPS spectrographs, and V- and R-band photometry taken over six years at the Dyer and Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth exoplanet in an 8.8-day orbit. However, the velocities of this star are also known to be contaminated by activity, particularly at the 39-day stellar rotation period. We have examined the magnetic activity of GJ 176 using the sodium I D lines, which have been shown to be a sensitive activity tracer in cool stars. In addition to rotational modulation, we see evidence of a long-term trend in our Na I D index, which may be part of a long-period activity cycle. The sodium index is well correlated with our RVs, and we show that this activity trend drives a corresponding slope in RV. Interestingly, the rotation signal remains in phase in photometry, but not in the spectral activity indicators. We interpret this phenomenon as the result of one or more large spot complexes or active regions which dominate the photometric variability, while the spectral indices are driven by the overall magnetic activity across the stellar surface. In light of these results, we discuss the potential for correcting activity signals in the RVs of M dwarfs

  19. How good a clock is rotation? The stellar rotation-mass-age relationship for old field stars

    International Nuclear Information System (INIS)

    Epstein, Courtney R.; Pinsonneault, Marc H.

    2014-01-01

    The rotation-mass-age relationship offers a promising avenue for measuring the ages of field stars, assuming the attendant uncertainties to this technique can be well characterized. We model stellar angular momentum evolution starting with a rotation distribution from open cluster M37. Our predicted rotation-mass-age relationship shows significant zero-point offsets compared to an alternative angular momentum loss law and published gyrochronology relations. Systematic errors at the 30% level are permitted by current data, highlighting the need for empirical guidance. We identify two fundamental sources of uncertainty that limit the precision of rotation-based ages and quantify their impact. Stars are born with a range of rotation rates, which leads to an age range at fixed rotation period. We find that the inherent ambiguity from the initial conditions is important for all young stars, and remains large for old stars below 0.6 M ☉ . Latitudinal surface differential rotation also introduces a minimum uncertainty into rotation period measurements and, by extension, rotation-based ages. Both models and the data from binary star systems 61 Cyg and α Cen demonstrate that latitudinal differential rotation is the limiting factor for rotation-based age precision among old field stars, inducing uncertainties at the ∼2 Gyr level. We also examine the relationship between variability amplitude, rotation period, and age. Existing ground-based surveys can detect field populations with ages as old as 1-2 Gyr, while space missions can detect stars as old as the Galactic disk. In comparison with other techniques for measuring the ages of lower main sequence stars, including geometric parallax and asteroseismology, rotation-based ages have the potential to be the most precise chronometer for 0.6-1.0 M ☉ stars.

  20. Flare stars in Pleiades. 6

    International Nuclear Information System (INIS)

    Mirzoyan, L.V.; Chavushyan, O.S.; Oganyan, G.B.; Ambaryan, V.V.; Garibdzhanyan, A.T.; Melikyan, N.D.; Natsvlishvili, R.Sh.; AN Gruzinskoj SSR, Abastumani. Abastumanskaya Astrofizicheskaya Observatoriya)

    1981-01-01

    The results of photographic observations of stellar flares in the Pleiades region carried out at the Byurakan and Abastumani astrophysical observatories during 1976-1979 are given. On the basis of these observations 17 new flare stars have been found. Total number of all known flare stars in the Pleiades region on 1 June 1980 reached 524, and the number of all flares-1244. The observational data on distribution of flare stars according to the observed flares is satisfactorily represented by the average frequency function introduced by V.A.Ambartsumian. The total number of the flare stars in the Pleiades is of the order of 1100. Using three telescopes, synchronous photographic observations of stellar flares in Pleiades in U, B, V, system are carried out. The colour indices U-B and B-V of stellar flares in periods including the maximum of the flare slightly differ from that of photoelectrically defined for flares of UV Ceti type stars, which testifies the physical relationship of flare stars in Pleiades and in the vicinity of the Sun [ru

  1. A new open-source code for spherically symmetric stellar collapse to neutron stars and black holes

    International Nuclear Information System (INIS)

    O'Connor, Evan; Ott, Christian D

    2010-01-01

    We present the new open-source spherically symmetric general-relativistic (GR) hydrodynamics code GR1D. It is based on the Eulerian formulation of GR hydrodynamics (GRHD) put forth by Romero-Ibanez-Gourgoulhon and employs radial-gauge, polar-slicing coordinates in which the 3+1 equations simplify substantially. We discretize the GRHD equations with a finite-volume scheme, employing piecewise-parabolic reconstruction and an approximate Riemann solver. GR1D is intended for the simulation of stellar collapse to neutron stars and black holes and will also serve as a testbed for modeling technology to be incorporated in multi-D GR codes. Its GRHD part is coupled to various finite-temperature microphysical equations of state in tabulated form that we make available with GR1D. An approximate deleptonization scheme for the collapse phase and a neutrino-leakage/heating scheme for the postbounce epoch are included and described. We also derive the equations for effective rotation in 1D and implement them in GR1D. We present an array of standard test calculations and also show how simple analytic equations of state in combination with presupernova models from stellar evolutionary calculations can be used to study qualitative aspects of black hole formation in failing rotating core-collapse supernovae. In addition, we present a simulation with microphysical equations of state and neutrino leakage/heating of a failing core-collapse supernova and black hole formation in a presupernova model of a 40 M o-dot zero-age main-sequence star. We find good agreement on the time of black hole formation (within 20%) and last stable protoneutron star mass (within 10%) with predictions from simulations with full Boltzmann neutrino radiation hydrodynamics.

  2. A new open-source code for spherically symmetric stellar collapse to neutron stars and black holes

    Energy Technology Data Exchange (ETDEWEB)

    O' Connor, Evan; Ott, Christian D, E-mail: evanoc@tapir.caltech.ed, E-mail: cott@tapir.caltech.ed [TAPIR, Mail Code 350-17, California Institute of Technology, Pasadena, CA 91125 (United States)

    2010-06-07

    We present the new open-source spherically symmetric general-relativistic (GR) hydrodynamics code GR1D. It is based on the Eulerian formulation of GR hydrodynamics (GRHD) put forth by Romero-Ibanez-Gourgoulhon and employs radial-gauge, polar-slicing coordinates in which the 3+1 equations simplify substantially. We discretize the GRHD equations with a finite-volume scheme, employing piecewise-parabolic reconstruction and an approximate Riemann solver. GR1D is intended for the simulation of stellar collapse to neutron stars and black holes and will also serve as a testbed for modeling technology to be incorporated in multi-D GR codes. Its GRHD part is coupled to various finite-temperature microphysical equations of state in tabulated form that we make available with GR1D. An approximate deleptonization scheme for the collapse phase and a neutrino-leakage/heating scheme for the postbounce epoch are included and described. We also derive the equations for effective rotation in 1D and implement them in GR1D. We present an array of standard test calculations and also show how simple analytic equations of state in combination with presupernova models from stellar evolutionary calculations can be used to study qualitative aspects of black hole formation in failing rotating core-collapse supernovae. In addition, we present a simulation with microphysical equations of state and neutrino leakage/heating of a failing core-collapse supernova and black hole formation in a presupernova model of a 40 M{sub o-dot} zero-age main-sequence star. We find good agreement on the time of black hole formation (within 20%) and last stable protoneutron star mass (within 10%) with predictions from simulations with full Boltzmann neutrino radiation hydrodynamics.

  3. Young Stellar Variability of GM Cephei by Circumstellar Dust Clumps

    Science.gov (United States)

    Huang, Po-Chieh; Chen, Wen-Ping; Hu, Chia-Ling; Burkhonov, Otabek; Ehgamberdiev, Shuhrat; Liu, Jinzhong; Naito, Hiroyuki; Pakstiene, Erika; Qvam, Jan Kare Trandem; Rätz, Stefanie; Semkov, Evgeni

    2018-04-01

    UX Orionis stars are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such an UX Orionis star in the young (∼ 4 Myr) open cluster Trumpler 37 at ∼ 900 pc, showing a prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2016 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical, occultation events, each lasting for a couple months, with a probable recurrence time of about two years, (iii) normal dust reddening as the star became redder when dimmer, (iv) the unusual "blueing" phenomena near the brightness minima, during which the star appeared bluer when dimmer, and (v) a noticeable polarization, from 3 to 9 percent in g', r', and i' -bands. The occultation events may be caused by dust clumps, signifying the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. The level of polarization was anti-correlated with the brightness in the bright state, when the dust clump backscattered stellar light. We discussed two potential hypotheses: orbiting dust clumps versus dust clumps along a spiral arm structure.

  4. Inferring probabilistic stellar rotation periods using Gaussian processes

    Science.gov (United States)

    Angus, Ruth; Morton, Timothy; Aigrain, Suzanne; Foreman-Mackey, Daniel; Rajpaul, Vinesh

    2018-02-01

    Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online.

  5. The Resolved Stellar Population of Leo A

    Science.gov (United States)

    Tolstoy, Eline

    1996-05-01

    New observations of the resolved stellar population of the extremely metal-poor Magellanic dwarf irregular galaxy Leo A in Thuan-Gunn r, g, i, and narrowband Hα filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an accurate color-magnitude diagram (CMD). We have used the Bavesian inference method described by Tolstoy & Saha to calculate the likelihood of a Monte Carlo simulation of the stellar population of Leo A being a good match to the data within the well understood errors in the data. The magnitude limits on our data are sensitive enough to look back at ~1 Gyr of star formation history at the distance of Leo A. To explain the observed ratio of red to blue stars in the observed CMD, it is necessary to invoke either a steadily decreasing star formation rate toward the present time or gaps in the star formation history. We also compare the properties of the observed stellar population with the known spatial distribution of the H I gas and H II regions to support the conclusions from CMD modeling. We consider the possibility that currently there is a period of diminished star formation in Leo A, as evidenced by the lack of very young stars in the CMD and the faint H II regions. How the chaotic H I distribution, with no observable rotation, fits into our picture of the evolution of Leo A is as yet unclear.

  6. The evolution of supermassive Population III stars

    Science.gov (United States)

    Haemmerlé, Lionel; Woods, T. E.; Klessen, Ralf S.; Heger, Alexander; Whalen, Daniel J.

    2018-02-01

    Supermassive primordial stars forming in atomically cooled haloes at z ˜ 15-20 are currently thought to be the progenitors of the earliest quasars in the Universe. In this picture, the star evolves under accretion rates of 0.1-1 M⊙ yr-1 until the general relativistic instability triggers its collapse to a black hole at masses of ˜105 M⊙. However, the ability of the accretion flow to sustain such high rates depends crucially on the photospheric properties of the accreting star, because its ionizing radiation could reduce or even halt accretion. Here we present new models of supermassive Population III protostars accreting at rates 0.001-10 M⊙ yr-1, computed with the GENEVA stellar evolution code including general relativistic corrections to the internal structure. We compute for the first time evolutionary tracks in the mass range M > 105 M⊙. We use the polytropic stability criterion to estimate the mass at which the collapse occurs, which has been shown to give a lower limit of the actual mass at collapse in recent hydrodynamic simulations. We find that at accretion rates higher than 0.01 M⊙ yr-1, the stars evolve as red, cool supergiants with surface temperatures below 104 K towards masses >105 M⊙. Moreover, even with the lower rates 0.001 M_{⊙} yr{^{-1}}feedback remains weak, reinforcing the case for direct collapse as the origin of the first quasars. We provide numerical tables for the surface properties of our models.

  7. High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

    International Nuclear Information System (INIS)

    Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

    2011-01-01

    The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

  8. Photometric Separation of Stellar Properties Using SDSS Filters

    Science.gov (United States)

    Lenz, Dawn D.; Newberg, Jo; Rosner, Robert; Richards, Gordon T.; Stoughton, Chris

    1998-12-01

    Using synthetic photometry of Kurucz model spectra, we explore the colors of stars as a function of temperature, metallicity, and surface gravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. The synthetic colors show qualitative agreement with the few published observations in these filters. We find that the locus of synthetic stars is basically two-dimensional for 4500 advantageous to use more than two colors when determining stellar properties by color. Strategic observations in SDSS filters are required to resolve the source of a ~5% discrepancy between synthetic colors of Gunn-Stryker stars, Kurucz models, and external determinations of the metallicities and surface gravities. The synthetic star colors can be used to investigate the properties of any normal star and to construct analytic expressions for the photometric prediction of stellar properties in special cases.

  9. Stellar configurations in f(R) theories of gravity

    International Nuclear Information System (INIS)

    Henttunen, K.; Multamaeki, T.; Vilja, I.

    2008-01-01

    We study stellar configurations and the space-time around them in metric f(R) theories of gravity. In particular, we focus on the polytropic model of the Sun in two specific cases: the f(R)=R-μ 4 /R model and a model with a stabilizing higher order term f(R)=R-μ 4 /R+βR 3 /(3μ 4 ). We show how the stellar configuration in the f(R) theory can, by appropriate initial conditions, be selected to be equal to that described by the Lane-Emden equation and how a simple scaling relation exists between the solutions. We also derive the correct solution analytically near the center of the star in f(R) theory. Previous analytical and numerical results are confirmed, indicating that the space-time around the Sun is incompatible with solar system constraints in the f(R)=R-μ 4 /R model. Numerical work shows that stellar configurations, with a regular metric at the center, lead to γ PPN ≅1/2 outside the star for both models, i.e., the Schwarzschild-de Sitter space-time is not the correct vacuum solution for such configurations. This shows that even when one fine-tunes the initial conditions inside a star such that the mass of the effective scalar in the equivalent scalar-tensor theory is large, γ PPN is still 1/2 outside the star. Conversely, by selecting the Schwarzschild-de Sitter metric as the outside solution, or equivalently setting the mass of the effective scalar to be large outside the star, we find that the stellar configuration is unchanged but the metric is irregular at the center. The possibility of constructing a f(R) theory compatible with the solar system experiments and possible new constraints arising from the radius-mass relation of stellar objects is discussed

  10. Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664

    Energy Technology Data Exchange (ETDEWEB)

    Han, Eunkyu; Muirhead, Philip S. [Department of Astronomy and Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Swift, Jonathan J. [The Thacher School, 5025 Thacher Road Ojai, CA 93023 (United States); Baranec, Christoph; Atkinson, Dani [Institute for Astronomy, University of Hawaiì at Mānoa, Hilo, HI 96720-2700 (United States); Law, Nicholas M. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Riddle, Reed [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Mace, Gregory N. [McDonald Observatory and The University of Texas, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); DeFelippis, Daniel, E-mail: eunkyuh@bu.edu [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)

    2017-09-01

    Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity, and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. Çakırlı et al. measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. Iglesias-Marzoa et al. independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, which is consistent with the inhibited convection scenario. However, in their mass determinations, Iglesias-Marzoa et al. lacked independent radial velocity measurements for the secondary component due to the star’s faintness at optical wavelengths. The secondary component is especially interesting, as its purported mass is near the transition from partially convective to a fully convective interior. In this article, we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival Kepler data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.

  11. Helium-burning flashes on accreting neutron stars: effects of stellar mass, radius, and magnetic field

    International Nuclear Information System (INIS)

    Joss, P.C.; Li, F.K.

    1980-01-01

    We have computed the evolution of the helium-burning shell in an accreting neutron star for various values of the stellar mass (M), radius (R), and surface magnetic fields strength (B). As shown in previous work, the helium-burning shell is often unstable and undergoes thermonuclear flashes that result in the emission of X-ray bursts from the neutron-star surface. The dependence of the properties of these bursts upon the values of M and R can be described by simple scaling relations. A strong magnetic field decreases the radiative and conductive opacities and inhibits convection in the neutron-star surface layers. For B 12 gauss, these effects are unimportant; for B> or approx. =10 13 gauss, the enhancement of the electron thermal conductivity is sufficiently large to stabilize the helium-burning shell against thermonuclear flashes. For intermediate values of B, the reduced opacities increase the recurrence intervals between bursts and the energy released per burst, while the inhibition of convection increases the burst rise times to about a few seconds. If the magnetic field funnels the accreting matter onto the magnetic polar caps, the instability of the helium-burning shell will be very strongly suppressed. These results suggest that it may eventually be possible to extract information on the macroscopic properties of neutron stars from the observed features of X-ray burst sources

  12. The evolution of stellar exponential discs

    NARCIS (Netherlands)

    Ferguson, AMN; Clarke, CJ

    2001-01-01

    Models of disc galaxies which invoke viscosity-driven radial flows have long been known to provide a natural explanation for the origin of stellar exponential discs, under the assumption that the star formation and viscous time-scales are comparable. We present models which invoke simultaneous star

  13. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10 6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ∼10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  14. Stellar and interstellar K lines - Gamma Pegasi and iota Herculis.

    Science.gov (United States)

    Hobbs, L. M.

    1973-01-01

    High-resolution scans show that the relatively strong (about 90 mA) K lines of Ca II in the early B stars gamma-Peg and iota-Her are almost entirely stellar in origin, although the latter case includes a small interstellar contribution. Such stellar lines can be of great importance in augmenting the interstellar absorption, up through the earliest of the B stars.

  15. Resonance line-profiles in galactic disk UV-bright stars

    International Nuclear Information System (INIS)

    Carrasco, L.; Costero, R.

    1987-01-01

    We have made a comparative analysis of UV resonance line-profiles in O-type stars members of young clusters and OB associations, with those of hot stars located away from sites of recent star formation (including ''runaway'' stars). The resonance line-profiles are found to be generally dominated by stellar winds that appear to depend mainly on the surface gravity and temperature of the star, and not on its mass. We also present the C IV, Si IV and N V resonance line-profiles for eleven stars not published in the previous two papers. The use of only the largest stellar wind velocity detectable in the resonance lines as a stellar population indicator, is disputed. (author)

  16. The disk wind in the rapidly spinning stellar-mass black hole 4U 1630-472 observed with NuSTAR

    DEFF Research Database (Denmark)

    King, Ashley L.; Walton, Dominic J.; Miller, Jon M.

    2014-01-01

    We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630-472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we...... find evidence for a rapidly spinning black hole, (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also...

  17. Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

    Science.gov (United States)

    Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; Serenelli, Aldo M.; Sheffield, Allyson; Li, Ting S.; Casagrande, Luca; Johnston, Kathryn V.; Laporte, Chervin F. P.; Price-Whelan, Adrian M.; Schönrich, Ralph; Gould, Andrew

    2018-03-01

    Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

  18. KamLAND Sensitivity to Neutrinos from Pre-supernova Stars

    Science.gov (United States)

    Asakura, K.; Gando, A.; Gando, Y.; Hachiya, T.; Hayashida, S.; Ikeda, H.; Inoue, K.; Ishidoshiro, K.; Ishikawa, T.; Ishio, S.; Koga, M.; Matsuda, S.; Mitsui, T.; Motoki, D.; Nakamura, K.; Obara, S.; Oura, T.; Shimizu, I.; Shirahata, Y.; Shirai, J.; Suzuki, A.; Tachibana, H.; Tamae, K.; Ueshima, K.; Watanabe, H.; Xu, B. D.; Kozlov, A.; Takemoto, Y.; Yoshida, S.; Fushimi, K.; Piepke, A.; Banks, T. I.; Berger, B. E.; Fujikawa, B. K.; O'Donnell, T.; Learned, J. G.; Maricic, J.; Matsuno, S.; Sakai, M.; Winslow, L. A.; Efremenko, Y.; Karwowski, H. J.; Markoff, D. M.; Tornow, W.; Detwiler, J. A.; Enomoto, S.; Decowski, M. P.; KamLAND Collaboration

    2016-02-01

    In the late stages of nuclear burning for massive stars (M > 8 M⊙), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of 25 M⊙ at a distance less than 690 pc with 3σ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

  19. Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

    Science.gov (United States)

    Yang, G.; Chen, C.-T. J.; Vito, F.; Brandt, W. N.; Alexander, D. M.; Luo, B.; Sun, M. Y.; Xue, Y. Q.; Bauer, F. E.; Koekemoer, A. M.; Lehmer, B. D.; Liu, T.; Schneider, D. P.; Shemmer, O.; Trump, J. R.; Vignali, C.; Wang, J.-X.

    2017-06-01

    We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M *) in the CANDELS/GOODS-South field in the redshift range of 0.5≤slant zteam through spectral energy distribution fitting. The average BHAR is correlated positively with both SFR and M *, and the BHAR-SFR and BHAR-M * relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M * than SFR. This result indicates that M * is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ({M}* ≳ {10}10{M}⊙ ) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between {M}{BH} and M * for local giant ellipticals and suggest that their {M}{BH}/{M}* is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher {M}{BH}/{M}* compared to dwarfs.

  20. Spot temperatures and area coverages on active dwarf stars

    Science.gov (United States)

    Sarr, Steven H.; Neff, James E.

    1990-01-01

    Two active K dwarfs are examined to determine the temperatures of the stars and to estimate the locations and sizes of cool spots on the stellar surfaces. Two wavelength regions with TiO absorption bands at different temperature sensitivities are modeled simultaneously using the method developed by Huenemoerder and Ramsey (1987). The spectrum of BD +26deg730 shows excess absorption in the TiO band, and the absence of the 8860 A band in HD 82558 indicates that its spots are warmer than those of BD +26deg730.

  1. A Photometric Machine-Learning Method to Infer Stellar Metallicity

    Science.gov (United States)

    Miller, Adam A.

    2015-01-01

    Following its formation, a star's metal content is one of the few factors that can significantly alter its evolution. Measurements of stellar metallicity ([Fe/H]) typically require a spectrum, but spectroscopic surveys are limited to a few x 10(exp 6) targets; photometric surveys, on the other hand, have detected > 10(exp 9) stars. I present a new machine-learning method to predict [Fe/H] from photometric colors measured by the Sloan Digital Sky Survey (SDSS). The training set consists of approx. 120,000 stars with SDSS photometry and reliable [Fe/H] measurements from the SEGUE Stellar Parameters Pipeline (SSPP). For bright stars (g' learning method is similar to the scatter in [Fe/H] measurements from low-resolution spectra..

  2. Wide cool and ultracool companions to nearby stars from Pan-STARRS 1

    International Nuclear Information System (INIS)

    Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Aller, Kimberly M.; Best, William M. J.; Bowler, Brendan P.; Burgett, William S.; Chambers, Kenneth C.; Flewelling, H.; Kaiser, Nick; Kudritzki, Rolf-Peter; Morgan, Jeff S.; Tonry, John L.; Dupuy, Trent; Mann, Andrew W.; Redstone, Joshua A.; Draper, Peter W.; Metcalfe, Nigel; Hodapp, Klaus W.; Price, Paul A.

    2014-01-01

    We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type of K7-L9 with the addition of one DA white dwarf. These were identified primarily from a dedicated common proper motion search around nearby stars, along with a few as serendipitous discoveries from our Pan-STARRS 1 brown dwarf search. Our discoveries include 23 new L dwarf companions and one known L dwarf not previously identified as a companion. The primary stars around which we searched for companions come from a list of bright stars with well-measured parallaxes and large proper motions from the Hipparcos catalog (8583 stars, mostly A-K dwarfs) and fainter stars from other proper motion catalogs (79170 stars, mostly M dwarfs). We examine the likelihood that our companions are chance alignments between unrelated stars and conclude that this is unlikely for the majority of the objects that we have followed-up spectroscopically. We also examine the entire population of ultracool (>M7) dwarf companions and conclude that while some are loosely bound, most are unlikely to be disrupted over the course of ∼10 Gyr. Our search increases the number of ultracool M dwarf companions wider than 300 AU by 88% and increases the number of L dwarf companions in the same separation range by 82%. Finally, we resolve our new L dwarf companion to HIP 6407 into a tight (0.''13, 7.4 AU) L1+T3 binary, making the system a hierarchical triple. Our search for these key benchmarks against which brown dwarf and exoplanet atmosphere models are tested has yielded the largest number of discoveries to date.

  3. The stellar metallicity gradients in galaxy discs in a cosmological scenario

    Science.gov (United States)

    Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

    2016-08-01

    Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside

  4. Environments of T Tauri stars

    International Nuclear Information System (INIS)

    Chevalier, R.A.

    1983-01-01

    The environments of T Tauri stars are probably determined by the interaction of a stellar wind with matter which is falling toward a newly formed star. As shown by Ulrich, the steady infall of cool gas with angular momentum toward the star leads to a density distribution with rhoproportionalr/sup -1/2/ inside a radius r/sub d/ and rhoproportionalr/sup -3/2/ outside r/sub d/. The radius r/sub d/ is determined by the angular momentum of the infalling gas. The expansion of the wind into this medium depends on the parameter α = M/sub w/v/sub w//M/sub in/v/sub in/(r/sub d/), where v/sub in/(r/sub d/) is the free-fall velocity at r/sub d/, M/sub in/ is the mass accretion rate, v/sub w/ is the wind velocity, and M/sub w/ is the mass loss rate. For α 14 cm, v/sub w/ = 150 km s -1 , M/sub in/ = 10 -7 M/sub sun/ yr -1 , and M/sub w/ = 3 x 10 -8 M/sub sun/ yr -1 . The inflow is clumpy. The shocked wind gives the radio emission and nebular emission from T Tauri, and dust within the clumps gives the infrared emission. T Tauri is in a transitory phase in which most of the wind has only recently propagated beyond r/sub d/. The model naturally predicts variable obscuration of T Tauri stars because the infalling clumps move on nonradial trajectories. The infrared emission can vary either because of structural changes in the circumstellar gas or because of variations in the stellar luminosity. Infrared variability should be small at short time scales because of light-travel time effects

  5. Making Sense of Atmospheric Models and Fundamental Stellar Properties at the Bottom of the Main Sequence

    Science.gov (United States)

    Dieterich, Sergio; Henry, Todd; Jao, W.-C.; Washington, Robert; Silverstein, Michele; Winters, J.; RECONS

    2018-01-01

    We present a detailed comparison of atmospheric model predictions and photometric observations for late M and L dwarfs. We discuss which wavelength regions are best for determining the fundamental properties of these cool stellar and substellar atmospheres and use this analysis to refine the HR diagram for the hydrogen burning limit first presented in 2014. We also add several new objects to the HR diagram and find little qualitative difference in the HR diagram's overall morphology when compared to our 2014 results. The L2 dwarf 2MASS 0523-1403 remains the smallest hydrogen burning star for which we calculated a radius, thus likely indicating the end of the stellar main sequence. This work is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship program through grant AST-1400680.

  6. Symbiotic star AG Dra

    International Nuclear Information System (INIS)

    Ipatov, A.P.; Yudin, B.F.; Moskovskij Gosudarstvennyj Univ.

    1986-01-01

    The results obtained from photometric (in the UBVRJHKLM system) and spectrophotometric (in the range 0.33-0.75 μm) observations of symbiotic star AG Dra are presented. The cool component of this star is a red giant with approximately constant brightness (ΔJ ≤ 0 m .3) classified as K4-K5. This red giant fills it's Roche loble and probably is on the assymptotic giant branch of the HR diagramm. The presence of IR excess in 5 μm associated with radiation of the gaseous envelope with the mass of M≅ 10 -6 M sun have been detected. Observations of AG Dra indicate that growing of the bolometric flux of a hot component is accompanied with decreasing effective temperature. The hot component of the system is probably an accerting red dwarf with the mass M≅ 0.4 M sun and disk accretion of matter of cool star with the rate M >or ∼ 10 -4 M sun year in equatorial region. Increase of accretion rate during the outburst of AG Dra leads to the increase of stellar wind from the red dwarf surface and the decrease of it's effective temperature. The hot component of AG Dra may also be considered as a white Dwarf with luminosity L 3 L sun and R eff >or approx. 0.2 R sun . In this case gravitational energy of accreting matter M > or ∼ 10 -6 M sun / year would be the source of the hot component outbursts. The luminosity between outbursts is determined by energy generation from the burning hydrogen layer source

  7. Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars

    Science.gov (United States)

    Jones, M. I.; Jenkins, J. S.; Brahm, R.; Wittenmyer, R. A.; Olivares E., F.; Melo, C. H. F.; Rojo, P.; Jordán, A.; Drass, H.; Butler, R. P.; Wang, L.

    2016-05-01

    Context. Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets. In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. Aims: During the past six years we have conducted a radial velocity follow-up program of 166 giant stars to detect substellar companions and to characterize their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. Methods: We took multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we computed precision radial velocities and derived atmospheric and physical parameters. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we detected the presence of several substellar companions. Results: We present four new planetary systems around the giant stars HIP 8541, HIP 74890, HIP 84056, and HIP 95124. Additionally, we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5-5.9% around stars with [Fe/H] ~ 0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆ ~ 1.0 and 2.1 M⊙, with a maximum of f = 13.0+10.1-4.2% at M⋆ = 2.1 M⊙. Conclusions: We conclude that giant planets are preferentially formed around metal-rich stars. In addition, we conclude that they are more efficiently formed around more massive stars, in the stellar mass range of ~1.0-2.1 M⊙. These observational results confirm previous findings for solar

  8. Stable numerical method in computation of stellar evolution

    International Nuclear Information System (INIS)

    Sugimoto, Daiichiro; Eriguchi, Yoshiharu; Nomoto, Ken-ichi.

    1982-01-01

    To compute the stellar structure and evolution in different stages, such as (1) red-giant stars in which the density and density gradient change over quite wide ranges, (2) rapid evolution with neutrino loss or unstable nuclear flashes, (3) hydrodynamical stages of star formation or supernova explosion, (4) transition phases from quasi-static to dynamical evolutions, (5) mass-accreting or losing stars in binary-star systems, and (6) evolution of stellar core whose mass is increasing by shell burning or decreasing by penetration of convective envelope into the core, we face ''multi-timescale problems'' which can neither be treated by simple-minded explicit scheme nor implicit one. This problem has been resolved by three prescriptions; one by introducing the hybrid scheme suitable for the multi-timescale problems of quasi-static evolution with heat transport, another by introducing also the hybrid scheme suitable for the multi-timescale problems of hydrodynamic evolution, and the other by introducing the Eulerian or, in other words, the mass fraction coordinate for evolution with changing mass. When all of them are combined in a single computer code, we can compute numerically stably any phase of stellar evolution including transition phases, as far as the star is spherically symmetric. (author)

  9. Synthetic Stromgren photometry for F dwarf stars

    Science.gov (United States)

    Bell, R. A.

    1988-01-01

    Recent synthetic spectrum and color calculations for cool dwarf star models are tested by comparison with observation. The accuracy of the computed dependence of the thermal colors B-V and b-y on effective temperature is examined, and H-beta indices are presented and compared with observed values. The accuracy of the predictions of the Stromgren uvby system metal-abundance indicator m1 and luminosity indicator c1 are tested. A new calibration of the c1, b-y diagram in terms of absolute magnitudes is given, making use of recent calculations of stellar isochrones. Observations of very metal-poor subdwarfs are used to study the accuracy of the isochrones. The c1, b-y diagram of the subdwarfs is compared with that of the turnoff-region stars in the very metal-poor globular cluster NGC 6397.

  10. Investigating the Magnetospheres of Rapidly Rotating B-type Stars

    Science.gov (United States)

    Fletcher, C. L.; Petit, V.; Nazé, Y.; Wade, G. A.; Townsend, R. H.; Owocki, S. P.; Cohen, D. H.; David-Uraz, A.; Shultz, M.

    2017-11-01

    Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

  11. Radio stars observed in the LAMOST spectral survey

    Science.gov (United States)

    Zhang, Li-Yun; Yue, Qiang; Lu, Hong-Peng; Han, Xian-Ming L.; Zhang, Yong; Shi, Jian-Rong; Wang, Yue-Fei; Hou, Yong-Hui; Zi-Huang, Cao

    2017-09-01

    Radio stars have attracted astronomers’ attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra, such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2 (DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5‧‧ and LAMOST objects classified as stars. We calculated the equivalent widths (EWs) of the Ca ii H&K, Hδ, Hγ, Hβ, Hα and Ca ii IRT lines by integrating the line profiles. Using the EWs of the Hα line, we detected 147 active stellar spectra of 89 objects having emissions above the Hα continuum. There were also 36 objects with repeated spectra, 28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca ii IRT lines. The low value of the EW8542/EW8498 ratio for these 14 radio stars possibly alludes to chromospheric plage regions.

  12. The structure of the nuclear stellar cluster of the Milky Way

    International Nuclear Information System (INIS)

    Schoedel, Rainer; Eckart, Andreas

    2006-01-01

    The structure of the nuclear stellar cluster of the Milky Way is of particular interest because it is the densest stellar cluster in our Galaxy, where the theoretical prediction of the formation of a stellar cusp around the central supermassive black hole, Sagittarius A* (Sgr A*) can be examined. We present high-resolution adaptive optics observations with multiple intermediate band liters of the inner ∼20'' around Sgr A*. From the images, stellar number counts and a detailed map of the interstellar extinction toward the central 0.5 pc of the Milky Way were determined. The extinction map is consistent with a putative southwest-northeast aligned outfbw from the central arcseconds. An azimuthally averaged, crowding and extinction corrected stellar density profle presents clear evidence for the existence of a stellar cusp around Sgr A*. We show that the profle of the surface brightness density is dominated by the brightest stars in the central arcseconds and is different from the shape of the stellar cluster as inferred from the number counts. Several density peaks found in the cluster may indicate clumping, possibly related to the last epoch of star formation in the Galactic Center. There is evidence for a common proper motion of the stars in one of these clumps

  13. QUANTIFYING KINEMATIC SUBSTRUCTURE IN THE MILKY WAY'S STELLAR HALO

    International Nuclear Information System (INIS)

    Xue Xiangxiang; Zhao Gang; Luo Ali; Rix, Hans-Walter; Bell, Eric F.; Koposov, Sergey E.; Kang, Xi; Liu, Chao; Yanny, Brian; Beers, Timothy C.; Lee, Young Sun; Bullock, James S.; Johnston, Kathryn V.; Morrison, Heather; Rockosi, Constance; Weaver, Benjamin A.

    2011-01-01

    We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative 'close pair distribution' as a statistic in the four-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20 kpc from the Galactic center exhibit stronger substructure than at r gc < 20 kpc.

  14. LIVING WITH A RED DWARF: ROTATION AND X-RAY AND ULTRAVIOLET PROPERTIES OF THE HALO POPULATION KAPTEYN’S STAR

    Energy Technology Data Exchange (ETDEWEB)

    Guinan, Edward F.; Engle, Scott G.; Durbin, Allyn, E-mail: scott.engle@villanova.edu [Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA 19085 (United States)

    2016-04-20

    As part of Villanova’s Living with a Red Dwarf program, we have obtained UV, X-ray, and optical data of the Population II red dwarf—Kapteyn’s Star. Kapteyn’s Star is noteworthy for its large proper motions and high radial velocity of ∼+245 km s{sup −1}. As the nearest Pop II red dwarf, it serves as an old age anchor for calibrating activity/irradiance–rotation–age relations, and an important test bed for stellar dynamos and the resulting X-ray–UV emissions of slowly rotating, near-fully convective red dwarf stars. Adding to the notoriety, Kapteyn’s Star has recently been reported to host two super-Earth candidates, one of which (Kapteyn b) is orbiting within the habitable zone. However, Robertson et al. questioned the planet’s existence since its orbital period may be an artifact of activity, related to the star’s rotation period. Because of its large Doppler-shift, measures of the important, chromospheric H i Lyα 1215.67 Å emission line can be reliably made, because it is mostly displaced from ISM and geo-coronal sources. Lyα emission dominates the FUV region of cool stars. Our measures can help determine the X-ray–UV effects on planets hosted by Kapteyn’s Star, and planets hosted by other old red dwarfs. Stellar X-ray and Lyα emissions have strong influences on the heating and ionization of upper planetary atmospheres and can (with stellar winds and flares) erode or even eliminate planetary atmospheres. Using our program stars, we have reconstructed the past exposures of Kapteyn’s Star's planets to coronal—chromospheric XUV emissions over time.

  15. LIVING WITH A RED DWARF: ROTATION AND X-RAY AND ULTRAVIOLET PROPERTIES OF THE HALO POPULATION KAPTEYN’S STAR

    International Nuclear Information System (INIS)

    Guinan, Edward F.; Engle, Scott G.; Durbin, Allyn

    2016-01-01

    As part of Villanova’s Living with a Red Dwarf program, we have obtained UV, X-ray, and optical data of the Population II red dwarf—Kapteyn’s Star. Kapteyn’s Star is noteworthy for its large proper motions and high radial velocity of ∼+245 km s −1 . As the nearest Pop II red dwarf, it serves as an old age anchor for calibrating activity/irradiance–rotation–age relations, and an important test bed for stellar dynamos and the resulting X-ray–UV emissions of slowly rotating, near-fully convective red dwarf stars. Adding to the notoriety, Kapteyn’s Star has recently been reported to host two super-Earth candidates, one of which (Kapteyn b) is orbiting within the habitable zone. However, Robertson et al. questioned the planet’s existence since its orbital period may be an artifact of activity, related to the star’s rotation period. Because of its large Doppler-shift, measures of the important, chromospheric H i Lyα 1215.67 Å emission line can be reliably made, because it is mostly displaced from ISM and geo-coronal sources. Lyα emission dominates the FUV region of cool stars. Our measures can help determine the X-ray–UV effects on planets hosted by Kapteyn’s Star, and planets hosted by other old red dwarfs. Stellar X-ray and Lyα emissions have strong influences on the heating and ionization of upper planetary atmospheres and can (with stellar winds and flares) erode or even eliminate planetary atmospheres. Using our program stars, we have reconstructed the past exposures of Kapteyn’s Star's planets to coronal—chromospheric XUV emissions over time

  16. Stellar Relics from the Early Galaxy T. Sivarani

    Indian Academy of Sciences (India)

    metal-poor stars is used to study the chemical history of the galaxy. Apart from this,. 5 .... They fit a color-magnitude diagram in order to trace different stellar population and derived a ... distinctly different stellar population with a different origin.

  17. Dynamical evolution of clusters with two stellar groups

    Energy Technology Data Exchange (ETDEWEB)

    Angeletti, L; Giannone, P. (Rome Univ. (Italy))

    1977-08-01

    The generalization of the fluid-dynamical approach from one-component star clusters to clusters with several stellar groups (as far as the star masses are concerned) has been applied to the study of two-component clusters. Rather extreme values of stellar masses and masses of groups were chosen in order to emphasize the different dynamical evolutions and asymptotic behaviors. Escape of stars from clusters and the problem of equipartition of kinetic energy among the two star groups are discussed. Comparisons of the main features of the results with those obtained by other authors have shown a good agreement. Some characteristic properties of the last computed models with an age of 18x10/sup 9/ yr have been pointed out and discussed in relation with some observed features of galactic globular clusters.

  18. Wimps and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.; Salati, P.

    1988-01-01

    We present the results of an analytic approximation to compute the effects of WIMPs on stellar structures in a self-consistent way. We examine in particular the case of the Sun and of horizontal branch stars

  19. TESTING THE ASTEROSEISMIC MASS SCALE USING METAL-POOR STARS CHARACTERIZED WITH APOGEE AND KEPLER

    Energy Technology Data Exchange (ETDEWEB)

    Epstein, Courtney R.; Johnson, Jennifer A.; Tayar, Jamie; Pinsonneault, Marc [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Elsworth, Yvonne P.; Chaplin, William J. [School of Physics and Astronomy, University of Birmingham, Edgbaston Park Road, West Midlands, Birmingham B15 2TT (United Kingdom); Shetrone, Matthew [McDonald Observatory, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Mosser, Benoît [LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, F-92195 Meudon Cedex (France); Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106-7215 (United States); Silva Aguirre, Víctor [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719, USA and JINA: Joint Institute for Nuclear Astrophysics (United States); Bizyaev, Dmitry [Apache Point Observatory, Sunspot, NM 88349 (United States); Bedding, Timothy R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); García, Rafael A. [Laboratoire AIM, CEA/DSM-CNRS, Universit Paris 7 Diderot, IRFU/SAp, Centre de Saclay, F-91191, Gif-sur-Yvette (France); Pérez, Ana E. García; Hearty, Fred R., E-mail: epstein@astronomy.ohio-state.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2014-04-20

    Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher (<ΔM > =0.17 ± 0.05 M {sub ☉}) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M {sub ☉} level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of ∼100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations.

  20. Stellar Sources of Gamma-ray Bursts

    OpenAIRE

    Luchkov, B. I.

    2011-01-01

    Correlation analysis of Swift gamma-ray burst coordinates and nearby star locations (catalog Gliese) reveals 4 coincidences with good angular accuracy. The random probability is 4\\times 10^{-5}, so evidencing that coincident stars are indeed gamma-ray burst sources. Some additional search of stellar gamma-ray bursts is discussed.