WorldWideScience

Sample records for cool stars stellar

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

    International Nuclear Information System (INIS)

    Wünsch, R.; Palouš, J.; Ehlerová, S.; Tenorio-Tagle, G.

    2017-01-01

    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 7 M ⊙ 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 he , and the mass loading, η ml . The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η he ≲ 10%, which is suggested by the observations. Furthermore, for low η 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. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    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.

  3. Photometric Amplitude Distribution of Stellar Rotation of KOIs—Indication for Spin-Orbit Alignment of Cool Stars and High Obliquity for Hot Stars

    Science.gov (United States)

    Mazeh, Tsevi; Perets, Hagai B.; McQuillan, Amy; Goldstein, Eyal S.

    2015-03-01

    The observed amplitude of the rotational photometric modulation of a star with spots should depend on the inclination of its rotational axis relative to our line of sight. Therefore, the distribution of observed rotational amplitudes of a large sample of stars depends on the distribution of their projected axes of rotation. Thus, comparison of the stellar rotational amplitudes of the Kepler objects of interest (KOIs) with those of Kepler single stars can provide a measure to indirectly infer the properties of the spin-orbit obliquity of Kepler planets. We apply this technique to the large samples of 993 KOIs and 33,614 single Kepler stars in temperature range of 3500-6500 K. We find with high significance that the amplitudes of cool KOIs are larger, on the order of 10%, than those of the single stars. In contrast, the amplitudes of hot KOIs are systematically lower. After correcting for an observational bias, we estimate that the amplitudes of the hot KOIs are smaller than the single stars by about the same factor of 10%. The border line between the relatively larger and smaller amplitudes, relative to the amplitudes of the single stars, occurs at about 6000 K. Our results suggest that the cool stars have their planets aligned with their stellar rotation, while the planets around hot stars have large obliquities, consistent with the findings of Winn et al. and Albrecht et al. We show that the low obliquity of the planets around cool stars extends up to at least 50 days, a feature that is not expected in the framework of a model that assumes the low obliquity is due to planet-star tidal realignment.

  4. Cool stars: spectral library of high-resolution echelle spectra and database of stellar parameters

    Science.gov (United States)

    Montes, D.

    2013-05-01

    During the last years our group have undertake several high resolution spectroscopic surveys of nearby FGKM stars with different spectrographs (FOCES, SARG, SOFIN, FIES, HERMES). A large number of stars have been already observed and we have already determined spectral types, rotational velocities as well as radial velocities, Lithium abundance and several chromospheric activity indicators. We are working now in a homogeneous determination of the fundamental stellar parameters (T_{eff}, log{g}, ξ and [Fe/H]) and chemical abundances of many elements of all these stars. Some fully reduced spectra in FITS format have been available via ftp and in the {http://www.ucm.es/info/Astrof/invest/actividad/spectra.html}{Worl Wide Web} (Montes et al. 1997, A&AS, 123, 473; Montes et al. 1998, A&AS, 128, 485; and Montes et al. 1999, ApJS, 123, 283) and some particular spectral regions of the echelle spectra are available at VizieR by López-Santiago et al. 2010, A&A, 514, A97. We are now working in made accessible all the spectra of our different surveys in a Virtual Observatory ({http://svo.cab.inta-csic.es/}{VO}) compliant library and database accessible using a common web interface following the standards of the International Virtual Observatory Alliance ({http://www.ivoa.net/}{IVOA}). The spectral library includes 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 40000 to 80000. The database will provide in addition the stellar parameters determined for these spectra using {http://cdsads.u-strasbg.fr/abs/2012arXiv1205.4879T}{StePar} (Tabernero et al. 2012, A&A, 547, A13).

  5. Cool WISPs for stellar cooling excesses

    Energy Technology Data Exchange (ETDEWEB)

    Giannotti, Maurizio [Barry Univ., Miami Shores, FL (United States). Physical Sciences; Irastorza, Igor [Zaragoza Univ. (Spain). Dept. de Fisica Teorica; Redondo, Javier [Zaragoza Univ. (Spain). Dept. de Fisica Teorica; Max-Planck-Institut fuer Physik, Muenchen (Germany); Ringwald, Andreas [DESY Hamburg (Germany). Theory Group

    2015-12-15

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a preference for a mild 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 represents the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO.

  6. Chromospheres of Luminous Cool Stars

    Science.gov (United States)

    Dupree, A. K.

    Direct ultraviolet imaging and spectroscopy of Alpha Orionis (Betelgeuse) reveals variable chromospheric structures and mass motions. Spectroscopy also demonstrates the changes of wind opacity, speeds, and mass loss in luminous stars. Cool stars have complex chromospheres that need to be considered in construction of stellar atmospheric models and subsequent spectral analyses.

  7. Investigation of stellar magnetic fields based on the strengths of spectral lines - Application to Omicron Pegasi and Cool AP Stars

    Science.gov (United States)

    Takeda, Yoichi

    1993-06-01

    A practical method for simultaneous determinations of H (magnetic field) and xi (microturbulence) in a stellar atmosphere is presented, which is based on the requirement that the scatter of the abundances derived from individual lines should be minimized for the best choice of H and xi. This procedure may be regarded as being an improved and extended version of the classical Hensberge-De Loore method, since it is based on a 'fine analysis' technique using a model atmosphere and the detailed Zeeman-split components of a line are explicitly taken into account with an approximate treatment of the polarization effect. This method was first applied to the hot Am star O Peg, resulting in H = 2 kG (and xi is about 1.5 km/s); this H value is fairly consistent with other estimates based either on the Stenflo-Lindegren technique or on the line-pair method. As an alternative application, surface magnetic fields of five cool Ap stars were also investigated, showing that the H-values by this method agree well with those derived from the method of differential Zeeman broadening and that the classical Hensberge-De Loore technique tends to yield somewhat underestimated values.

  8. 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

  9. 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...

  10. A survey of stellar X-ray flares from the XMM-Newton serendipitous source catalogue: HIPPARCOS-Tycho cool stars

    Science.gov (United States)

    Pye, J. P.; Rosen, S.; Fyfe, D.; Schröder, A. C.

    2015-09-01

    Context. The X-ray emission from flares on cool (i.e. spectral-type F-M) stars is indicative of very energetic, transient phenomena, associated with energy release via magnetic reconnection. Aims: We present a uniform, large-scale survey of X-ray flare emission. The XMM-Newton Serendipitous Source Catalogue and its associated data products provide an excellent basis for a comprehensive and sensitive survey of stellar flares - both from targeted active stars and from those observed serendipitously in the half-degree diameter field-of-view of each observation. Methods: The 2XMM Catalogue and the associated time-series ("light-curve") data products have been used as the basis for a survey of X-ray flares from cool stars in the Hipparcos-Tycho-2 catalogue. In addition, we have generated and analysed spectrally-resolved (i.e. hardness-ratio), X-ray light-curves. Where available, we have compared XMM OM UV/optical data with the X-ray light-curves. Results: Our sample contains ~130 flares with well-observed profiles; they originate from ~70 stars. The flares range in duration from ~103 to ~104 s, have peak X-ray fluxes from ~10-13 to ~10-11erg cm-2 s-1, peak X-ray luminosities from ~1029 to ~1032erg s-1, and X-ray energy output from ~1032 to ~1035 erg. Most of the ~30 serendipitously-observed stars have little previously reported information. The hardness-ratio plots clearly illustrate the spectral (and hence inferred temperature) variations characteristic of many flares, and provide an easily accessible overview of the data. We present flare frequency distributions from both target and serendipitous observations. The latter provide an unbiased (with respect to stellar activity) study of flare energetics; in addition, they allow us to predict numbers of stellar flares that may be detected in future X-ray wide-field surveys. The serendipitous sample demonstrates the need for care when calculating flaring rates, especially when normalising the number of flares to a total

  11. 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.

  12. High resolution interferometry of cool stars

    Science.gov (United States)

    Lambert, D. L.

    1974-01-01

    A description is given of results obtained in a program of infrared high resolution spectroscopy of cool stars. The nature of infrared stellar spectra is considered along with questions regarding astrophysics and stellar infrared spectroscopy. An abundance analysis for alpha Ori (Betelgeuse) is conducted. The C-12/C-13 abundance ratio is examined and attention is given to the O-16/O-18 and O-16/O-17 abundance ratios. M stars and SiO vibration-rotation bands are discussed and questions regarding the characteristics of the molecular hydrogen quadrupole vibration-rotation lines are explored.

  13. Hot Jupiters and cool stars

    Energy Technology Data Exchange (ETDEWEB)

    Villaver, Eva; Mustill, Alexander J. [Department of Theoretical Physics, Universidad Autónoma de Madrid, Módulo 8, 28049 Madrid (Spain); Livio, Mario [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Siess, Lionel, E-mail: eva.villaver@uam.es [Institut d' Astronomie et d' Astrophysique, Université Libre de Bruxelles, B-1050 Bruxelles (Belgium)

    2014-10-10

    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 {sub ☉}), 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.

  14. 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.)

  15. 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.

  16. Sun-like stars unlike the Sun: Clues for chemical anomalies of cool stars

    OpenAIRE

    Adibekyan, V.; Delgado-Mena, E.; Feltzing, S.; Hernández, J. I. González; Hinkel, N. R.; Korn, A. J.; Asplund, M.; Beck, P. G.; Deal, M.; Gustafsson, B.; Honda, S.; Lind, K.; Nissen, P. E.; Spina, L.

    2017-01-01

    We present a summary of the splinter session "Sun-like stars unlike the Sun" that was held on 09 June 2016 as part of the Cool Stars 19 conference (Uppsala, Sweden). We discussed the main limitations (in the theory and observations) in the derivation of very precise stellar parameters and chemical abundances of Sun-like stars. We outlined and discussed the most important and most debated processes that can produce chemical peculiarities in solar-type stars. Finally, in an open discussion betw...

  17. 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.

  18. Stellar Atmospheres, Atmospheric Extension, and Fundamental Parameters: Weighing Stars Using the Stellar Mass Index

    Science.gov (United States)

    Neilson, Hilding R.; Baron, Fabien; Norris, Ryan; Kloppenborg, Brian; Lester, John B.

    2016-10-01

    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. 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.

  20. 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.

  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. Stars and singularities: Stellar phenomena near a massive black hole

    OpenAIRE

    Alexander, Tal

    2002-01-01

    This is a pedagogical review of recent results on the interactions of central massive black holes with stars very near them, focused on the black hole in the center of the Milky Way. Table of contents: [1] Introduction [2] Stellar dynamics near a black hole [2.1] Physical scales [2.2] A relaxed stellar system around a MBH [3] The stellar collider in the Galactic Center [3.1] The case for a dense stellar cusp in the Galactic Center [3.2] Tidal spin-up [3.3] Tidal scattering [4] The gravitation...

  3. 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.

  4. 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.

  5. Neutron star cooling: effects of envelope physics

    International Nuclear Information System (INIS)

    Van Riper, K.A.

    1982-01-01

    Neutron star cooling calculations are reported which employ improved physics in the calculation of the temperature drop through the atmosphere. The atmosphere microphysics is discussed briefly. The predicted neutron star surface temperatures, in the interesting interval 200 less than or equal to t (yr) less than or equal to 10 5 , do not differ appreciably from the earlier results of Van Riper and Lamb (1981) for a non-magnetic star; for a magnetic star, the surface temperature is lower than in the previous work. Comparison with observational limits show that an exotic cooling mechanism, such as neutrino emission from a pion condensate or in the presence of percolating quarks, is not required unless the existence of a neutron star in the Tycho or SN1006 SNRs is established

  6. High-velocity stars from decay of small stellar systems

    Science.gov (United States)

    Kiseleva, L. G.; Colin, J.; Dauphole, B.; Eggleton, P.

    1998-12-01

    In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s^-1. These numerical experiments confirm that small N-body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s^-1 is ~1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc.

  7. 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.

  8. 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.

  9. 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.

  10. 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).

  11. Advanced Spectral Library (ASTRAL): Cool stars edition

    Science.gov (United States)

    Ayres, T. R.

    2013-02-01

    ASTRAL is a project to create high-resolution, high-S/N UV (1150-3200 Å) atlases of bright stars utilizing {HST}/STIS. During Cycle 18 (2010-2011), eight cool star targets were observed, including key objects like Procyon and Betelgeuse, churning through 146 orbits in the process. The new spectral atlases are publically available through the project website. Data were obtained with the Hubble Space Telescope.

  12. 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.

  13. Multicomponent stellar wind from hot subdwarfs stars

    Czech Academy of Sciences Publication Activity Database

    Votruba, Viktor; Feldmeier, A.; Krtička, J.; Kubát, Jiří

    2010-01-01

    Roč. 329, 1-2 (2010), s. 159-161 ISSN 0004-640X R&D Projects: GA ČR GP205/09/P476 Institutional research plan: CEZ:AV0Z10030501 Keywords : stellar wind * hot subdwarfs * decoupling Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.437, year: 2010

  14. 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

  15. 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.

  16. 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.

  17. 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

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

    Science.gov (United States)

    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

    2013-09-01

    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.

  19. 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

  20. 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.

  1. CHLORINE ABUNDANCES IN COOL STARS

    Energy Technology Data Exchange (ETDEWEB)

    Maas, Z. G.; Pilachowski, C. A. [Indiana University Bloomington, Astronomy Department, Swain West 319, 727 East Third Street, Bloomington, IN 47405-7105 (United States); Hinkle, K., E-mail: zmaas@indiana.edu, E-mail: cpilacho@indiana.edu, E-mail: hinkle@noao.edu [National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States)

    2016-12-01

    Chlorine abundances are reported in 15 evolved giants and 1 M dwarf in the solar neighborhood. The Cl abundance was measured using the vibration-rotation 1-0 P8 line of H{sup 35}Cl at 3.69851 μ m. The high-resolution L -band spectra were observed using the Phoenix infrared spectrometer on the Kitt Peak Mayall 4 m telescope. The average [{sup 35}Cl/Fe] abundance in stars with −0.72 < [Fe/H] < 0.20 is [{sup 35}Cl/Fe] = (−0.10 ± 0.15) dex. The mean difference between the [{sup 35}Cl/Fe] ratios measured in our stars and chemical evolution model values is (0.16 ± 0.15) dex. The [{sup 35}Cl/Ca] ratio has an offset of ∼0.35 dex above model predictions, suggesting that chemical evolution models are underproducing Cl at the high metallicity range. Abundances of C, N, O, Si, and Ca were also measured in our spectral region and are consistent with F and G dwarfs. The Cl versus O abundances from our sample match Cl abundances measured in planetary nebula and H ii regions. In one star where both H{sup 35}Cl and H{sup 37}Cl could be measured, a {sup 35}Cl/{sup 37}Cl isotope ratio of 2.2 ± 0.4 was found, consistent with values found in the Galactic ISM and predicted chemical evolution models.

  2. Stars defy theories of stellar matter

    CERN Multimedia

    2002-01-01

    Two bizarre objects called RXJ1856 and 3C58, found by an orbiting X-ray telescope may represent a new class of star and may contain a new form of matter, defying current particle physics theories (1/2 page).

  3. Stellar wind models of subluminous hot stars

    Czech Academy of Sciences Publication Activity Database

    Krtička, J.; Kubát, Jiří; Krtičková, I.

    2016-01-01

    Roč. 593, September (2016), A101/1-A101/14 ISSN 0004-6361 R&D Projects: GA ČR GA13-10589S Grant - others:GA MŠk(CZ) LM2010005 Institutional support: RVO:67985815 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  4. Stellar Content and Star Formation Histories

    OpenAIRE

    Tosi, M.

    1993-01-01

    The evolution of irregular galaxies is examined from two points of view: on the one hand, models of galactic chemical evolution have been computed and their predictions compared with the corresponding observational data on the element abundances, and on the other hand, the results of a new method to derive the star formation history in the last 1 Gyr in nearby irregulars are presented.

  5. 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.

  6. 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.

  7. 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.

  8. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    International Nuclear Information System (INIS)

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-01-01

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10 4 K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  9. Connection between nonradial pulsations and stellar winds in massive stars. IV. Atmospheric structure and mass loss from pulsation with speculative application to B and Be stars

    International Nuclear Information System (INIS)

    Willson, L.A.

    1986-01-01

    Pulsation produces alterations in the density structure of a stellar atmosphere, and it drives or enhances mass loss. A summary is provided of some very general results which were obtained on the basis of an analysis of models calculated by Bowen (1985) for the atmospheres of radially pulsating cool stars. It is pointed out that four parameters are needed to characterize the structure of the atmosphere of a pulsating star, if simplifying assumptions are made regarding isothermal conditions with respect to shocks and the global temperature distribution. Some possible implications of the nonradial pulsations observed in B and Be stars for the structure of their atmospheres are discussed. Attention is given to the stellar wind, and applications to B and Be stars. 9 references

  10. A spin-down clock for cool stars from observations of a 2.5-billion-year-old cluster.

    Science.gov (United States)

    Meibom, Søren; Barnes, Sydney A; Platais, Imants; Gilliland, Ronald L; Latham, David W; Mathieu, Robert D

    2015-01-29

    The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult to derive because traditional dating methods use stellar properties that either change little as the stars age or are hard to measure. The rotation rates of all cool stars decrease substantially with time as the stars steadily lose their angular momenta. If properly calibrated, rotation therefore can act as a reliable determinant of their ages based on the method of gyrochronology. To calibrate gyrochronology, the relationship between rotation period and age must be determined for cool stars of different masses, which is best accomplished with rotation period measurements for stars in clusters with well-known ages. Hitherto, such measurements have been possible only in clusters with ages of less than about one billion years, and gyrochronology ages for older stars have been inferred from model predictions. Here we report rotation period measurements for 30 cool stars in the 2.5-billion-year-old cluster NGC 6819. The periods reveal a well-defined relationship between rotation period and stellar mass at the cluster age, suggesting that ages with a precision of order 10 per cent can be derived for large numbers of cool Galactic field stars.

  11. 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

  12. 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

  13. 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.

  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. Discovery of Fluorine in Cool Extreme Helium Stars

    OpenAIRE

    Pandey, Gajendra

    2006-01-01

    Neutral fluorine (F I) lines are identified in the optical spectra of cool EHe stars. These are the first identification of F I lines in a star's spectrum, and provide the first measurement of fluorine abundances in EHe stars. The results show that fluorine is overabundant in EHe stars. The overabundance of fluorine provides evidence for the synthesis of fluorine in these stars, that is discussed in the light of asymptotic giant branch (AGB) evolution, and the expectation from accretion of an...

  16. 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

  17. Determination of the spectroscopic stellar parameters for 257 field giant stars

    OpenAIRE

    Alves, S.; Benamati, L.; Santos, N. C.; Adibekyan, V. Zh.; Sousa, S. G.; Israelian, G.; De Medeiros, J. R.; Lovis, C.; Udry, S.

    2015-01-01

    The study of stellar parameters of planet-hosting stars, such as metallicity and chemical abundances, help us to understand the theory of planet formation and stellar evolution. Here, we present a catalogue of accurate stellar atmospheric parameters and iron abundances for a sample of 257 K and G field evolved stars that are being surveyed for planets using precise radial--velocity measurements as part of the CORALIE programme to search for planets around giants. The analysis was done using a...

  18. 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.

  19. Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres : numerical methods and application to the quiet, non-magnetic, surface of a solar-type star

    NARCIS (Netherlands)

    Hayek, W.; Asplund, M.; Carlsson, M.; Trampedach, R.; Collet, R.; Gudiksen, B.V.; Hansteen, V.H.; Leenaarts, J.|info:eu-repo/dai/nl/304837946

    2010-01-01

    Aims. We present the implementation of a radiative transfer solver with coherent scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD) simulations of stellar surface convection. The code is fully parallelized using MPI domain decomposition, which allows for large grid sizes

  20. rhapsody-g simulations - I. The cool cores, hot gas and stellar content of massive galaxy clusters

    Science.gov (United States)

    Hahn, Oliver; Martizzi, Davide; Wu, Hao-Yi; Evrard, August E.; Teyssier, Romain; Wechsler, Risa H.

    2017-09-01

    We present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the Mvir ˜ 1015 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 M500-Y500 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. 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.

  1. STELLAR 'EGGS' EMERGE FROM MOLECULAR CLOUD (Star-Birth Clouds in M16)

    Science.gov (United States)

    2002-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation'. As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules'. The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 6,500 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo:

  2. Combined stellar evolution and atmospheric modeling of massive stars: implications for how stars evolve and die

    Science.gov (United States)

    Groh, Jose

    2015-08-01

    Our big picture of stellar evolution and the links between the different classes of massive stars is often built by comparing evolutionary models and observations. However, this comparison is far from trivial, in particular when the effects of mass loss are significant. To tackle this problem, we recently combined stellar evolution calculations using the Geneva code with atmospheric/wind CMFGEN modeling. For the first time, we determined the interior and spectroscopic evolution of massive stars from the zero-age main sequence to the pre-supernova stage. In this talk, I will discuss the spectroscopic evolution of massive stars at solar metallicity, the lifetimes of the different spectroscopic phases (e.g. O-type, RSG, BSG, LBV, WR), and how they are related to evolutionary phases (H-core burning, H-shell burning, He-core burning). I will also show how this is affected by mass loss at different stages of the evolution and the implications for our understanding of massive star evolution and death.

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

    International Nuclear Information System (INIS)

    Levesque, Emily M.; Leitherer, Claus

    2013-01-01

    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 6 M ☉ instantaneous burst and a continuous star formation rate of 1 M ☉ yr –1 ), and two different treatments of initial rotation rate (v rot = 0.0v crit and 0.4v 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.

  4. 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.

  5. 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.

  6. 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.

  7. Stellar evolution on the borderline of white dwarf and neutron star formation

    NARCIS (Netherlands)

    Poelarends, A.J.T.

    2007-01-01

    This thesis is about the evolution of stars, specifically about the final fate of stars at the borderline between the formation of white dwarfs and neutron stars. It is well known that the mass and the metallicity are the two determining factors in stellar evolution, and for a given initial chemical

  8. Cosmic reionization by stellar sources: Population II stars

    Science.gov (United States)

    Sokasian, Aaron; Abel, Tom; Hernquist, Lars; Springel, Volker

    2003-09-01

    We study the reionization of the Universe by stellar sources using a numerical approach that combines fast 3D radiative transfer calculations with high-resolution hydrodynamical simulations. By supplementing a one-step radiative transfer code specifically designed for following ionization processes with an adaptive ray-tracing algorithm, we are able to speed up the calculations significantly to the point where handling a vast number of sources becomes technically feasible. This allows us to study how dim low-mass sources, excluded in previous investigations owing to computational limitations, affect the morphological evolution of the reionization process. Ionizing fluxes for the sources are derived from intrinsic star formation rates computed in the underlying hydrodynamical simulations. Analysis of numerically converged results for star formation rates and halo mass functions allows us to assess the consequences of not including low-mass objects and enables us to correct for resolution effects. With these corrections, we are able to reduce the effective mass resolution limit for sources to M~ 4.0 × 107h-1 Msolar in a 10 h-1 Mpc comoving box. Our calculations reveal that the process by which ionized regions in the intergalactic medium (IGM) percolate is complex and is especially sensitive to the inclusion of dim sources. Moreover, we find that, given the same level of cosmic star formation, the number of ionizing photons required to reionize the Universe is significantly overestimated if sources with masses below ~109h-1 Msolar are excluded. This result stems from the fact that low-mass sources preferentially reside in less clumpy environments than their massive counterparts. Consequently, their exclusion has the net effect of concentrating more of the cosmic ionizing radiation in regions which have higher recombination rates. We present the results of our reionization simulation assuming a range of escape fractions for ionizing photons and make statistical

  9. Star-formation and stellar feedback recipes in galaxy evolution models

    Science.gov (United States)

    Hensler, Gerhard; Recchi, Simone; Ploeckinger, Sylvia; Kuehtreiber, Matthias; Steyrleithner, Patrick; Liu, Lei

    2015-08-01

    Modeling galaxy formation and evolution is critically depending on star formation (SF). Since cosmological and galaxy-scale simulations cannot resolve the spatial and density scales on which SF acts, a large variety of methods are developed and applied over the last decades. Nonetheless, we are still in the test phase how the choice of parameters affects the models and how they agree with observations.As a simple ansatz, recipes are based on power-law SF dependences on gas density as justified by gas cooling and collapse timescales. In order to prevent SF spread throughout the gas, temperature and density thresholds are also used, although gas dynamical effects, like e.g. gas infall, seem to trigger SF significantly.The formed stars influence their environment immediately by energetic and materialistic feedback. It has been experienced in numerical models that supernova typeII explosions act with a too long time delay to regulate the SF, but that winds and ionizing radiation by massive stars must be included. The implementation of feedback processes, their efficiencies and timescales, is still in an experimental state, because they depend also on the physical state of the surrounding interstellar medium (ISM).Combining a SF-gas density relation with stellar heating vs. gas cooling and taking the temperature dependence into account, we have derived an analytical expression of self-regulated SF which is free of arbitrary parameters. We have performed numerical models to study this recipe and different widely used SF criteria in both, particle and grid codes. Moreover, we compare the SF behavior between single-gas phase and multi-phase treatments of the ISM.Since dwarf galaxies (DGs) are most sensitive to environmental influences and contain only low SF rates, we explore two main affects on their models: 1. For external effects we compare SF rates of isolated and ram-pressure suffering DGs. Moreover, we find a SF enhancement in tidal-tail DGs by the compressive tidal

  10. WIMP Annihilation and Cooling of Neutron Stars

    DEFF Research Database (Denmark)

    Kouvaris, Christoforos

    2007-01-01

    We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars, might affect the temperature of stars older than 10 million years, flattening out the temperature at $\\sim 10^4$ K for a typical...

  11. 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.

  12. 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.

  13. 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.

  14. 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:

  15. Cooling of Compact Stars with Nucleon Superfluidity and Quark Superconductivity

    Science.gov (United States)

    Noda, Tsuneo; Hashimoto, Masa-aki; Yasutake, Nobutoshi; Maruyama, Toshiki; Tatsumi, Toshitaka

    We show a cooling scenario of compact stars to satisfy recent observations of compact stars. The central density of compact stars can exceed the nuclear density, and it is considered that many hadronic phases appear at such a density. It is discussed that neutron superfluidity (1S0 for lower density, and 3P2 for higher density) and proton superfluidity/superconductivity (1S0) appears in all compact stars. And some "Exotic" states are considered to appear in compact stars, such as meson condensation, hyperon mixing, deconfinement of quarks and quark colour superconductivity. These exotic states appear at the density region above the threshold densities of each state. We demonstrate the thermal evolution of isolated compact stars, adopting the effects of nucleon superfluidity and quark colour superconductivity. We assume large gap energy (Δ > 10 MeV) for colour superconducting quark phase, and include the effects of nucleon superfluidity with parametrised models. We simulate the cooling history of compact stars, and shows that the heavier star does not always cool faster than lighter one, which is determined by the parameters of neutron 3P2 superfluidity.

  16. Strong algorithmic cooling in large star-topology quantum registers

    Science.gov (United States)

    Pande, Varad R.; Bhole, Gaurav; Khurana, Deepak; Mahesh, T. S.

    2017-07-01

    Cooling the qubit into a pure initial state is crucial for realizing fault-tolerant quantum information processing. Here we envisage a star-topology arrangement of reset and computation qubits for this purpose. The reset qubits cool or purify the computation qubit by transferring its entropy to a heat bath with the help of a heat-bath algorithmic cooling procedure. By combining standard NMR methods with powerful quantum control techniques, we cool central qubits of two large star-topology systems, with 13 and 37 spins, respectively. We obtain polarization enhancements by a factor of over 24, and an associated reduction in the spin temperature from 298 K down to 12 K. Exploiting the enhanced polarization of computation qubit, we prepare combination coherences of orders up to 15. By benchmarking the decay of these coherences we investigate the underlying noise process. Further, we also cool a pair of computation qubits and subsequently prepare them in an effective pure state.

  17. Analysis of the structure and dynamics of the stellar tails of open star clusters

    Science.gov (United States)

    Chumak, Ya. O.; Rastorguev, A. S.

    2006-03-01

    We have analyzed the formation, structure, and dynamical evolution of the population of stars that escaped from open clusters by numerical simulations using S. Aarseth’s modified NBODY6 code. In the Galactic tidal field, the population of stars that escaped from a cluster is shown to be elongated along the orbit of the cluster symmetrically about its core in the form of stellar tails of increasing sizes. We analyze the parameters of stellar tails as a function of such initial simulation conditions as the number of stars, the cluster density, the eccentricity of the Galactic cluster orbit in the plane of the Galactic disk, and the z velocity component. As a result, we constructed a grid of model stellar tails of open clusters. The grid includes such time-dependent parameters of the stellar tails as the length, the cross section, the number of stars, the velocity distribution, etc. Our simulations allow us to clarify the origin of moving clusters and stellar streams and to assess the role of star clusters in forming the stellar velocity field in the solar neighborhood.

  18. 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

  19. 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.

  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. General relativistic effects on the cooling of neutron stars

    International Nuclear Information System (INIS)

    Kindl, C.; Straumann, N.

    1981-01-01

    The authors present a discussion of general relativistic effects on the cooling of neutron stars and show analytically that these almost cancel for the dominant neutrino processes and a very stiff equation of state (apart from a trivial redshift of the surface temperature for an observer ''at infinity''). Numerical results for a ''realistic'' equation of state show larger general relativistic corrections. These are, however, still smaller than the uncertainties in the neutrino loss rates. Previous results of cooling curves would thus not be changed significantly by a general relativistic treatment of the thermal properties of neutron stars. (Auth.)

  2. Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

    Science.gov (United States)

    Rab, Ch.; Güdel, M.; Padovani, M.; Kamp, I.; Thi, W.-F.; Woitke, P.; Aresu, G.

    2017-07-01

    Context. Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E ≳ 10 MeV). The particle flux of the contemporary Sun cannot explain these anomalies. However, similar to T Tauri stars the young Sun was more active and probably produced enough high energy particles to explain those anomalies. Aims: We aim to study the interaction of stellar energetic particles with the gas component of the disk (I.e. ionization of molecular hydrogen) and identify possible observational tracers of this interaction. Methods: We used a 2D radiation thermo-chemical protoplanetary disk code to model a disk representative for T Tauri stars. We used a particle energy distribution derived from solar flare observations and an enhanced stellar particle flux proposed for T Tauri stars. For this particle spectrum we calculated the stellar particle ionization rate throughout the disk with an accurate particle transport model. We studied the impact of stellar particles for models with varying X-ray and cosmic-ray ionization rates. Results: We find that stellar particle ionization has a significant impact on the abundances of the common disk ionization tracers HCO+ and N2H+, especially in models with low cosmic-ray ionization rates (e.g. 10-19 s-1 for molecular hydrogen). In contrast to cosmic rays and X-rays, stellar particles cannot reach the midplane of the disk. Therefore molecular ions residing in the disk surface layers are more affected by stellar particle ionization than molecular ions tracing the cold layers and midplane of the disk. Conclusions: Spatially resolved observations of molecular ions tracing different vertical layers of the disk allow to disentangle the contribution of stellar particle ionization from other competing ionization sources. Modelling such observations with a model like the one presented here allows to constrain the stellar particle flux in

  3. THE STELLAR POPULATION AND STAR FORMATION PROPERTIES OF BLUE COMPACT DWARF GALAXIES

    International Nuclear Information System (INIS)

    Zhao Yinghe; Gao Yu; Gu Qiusheng

    2011-01-01

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger (∼10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10 -3 to ∼1 M sun yr -1 , with a median value of ∼0.1 M sun yr -1 . We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  4. Tracing galaxy evolution through resolved stellar populations and star clusters

    NARCIS (Netherlands)

    Silva Villa, E.

    2011-01-01

    Field stars and star clusters contain a big part of the galaxy’s history. To understand galaxy formation and evolution we need then to understand the parts of which galaxies are composed. It has commonly been assumed that most stars formed in clusters. However, the connection between these two

  5. 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

    2018-02-01

    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 disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc onto 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% of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7% of the mass and 5% 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.

  6. Infrared spectroscopy of stars

    Science.gov (United States)

    Merrill, K. M.; Ridgway, S. T.

    1979-01-01

    This paper reviews applications of IR techniques in stellar classification, studies of stellar photospheres, elemental and isotopic abundances, and the nature of remnant and ejected matter in near-circumstellar regions. Qualitative IR spectral classification of cool and hot stars is discussed, along with IR spectra of peculiar composite star systems and of obscured stars, and IR characteristics of stellar populations. The use of IR spectroscopy in theoretical modeling of stellar atmospheres is examined, IR indicators of stellar atmospheric composition are described, and contributions of IR spectroscopy to the study of stellar recycling of interstellar matter are summarized. The future of IR astronomy is also considered.

  7. 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.

  8. Chromospheric structure of cool carbon stars

    Science.gov (United States)

    Luttermoser, Donald G.; Johnson, Hollis R.; Avrett, Eugene H.; Loeser, Rudolf

    1989-01-01

    A semiempirical chromospheric model is proposed for TX Psc which is a prototype for the N-type carbon stars. Observational data imply that the chromospheric temperature rise must begin at a low density, that the temperature gradient in the lower chromosphere must be steep, that partial redistribution must be employed in the Mg II calculation, and that the lower chromosphere is expanding away from the photosphere with a velocity of close to 50 km/s. The present model also shows that the microturbulent velocity is about 7 km/s at the temperature minimum region, dropping to 5 km/s in the chromosphere, and that the Lyman lines are optically thick in the chromosphere.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kane, Stephen R.; Hinkel, Natalie R. [Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132 (United States); Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Horch, Elliott P. [Department of Physics, Southern Connecticut State University, New Haven, CT 06515 (United States); Feng, Ying; Wright, Jason T. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Ciardi, David R. [NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue, Pasadena, CA 91125 (United States); Everett, Mark E. [National Optical Astronomy Observatory, 950 N. Cherry Ave, Tucson, AZ 85719 (United States); Howard, Andrew W., E-mail: skane@sfsu.edu [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

    2014-04-20

    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.

  16. 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.

  17. Diffuse interstellar band at 8620 Å in rave: A new method for detecting the diffuse interstellar band in spectra of cool stars

    Energy Technology Data Exchange (ETDEWEB)

    Kos, J.; Zwitter, T. [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana (Slovenia); Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg (Germany); Bienayme, O.; Siebert, A. [Observatorie astronomique de Strasbourg, Université de Strasbourg, 11 rue de l' Université, F-67000 Strasbourg (France); Binney, J. [Rudolf Peierls Centre for Theoretical Physics, Keble Road, Oxford OX1 3NP (United Kingdom); Bland-Hawthorn, J. [Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2008 (Australia); Freeman, K. C. [Research School of Astronomy and Astrophysics, Australian National University, Canberra (Australia); Gibson, B. K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilmore, G.; Kordopatis, G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Navarro, J. F. [University of Victoria, Victoria, BC V8P 5C2 (Canada); Parker, Q.; Reid, W. A. [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, G. [Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT (United Kingdom); Siviero, A.; Steinmetz, M. [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Watson, F. [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Wyse, R. F. G., E-mail: janez.kos@fmf.uni-lj.si [Johns Hopkins University, Homewood Campus, 3400 North Charles Street, Baltimore, MD 21218 (United States)

    2013-12-01

    Diffuse interstellar bands (DIBs) are usually observed in spectra of hot stars, where interstellar lines are rarely blended with stellar ones. The need for hot stars is a strong limitation in the number of sightlines we can observe and their distribution in the Galaxy, as hot stars are rare and concentrated in the Galactic plane. We are introducing a new method, where interstellar lines can be observed in spectra of cool stars in large spectroscopic surveys. The method is completely automated and does not require prior knowledge of the stellar parameters. The main step is a construction of the stellar spectrum, which is done by finding other observed spectra that lack interstellar features and are otherwise very similar to the spectrum in question. Such spectra are then combined into a single stellar spectrum template, matching the stellar component of the observed spectrum. We demonstrate the performance of this new method on a sample of 482,430 Radial Velocity Experiment survey spectra. However, many spectra have to be combined (48 on average) in order to achieve a signal-to-noise ratio high enough to measure the profile of the DIB at 8620 Å, hence limiting the spatial information about the interstellar medium. We compare its equivalent width with extinction maps and with Bayesian reddening, calculated for individual stars, and provide a linear relation between the equivalent width and reddening. Separately from the introduced method, we calculate equivalent widths of the DIB in spectra of hot stars with known extinction and compare all three linear relations.

  18. Diffuse interstellar band at 8620 Å in rave: A new method for detecting the diffuse interstellar band in spectra of cool stars

    International Nuclear Information System (INIS)

    Kos, J.; Zwitter, T.; Grebel, E. K.; Bienayme, O.; Siebert, A.; Binney, J.; Bland-Hawthorn, J.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Kordopatis, G.; Navarro, J. F.; Parker, Q.; Reid, W. A.; Seabroke, G.; Siviero, A.; Steinmetz, M.; Watson, F.; Wyse, R. F. G.

    2013-01-01

    Diffuse interstellar bands (DIBs) are usually observed in spectra of hot stars, where interstellar lines are rarely blended with stellar ones. The need for hot stars is a strong limitation in the number of sightlines we can observe and their distribution in the Galaxy, as hot stars are rare and concentrated in the Galactic plane. We are introducing a new method, where interstellar lines can be observed in spectra of cool stars in large spectroscopic surveys. The method is completely automated and does not require prior knowledge of the stellar parameters. The main step is a construction of the stellar spectrum, which is done by finding other observed spectra that lack interstellar features and are otherwise very similar to the spectrum in question. Such spectra are then combined into a single stellar spectrum template, matching the stellar component of the observed spectrum. We demonstrate the performance of this new method on a sample of 482,430 Radial Velocity Experiment survey spectra. However, many spectra have to be combined (48 on average) in order to achieve a signal-to-noise ratio high enough to measure the profile of the DIB at 8620 Å, hence limiting the spatial information about the interstellar medium. We compare its equivalent width with extinction maps and with Bayesian reddening, calculated for individual stars, and provide a linear relation between the equivalent width and reddening. Separately from the introduced method, we calculate equivalent widths of the DIB in spectra of hot stars with known extinction and compare all three linear relations.

  19. Hot stars in old stellar populations : a continuing need for intermediate ages

    NARCIS (Netherlands)

    Trager, SC; Worthey, G; Faber, SM; Dressler, A

    2005-01-01

    We investigate the effect of a low-level contamination of hot, old, metal-poor starlight on the inferred stellar populations of early-type galaxies in the core of the Coma Cluster. We find that the required correction to the Balmer and metal absorption-line strengths for old, metal-poor stars does

  20. 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.; 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.

    2018-02-01

    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 spectro-photometric distance code, that can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectro-photometric 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 acommodate different observational datasets, 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 precision (obtained from realistic simulations of an APOGEE+Gaia-like sample) are ≃ 8% in distance, ≃ 20% in age,≃ 6% 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 ≃ [0, 2]% for distances, ≃ [12, 31]% for ages, ≃ [4, 12]% 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.

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

    Science.gov (United States)

    Alonso, E. Díez; 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.

    2018-03-01

    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 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 days. 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.

  2. 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

  3. 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/.

  4. Investigating stellar magnetism (in evolved stars) in Mexico

    Science.gov (United States)

    Sabin, L.; Ramiréz Veléz, J.; Hiriart, D.; Castro Chacón, J. H.; Nuñez, M.; Valdez, J.

    2018-01-01

    We present the latest instrumental and theoretical developments performed at the Universidad Nacional Autónoma de México (UNAM) regarding the search and analysis of magnetic fields in various type of stars among the more evolved ones. This work is the prelude to a wider assessment of magnetism across the Hertzsprung-Russell diagram.

  5. 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.

  6. 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.

  7. The Origin and Evolution of the Galaxy Star Formation Rate-Stellar Mass Correlation

    Science.gov (United States)

    Gawiser, Eric; Iyer, Kartheik

    2018-01-01

    The existence of a tight correlation between galaxies’ star formation rates and stellar masses is far more surprising than usually noted. However, a simple analytical calculation illustrates that the evolution of the normalization of this correlation is driven primarily by the inverse age of the universe, and that the underlying correlation is one between galaxies’ instantaneous star formation rates and their average star formation rates since the Big Bang.Our new Dense Basis method of SED fitting (Iyer & Gawiser 2017, ApJ 838, 127) allows star formation histories (SFHs) to be reconstructed, along with uncertainties, for >10,000 galaxies in the CANDELS and 3D-HST catalogs at 0.5star formation rates, providing new constraints on the level of stochasticity in galaxy formation.

  8. Radio Supernovae: Circum-Stellar Investigation (C.S.I.) of Supernova Progenitor Stars

    Science.gov (United States)

    2009-02-24

    ar X iv :0 90 2. 40 59 v1 [ as tr o- ph .H E ] 2 4 Fe b 20 09 Radio Supernovae : Circum-Stellar Investigation (C.S.I.) of Supernova Progenitor...FEB 2009 2. REPORT TYPE 3. DATES COVERED 00-00-2009 to 00-00-2009 4. TITLE AND SUBTITLE Radio Supernovae : Circum-Stellar Investigation (C.S.I...of Supernova Progenitor Stars 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f

  9. 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 Msoftware 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Matzner, Christopher D.; Jumper, Peter H., E-mail: matzner@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario, M5S 3H4 (Canada)

    2015-12-10

    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.

  11. High-contrast imaging search for stellar and substellar companions of exoplanet host stars

    Science.gov (United States)

    Mugrauer, M.; Ginski, C.

    2015-07-01

    We present the results of our high-contrast imaging survey of close stellar and substellar companions of exoplanet host stars, carried out with the adaptive optics imager NACO at the ESO Paranal observatory, in Chile. In total, 33 exoplanet host stars were observed with NACO in the Ks-band. New comoving companions could be identified close to the stars HD 9578, HD 96167, and HD 142245. The newly detected companions exhibit masses between 0.21 and 0.56 M⊙ and are located at projected separations from their primaries between about 190 and 510 au. In the case of HD 142245, we found evidence that the detected companion is actually a close binary itself with a projected separation of only about 4 au, i.e. HD 142245 might be a hierarchical triple stellar system, which hosts an exoplanet, a new member in the short list of such systems, presently known. In our imaging campaign, a limiting magnitude of Ks = 18.5 mag is reached in average in the background noise limited region around our targets at projected separations beyond about 100 au, which allows the detection of substellar companions with masses down to about 60 MJup. With our NACO observations we can rule out additional stellar companions at projected separations between about 30 and 370 au around the observed exoplanet host stars.

  12. The fundamental stellar parameters of FGK stars in the SEEDS survey Norman, OK 73071, USA

    Science.gov (United States)

    Rich, Evan A.; Wisniewski, John P.; McElwain, Michael W.; Hashimoto, Jun; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Okamoto, Yoshiko K.; Abe, Lyu; Akiyama, Eiji; Brandner, Wolfgang; Brandt, Timothy D.; Cargile, Phillip; Carson, Joseph C.; Currie, Thayne M.; Egner, Sebastian; Feldt, Markus; Fukagawa, Misato; Goto, Miwa; Grady, Carol A.; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Hebb, Leslie; Hełminiak, Krzysztof G.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; Mayama, Satoshi; Miyama, Shoken; Momose, Munetake; Morino, Jun-Ichi; Moro-Martin, Amaya; Nakagawa, Takao; Nishimura, Tetsuo; Oh, Daehyeon; Pyo, Tae-Soo; Schlieder, Joshua; Serabyn, Eugene; Sitko, Michael L.; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Tomono, Daigo; Turner, Edwin L.; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2017-12-01

    Large exoplanet surveys have successfully detected thousands of exoplanets to-date. Utilizing these detections and non-detections to constrain our understanding of the formation and evolution of planetary systems also requires a detailed understanding of the basic properties of their host stars. We have determined the basic stellar properties of F, K and G stars in the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey from Echelle spectra taken at the Apache Point Observatory's 3.5m telescope. Using ROBOSPECT to extract line equivalent widths and Temperature Gravity microtrubulent Velocity ITerations to calculate the fundamental parameters, we have computed Teff, log(g), vt, [Fe/H], chromospheric activity and the age for our sample. Our methodology was calibrated against previously published results for a portion of our sample. The distribution of [Fe/H] in our sample is consistent with that typical of the Solar neighbourhood. Additionally, we find the ages of most of our sample are <500 Myr, but note that we cannot determine robust ages from significantly older stars via chromospheric activity age indicators. The future meta-analysis of the frequency of wide stellar and sub-stellar companions imaged via the SEEDS survey will utilize our results to constrain the occurrence of detected comoving companions with the properties of their host stars.

  13. A Disk of Young Stars at the Galactic Center as Determined by Individual Stellar Orbits

    Science.gov (United States)

    Lu, J. R.; Ghez, A. M.; Hornstein, S. D.; Morris, M. R.; Becklin, E. E.; Matthews, K.

    2009-01-01

    We present new proper motions from the 10 m Keck telescopes for a puzzling population of massive, young stars located within 3farcs5 (0.14 pc) of the supermassive black hole at the Galactic center. Our proper motion measurements have uncertainties of only 0.07 mas yr-1 (3 km s-1), which is gsim 7 times better than previous proper motion measurements for these stars, and enables us to measure accelerations as low as 0.2 mas yr-2 (7 km s-1 yr-1). Using these measurements, line-of-sight velocities from the literature, and three-dimensional velocities for additional young stars in the central parsec, we constrain the true orbit of each individual star and directly test the hypothesis that the massive stars reside in two stellar disks as has been previously proposed. Analysis of the stellar orbits reveals only one of the previously proposed disks of young stars using a method that is capable of detecting disks containing at least seven stars. The detected disk contains 50% of the young stars, is inclined by ~115° from the plane of the sky, and is oriented at a position angle of ~100° east of north. Additionally, the on-disk and off-disk populations have similar K-band luminosity functions and radial distributions that decrease at larger radii as vpropr -2. The disk has an out-of-the-disk velocity dispersion of 28 ± 6 km s-1, which corresponds to a half-opening angle of 7° ± 2°, and several candidate disk members have eccentricities greater than 0.2. Our findings suggest that the young stars may have formed in situ but in a more complex geometry than a simple, thin circular disk.

  14. Stellar Variability of the Exoplanet Hosting Star HD 63454

    OpenAIRE

    {Kane} S.~R.; {Dragomir} D.; {Ciardi} D.~R.; {Lee} J.-W.; {Lo Curto} G.; {Lovis} C.; {Naef} D.; {Mahadevan} S.; {Pilyavsky} G.; {Udry} S.; {Wang} X.; {Wright} J.

    2011-01-01

    Of the hundreds of exoplanets discovered using the radial velocity technique, many are orbiting close to their host stars with periods less than 10 days. One of these, HD 63454, is a young active K dwarf which hosts a Jovian planet in a 2.82 day period orbit. The planet has a 14% transit probability and a predicted transit depth of 1.2%. Here we provide a re-analysis of the radial velocity data to produce an accurate transit ephemeris. We further analyse 8 nights of time series data to search...

  15. 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.

  16. 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.

  17. The Sun as a star: empirical estimates of stellar coronal mass ejection rates and properties

    Science.gov (United States)

    Aarnio, Alicia

    2017-05-01

    Our nearest star provides exquisite, up-close views of the physical processes driving energetic phenomena we observe on stars and cannot yet spatially resolve. Stars provide a statistical ensemble of solar analogs spanning a range of ages representing snapshots along our Sun's full life cycle. In this talk, I will share a project bringing the astronomer's large scale statistical approach to bear on solar data. Combining a decades' worth of solar flare and CME data, we characterize for the first time a relationship between flare and CME properties in order to extend analogy to readily observable stellar flares. We aim to better understand the properties and evolution of magnetic activity on Sun-like stars and exoweather on planets about distant Suns.

  18. 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.

  19. 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.

  20. Combined stellar structure and atmosphere models for massive stars. II. Spectral evolution on the main sequence.

    Science.gov (United States)

    Schaerer, D.; de Koter, A.; Schmutz, W.; Maeder, A.

    1996-08-01

    In Schaerer et al. (1995, Paper I) we have presented the first ``combined stellar structure and atmosphere models'' (CoStar) for massive stars, which consistently treat the entire mass loosing star from the center out to the outer region of the stellar wind. The models use up-to-date input physics and state-of-the-art techniques to model both the stellar interior and the spherically expanding non-LTE atmosphere. The atmosphere models include line blanketing for all elements from hydrogen to zinc. The present publication covers the spectral evolution corresponding to the main sequence interior evolution discussed in Paper I. The CoStar results presented in this paper comprise: (a) flux distributions, from the EUV to the far IR, and the ionizing fluxes in the hydrogen and helium continua, (b) absolute optical and infrared UBVRIJHKLMN photometric magnitudes and UV colors, (c) detailed line blanketed UV spectra, and (d) non-LTE hydrogen and helium line spectra in the optical and IR, including theoretical K band spectra. These results may, e.g., be used for population synthesis models intended to study the massive star content in young starforming regions. We compare our results with other predictions from LTE and non-LTE plane parallel models and point out the improvements and the importance of using adequate atmosphere models including stellar winds for massive stars. Particular emphasis is given to comparisons of the UV spectral evolution with observations, including continuum indices and several metal line signatures of P-Cygni lines and broad absorption features. Good agreement is found for most UV features. In particular, we are able to reproduce the strong observed Fe III 1920A feature in late O and early B giants and supergiants. This feature is found to depend sensitively on temperature and may be used to derive effective temperatures for these stars. We also derive a simple formula to determine mass loss rates from the equivalent width of hydrogen

  1. Evolution of Super Star Cluster Winds with Strong Cooling

    Science.gov (United States)

    Wünsch, Richard; Silich, Sergiy; Palouš, Jan; Tenorio-Tagle, Guillermo; Muñoz-Tuñón, Casiana

    2011-10-01

    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.

  2. 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.

  3. Evolution of the mass, size, and star formation rate in high redshift merging galaxies. MIRAGE - A new sample of simulations with detailed stellar feedback

    Science.gov (United States)

    Perret, V.; Renaud, F.; Epinat, B.; Amram, P.; Bournaud, F.; Contini, T.; Teyssier, R.; Lambert, J.-C.

    2014-02-01

    Context. In Λ-CDM models, galaxies are thought to grow both through continuous cold gas accretion coming from the cosmic web and episodic merger events. The relative importance of these different mechanisms at different cosmic epochs is nevertheless not yet understood well. Aims: We aim to address questions related to galaxy mass assembly through major and minor wet merging processes in the redshift range 1 adaptive mesh-refinement code RAMSES, we build the Merging and Isolated high redshift Adaptive mesh refinement Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized disks simulations, which sample disk orientations and merger masses. Our simulations can reach a physical resolution of 7 parsecs, and include star formation, metal line cooling, metallicity advection, and a recent physically-motivated implementation of stellar feedback that encompasses OB-type stars radiative pressure, photo-ionization heating, and supernovae. Results: The star formation history of isolated disks shows a stochastic star formation rate, which proceeds from the complex behavior of the giant clumps. Our minor and major gas-rich merger simulations do not trigger starbursts, suggesting a saturation of the star formation due to the detailed accounting of stellar feedback processes in a turbulent and clumpy interstellar medium fed by substantial accretion from the circumgalactic medium. Our simulations are close to the normal regime of the disk-like star formation on a Schmidt-Kennicutt diagram. The mass-size relation and its rate of evolution in the redshift range 1 < z < 2 matches observations, suggesting that the inside-out growth mechanisms of the stellar disk do not necessarily require cold accretion. Appendix A is available in electronic form at http://www.aanda.org

  4. 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

  5. Star Counts in the Globular Cluster ω Centauri. I. Bright Stellar Components

    Science.gov (United States)

    Castellani, V.; Calamida, A.; Bono, G.; Stetson, P. B.; Freyhammer, L. M.; Degl'Innocenti, S.; Moroni, P. Prada; Monelli, M.; Corsi, C. E.; Nonino, M.; Buonanno, R.; Caputo, F.; Castellani, M.; Dall'Ora, M.; Del Principe, M.; Ferraro, I.; Iannicola, G.; Piersimoni, A. M.; Pulone, L.; Vuerli, C.

    2007-07-01

    We present a photometric investigation on HB, RGB, and MSTO stars in ω Cen=NGC 5139. The center of the cluster was covered with a mosaic of F435W, F625W, and F658N band data collected with HST ACS. The outer reaches were covered with a mosaic of U-, B-, V-, and I-band data collected with the 2.2 m ESO/MPI telescope. The final catalog includes ~1.7 million stars. We identified more than 3200 likely HB stars, the largest sample ever collected in a globular cluster. We found that the HB morphology changes with the radial distance from the cluster center. The relative number of extreme HB stars decreases from ~30% to ~21% when moving from the center toward the outer reaches of the cluster, while the fraction of less hot HB stars increases from ~62% to ~72%. The comparison between theory and observations indicates that the empirical star counts of HB stars are on average larger (30%-40%) than predicted by canonical evolutionary models. Moreover, the rate of HB stars is ~43% larger than the MSTO rate. We also compared theory and observations by assuming a mix of stellar populations made with 70% of canonical He (Y=0.23) stars and 30% of He-enhanced (Y=0.33, 0.42) stars. We found that the observed RG/MSTO ratio agrees with the predicted lifetimes of He-mixed stellar populations. The discrepancy between theory and observations decreases by a factor of 2 when compared with rates predicted by canonical He content models, but still 15%-25% (Y=0.42) and 15%-20% (Y=0.33) higher than observed. Furthermore, the ratios between HB and MSTO star counts are ~24% (Y=0.42) and 30% (Y=0.33) larger than predicted lifetime ratios. During the revision of this manuscript, Vittorio Castellani passed away on 2006 May 19. His suggestions, ideas, and personality will be greatly missed. Based on data obtained from the ESO Science Archive Facility and the Hubble Space Telescope Archive Facility.

  6. NuSTAR Observations of X-Ray Flares from Young Stellar Objects

    Science.gov (United States)

    Vievering, Juliana; Glesener, Lindsay; Grefenstette, Brian; Smith, David

    2018-01-01

    Young stellar objects (YSOs), which tend to flare more frequently and at higher temperatures than what is typically observed on Sun-like stars, are excellent targets for studying the physical processes behind large flaring events. In the hard x-ray regime, radiation can penetrate through dense circumstellar material, and it is possible to measure thermal emission from hot plasma and to search for nonthermal emission from accelerated particles, which are key components for understanding the nature of energy release in these flares. Additionally, high-energy x-ray emission can ionize material in the disk, which may have implications for planet formation. To investigate hard x-ray emission from YSOs, three 50ks observations of a star-forming region called rho Ophiuchi have been taken with the Nuclear Spectroscopic Telescope Array (NuSTAR). Through use of direct focusing optics, NuSTAR provides unprecedented sensitivity in the hard x-ray regime, making these YSO observations the first of their kind. Multiple stellar flares have been identified in the data set; here we present the current spectral and timing analyses of the brightest of the these events, exploring the way energy is released as well as the effects of these large flares on the surrounding environment.

  7. 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

  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. 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}.

  10. 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

  11. A survey of long-term X-ray variability in cool stars

    Science.gov (United States)

    Pye, J.; Rosen, S.; Read, A.; Law-Green, D.; Watson, M.; O'Brien, P.; Garreffa, M.

    2017-10-01

    X-ray variability in cool stars can be indicative of coronal magnetic field changes and reconfiguration from a variety of phenomena, including flare events (typical timescales of minutes - hours), active-region evolution (hours - days - weeks), rotational modulation (hours - days - weeks), and activity cycles (years - decades). As part of the EXTraS project (Exploring the X-ray transient and variable sky - http://www.extras-fp7.eu/ ), we have performed a systematic survey of long-term X-ray variability using the ˜decade-long public database of XMM-Newton observations (3XMM). We are thus focussing here on timescales from ˜a day to ˜a decade, using average flux values from individual XMM-Newton observations. Though the resulting sampling is often highly non-uniform in time, the light-curves can provide valuable insights into the magnetic activity outside of shorter-term flaring episodes. We have taken a number of stellar samples and evaluated statistical properties of the flux distributions, and compared these across, for example spectral type, and with previously-published estimates. We have also examined the potential effects of flare events on the apparent long-term variability estimates. We report here on overall variability distributions and extreme cases, focussing on serendipitously-observed stars (yielding,in some sense an unbiased sample).

  12. 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.

  13. 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.

  14. Variable Stars and Stellar Populations in Andromeda XXVII. IV. An Off-centered, Disrupted Galaxy

    Science.gov (United States)

    Cusano, Felice; Garofalo, Alessia; Clementini, Gisella; Cignoni, Michele; Muraveva, Tatiana; Tessicini, Gianni; Testa, Vincenzo; Paris, Diego; Federici, Luciana; Marconi, Marcella; Ripepi, Vincenzo; Musella, Ilaria

    2017-12-01

    We present B and V time-series photometry of the M31 satellite galaxy Andromeda XXVII (And XXVII) that we observed with the Large Binocular Cameras of the Large Binocular Telescope. In the field of And XXVII we have discovered a total of 90 variables: 89 RR Lyrae stars and 1 Anomalous Cepheid. The average period of the fundamental mode RR Lyrae stars (RRab) =0.59 {days} (σ = 0.05 day) and the period-amplitude diagram place And XXVII in the class of Oosterhoff I/Intermediate objects. Combining information from the color-magnitude diagram (CMD) and the variable stars, we find evidence for a single old and metal-poor stellar population with [Fe/H] ˜ -1.8 dex and t ˜ 13 Gyr in And XXVII. The spatial distributions of RR Lyrae and red giant branch (RGB) stars give clear indication that And XXVII is a completely disrupted system. This is also supported by the spread observed along the line of sight in the distance to the RR Lyrae stars. The highest concentration of RGB and RR Lyrae stars is found in a circular area of 4 arcmin in radius, centered about 0.°2 in the southeast direction from Richardson et al.’s center coordinates of And XXVII. The CMD of this region is well-defined, with a prominent RGB and 15 RR Lyrae stars (out of the 18 found in the region) tracing a very tight horizontal branch at =25.24 {mag} σ = 0.06 mag (average over 15 stars). We show that And XXVII is a strong candidate building block of the M31 halo. Based on data collected with the Large Binocular Cameras at the Large Binocular Telescope, PI: G. Clementini.

  15. Role of nuclear reactions on stellar evolution of intermediate-mass stars

    Science.gov (United States)

    Möller, H.; Jones, S.; Fischer, T.; Martínez-Pinedo, G.

    2018-01-01

    The evolution of intermediate-mass stars (8 - 12 solar masses) represents one of the most challenging subjects in nuclear astrophysics. Their final fate is highly uncertain and strongly model dependent. They can become white dwarfs, they can undergo electron-capture or core-collapse supernovae or they might even proceed towards explosive oxygen burning and a subsequent thermonuclear explosion. We believe that an accurate description of nuclear reactions is crucial for the determination of the pre-supernova structure of these stars. We argue that due to the possible development of an oxygen-deflagration, a hydrodynamic description has to be used. We implement a nuclear reaction network with ∼200 nuclear species into the implicit hydrodynamic code AGILE. The reaction network considers all relevant nuclear electron captures and beta-decays. For selected relevant nuclear species, we include a set of updated reaction rates, for which we discuss the role for the evolution of the stellar core, at the example of selected stellar models. We find that the final fate of these intermediate-mass stars depends sensitively on the density threshold for weak processes that deleptonize the core.

  16. 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

  17. 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.

  18. 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.

  19. Exo-geneology: Stellar Abundances in Solar-like Stars with Planets

    Science.gov (United States)

    Teske, Johanna; SDSS-IV APOGEE-2

    2018-01-01

    Through the process of star and planet formation, we think that the chemical abundances, or ``genes’’, of host stars are passed on to their orbiting planets. One prominent example of this is the giant planet-metallicity (iron abundance) correlation, but could other stellar ``genes’’ help explain the growing menagerie of exoplanets? Particularly interesting is the relative importance of C, O, Mg, and Si – for instance, are giant planet cores dominated by ice-forming or rock-forming elements? The ratios of these elements in terrestrial planets also control their interior structure and mineralogy, and can thus affect their similarity (or not) to Earth. In this talk I will discuss how high resolution spectroscopic studies of host stars have been and are being used to investigate how/to what extent planet properties are dependent on host star properties, focusing on solar-like (FGK) stars. I will also highlight the role that upcoming facilities can play in understanding the diversity of planets in the Galaxy.

  20. Numerical simulations of bubble-induced star formation in dwarf irregular galaxies with a novel stellar feedback scheme

    Science.gov (United States)

    Kawata, Daisuke; Gibson, Brad K.; Barnes, David J.; Grand, Robert J. J.; Rahimi, Awat

    2014-02-01

    To study the star formation and feedback mechanism, we simulate the evolution of an isolated dwarf irregular galaxy (dIrr) in a fixed dark matter halo, similar in size to Wolf-Lundmark-Melotte, using a new stellar feedback scheme. We use the new version of our original N-body/smoothed particle chemodynamics code, GCD+, which adopts improved hydrodynamics, metal diffusion between the gas particles and new modelling of star formation and stellar wind and supernovae feedback. Comparing the simulations with and without stellar feedback effects, we demonstrate that the collisions of bubbles produced by strong feedback can induce star formation in a more widely spread area. We also demonstrate that the metallicity in star-forming regions is kept low due to the mixing of the metal-rich bubbles and the metal-poor interstellar medium. Our simulations also suggest that the bubble-induced star formation leads to many counter-rotating stars. The bubble-induced star formation could be a dominant mechanism to maintain star formation in dIrrs, which is different from larger spiral galaxies where the non-axisymmetric structures, such as spiral arms, are a main driver of star formation.

  1. 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.

  2. Nuclear Star Clusters and the Stellar Spheroids of their Host Galaxies

    OpenAIRE

    Leigh, Nathan; Böker, Torsten; Knigge, Christian

    2012-01-01

    (Abridged) We combine published photometry for the nuclear star clusters (NSCs) and stellar spheroids of 51 low-mass, early-type galaxies in the Virgo cluster with empirical mass-to-light ratios, in order to complement previous studies that explore the dependence of NSC masses (M_{NSC}) on various properties of their host galaxies. We confirm a roughly linear relationship between M_{NSC} and luminous host spheroid mass (M_{Sph}), albeit with considerable scatter (0.57 dex). We estimate veloci...

  3. 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 ...

  4. Radial velocity variability and stellar properties of FGK stars in the cores of NGC 2516 and NGC 2422

    Science.gov (United States)

    Bailey, John I.; Mateo, Mario; White, Russel J.; Shectman, Stephen A.; Crane, Jeffrey D.

    2018-04-01

    We present multi-epoch high-dispersion optical spectra obtained with the Michigan/Magellan Fibre System of 126 and 125 Sun-like stars in the young clusters NGC 2516 (141 Myr) and NGC 2422 (73 Myr). We determine stellar properties including radial velocity (RV), Teff, [Fe/H], [α/Fe] and the line-of-sight rotation rate, vrsin (i), from these spectra. Our median RV precision of 80 m s-1 on individual epochs that span a temporal baseline of 1.1 yr enables us to investigate membership and stellar binarity, and to search for sub-stellar companions. We determine membership probabilities and RV variability probabilities for our sample along with candidate companion orbital periods for a select subset of stars. In NGC 2516, we identified 81 RV members, 27 spectroscopic binaries (17 previously identified as photometric binaries) and 16 other stars that show significant RV variability after accounting for average stellar jitter at the 74 m s-1 level. In NGC 2422, we identify 57 members, 11 spectroscopic binaries and three other stars that show significant RV variability after accounting for an average jitter of 138 m s-1. We use Monte Carlo simulations to verify our stellar jitter measurements, determine the proportion of exoplanets and stellar companions to which we are sensitive, and estimate companion-mass limits for our targets. We also report mean cluster metallicity, velocity and velocity dispersion based on our member targets. We identify 58 non-member stars as RV variables, 24 of which have RV amplitudes that imply stellar or brown-dwarf mass companions. Finally, we note the discovery of a separate RV clustering of stars in our NGC 2422 sample.

  5. Estimation of the stellar effective temperature and stellar wind detection in a Herbig Ae/Be type star from spectra acquired in Bogotá - Colombia

    Science.gov (United States)

    Guasca Garnica, I. L.; Ramírez Suárez, O. L.; Oostra Vannoppen, B.; Chaparro Molano, G.; Restrepo Gaitán, O. A.

    2017-07-01

    We present the results of spectroscopic observations in the range of 4280-6800 Å of AB Aur, a Herbig Ae/Be type star. These observations were carried out at the Observatory of the Universidad de los Andes in Bogotá - Colombia in 2015. We select the 4280-6000 Å spectral window for fitting our data to a black-body model of the star. In this range, the effects due to circumstellar disk emission are negligible and the nighborhood of the prominent accretion Hα emission line is neglected. In this window the dominant lines due atomic processes are the Balmer series lines Hβ and Hγ. We remove data around 3σ for each of these lines in order to ignore quantum effects. We model the stellar continuum by doing a Monte Carlo bootstrap-sampled fitting of three parameters: (i) a bolometric correction factor due to atmospheric absorption and/or defect electronics, (ii) measured (relative) continuum flux, and (iii) stellar temperature Teff. We obtain a value for the stellar temperature of 9400K-9700K, in agreement with the temperature reported by Tannirkulam et al. 2008. We also successfully fitted the H lines using a two-component gaussian fit, which shows the effects of stellar wind on top of the gas accretion onto the star. Our measurements strongly suggest that even in the harsh observational conditions present in Colombia, it is possible to obtain quality astronomical data for teaching astrophysics at an undergraduate level.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. The evolution of kicked stellar-mass black holes in star cluster environments

    Science.gov (United States)

    Webb, Jeremy J.; Leigh, Nathan W. C.; Singh, Abhishek; Ford, K. E. Saavik; McKernan, Barry; Bellovary, Jillian

    2018-03-01

    We consider how dynamical friction acts on black holes that receive a velocity kick while located at the centre of a gravitational potential, analogous to a star cluster, due to either a natal kick or the anisotropic emission of gravitational waves during a black hole-black hole merger. Our investigation specifically focuses on how well various Chandrasekhar-based dynamical friction models can predict the orbital decay of kicked black holes with mbh ≲ 100 M⊙ due to an inhomogeneous background stellar field. In general, the orbital evolution of a kicked black hole follows that of a damped oscillator where two-body encounters and dynamical friction serve as sources of damping. However, we find models for approximating the effects of dynamical friction do not accurately predict the amount of energy lost by the black hole if the initial kick velocity vk is greater than the stellar velocity dispersion σ. For all kick velocities, we also find that two-body encounters with nearby stars can cause the energy evolution of a kicked BH to stray significantly from standard dynamical friction theory as encounters can sometimes lead to an energy gain. For larger kick velocities, we find the orbital decay of a black hole departs from classical theory completely as the black hole's orbital amplitude decays linearly with time as opposed to exponentially. Therefore, we have developed a linear decay formalism, which scales linearly with black hole mass and v_k/σ in order to account for the variations in the local gravitational potential.

  11. Stellar Populations and Ionization States of Lyman Alpha Emitters During the Epoch of Peak Star Formation

    Science.gov (United States)

    Reddy, Naveen

    2014-10-01

    Low luminosity galaxies contribute significantly to the mass and star-formation density of the early Universe. Ly-alpha emitting galaxies (LAEs) are powerful probes of the faint-end of the luminosity function and early mass assembly. LAE studies at z>2 have typically used stacked optical and/or Spitzer data to discern their median properties, but the actual distribution of stellar masses and ionization states of LAEs remain largely unconstrained. To advance our understanding of this important population, we have successfully identified large samples of LAEs (~900 in four 0.33 deg^2 fields) at z~1.9, and have spectroscopically confirmed our selection using Keck. Here we propose to leverage our existing deep HST near-IR and Spitzer/IRAC imaging with the WFC3 G141 grism to measure [OIII]+H-beta for 76 LAE candidates from our sample, 13 of which are already spectroscopically confirmed at z=1.9+/-0.1. Combined with [OII] measurements from the ground, we will: (1) correct the emission line contribution to the HST broadband photometry and thus more accurately measure stellar masses and ages of LAEs; (2) measure ionization states with [OIII]/[OII] to discern the physical conditions in the ISM of these faint, low-mass galaxies; and (3) use systemic velocities derived from [OIII]+Hb, combined with our rest-UV spectra of the Ly-alpha and interstellar absorption lines, to deduce the kinematics of the ISM and the prevalence of galaxy-scale outflows. An economical investment of 16 orbits will enable robust stellar population, ionization, and ISM structure measurements for LAEs, thus illuminating their significance at a time when galaxies were forming most of their stars.

  12. The anatomy of the NGC5044 group - II. Stellar populations and star formation histories

    Science.gov (United States)

    Mendel, J. Trevor; Proctor, Robert N.; Rasmussen, Jesper; Brough, Sarah; Forbes, Duncan A.

    2009-07-01

    The distribution of galaxy properties in groups and clusters holds important information on galaxy evolution and growth of structure in the Universe. While clusters have received appreciable attention in this regard, the role of groups as fundamental to formation of the present-day galaxy population has remained relatively unaddressed. Here, we present stellar ages, metallicities and α-element abundances derived using Lick indices for 67 spectroscopically confirmed members of the NGC5044 galaxy group with the aim of shedding light on galaxy evolution in the context of the group environment. We find that galaxies in the NGC5044 group show evidence for a strong relationship between stellar mass and metallicity, consistent with their counterparts in both higher and lower mass groups and clusters. Galaxies show no clear trend of age or α-element abundance with mass, but these data form a tight sequence when fitted simultaneously in age, metallicity and stellar mass. In the context of the group environment, our data support the tidal disruption of low-mass galaxies at small group-centric radii, as evident from an apparent lack of galaxies below ~109Msolar within ~100kpc of the brightest group galaxy. Using a joint analysis of absorption- and emission-line metallicities, we are able to show that the star-forming galaxy population in the NGC5044 group appears to require gas removal to explain the ~1.5dex offset between absorption- and emission-line metallicities observed in some cases. A comparison with other stellar population properties suggests that this gas removal is dominated by galaxy interactions with the hot intragroup medium.

  13. 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.

  14. 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.

  15. Variable Stars and Constant Commitments: The Stellar Career of Dorrit Hoffleit

    Science.gov (United States)

    Larsen, Kristine

    2011-05-01

    Astronomer, educator, and science historian Dorrit Hoffleit (1907-2007) was widely respected by the amateur and professional astronomical community as a mentor and an ardent supporter of independent research. Her more than 600 catalogues, books, articles, book reviews, and news columns cover myriad aspects of astronomy, from variable stars and stellar properties to meteor showers, quasars, and rocketry. She also made important contributions to the history of astronomy. Hoffleit worked at the Harvard College Observatory from 1927-1956, where she discovered over 1200 variable stars. When Director Harlow Shapley retired from Harvard, Hoffleit gave up her tenured position and moved to Yale University, where she was placed in charge of the Yale Catalog of Bright Stars. At the same time, she was offered a position as director of the Maria Mitchell Observatory on Nantucket Island in Massachusetts. Hoffleit split her dual positions into six-month stints and remained director at the Mitchell Observatory for 21 years, developing a summer research program that engaged more than 100 undergraduate students (all but three of them women) in variable star research. Up until shortly before her death, she continued to work tirelessly on selected projects, and she was in high demand as a collaborator with colleagues at Yale and elsewhere. She was especially devoted to the American Association of Variable Star Observers (AAVSO) in part because it brought together amateur and professional astronomers in collaboration. She served on the organization's council for 23 years and as its president from 1961-1963. In 2002, the AAVS0 published her autobiography, Misfortunes as Blessings in Disguise, in which Hoffleit explains how she always felt blessed by the opportunities in her life, even those which initially seemed misfortunes, and above all else valued creativity, flexibility, collegiality, and intellectual freedom in her professional life.

  16. The Stellar Commodity Market: Cu, Ag, And Au In The Sun And Solar-type Stars

    Science.gov (United States)

    Wahlgren, Glenn Michael; Carpenter, K. G.; Nave, G.

    2010-01-01

    The elements copper, silver and gold occupy the same column of the periodic table and share the property that their only stable isotopes are odd-numbered, which implies a need for hyperfine structure data when analyzing their spectral lines. A comparison of their solar photospheric abundances with the standard meteoritic element abundances shows that for two of them (Ag, Au) the differences are as large as or larger than the sum of the uncertainties. With some exceptions, the study of the chemical composition of most stars stops at the end of the iron group of elements. Heavier elements are typically not analyzed, often due to the lack of accurate atomic line data. While the post iron-group elements make a small contribution to the total abundance one can argue that, for many reasons, life on earth would not be the same without copper, silver and gold. We first revisit the abundances of these elements in the solar photosphere, accounting for the revisions in atomic data since these elements were last analyzed in the photosphere. The hyperfine structure of Cu I and Ag I is included in our synthetic spectrum calculations. The spectra Cu I and Cu II are of current interest to us for the determination of hfs constants based on our new laboratory Fourier transform spectrometer data. We then determine the abundances for these elements in the high-resolution spectra for a sample of solar-like stars, obtained from on-line data bases, using synthetic spectrum techniques. The analysis aims to determine the abundance dispersion of these elements in solar-like stars in the solar neighborhood. Some of these stars are known to possess exo-planets, and the abundances of these elements will be correlated with host star metallicity. In general, we aim to encourage a more extensive use of the periodic table for stellar astrophysics.

  17. High-precision abundances of elements in Kepler LEGACY stars. Verification of trends with stellar age

    Science.gov (United States)

    Nissen, P. E.; Silva Aguirre, V.; Christensen-Dalsgaard, J.; Collet, R.; Grundahl, F.; Slumstrup, D.

    2017-12-01

    Context. A previous study of solar twin stars has revealed the existence of correlations between some abundance ratios and stellar age providing new knowledge about nucleosynthesis and Galactic chemical evolution. Aims: High-precision abundances of elements are determined for stars with asteroseismic ages in order to test the solar twin relations. Methods: HARPS-N spectra with signal-to-noise ratios S/N ≳ 250 and MARCS model atmospheres were used to derive abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, and Y in ten stars from the Kepler LEGACY sample (including the binary pair 16 Cyg A and B) selected to have metallicities in the range - 0.15 LTE iron abundances derived from Fe I and Fe II lines. Available non-LTE corrections were also applied when deriving abundances of the other elements. Results: The abundances of the Kepler stars support the [X/Fe]-age relations previously found for solar twins. [Mg/Fe], [Al/Fe], and [Zn/Fe] decrease by 0.1 dex over the lifetime of the Galactic thin disk due to delayed contribution of iron from Type Ia supernovae relative to prompt production of Mg, Al, and Zn in Type II supernovae. [Y/Mg] and [Y/Al], on the other hand, increase by 0.3 dex, which can be explained by an increasing contribution of s-process elements from low-mass AGB stars as time goes on. The trends of [C/Fe] and [O/Fe] are more complicated due to variations of the ratio between refractory and volatile elements among stars of similar age. Two stars with about the same age as the Sun show very different trends of [X/H] as a function of elemental condensation temperature Tc and for 16 Cyg, the two components have an abundance difference, which increases with Tc. These anomalies may be connected to planet-star interactions. Based on spectra obtained with HARPS-N@TNG under programme A33TAC_1.Tables 1 and 2 are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc

  18. 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

  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

    International Nuclear Information System (INIS)

    Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji; Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G.; Crepp, Justin R.; Porto de Mello, Gustavo F.; Ferreira, Letícia D.; Esposito, Massimiliano; Femenia, Bruno; González Hernández, Jonay I.; Gaudi, B. Scott; Ghezzi, Luan; Wisniewski, John P.; Agol, Eric

    2013-01-01

    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 +0.0188 -0.0187 days, an eccentricity of 0.4375 ± 0.0040, and a semi-amplitude of 2948.14 +16.65 -16.55 m s –1 . Using additional high-resolution spectroscopy, we find the host star has an effective temperature T 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 ☉ and 0.92 ± 0.19 R ☉ . The minimum mass of MARVELS-5b is 65.0 ± 2.9M 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 ☉ at a separation larger than 40 AU

  20. 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.

  1. Auto-consistent test of Galaxy star formation histories derived from resolved stellar population and integral spectroscopy

    Science.gov (United States)

    Rodrigues, M.; Patricio, V.; Rothberg, B.; Sanchez-Janssen, R.; Vale Asari, N.

    We present the first results of our observational project 'Starfish' (STellar Population From Integrated Spectrum). The goal of this project is to calibrate, for the first time, the properties of stellar populations derived from integrated spectra with the same properties derived from direct imaging of stellar populations in the same set of galaxies. These properties include the star-formation history (SFH), stellar mass, age, and metallicity. To date, such calibrations have been demonstrated only in star clusters, globular clusters with single stellar populations, not in complex and composite objects such as galaxies. We are currently constructing a library of integrated spectra obtained from a sample of 38 nearby dwarf galaxies obtained with GEMINI/GMOS-N&S (25h) and VLT/VIMOS-IFU (43h). These are to be compared with color magnitude diagrams (CMDs) of the same galaxies constructed from archival HST imaging sensitive to at least 1.5 magnitudes below the tip of the red giant branch. From this comparison we will assess the systematics and uncertainties from integrated spectral techniques. The spectra library will be made publicly available to the community via a dedicated web-page and Vizier database. This dataset will provide a unique benchmark for testing fitting procedures and stellar population models for both nearby and distant galaxies. http://www.sc.eso.org/˜marodrig/Starfish/

  2. Young Stellar Objects in the Massive Star-forming Regions W51 and W43

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Audard, M. [Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix (Switzerland); Hora, J. L.; Martínez-Galarza, J. R.; Smith, H. A. [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); Motte, F. [Institut de Plantologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes—CNRS-INSU, BP 53, F-38041 Grenoble Cedex 9 (France); Nguyen-Luong, Q. [National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saygac, A. T. [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2017-04-20

    We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color–magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH ii regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H ii regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

  3. Stellar Population Synthesis of Star-forming Clumps in Galaxy Pairs and Non-interacting Spiral Galaxies

    Science.gov (United States)

    Zaragoza-Cardiel, Javier; Smith, Beverly J.; Rosado, Margarita; Beckman, John E.; Bitsakis, Theodoros; Camps-Fariña, Artemi; Font, Joan; Cox, Isaiah S.

    2018-02-01

    We have identified 1027 star-forming complexes in a sample of 46 galaxies from the Spirals, Bridges, and Tails (SB&T) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (NIS) galaxies in 8 μm observations from the Spitzer Infrared Array Camera. We have used archival multi-wavelength UV-to IR observations to fit the observed spectral energy distribution of our clumps with the Code Investigating GALaxy Emission using a double exponentially declined star formation history. We derive the star formation rates (SFRs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. The resolved star formation main sequence holds on 2.5 kpc scales, although it does not hold on 1 kpc scales. We analyzed the relation between SFR, stellar mass, and age of the recent burst in the SB&T and NIS samples, and we found that the SFR per stellar mass is higher in the SB&T galaxies, and the clumps are younger in the galaxy pairs. We analyzed the SFR radial profile and found that the SFR is enhanced through the disk and in the tidal features relative to normal spirals.

  4. 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] 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.

  5. STELLAR PARAMETERS AND METALLICITIES OF STARS HOSTING JOVIAN AND NEPTUNIAN MASS PLANETS: A POSSIBLE DEPENDENCE OF PLANETARY MASS ON METALLICITY

    International Nuclear Information System (INIS)

    Ghezzi, L.; Cunha, K.; De Araujo, F. X.; De la Reza, R.; Smith, V. V.; Schuler, S. C.

    2010-01-01

    The metal content of planet-hosting stars is an important ingredient that may affect the formation and evolution of planetary systems. Accurate stellar abundances require the determinations of reliable physical parameters, namely, the effective temperature, surface gravity, microturbulent velocity, and metallicity. This work presents the homogeneous derivation of such parameters for a large sample of stars hosting planets (N = 117), as well as a control sample of disk stars not known to harbor giant, closely orbiting planets (N = 145). Stellar parameters and iron abundances are derived from an automated analysis technique developed for this work. As previously found in the literature, the results in this study indicate that the metallicity distribution of planet-hosting stars is more metal rich by ∼0.15 dex when compared to the control sample stars. A segregation of the sample according to planet mass indicates that the metallicity distribution of stars hosting only Neptunian-mass planets (with no Jovian-mass planets) tends to be more metal poor in comparison with that obtained for stars hosting a closely orbiting Jovian planet. The significance of this difference in metallicity arises from a homogeneous analysis of samples of FGK dwarfs which do not include the cooler and more problematic M dwarfs. This result would indicate that there is a possible link between planet mass and metallicity such that metallicity plays a role in setting the mass of the most massive planet. Further confirmation, however, must await larger samples.

  6. 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).

  7. Stellar Masses in the Mysterious Young Triple Star System AS 205

    Science.gov (United States)

    Encalada, Frankie; Rosero, Viviana A.; Prato, Lisa A.; Bruhns, Sara

    2015-01-01

    The lack of accurate absolute mass measurements for young, low-mass pre-main sequence stars is problematic for the calibration of stellar evolutionary track models. An on-going program to increase the sample of young star masses begins with mass ratio measurements in spectroscopic binaries. By the end of its 5-year duration, the GAIA all-sky mission will provide new astrometric measurements for young spectroscopic binaries down to separations of tens of microarcseconds, yielding absolute masses for double-lined systems. We obtain mass ratios by taking high-resolution spectra of young double-lined spectroscopic binaries over a few epochs to construct a radial velocity versus phase diagram. For the young spectroscopic binary AS 205B, using eight of our own spectra supplied by the CSHELL instrument on the IRTF at Mauna Kea, plus one from the literature, we estimate a period of approximately 140 days, an eccentricity of 0.7, and a mass-ratio of 0.5. This spectroscopic system comprises the secondary in a 1.4'' visual binary in which both the A and B components are surrounded by optically thick, actively accreting disks, making AS 205B a member of that rare class of young spectroscopic binaries with a primordial circumbinary disk.

  8. 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

  9. Prospects of Detecting Baryon and Quark Superfluidity from Cooling Neutron Stars

    OpenAIRE

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

    2000-01-01

    Baryon and quark superfluidity in the cooling of neutron stars are investigated. Observations could 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 ...

  10. 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.

  11. 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.

  12. MESA: Modules for Experiments in Stellar Astrophysics

    Science.gov (United States)

    Paxton, Bill; Bildsten, Lars; Dotter, Aaron; Herwig, Falk; Lesaffre, Pierre; Timmes, Frank

    2010-10-01

    Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source libraries for a wide range of applications in computational stellar astrophysics. A newly designed 1-D stellar evolution module, MESA star, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very-low mass to massive stars, including advanced evolutionary phases. MESA star solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. Independently usable modules provide equation of state, opacity, nuclear reaction rates, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own public interface. Examples include comparisons to other codes and show evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets; the complete evolution of a 1 Msun star from the pre-main sequence to a cooling white dwarf; the Solar sound speed profile; the evolution of intermediate mass stars through the thermal pulses on the He-shell burning AGB phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; evolutionary tracks of massive stars from the pre-main sequence to the onset of core collapse; stars undergoing Roche lobe overflow; and accretion onto a neutron star.

  13. 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

  14. 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 ($algorithm incorporates a combined probabilistic model of the blended SEDs and the unresolved images in the long-wavelength end. We find that our results are compatible with competitive accretion in the central regions of young clusters, with the most massive stars forming early on in the process and less massive stars forming about 1Myr later. We also find evidence for a relationship between the total stellar mass of the cluster and the mass of the most massive member that favors optimal sampling in the cluster and disfavors random sampling for the canonical IMF, implying that star formation is self-regulated, and that the mass of the most massive star in a cluster depends on the available resources. The method presented here is easily adapted to future observations of clustered regions of star formation with JWST and other high resolution facilities.

  15. 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.

  16. 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.

  17. A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups

    Science.gov (United States)

    Maldonado, J.; Martínez-Arnáiz, R. M.; Eiroa, C.; Montes, D.; Montesinos, B.

    2010-10-01

    Context. Nearby late-type stars are excellent targets for seeking young objects in stellar associations and moving groups. The origin of these structures is still misunderstood, and lists of moving group members often change with time and also from author to author. Most members of these groups have been identified by means of kinematic criteria, leading to an important contamination of previous lists by old field stars. Aims: We attempt to identify unambiguous moving group members among a sample of nearby-late type stars by studying their kinematics, lithium abundance, chromospheric activity, and other age-related properties. Methods: High-resolution echelle spectra (R ~ 57 000) of a sample of nearby late-type stars are used to derive accurate radial velocities that are combined with the precise Hipparcos parallaxes and proper motions to compute galactic-spatial velocity components. Stars are classified as possible members of the classical moving groups according to their kinematics. The spectra are also used to study several age-related properties for young late-type stars, i.e., the equivalent width of the lithium Li i 6707.8 Å line or the R'HK index. Additional information like X-ray fluxes from the ROSAT All-Sky Survey or the presence of debris discs is also taken into account. The different age estimators are compared and the moving group membership of the kinematically selected candidates are discussed. Results: From a total list of 405 nearby stars, 102 have been classified as moving group candidates according to their kinematics. i.e., only ~25.2% of the sample. The number reduces when age estimates are considered, and only 26 moving group candidates (25.5% of the 102 candidates) have ages in agreement with the star having the same age as an MG member. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andaluc

  18. Beyond the classical paradigm of stellar winds: Investigating clumping, rotation and the weak wind problem in SMC O stars

    Science.gov (United States)

    Hubeny, Ivan

    2009-07-01

    SMC O stars provide an unrivaled opportunity to probe star formation, evolution, and the feedback of massive stars in an environment similar to the epoch of the peak in star formation history. Two recent breakthroughs in the study of hot, massive stars have important consequences for understanding the chemical enrichment and buildup of stellar mass in the Universe. The first is the realization that rotation plays a major role in influencing the evolution of massive stars and their feedback on the surrounding environment. The second is a drastic downward revision of the mass loss rates of massive stars coming from an improved description of their winds. STIS spectroscopy of SMC O stars combined with state-of-the-art NLTE analyses has shed new light on these two topics. A majority of SMC O stars reveal CNO-cycle processed material brought at their surface by rotational mixing. Secondly, the FUV wind lines of early O stars provide strong indications of the clumped nature of their wind. Moreover, we first drew attention to some late-O dwarfs showing extremely weak wind signatures. Consequently, we have derived mass loss rates from STIS spectroscopy that are significantly lower than the current theoretical predictions used in evolutionary models. Because of the limited size of the current sample {and some clear bias toward stars with sharp-lined spectra}, these results must however be viewed as tentative. Thanks to the high efficiency of COS in the FUV range, we propose now to obtain high-resolution FUV spectra with COS of a larger sample of SMC O stars to study systematically rotation and wind properties of massive stars at low metallicity. The analysis of the FUV wind lines will be based on our 2D extension of CMFGEN to model axi-symmetric rotating winds.

  19. The stellar mass, star formation rate and dark matter halo properties of LAEs at z ˜ 2

    Science.gov (United States)

    Kusakabe, Haruka; Shimasaku, Kazuhiro; Ouchi, Masami; Nakajima, Kimihiko; Goto, Ryosuke; Hashimoto, Takuya; Konno, Akira; Harikane, Yuichi; Silverman, John D.; Capak, Peter L.

    2018-01-01

    We present average stellar population properties and dark matter halo masses of z ˜ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, using ≃ 1250 objects (NB387≤25.5) in four separate fields of ≃ 1 deg2 in total. With an average stellar mass of 10.2 ± 1.8 × 108 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr-1, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be 4.0_{-2.9}^{+5.1} × 10^{10}{ }M_{⊙} with an effective bias of 1.22^{+0.16}_{-0.18}, which is lower than that of z ˜ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H I gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ˜ 2 as some previous studies have reported for the LMC itself.

  20. Measuring the Stellar Populations of Individual Lyman Alpha Emitters During the Epoch of Peak Star Formation

    Science.gov (United States)

    Reddy, Naveen

    2010-09-01

    Selecting galaxies by their strong Lyman-alpha emission provides a powerful means of probing the reionization epoch and the faint/low-mass galaxies that dominate star formation at high redshift. Yet, our understanding of high-redshift Lyman-alpha emitters {LAEs} has lagged behind that of other well-studied populations {e.g., Lyman break galaxies} due to their continuum faintness and the shifting of age/mass-sensitive features into the near-IR where the high terrestrial background inhibits deep observations. All existing studies of LAEs at z>2 have used stacked optical and/or Spitzer infrared data to discern their median properties, but the actual distributions of ages, reddenings, and stellar masses for these populations are poorly characterized. To fill this glaring gap in the observations and advance our understanding of this important population, we propose WFC3/IR+F160W imaging of fields where we have conducted a survey of low redshift {z 1.9} Lyman-alpha emitters {LAEs}, in order to measure their ages and stellar masses at an epoch where such observations directly probe the age-sensitive Balmer/4000 AA breaks. The targeted sample will include 45-50 spectroscopically confirmed LAEs at z=1.7-2.1 and roughly twice as many candidates, making it the largest sample of homogeneously selected LAEs with individual measurements of the ages, masses, and dust extinction. With these data we will {1} carefully take into account the age-dependence of the extinction curve to make robust comparisons between LAEs and continuum-selected galaxies at the same redshifts; {2} combine clustering and stellar mass measurements to infer the duty cycles of LAEs and determine if they are triggered in the presence of large-scale structures; and {3} quantify the importance of the LAE phase at different galaxy luminosity and mass scales, over a large dynamic range in these properties. An economical investment of just 12 orbits will allow us to accomplish these goals, and remains the only

  1. 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

  2. Updated Colors for Cool Stars in the SDSS

    OpenAIRE

    West, Andrew A.; Walkowicz, Lucianne M.; Hawley, Suzanne L.

    2005-01-01

    We present updated colors for M and L dwarfs based on photometry from the third data release of the Sloan Digital Sky Survey (SDSS). These data are improved in quality and number from earlier results. We also provide updated equations for determining photometric parallaxes from SDSS colors of late-type stars. Walkowicz, Hawley & West (2004) have recently presented new techniques for studying the magnetic activity of low-mass stars and their method relies on an accurate determination of SDSS c...

  3. 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.

  4. 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.

  5. Stellar parameters of the post-AGB star HD 56126 from observations and non-linear radiative pulsation models

    Science.gov (United States)

    Le Coroller, Herve; Fokin, A. B.; Lèbre, A.; Gillet, D.

    2001-05-01

    After the AGB phase and before becoming planetary nebulae, the stars cross a post-AGB phase during a short time of approximately 10 000 years. Stars at this evolution stage are thus statistically rare and their pulsation mechanisms, probably related to the propagation of shocks in their atmosphere, remain badly known. It thus appeared essential to carry out an in-depth study on a typical post-AGB object. Thus, we present an analysis of the spectroscopic and photometric data on HD 56126, a post-AGB variable star, rich in carbon. A previous work (Barthes et al, 2000, A&A 359,168) finds a 37 days pulsation period. We present here the results of a non-linear model which allowed to deduce the stellar parameters of this star (Teff, L, M). We also discuss the limits of such a model to simulate the complex atmospheric dynamics of post-AGB objects.

  6. On the Photometric Variability of Very Sharp-lined Cool mCP Stars

    Science.gov (United States)

    Pyper, Diane M.; Adelman, Saul J.

    2017-10-01

    We investigate the photometric variability of very sharp-lined cool mCP stars from a list published in 1970 by Dr. George W. Preston who suggested that some belonged to the long-period tail of the period distribution. In this study, we discuss our Strömgren uvby observations obtained with the Four College Automated Photometric Telescope (FCAPT) at the Fairborn Observatory for 22 of the stars in Preston’s list. We improved the periods of 11 stars. Further, we discuss results from the literature concerning the light, magnetic, and spectrum variability of these stars. Eleven of the stars are found to have periods longer than 20 days, and all but one of these stars display variations in the u and v filters that cannot be explained by the simple oblique rotator theory. We discuss some possible causes of this behavior.

  7. 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.

  8. 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.

  9. Variable stars in Leo A : RR Lyrae stars, short-period cepheids, and implications for stellar content

    NARCIS (Netherlands)

    Dolphin, AE; Saha, A; Claver, J; Skillman, ED; Cole, AA; Gallagher, JS; Tolstoy, E; Dohm-Palmer, RC; Mateo, M

    We present the results of a search for short-period variable stars in Leo A. We have found 92 candidate variables, including eight candidate RR Lyrae stars. From the RR Lyrae stars, we measure a distance modulus of (m - M)(0) = 24.51 +/- 0.12, or 0.80 +/- 0.04 Mpc. This discovery of RR Lyrae stars

  10. THE INTERACTION OF VENUS-LIKE, M-DWARF PLANETS WITH THE STELLAR WIND OF THEIR HOST STAR

    International Nuclear Information System (INIS)

    Cohen, O.; Drake, J. J.; Garraffo, C.; Ma, Y.; Glocer, A.; Bell, J. M.; Gombosi, T. I.

    2015-01-01

    We study the interaction between the atmospheres of Venus-like, non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using a multi-species MHD model. We focus our investigation on the effect of enhanced stellar wind and enhanced EUV flux as the planetary distance from the star decreases. Our simulations reveal different topologies of the planetary space environment for sub- and super-Alfvénic stellar wind conditions, which could lead to dynamic energy deposition into the atmosphere during the transition along the planetary orbit. We find that the stellar wind penetration for non-magnetized planets is very deep, up to a few hundreds of kilometers. We estimate a lower limit for the atmospheric mass-loss rate and find that it is insignificant over the lifetime of the planet. However, we predict that when accounting for atmospheric ion acceleration, a significant amount of the planetary atmosphere could be eroded over the course of a billion years

  11. 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.

  12. The thermodynamic requirements on atmospheric models imposed by observed stellar nonthermal mass-fluxes and by those observed nonthermal features enhanced in Xe stars

    International Nuclear Information System (INIS)

    Thomas, R.N.

    1979-01-01

    The author presents the case for the 'imperfect wind-tunnel' model both for nonthermal mass-flux and for other observed nonthermal phenomena, in stellar atmospheres generally, not just in O stars particlarly. He asserts, that in studying nonthermal mass-flux from O stars, if attention is limited only to nonthermal mass-flux, and only to O stars, this handicaps, a priori, the chance of understanding what is required for the general model of a stellar atmosphere, in order to produce this variety of nonthermal phenomena observed, alike in all varieties of stars. (Auth.)

  13. The formation of high-mass stars and stellar clusters in the extreme environment of the Central Molecular Zone

    Science.gov (United States)

    Walker, Daniel Lewis

    2017-08-01

    The process of converting gas into stars underpins much of astrophysics, yet many fundamental questions surrounding this process remain unanswered. For example - how sensitive is star formation to the local environmental conditions? How do massive and dense stellar clusters form, and how does this crowded environment influence the stars that form within it? How do the most massive stars form and is there an upper limit to the stellar initial mass function (IMF)? Answering questions such as these is crucial if we are to construct an end-to-end model of how stars form across the full range of conditions found throughout the Universe. The research described in this thesis presents a study that utilises a multi-scale approach to identifying and characterising the early precursors to young massive clusters and high-mass proto-stars, with a specific focus on the extreme environment in the inner few hundred parsecs of the Milky Way - the Central Molecular Zone (CMZ). The primary sources of interest that are studied in detail belong to the Galactic centre dust ridge - a group of six high-mass (M 10^(4-5) Msun), dense (R 1-3 pc, n > 10^(4) cm^(-3)), and quiescent molecular clouds. These properties make these clouds ideal candidates for representing the earliest stages of high-mass star and cluster formation. The research presented makes use of single-dish and interferometric far-infrared and (sub-)millimetre observations to study their global and small-scale properties. A comparison of the known young massive clusters (YMCs) and their likely progenitors (the dust ridge clouds) in the CMZ shows that the stellar content of YMCs is much more dense and centrally concentrated than the gas in the clouds. If these clouds are truly precursors to massive clusters, the resultant stellar population would have to undergo significant dynamical evolution to reach central densities that are typical of YMCs. This suggests that YMCs in the CMZ are unlikely to form monolithically. Extending

  14. Starspots: A Key to the Stellar Dynamo

    Directory of Open Access Journals (Sweden)

    Berdyugina Svetlana V.

    2005-12-01

    Full Text Available Magnetic activity similar to that of the Sun is observed on a variety of cool stars with external convection envelopes. Stellar rotation coupled with convective motions generate strong magnetic fields in the stellar interior and produce a multitude of magnetic phenomena including starspots in the photosphere, chromospheric plages, coronal loops, UV, X-ray, and radio emission and flares. Here I review the phenomenon of starspots on different types of cool stars, observational tools and diagnostic techniques for studying starspots as well as starspot properties including their temperatures, areas, magnetic field strengths, lifetimes, active latitudes and longitudes, etc. Evolution of starspots on various time scales allows us to investigate stellar differential rotation, activity cycles, and global magnetic fields. Together these constitute the basis for our understanding of stellar and solar dynamos and provide valuable constraints for theoretical models.

  15. Evolution of super star cluster winds with strong cooling

    Czech Academy of Sciences Publication Activity Database

    Wünsch, Richard; Silich, S.; Palouš, Jan; Tenorio-Tagle, G.; Munoz-Tunon, C.

    2011-01-01

    Roč. 740, č. 2 (2011), A75/1-A75/7 ISSN 0004-637X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : galaxies * star clusters * HII regions Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 6.024, year: 2011

  16. 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.

  17. Nuclear star clusters and the stellar spheroids of their host galaxies

    Science.gov (United States)

    Leigh, Nathan; Böker, Torsten; Knigge, Christian

    2012-08-01

    We combine published photometry for the nuclear star clusters (NSCs) and stellar spheroids of 51 low-mass, early-type galaxies in the Virgo cluster with empirical mass-to-light ratios, in order to complement previous studies that explore the dependence of NSC masses on various properties of their host galaxies. We confirm a roughly linear relationship between NSC mass and luminous host spheroid mass, albeit with considerable scatter (0.57 dex). In order to translate this into an MNSC-σ relation, we estimate velocity dispersions from the virial theorem, assuming that all galaxies in our sample share a common dark matter fraction and are dynamically relaxed. We then find that MNSC ˜ σ2.73 ± 0.29, with a slightly reduced scatter of 0.54 dex. This confirms recent results that the shape of the MCMO-σ relation is different for NSCs and super-massive black holes. We discuss this result in the context of the generalized idea of 'central massive objects' (CMOs). In order to assess which physical parameters drive the observed nuclear cluster masses, we also carry out a joint multivariate power-law fit to the data. In this, we allow the nuclear cluster mass to depend on spheroid mass and radius (and hence implicitly on velocity dispersion), as well as on the size of the globular cluster reservoir. When considered together, the dependences on MSph and RSph are roughly consistent with the virial theorem, and therefore MNSC ∝ σ2. However, the only statistically significant correlation appears to be a simple linear scaling between NSC mass and luminous spheroid mass. We proceed to directly compare the derived NSC masses with predictions for two popular models for NSC formation, namely (i) globular cluster infall due to dynamical friction and (ii) in situ formation during the early phases of galaxy formation that is regulated via momentum feedback from stellar winds and/or supernovae. Neither model can directly predict the observations, and we discuss possible

  18. Cryogenic Cooling for Myriad Applications-A STAR Is Born

    Science.gov (United States)

    2006-01-01

    Cryogenics, the science of generating extremely low temperatures, has wide applicability throughout NASA. The Agency employs cryogenics for rocket propulsion, high-pressure gas supply, breathable air in space, life support equipment, electricity, water, food preservation and packaging, medicine, imaging devices, and electronics. Cryogenic liquid oxygen and liquid hydrogen systems are also replacing solid rocket motor propulsion systems in most of the proposed launch systems, a reversion to old-style liquid propellants. In the late 1980s, NASA wanted a compact linear alternator/motor with reduced size and mass, as well as high efficiency, that had unlimited service life for use in a thermally driven power generator for space power applications. Prior development work with free-piston Stirling converters (a Stirling engine integrated with a linear actuator that produces electrical power output) had shown the promise of that technology for high-power space applications. A dual use for terrestrial applications exists for compact Stirling converters for onsite combined heat and power units. The Stirling cycle is also usable in reverse as a refrigeration cycle suitable for cryogenic cooling, so this Stirling converter work promised double benefits as well as dual uses. The uses for cryogenic coolers within NASA abound; commercial applications are similarly wide-ranging, from cooling liquid oxygen and nitrogen, to cryobiology and bio-storage, cryosurgery, instrument and detector cooling, semiconductor manufacturing, and support service for cooled superconducting power systems.

  19. 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.)

  20. 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.

  1. On the structure of the outer layers of cool carbon stars

    Science.gov (United States)

    Querci, F.; Querci, M.; Wing, R. F.; Cassatella, A.; Heck, A.

    1982-01-01

    Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.

  2. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    Science.gov (United States)

    Meynet, Georges; Kudritzki, Rolf-Peter; Georgy, Cyril

    2015-09-01

    Context. The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g/T_text{eff ^4}. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool for determining extragalactic distances. Aims: Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal for using as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation for the FGLR as an extragalactic distance indicator. Methods: We used different grids of stellar models for initial masses between 9 and 40 M⊙ and for metallicities between Z = 0.002 and 0.014, with and without rotation, which were computed with various mass loss rates during the red supergiant phase. For each of these models, we discuss the details of post-main sequence evolution and construct theoretical FGLRs by means of population synthesis models that we then compare with the observed FGLR. Results: In general, the stellar evolution model FGLRs agree reasonably well with the observed one. There are, however, differences between the models, in particular with regard to the shape and width (scatter) in the flux-weighted gravity-luminosity plane. The best agreement is obtained with models that include the effects of rotation and assume that the large majority, if not all, of the observed BSG evolve toward the red supergiant phase and that only a few are evolving back from this stage. The effects of metallicity on the shape and scatter of the FGLR are small. Conclusions: The shape, scatter, and metallicity dependence of the observed FGLR are explained well by stellar evolution models. This provides a solid theoretical foundation for using this relationship as a robust extragalactic distance indicator.

  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. The Gravitational Wave Signature of Stellar Collapse and Dynamics of Compact Stars

    Science.gov (United States)

    Abdikamalov, E. B.

    2009-10-01

    This thesis is devoted to the study of the gravitational wave (GW) signature of stellar collapse and the dynamical behavior compact stars. The thesis consists of two parts. In the first one, we study the dynamics of the phase-transition-induced collapse of neutron stars (NSs) and the accretion-induced collapse of white dwarfs (WDs) as well as the associated GW emission. The second part is concerned with the study of the effects of general relativity on the magnetosphere of oscillating NSs. An increase in the central density of a NS may trigger a phase transition from hadronic matter to deconfined quark matter in the core, causing it to collapse to a more compact hybrid-star configuration. We present a study of this, using general relativistic hydrodynamics simulations with a simplified equation of state and considering the case of supersonic phase transition. We confirm that the emitted GW spectrum is dominated by the fundamental quasi-radial and quadrupolar pulsation modes. We observe a nonlinear mode resonance which substantially enhances the emission in some cases. We explain the damping mechanisms operating and estimate the detectability of the GWs. In massive accreting oxygen-neon WDs, their core material may in several circumstances experience rapid electron captures leading to collapse of the WD to a protoneutron star and collapse-driven supernova (SN) explosion. This process is called accretion-induced collapse (AIC) and represents a path alternative to thermonuclear disruption of accreting WDs in Type Ia SNe. An AIC-driven SN explosion is expected to be weak and of short duration, making it hard to detect by electromagnetic means alone. Neutrino and GW observations may provide crucial information necessary to reveal a potential AIC event. Motivated by the need for systematic predictions of the GW signature of AIC, we present results from an extensive set of general-relativistic simulations of AIC using a microphysical finite-temperature equation of state

  5. Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

    Science.gov (United States)

    Ezzeddine, Rana; Frebel, Anna; Plez, Bertrand

    2017-10-01

    We present new ultra-metal-poor stars parameters with [Fe/H] LTE in their atmospheric parameters and show that they can grow up to ˜1.00 dex in [Fe/H], ˜150 K in {T}{eff} and ˜0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely second-generation stars to investigate the early universe and how the chemical elements were formed.

  6. 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.

  7. 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.

  8. The non-LTE formation of Li I lines in cool stars

    NARCIS (Netherlands)

    Carlsson, M.; Rutten, R.J.; Bruls, J.H.M.J.; Shchukina, N. G.

    1994-01-01

    We study the non-LTE (non local thermodynamic equilibrium) formation of Li I lines in the spectra of cool stars for a grid of radiative-equilibrium model atmospheres with variation in effective temperature, gravity, metallicity and lithium abundance. We analyze the mechanisms by which departures

  9. 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.

  10. Rotation, activity, and lithium abundance in cool binary stars

    Science.gov (United States)

    Strassmeier, K. G.; Weber, M.; Granzer, T.; Järvinen, S.

    2012-10-01

    We have used two robotic telescopes to obtain time-series high-resolution optical echelle spectroscopy and V I and/or by photometry for a sample of 60 active stars, mostly binaries. Orbital solutions are presented for 26 double-lined systems and for 19 single-lined systems, seven of them for the first time but all of them with unprecedented phase coverage and accuracy. Eighteen systems turned out to be single stars. The total of 6609 {R=55 000} échelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute Hα-core fluxes as a function of time. The photometry is used to infer unspotted brightness, {V-I} and/or b-y colors, spot-induced brightness amplitudes and precise rotation periods. An extra 22 radial-velocity standard stars were monitored throughout the science observations and yield a new barycentric zero point for our STELLA/SES robotic system. Our data are complemented by literature data and are used to determine rotation-temperature-activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74 % of all known rapidly-rotating active binary stars are synchronized and in circular orbits but 26 % (61 systems) are rotating asynchronously of which half have {P_rot>P_orb} and {e>0}. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin-down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars, P_rot ∝ T_eff-7, for both single and binaries, main sequence and evolved. For inactive, single giants with {P_rot>100} d, the relation is much weaker, {P_rot ∝ T_eff-1.12}. Our data also indicate a period-activity relation for Hα of the form {R_Hα ∝ P

  11. Glimpses of stellar surfaces. I. Spot evolution and differential rotation of the planet host star Kepler-210

    Science.gov (United States)

    Ioannidis, P.; Schmitt, J. H. M. M.

    2016-10-01

    We use high accuracy photometric data obtained with the Kepler satellite to monitor the activity modulations of the Kepler-210 planet host star over a time span of more than four years. Following the phenomenology of the star's light curve in combination with a five spot model, we identify six different so-called spot seasons. A characteristic, which is common in the majority of the seasons, is the persistent appearance of spots in a specific range of longitudes on the stellar surface. The most prominent period of the observed activity modulations is different for each season and appears to evolve following a specific pattern, resembling the changes in the sunspot periods during the solar magnetic cycle. Under the hypothesis that the star exhibits solar-like differential rotation, we suggest differential rotation values of Kepler-210 that are similar to or smaller than that of the Sun. Finally, we estimate spot life times between ~60 days and ~90 days, taking into consideration the evolution of the total covered stellar surface computed from our model.

  12. Exploring the origins of the young stars in the central parsec of the Galaxy with stellar dynamics

    Science.gov (United States)

    Lu, Jessica Ryan

    One of the most perplexing problems associated with the supermassive black hole at the center of our Galaxy is the origin of the young stars in its close vicinity. In this thesis, the question of the young stars' origins is addressed using high-resolution infrared images obtained at the W. M. Keck telescopes to study both the distribution and kinematics of the young stellar population. First, using proper motion measurements and stellar number density counts based on 9 years of diffraction-limited K(2.2 microm)-band speckle imaging at the W. M. Keck 10-meter telescopes, we have identified a new comoving group of stars, which we call the IRS 16SW comoving group, located 1'' .9 (0.08 pc, in projection) from the central black hole. Four of the five members of this comoving group have been spectroscopically identified as massive young stars, specifically He I emission-line stars and OBN stars. This is the second young comoving group within the central parsec of the Milky Way to be recognized and is the closest, by a factor of 2, in projection to the central black hole. Second, we present new proper motions from the 10 m Keck telescopes for a puzzling population of massive, young stars located within a parsec of the supermassive black hole at the Galactic Center. Our proper motion measurements have uncertainties of only 0.07 mas/yr (3 km/s), which is ≳ 7 times better than previous proper motion measurements for these stars, and enables us to measure accelerations as low as 0.2 mas/yr 2 (7 km/s/yr). These measurements, along with stellar line-of-sight velocities from the literature, constrain the true orbit of each individual star and allow us to directly test the hypothesis that the massive stars reside in two stellar disks as has been previously proposed. Analysis of the stellar orbits reveals only one disk of young stars. No second disk was detected using a method that is capable of detecting disks with half-opening angles of 19° and containing at least 7 stars

  13. Assessing the fundamental limits of multiple star formation: An imaging search for the lowest mass stellar companions to intermediate-mass stars

    Science.gov (United States)

    Duchene, Gaspard; Tzern Oon, Jner; Kantorski, Patrick; De Rosa, Robert J.; Thomas, Sandrine; Patience, Jennifer; Pueyo, Laurent; Nielsen, Eric L.; Konopacky, Quinn M.

    2017-01-01

    Stellar binaries are a common byproduct of star formation and therefore inform us on the processes of collapse and fragmentation of prestellar cores. While multiplicity surveys generally reveal an extensive diversity of multiple systems, with broad ranges of semi-major axis, mass ratio and eccentricities, one remarkable feature that was identified in the last two decades is the so-called brown dwarf desert, i.e., the apparent paucity of (non-planetary) substellar companions to solar-type stars. This "desert" was primarily identified among spectroscopic binaries but also appears to be a significant feature of wider, visual binaries. The physical origin of this feature has not been fully accounted for but is likely established during the formation of the systems. One way to shed new light on this question is to study the frequency of low-mass stellar companions to intermediate-mass star (late-B type, or 3-5 Msun), as those form through a similar, albeit scaled-up, mechanism as solar-type stars. Here we present preliminary results from two adaptive-optics based surveys to search for such multiple systems. Specifically, we are using the new ShaneAO system on the Lick3m telescope (~100 stars observed to date) and the Gemini Planet Imager (45 stars observed). We are targeting stars located both in open clusters and scattered in the Galactic field to search for potential evidence of dynamic evolution. To identify candidate low-mass companions as close in to target stars, we use advanced point spread function (PSF) subtraction algorithms, specifically implementations of the LOCI and KLIP algorithms. In the case of the ShaneAO observations, which do not allow for field rotation, we use LOCI in combination with Reference Differential Imaging (ADI), using our library of science images as input for PSF subtraction. In this contribution, we will discuss the potential of ShaneAO to reveal faint, subarcsecond companions in this context and present candidate companions from both

  14. THE 300 km s–1 STELLAR STREAM NEAR SEGUE 1: INSIGHTS FROM HIGH-RESOLUTION SPECTROSCOPY OF ITS BRIGHTEST STAR

    International Nuclear Information System (INIS)

    Frebel, Anna; Casey, Andrew R.; Lunnan, Ragnhild; Norris, John E.; Wyse, Rosemary F. G.; Gilmore, Gerard

    2013-01-01

    We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km s –1 stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan/MIKE spectrum, we determine a metallicity of [Fe/H] = –1.46 ± 0.05 ± 0.23 (random and systematic uncertainties) for star 300S-1, and find an abundance pattern similar to typical halo stars at this metallicity. Comparing our stellar parameters to theoretical isochrones, we estimate a distance of 18 ± 7 kpc. Both the metallicity and distance estimates are in good agreement with what can be inferred from comparing the Sloan Digital Sky Survey photometric data of the stream stars to globular cluster sequences. While several other structures overlap with the stream in this part of the sky, the combination of kinematic, chemical, and distance information makes it unlikely that these stars are associated with either the Segue 1 galaxy, the Sagittarius Stream, or the Orphan Stream. Streams with halo-like abundance signatures, such as the 300 km s –1 stream, present another observational piece for understanding the accretion history of the Galactic halo.

  15. On the Onset of Secondary Stellar Generations in Giant Star-forming Regions and Massive Star Clusters

    Czech Academy of Sciences Publication Activity Database

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

    2014-01-01

    Roč. 792, č. 2 (2014), 105/1-105/10 ISSN 0004-637X R&D Projects: GA ČR GAP209/12/1795 Institutional support: RVO:67985815 Keywords : galaxies: ISM * star clusters: general * galaxies: star formation Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.993, year: 2014

  16. 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.

  17. Quantitative UV spectroscopy of early O stars on the Magellanic Clouds: The determination of the stellar metallicities

    Science.gov (United States)

    Haser, Stefan M.; Pauldrach, Adalbert W. A.; Lennon, Danny J.; Kudritzki, Rolf-Peter; Lennon, Maguerite; Puls, Joachim; Voels, Stephen A.

    1997-01-01

    Ultraviolet spectra of four O stars in the Magellanic Clouds obtained with the faint object spectrograph of the Hubble Space Telescope are analyzed with respect to their metallicity. The metal abundances are derived from the stellar parameters and the mass loss rate with a two step procedure: hydrodynamic radiation-driven wind models with metallicity as a free parameter are constructed to fit the observed wind momentum rate and thus yield a dynamical metallicity, and synthetic spectra are computed for different metal abundances and compared to the observed spectra in order to obtain a spectroscopic metallicity.

  18. Multiple stellar populations in Magellanic Cloud clusters. VI. A survey of multiple sequences and Be stars in young clusters

    Science.gov (United States)

    Milone, A. P.; Marino, A. F.; Di Criscienzo, M.; D'Antona, F.; Bedin, L. R.; Da Costa, G.; Piotto, G.; Tailo, M.; Dotter, A.; Angeloni, R.; Anderson, J.; Jerjen, H.; Li, C.; Dupree, A.; Granata, V.; Lagioia, E. P.; Mackey, A. D.; Nardiello, D.; Vesperini, E.

    2018-03-01

    The split main sequences (MSs) and extended MS turnoffs (eMSTOs) detected in a few young clusters have demonstrated that these stellar systems host multiple populations differing in a number of properties such as rotation and, possibly, age. We analyze Hubble Space Telescope photometry for thirteen clusters with ages between ˜40 and ˜1000 Myrs and of different masses. Our goal is to investigate for the first time the occurrence of multiple populations in a large sample of young clusters. We find that all the clusters exhibit the eMSTO phenomenon and that MS stars more massive than ˜1.6 M_⊙ define a blue and red MS, with the latter hosting the majority of MS stars. The comparison between the observations and isochrones suggests that the blue MSs are made of slow-rotating stars, while the red MSs host stars with rotational velocities close to the breakup value. About half of the bright MS stars in the youngest clusters are H-alpha emitters. These Be stars populate the red MS and the reddest part of the eMSTO thus supporting the idea that the red MS is made of fast rotators. We conclude that the split MS and the eMSTO are a common feature of young clusters in both Magellanic Clouds. The phenomena of a split MS and an eMSTO occur for stars that are more massive than a specific threshold which is independent of the host-cluster mass. As a by-product, we report the serendipitous discovery of a young SMC cluster, GALFOR1.

  19. 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.

  20. Dark stars: a review.

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  1. 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.

  2. A STAR IN THE M31 GIANT STREAM: THE HIGHEST NEGATIVE STELLAR VELOCITY KNOWN

    International Nuclear Information System (INIS)

    Caldwell, Nelson; Kenyon, Scott J.; Morrison, Heather; Harding, Paul; Schiavon, Ricardo; Rose, James A.

    2010-01-01

    We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s -1 . Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

  3. A temperate rocky super-Earth transiting a nearby cool star

    Science.gov (United States)

    Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D.; Berta-Thompson, Zachory K.; Newton, Elisabeth R.; Rodriguez, Joseph E.; Winters, Jennifer G.; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C.; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A.; Latham, David W.; Dressing, Courtney D.

    2017-04-01

    M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

  4. A temperate rocky super-Earth transiting a nearby cool star.

    Science.gov (United States)

    Dittmann, Jason A; Irwin, Jonathan M; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D; Berta-Thompson, Zachory K; Newton, Elisabeth R; Rodriguez, Joseph E; Winters, Jennifer G; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A; Latham, David W; Dressing, Courtney D

    2017-04-19

    M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

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

    Energy Technology Data Exchange (ETDEWEB)

    Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Joerg-Uwe; Mueller, Andre; Bonnefoy, Mickaeel; Henning, Thomas [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Lacour, Sylvestre; Thebault, Philippe [LESIA, CNRS/UMR-8109, Observatoire de Paris, UPMC, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon (France); Juhasz, Attila [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Sicilia-Aguilar, Aurora [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Cantoblanco, Madrid (Spain); Tuthill, Peter [School of Physics, University of Sydney, NSW 2006 (Australia); Crida, Aurelien, E-mail: biller@mpia.de [Universite de Nice - Sophia antipolis/C.N.R.S./Observatoire de la Cote d' Azur, Laboratoire Lagrange (UMR 7293), Boulevard de l' Observatoire, B.P. 4229 06304 NICE cedex 04 (France)

    2012-07-10

    With the uniquely high contrast within 0.''1 ({Delta}mag(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 (3{sigma} 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 {approx}0.1-0.4 M{sub Sun }. 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.

  6. 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

  7. 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.

  8. Kiloparsec-scale Simulations of Star Formation in Disk Galaxies. IV. Regulation of Galactic Star Formation Rates by Stellar Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Butler, Michael J. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Tan, Jonathan C. [Departments of Astronomy and Physics, University of Florida, Gainesville, FL 32611 (United States); Teyssier, Romain; Nickerson, Sarah [Institute for Computational Science, University of Zurich, 8049 Zurich (Switzerland); Rosdahl, Joakim [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2017-06-01

    Star formation from the interstellar medium of galactic disks is a basic process controlling the evolution of galaxies. Understanding the star formation rate (SFR) in a local patch of a disk with a given gas mass is thus an important challenge for theoretical models. Here we simulate a kiloparsec region of a disk, following the evolution of self-gravitating molecular clouds down to subparsec scales, as they form stars that then inject feedback energy by dissociating and ionizing UV photons and supernova explosions. We assess the relative importance of each feedback mechanism. We find that H{sub 2}-dissociating feedback results in the largest absolute reduction in star formation compared to the run with no feedback. Subsequently adding photoionization feedback produces a more modest reduction. Our fiducial models that combine all three feedback mechanisms yield, without fine-tuning, SFRs that are in excellent agreement with observations, with H{sub 2}-dissociating photons playing a crucial role. Models that only include supernova feedback—a common method in galaxy evolution simulations—settle to similar SFRs, but with very different temperatures and chemical states of the gas, and with very different spatial distributions of young stars.

  9. Kiloparsec-scale Simulations of Star Formation in Disk Galaxies. IV. Regulation of Galactic Star Formation Rates by Stellar Feedback

    International Nuclear Information System (INIS)

    Butler, Michael J.; Tan, Jonathan C.; Teyssier, Romain; Nickerson, Sarah; Rosdahl, Joakim; Van Loo, Sven

    2017-01-01

    Star formation from the interstellar medium of galactic disks is a basic process controlling the evolution of galaxies. Understanding the star formation rate (SFR) in a local patch of a disk with a given gas mass is thus an important challenge for theoretical models. Here we simulate a kiloparsec region of a disk, following the evolution of self-gravitating molecular clouds down to subparsec scales, as they form stars that then inject feedback energy by dissociating and ionizing UV photons and supernova explosions. We assess the relative importance of each feedback mechanism. We find that H 2 -dissociating feedback results in the largest absolute reduction in star formation compared to the run with no feedback. Subsequently adding photoionization feedback produces a more modest reduction. Our fiducial models that combine all three feedback mechanisms yield, without fine-tuning, SFRs that are in excellent agreement with observations, with H 2 -dissociating photons playing a crucial role. Models that only include supernova feedback—a common method in galaxy evolution simulations—settle to similar SFRs, but with very different temperatures and chemical states of the gas, and with very different spatial distributions of young stars.

  10. Stellar Dynamics and Star Formation Histories of z ˜ 1 Radio-loud Galaxies

    Science.gov (United States)

    Barišić, Ivana; van der Wel, Arjen; Bezanson, Rachel; Pacifici, Camilla; Noeske, Kai; Muñoz-Mateos, Juan C.; Franx, Marijn; Smolčić, Vernesa; Bell, Eric F.; Brammer, Gabriel; Calhau, João; Chauké, Priscilla; van Dokkum, Pieter G.; van Houdt, Josha; Gallazzi, Anna; Labbé, Ivo; Maseda, Michael V.; Muzzin, Adam; Sobral, David; Straatman, Caroline; Wu, Po-Feng

    2017-09-01

    We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities (L 3 GHz > 1023 W Hz-1) at 0.6 175 km s-1, corresponding to black hole masses in excess of 108 M ⊙. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z ˜ 1 is five to 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z ˜ 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black hole masses, radio loudness, and quiescence at z ˜ 1.

  11. The evolution of CNO isotopes: a new window on cosmic star formation history and the stellar IMF in the age of ALMA

    Science.gov (United States)

    Romano, D.; Matteucci, F.; Zhang, Z.-Y.; Papadopoulos, P. P.; Ivison, R. J.

    2017-09-01

    We use state-of-the-art chemical models to track the cosmic evolution of the CNO isotopes in the interstellar medium of galaxies, yielding powerful constraints on their stellar initial mass function (IMF). We re-assess the relative roles of massive stars, asymptotic giant branch (AGB) stars and novae in the production of rare isotopes such as 13C, 15N, 17O and 18O, along with 12C, 14N and 16O. The CNO isotope yields of super-AGB stars, novae and fast-rotating massive stars are included. Having reproduced the available isotope enrichment data in the solar neighbourhood, and across the Galaxy, and having assessed the sensitivity of our models to the remaining uncertainties, e.g. nova yields and star formation history, we show that we can meaningfully constrain the stellar IMF in galaxies using C, O and N isotope abundance ratios. In starburst galaxies, where data for multiple isotopologue lines are available, we find compelling new evidence for a top-heavy stellar IMF, with profound implications for their star formation rates and efficiencies, perhaps also their stellar masses. Neither chemical fractionation nor selective photodissociation can significantly perturb globally averaged isotopologue abundance ratios away from the corresponding isotope ones, as both these processes will typically affect only small mass fractions of molecular clouds in galaxies. Thus, the Atacama Large Millimeter Array now stands ready to probe the stellar IMF, and even the ages of specific starburst events in star-forming galaxies across cosmic time unaffected by the dust obscuration effects that plague optical/near-infrared studies.

  12. Stellar Rotation with Kepler and Gaia: Evidence for a Bimodal Star Formation History

    Science.gov (United States)

    Davenport, James

    2018-01-01

    Kepler stars with rotation periods measured via starspot modulations in their light curves have been matched against the astrometric data from Gaia Data Release 1. A total of 1,299 bright rotating stars were recovered, most with temperatures hotter than 5000 K. From these, 894 were selected as being near the main sequence. These main sequence stars show a bimodality in their rotation period distribution, centered around a ~600 Myr rotation-isochrone. This feature matches the bimodal period distribution found in cooler stars with Kepler, but was previously undetected for solar-type stars due to sample contamination by subgiant and binary stars. A tenuous connection between the rotation period and total proper motion is found, suggesting the period bimodality is due to the age distribution of stars within 300pc of the Sun, rather than a phase of rapid angular momentum loss. I will discuss how the combination of Kepler/K2/TESS with Gaia will enable us to map the star formation history of our galactic neighborhood.

  13. Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star

    Energy Technology Data Exchange (ETDEWEB)

    Van Grootel, V.; Gillon, M.; Scuflaire, R. [Institut d' Astrophysique et de Géophysique, Université de Liège, 17 Allée du 6 Août, B-4000 Liège (Belgium); Valencia, D. [Department of Physical and Environmental Sciences, University of Toronto, 1265 Military Trail, Toronto, ON, M1C 1A4 (Canada); Madhusudhan, N.; Demory, B.-O.; Queloz, D. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Dragomir, D. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr. Suite 102, Goleta, CA 93117 (United States); Howe, A. R.; Burrows, A. S. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Deming, D. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Ehrenreich, D.; Lovis, C.; Mayor, M.; Pepe, F.; Segransan, D.; Udry, S. [Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, CH-1290 Sauverny (Switzerland); Seager, S., E-mail: valerie.vangrootel@ulg.ac.be [Department of Earth, Atmospheric and Planetary Sciences, Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)

    2014-05-01

    Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass (M {sub *} = 0.77 ± 0.05 M {sub ☉}) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-High Resolution Echelle Spectrometer (Keck-HIRES) radial velocities and Microvariability and Oscillations of STars (MOST) and Spitzer photometry. HD 97658 b is a massive (M{sub P}=7.55{sub −0.79}{sup +0.83} M{sub ⊕}) and large (R{sub P}=2.247{sub −0.095}{sup +0.098}R{sub ⊕} at 4.5 μm) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, of at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for upcoming space missions such as the Transiting Exoplanet Survey Satellite (TESS), the Characterizing Exoplanet Satellite (CHEOPS), the Planetary Transits and Oscillations of stars (PLATO), and the James Webb Space Telescope to characterize thoroughly its structure and atmosphere.

  14. The evolution of magnetic hot massive stars: Implementation of the quantitative influence of surface magnetic fields in modern models of stellar evolution

    Science.gov (United States)

    Keszthelyi, Zsolt; Wade, Gregg A.; Petit, Veronique

    2017-11-01

    Large-scale dipolar surface magnetic fields have been detected in a fraction of OB stars, however only few stellar evolution models of massive stars have considered the impact of these fossil fields. We are performing 1D hydrodynamical model calculations taking into account evolutionary consequences of the magnetospheric-wind interactions in a simplified parametric way. Two effects are considered: i) the global mass-loss rates are reduced due to mass-loss quenching, and ii) the surface angular momentum loss is enhanced due to magnetic braking. As a result of the magnetic mass-loss quenching, the mass of magnetic massive stars remains close to their initial masses. Thus magnetic massive stars - even at Galactic metallicity - have the potential to be progenitors of "heavy" stellar mass black holes. Similarly, at Galactic metallicity, the formation of pair instability supernovae is plausible with a magnetic progenitor.

  15. Stellar Dynamics and Star Formation Histories of z ∼ 1 Radio-loud Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Barišić, Ivana; Van der Wel, Arjen; Chauké, Priscilla; Van Houdt, Josha; Straatman, Caroline [Max-Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); Bezanson, Rachel [Department of Astrophysics, Princeton University, Princeton, NJ 08544 (United States); Pacifici, Camilla [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Noeske, Kai [experimenta gGmbH, Kranenstraße 14, 74072 Heilbronn (Germany); Muñoz-Mateos, Juan C. [European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago (Chile); Franx, Marijn; Labbé, Ivo; Maseda, Michael V.; Sobral, David [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 AA Leiden (Netherlands); Smolčić, Vernesa [Department of Physics, Faculty of Science, University of Zagreb, Bijenicka cesta 32, 10000 Zagreb (Croatia); Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109 (United States); Brammer, Gabriel [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Calhau, João [Department of Physics, Lancaster University, Lancaster LA1 4 YB (United Kingdom); Van Dokkum, Pieter G. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Gallazzi, Anna [INAF-Osservatorio Astrofsico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Muzzin, Adam, E-mail: barisic@mpia.de [Department of Physics and Astronomy, York University, 4700 Keele Street, Toronto, Ontario, ON MJ3 1P3 (Canada); and others

    2017-09-20

    We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities ( L {sub 3} {sub GHz} > 10{sup 23} W Hz{sup −1}) at 0.6 < z < 1. This sample is constructed by cross-matching galaxies from the deep VLT/VIMOS LEGA-C spectroscopic survey with the VLA 3 GHz data set. The LEGA-C continuum spectra reveal for the first time stellar velocity dispersions and age indicators of z ∼ 1 radio galaxies. We find that z ∼ 1 radio-loud active galactic nucleus (AGN) occur exclusively in predominantly old galaxies with high velocity dispersions: σ {sub *} > 175 km s{sup −1}, corresponding to black hole masses in excess of 10{sup 8} M {sub ⊙}. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z ∼ 1 is five to 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z ∼ 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black hole masses, radio loudness, and quiescence at z ∼ 1.

  16. 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.

  17. 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...... 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...

  18. Extreme star formation in the Milky Way: Luminosity distributions of young stellar objects in W49A and W51

    Science.gov (United States)

    Eden, D. J.; Moore, T. J. T.; Urquhart, J. S.; Elia, D.; Plume, R.; König, C.; Baldeschi, A.; Schisano, E.; Rigby, A. J.; Morgan, L. K.; Thompson, M. A.

    2018-03-01

    We have compared the star-formation properties of the W49A and W51 regions by using far-infrared data from the Herschel infrared Galactic Plane Survey (Hi-GAL) and 850-μm observations from the James Clerk Maxwell Telescope (JCMT) to obtain luminosities and masses, respectively, of associated compact sources. The former are infrared luminosities from the catalogue of Elia et al. (2017), while the latter are from the JCMT Plane survey source catalogue as well as measurements from new data. The clump-mass distributions of the two regions are found to be consistent with each other, as are the clump-formation efficiency and star-formation efficiency analogues. However, the frequency distributions of the luminosities of the young stellar objects are significantly different. While the luminosity distribution in W51 is consistent with Galaxy-wide samples, that of W49A is top-heavy. The differences are not dramatic, and are concentrated in the central regions of W49A. However, they suggest that physical conditions there, which are comparable in part to those in extragalactic starbursts, are significantly affecting the star-formation properties or evolution of the dense clumps in the region.

  19. Binary systems, star clusters and the Galactic-field population. Applied stellar dynamics

    Science.gov (United States)

    Kroupa, Pavel

    2002-01-01

    This book contains the results of recent theoretical work on the evolution of primordial binary systems in young star clusters, their effect on the evolution of their host clusters, implications for the distribution of young stars in the Milky Way, and the formation of bound star clusters. This work shows that if the Galactic-field binary population is a dynamically evolved version of the Taurus-Auriga pre-main sequence population, then most stars form in clusters with typically a few hundred binaries within a radius of about 0.5-1 pc. The results also suggest that the population I primordial binary-star orbital-parameter distribution functions may be universal, much like the initial mass function. Most solar-like planetary systems can survive in such clusters. The work presented here also establishes that most observed triple and quadruple systems must be primordial, but that α Cen A/B-Proxima Cen-like systems can form in clusters through dynamical capture. Precise N-body calculations using Aarseth's N-body codes of clusters containing up to 104 stars are used to create an extensive young-cluster library. These data demonstrate that the primordial binary systems are disrupted on a crossing-time scale, and that the truncation of the surviving period distribution measures the maximum concentration the cluster ever experienced. The N-body calculations demonstrate that Galactic star clusters form readily as nuclei of expanding OB associations despite a star-formation efficiency of typically 30 per cent and gas-expulsion over a time-span shorter than the cluster crossing time.

  20. The complex magnetic field topology of the cool Ap star 49 Cam

    Science.gov (United States)

    Silvester, J.; Kochukhov, O.; Rusomarov, N.; Wade, G. A.

    2017-10-01

    49 Cam is a cool magnetic chemically peculiar star that has been noted for showing strong, complex Zeeman linear polarization signatures. This paper describes magnetic and chemical surface maps obtained for 49 Cam using the Invers10 magnetic Doppler imaging code and high-resolution spectropolarimetric data in all four Stokes parameters collected with the ESPaDOnS and Narval spectropolarimeters at the Canada-France-Hawaii Telescope and Pic du Midi Observatory. The reconstructed magnetic field maps of 49 Cam show a relatively complex structure. Describing the magnetic field topology in terms of spherical harmonics, we find significant contributions of modes up to ℓ = 3, including toroidal components. Observations cannot be reproduced using a simple low-order multipolar magnetic field structure. 49 Cam exhibits a level of field complexity that has not been seen in magnetic maps of other cool Ap stars. Hence, we concluded that relatively complex magnetic fields are observed in Ap stars at both low and high effective temperatures. In addition to mapping the magnetic field, we also derive surface abundance distributions of nine chemical elements, including Ca, Sc, Ti, Cr, Fe, Ce, Pr, Nd and Eu. Comparing these abundance maps with the reconstructed magnetic field geometry, we find no clear relationship of the abundance distributions with the magnetic field for some elements. However, for other elements some distinct patterns are found. We discuss these results in the context of other recent magnetic mapping studies and theoretical predictions of radiative diffusion.

  1. Population synthesis to constrain Galactic and stellar physics. I. Determining age and mass of thin-disc red-giant stars

    Science.gov (United States)

    Lagarde, N.; Robin, A. C.; Reylé, C.; Nasello, G.

    2017-05-01

    Context. The cornerstone mission of the European Space Agency, Gaia, together with forthcoming complementary surveys (CoRoT, Kepler, K2, APOGEE, and Gaia-ESO), will revolutionize our understanding of the formation and history of our Galaxy, providing accurate stellar masses, radii, ages, distances, as well as chemical properties for a very large sample of stars across different Galactic stellar populations. Aims: Using an improved population synthesis approach and new stellar evolution models we attempt to evaluate the possibility of deriving ages and masses of clump stars from their chemical properties. Methods: A new version of the Besançon Galaxy models (BGM) is used in which new stellar evolutionary tracks are computed from the stellar evolution code STAREVOL. These provide global, chemical, and seismic properties of stars from the pre-main sequence to the early-AGB. For the first time, the BGM can explore the effects of an extra-mixing occurring in red-giant stars. In particular we focus on the effects of thermohaline instability on chemical properties as well as on the determination of stellar ages and masses using the surface [C/N] abundance ratio. Results: The impact of extra-mixing on 3He, 12C/13C, nitrogen, and [C/N] abundances along the giant branch is quantified. We underline the crucial contribution of asteroseismology to discriminate between evolutionary states of field giants belonging to the Galactic disc. The inclusion of thermohaline instability has a significant impact on 12C/13C, 3He as well as on the [C/N] values. We clearly show the efficiency of thermohaline mixing at different metallicities and its influence on the determined stellar mass and age from the observed [C/N] ratio. We then propose simple relations to determine ages and masses from chemical abundances according to these models. Conclusions: We emphasize the usefulness of population synthesis tools to test stellar models and transport processes inside stars. We show that transport

  2. 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...... mass density of the universe was only 50%, 10%, and 1% of its current value at z 0.75, 2.0, and 3.5, respectively. The quiescent population drives most of the overall growth, with the stellar mass density of these galaxies increasing as ρ(1 + z) since z = 3.5, whereas the mass density of star......-forming galaxies increases as ρ(1 + z). At z > 2.5, star-forming galaxies dominate the total SMF at all stellar masses, although a non-zero population of quiescent galaxies persists to z = 4. Comparisons of the Ks -selected star-forming galaxy SMFs with UV-selected SMFs at 2.5

  3. THE STELLAR POPULATION OF h AND χ PERSEI: CLUSTER PROPERTIES, MEMBERSHIP, AND THE INTRINSIC COLORS AND TEMPERATURES OF STARS

    International Nuclear Information System (INIS)

    Currie, Thayne; Irwin, Jonathan; Kenyon, Scott J.; Tokarz, Susan; Hernandez, Jesus; Balog, Zoltan; Bragg, Ann; Berlind, Perry; Calkins, Mike

    2010-01-01

    From photometric observations of ∼ 47,000 stars and spectroscopy of ∼ 11,000 stars, we describe the first extensive study of the stellar population of the famous Double Cluster, h and χ Persei, down to subsolar masses. By analyzing optical spectra and optical/infrared photometry, we constrain the distance moduli (dM), reddening (E(B - V)), and ages for h Persei, χ Persei, and the low-density halo population surrounding both cluster cores. With the exception of mass and spatial distribution, the clusters are nearly identical in every measurable way. Both clusters have E(B - V) ∼ 0.52-0.55 and dM = 11.8-11.85; the halo population, while more poorly constrained, likely has identical properties. As determined from the main-sequence turnoff, the luminosity of M supergiants, and pre-main-sequence isochrones, ages for h Persei, χ Persei, and the halo population all converge on ∼14 Myr, thus showing a stunning agreement between estimates based on entirely different physics. From these data, we establish the first spectroscopic and photometric membership lists of cluster stars down to early/mid M dwarfs. At minimum, there are ∼ 5000 members within 10' of the cluster centers, while the entire h and χ Persei region has at least ∼ 13,000 and as many as 20,000 members. The Double Cluster contains ∼ 8400 M sun of stars within 10' of the cluster centers. We estimate a total mass of at least 20,000 M sun . We conclude our study by outlining outstanding questions regarding the past and present properties of h and χ Persei. From comparing recent work, we compile a list of intrinsic colors and derive a new effective temperature scale for O-M dwarfs, giants, and supergiants.

  4. 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

  5. UCAC4 Nearby Star Survey: A Search for Our Stellar Neighbors

    Science.gov (United States)

    Subasavage, John P.; Finch, Charlie T.; Zacharias, Norbert; Henry, Todd J.; Riedel, Adric R.

    2015-01-01

    We present 16 photometric color-M_K relations using the U. S. Naval Observatory Fourth CCD Astrograph Catalog (UCAC4). These relations estimate distances to nearby red dwarfs at the ˜15% accuracy level using photometry from the Two-Micron All-Sky Survey (2MASS) and the AAVSO Photometric All-Sky Survey (APASS). A sample of nearby stars from the Research Consortium On Nearby Stars (RECONS) group along with a supplemental list of very red stars all having accurate trigonometric parallaxes are used to generate the relations. Color, proper motion, and existing literature sources are used in an attempt to attain a clean sample of red dwarfs while limiting the amount of contamination from background giants. From this sample, we find 1761 candidate nearby M dwarfs estimated to be within 25 pc. Of this sample, 339 have no previously known published parallax or distance estimate and five of these are estimated to be within 10 pc. The nearest distance estimate of 5.9 pc was found for a star with V magnitude of 10.5. That several hundred new stars have been revealed so close to the Sun illustrates once again that there is considerable work yet to be done to map the solar neighborhood.

  6. Emission-line widths and stellar-wind flows in T Tauri stars

    International Nuclear Information System (INIS)

    Sa, C.; Lago, M.T.V.T.

    1986-01-01

    Spectra are reported of T Tauri stars taken with the IPCS on the Isaac Newton Telescope at the Observatorio del Roque de los Muchachos at a dispersion of l7 A mm -1 . These were taken in order to determine emission-line widths and hence flow velocities in the winds of these stars following the successful modelling of the wind from RU Lupi using such data. Line widths in RW Aur suggest a similar pattern to the wind flow as in RU Lupi with velocities rising in the inner chromosphere of the star and then entering a 'ballistic' zone. The wind from DFTau is also similar but velocities are generally much lower and the lines sharper. (author)

  7. Stellar dynamics. The fastest unbound star in our Galaxy ejected by a thermonuclear supernova.

    Science.gov (United States)

    Geier, S; Fürst, F; Ziegerer, E; Kupfer, T; Heber, U; Irrgang, A; Wang, B; Liu, Z; Han, Z; Sesar, B; Levitan, D; Kotak, R; Magnier, E; Smith, K; Burgett, W S; Chambers, K; Flewelling, H; Kaiser, N; Wainscoat, R; Waters, C

    2015-03-06

    Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy. Several acceleration mechanisms have been discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we present a spectroscopic and kinematic analysis of US 708. Traveling with a velocity of ~1200 kilometers per second, it is the fastest unbound star in our Galaxy. In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVSs. Furthermore, we detected that US 708 is a fast rotator. According to our binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova. Copyright © 2015, American Association for the Advancement of Science.

  8. 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.

  9. BAYESIAN ANALYSIS TO IDENTIFY NEW STAR CANDIDATES IN NEARBY YOUNG STELLAR KINEMATIC GROUPS

    International Nuclear Information System (INIS)

    Malo, Lison; Doyon, René; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan; Baron, Frédérique; Riedel, Adric

    2013-01-01

    We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the β Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as Hα and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in β Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for β Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 Å equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the β Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.

  10. Correlations between the stellar and disc properties of Taurus PMS stars in the GASPS sample

    NARCIS (Netherlands)

    Alonso-Martínez, Miguel; Riviere-Marichalar, Pablo; Pascual, Natalia; Montesinos, Benjamín; Howard, Christian D.; Sandell, Göran; Meeus, Gwendolyn; Eiroa, Carlos; Dent, Bill

    The Herschel Open Time Key Programme GASPS (P.I. B. Dent) has observed a large number of pre-main sequence TTauri stars in Taurus with PACS (photometry and spectroscopy). In addition, we have also carried out new ground-based optical and near-IR observations (photometry and spectroscopy) of most of

  11. Stellar and circumstellar activity of the Be star .mu. Cen. IV. Spectroscopic data

    Czech Academy of Sciences Publication Activity Database

    Rivinius, T.; Štefl, Stanislav; Stahl, O.; Kaufner, A.; Baade, D.

    2001-01-01

    Roč. 7, - (2001), s. - ISSN 1385-3945 R&D Projects: GA ČR GA202/97/0326; GA AV ČR IAA3003001 Institutional research plan: CEZ:AV0Z1003909 Keywords : Be stars * spectroscopy Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  12. Testing stellar evolution models with the retired A star HD 185351

    DEFF Research Database (Denmark)

    Hjørringgaard, J. G.; Silva Aguirre, V.; White, T. R.

    2017-01-01

    The physical parameters of the retired A star HD 185351 were analysed in great detail by Johnson et al. using interferometry, spectroscopy, and asteroseismology. Results from all independent methods are consistent with HD 185351 having a mass in excess of 1.5 M⊙. However, the study also showed...

  13. Modules for Experiments in Stellar Astrophysics (MESA)

    Science.gov (United States)

    Paxton, Bill; Bildsten, Lars; Dotter, Aaron; Herwig, Falk; Lesaffre, Pierre; Timmes, Frank

    2011-01-01

    Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source, robust, efficient, thread-safe libraries for a wide range of applications in computational stellar astrophysics. A one-dimensional stellar evolution module, MESAstar, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very low mass to massive stars, including advanced evolutionary phases. MESAstar solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. State-of-the-art modules provide equation of state, opacity, nuclear reaction rates, element diffusion data, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own explicitly defined public interface to facilitate independent development. Several detailed examples indicate the extensive verification and testing that is continuously performed and demonstrate the wide range of capabilities that MESA possesses. These examples include evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets to very old ages; the complete evolutionary track of a 1 M sun star from the pre-main sequence (PMS) to a cooling white dwarf; the solar sound speed profile; the evolution of intermediate-mass stars through the He-core burning phase and thermal pulses on the He-shell burning asymptotic giant branch phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; the complete evolutionary tracks of massive stars from the PMS to the onset of core collapse; mass transfer from stars undergoing Roche lobe overflow; and the evolution of helium accretion onto a neutron star. MESA can be downloaded from the project Web site (http://mesa.sourceforge.net/).

  14. 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.

  15. A GALEX-BASED SEARCH FOR THE SPARSE YOUNG STELLAR POPULATION IN THE TAURUS-AURIGAE STAR FORMING REGION

    International Nuclear Information System (INIS)

    Gómez de Castro, Ana I.; Lopez-Santiago, Javier; López-Martínez, Fatima; Sánchez, Néstor; Sestito, Paola; Gestoso, Javier Yañez; De Castro, Elisa; Cornide, Manuel

    2015-01-01

    In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J–K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J–K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions

  16. A GALEX-BASED SEARCH FOR THE SPARSE YOUNG STELLAR POPULATION IN THE TAURUS-AURIGAE STAR FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Gómez de Castro, Ana I.; Lopez-Santiago, Javier; López-Martínez, Fatima; Sánchez, Néstor; Sestito, Paola; Gestoso, Javier Yañez [AEGORA Research Group, Universidad Complutense de Madrid, Plaza de Ciencias 3, E-28040 Madrid (Spain); De Castro, Elisa; Cornide, Manuel [Fac. de CC. Físicas, Universidad Complutense de Madrid, Plaza de Ciencias 1, E-28040 Madrid (Spain)

    2015-02-01

    In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J–K color-color diagram is ideally suited for this purpose. From an initial sample of 163,313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J–K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.

  17. Stellar Metamorphosis:

    Science.gov (United States)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  18. Starspot-induced radial velocity jitter during a stellar cycle

    DEFF Research Database (Denmark)

    Korhonen, Heidi Helena; Andersen, Jan Marie; Järvinen, Silva

    2012-01-01

    Late-type stars exhibit cool regions on their surface, the stellar equivalent of sunspots. These dark starspots can also mimic the radial velocity variations caused by orbiting planets, making it at times difficult to distinguish between planets and activity signatures. The amount of spots...

  19. 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.

  20. Relative stellar occurrence of exoplanets in habitable zones of the main sequence F, G, K stars

    Czech Academy of Sciences Publication Activity Database

    Pintr, Pavel; Peřinová, V.; Lukš, A.; Pathak, A.

    2014-01-01

    Roč. 99, sept2014 (2014), s. 1-6 ISSN 0032-0633 R&D Projects: GA MŠk(CZ) ED2.1.00/03.0079 Institutional support: RVO:61389021 Keywords : Exoplanets * Methods: statistical * Stars: planetary systems Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.875, year: 2014 http://www.sciencedirect.com/science/article/pii/S003206331400172X#

  1. GAMA/G10-COSMOS/3D-HST: the 0 < z < 5 cosmic star formation history, stellar-mass, and dust-mass densities

    Science.gov (United States)

    Driver, Simon P.; Andrews, Stephen K.; da Cunha, Elisabete; Davies, Luke J.; Lagos, Claudia; Robotham, Aaron S. G.; Vinsen, Kevin; Wright, Angus H.; Alpaslan, Mehmet; Bland-Hawthorn, Joss; Bourne, Nathan; Brough, Sarah; Bremer, Malcolm N.; Cluver, Michelle; Colless, Matthew; Conselice, Christopher J.; Dunne, Loretta; Eales, Steve A.; Gomez, Haley; Holwerda, Benne; Hopkins, Andrew M.; Kafle, Prajwal R.; Kelvin, Lee S.; Loveday, Jon; Liske, Jochen; Maddox, Steve J.; Phillipps, Steven; Pimbblet, Kevin; Rowlands, Kate; Sansom, Anne E.; Taylor, Edward; Wang, Lingyu; Wilkins, Stephen M.

    2018-04-01

    We use the energy-balance code MAGPHYS to determine stellar and dust masses, and dust corrected star formation rates for over 200 000 GAMA galaxies, 170 000 G10-COSMOS galaxies, and 200 000 3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous data set spanning a broad range in stellar-mass (108-1012 M⊙), dust-mass (106-109 M⊙), and star formation rates (0.01-100 M⊙yr-1), and over a broad redshift range (0.0 measure the cosmic star formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous data set using consistent mass and star formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our CSFH we precisely reproduce the SMD with an interstellar medium replenishment factor of 0.50 ± 0.07, consistent with our choice of Chabrier initial mass function plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust-mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065-0.004 units of dust mass is also formed. (2) Over the history of the Universe approximately 90-95 per cent of all dust formed has been destroyed and/or ejected.

  2. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    International Nuclear Information System (INIS)

    Craig, Jonathan; Krumholz, Mark R.

    2013-01-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  3. CLOSE STELLAR ENCOUNTERS IN YOUNG, SUBSTRUCTURED, DISSOLVING STAR CLUSTERS: STATISTICS AND EFFECTS ON PLANETARY SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Craig, Jonathan; Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  4. Close Stellar Encounters in Young, Substructured, Dissolving Star Clusters: Statistics and Effects on Planetary Systems

    Science.gov (United States)

    Craig, Jonathan; Krumholz, Mark R.

    2013-06-01

    Both simulations and observations indicate that stars form in filamentary, hierarchically clustered associations, most of which disperse into their galactic field once feedback destroys their parent clouds. However, during their early evolution in these substructured environments, stars can undergo close encounters with one another that might have significant impacts on their protoplanetary disks or young planetary systems. We perform N-body simulations of the early evolution of dissolving, substructured clusters with a wide range of properties, with the aim of quantifying the expected number and orbital element distributions of encounters as a function of cluster properties. We show that the presence of substructure both boosts the encounter rate and modifies the distribution of encounter velocities compared to what would be expected for a dynamically relaxed cluster. However, the boost only lasts for a dynamical time, and as a result the overall number of encounters expected remains low enough that gravitational stripping is unlikely to be a significant effect for the vast majority of star-forming environments in the Galaxy. We briefly discuss the implications of this result for models of the origin of the solar system, and of free-floating planets. We also provide tabulated encounter rates and orbital element distributions suitable for inclusion in population synthesis models of planet formation in a clustered environment.

  5. THE EVOLUTION OF THE STELLAR MASS FUNCTIONS OF STAR-FORMING AND QUIESCENT GALAXIES TO z = 4 FROM THE COSMOS/UltraVISTA SURVEY

    International Nuclear Information System (INIS)

    Muzzin, Adam; Franx, Marijn; Labbé, Ivo; Marchesini, Danilo; Stefanon, Mauro; McCracken, Henry J.; Milvang-Jensen, Bo; Fynbo, J. P. U.; Dunlop, James S.; Brammer, Gabriel; Van Dokkum, Pieter G.

    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 K s -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 mass density of the universe was only 50%, 10%, and 1% of its current value at z ∼ 0.75, 2.0, and 3.5, respectively. The quiescent population drives most of the overall growth, with the stellar mass density of these galaxies increasing as ρ star ∝(1 + z) –4.7±0.4 since z = 3.5, whereas the mass density of star-forming galaxies increases as ρ star ∝(1 + z) –2.3±0.2 . At z > 2.5, star-forming galaxies dominate the total SMF at all stellar masses, although a non-zero population of quiescent galaxies persists to z = 4. Comparisons of the K s -selected star-forming galaxy SMFs with UV-selected SMFs at 2.5 3.5. We estimate the average mass growth of individual galaxies by selecting galaxies at fixed cumulative number density. The average galaxy with log(M star /M ☉ ) = 11.5 at z = 0.3 has grown in mass by only 0.2 dex (0.3 dex) since z = 2.0 (3.5), whereas those with log(M star /M ☉ ) = 10.5 have grown by >1.0 dex since z = 2. At z < 2, the time derivatives of the mass growth are always larger for lower-mass galaxies, which demonstrates that the mass growth in galaxies since that redshift is mass-dependent and primarily bottom-up. Lastly, we examine potential sources of systematic uncertainties in the SMFs and find that those from photo-z templates, stellar population synthesis modeling, and the definition of quiescent galaxies dominate the total error budget in the SMFs

  6. Calculations of the stellar structure of so-called degenerate stars using a new pressure function

    International Nuclear Information System (INIS)

    Steuerwald, J.; Wulff, H.

    1977-07-01

    Masses and radii of degenerate stars were calculated using a pressure function which significantly deviates from the usual one based on the Fermi energy of free electrons. Assuming only a central number density ranging from 10 30 cm -3 to 10 36 cm -3 , the calculations yield masses between those of Jupiter and the sun. The masses were found to be a function of the composition of the elements. The maximum masses and the cosmic abundance of the elements are correlated. The radii come close to those of pulsars at high central densities, while at low densities they are equal to those of white dwarves. (orig.) [de

  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. Development of actively cooled windows for plasma observation during quasi-continuous operation of the W7-X stellarator

    International Nuclear Information System (INIS)

    Konig, R.; Grosser, K.; Hildebrandt, D.; Pasch, E.; Werner, T.; Klinger, T.; Ogorodnikova, O.

    2005-01-01

    With the stellarator W7-X a step to quasi-continuous plasma operation will be made. The cooling system of the machine is designed such that two 30 min discharges can be run per day. Right from the start of operation 10 MW of ECRH heating power will be available for quasi-continuous operation. A working group 'Plasma Facing Optical Components' has been formed which presently concentrates on the development of water cooled windows for UV/VR/IR periscopes which can withstand the expected maximum heat loads of up to 50 kW/m 2 which due to the predominantly short wavelength nature of the radiation emitted by the plasma will be absorbed within the first millimeter of any window. We will report on the detailed Finite Element (ANSYS R ) calculations of the heat and stress distribution across the windows. Calculations have been undertaken for a large number of different window materials which are required for the various spectral regions covered by the miscellaneous diagnostics, so that the most suitable material for each application can easily be identified. Also the dependence of the cooling rate on the window diameter and thickness has been studied. The calculations show that at a power load of 50 kW/m 2 cooled sapphire windows can be used for window sizes up to ∼200 mm diameter but that for many of the other materials like ZnSe, ZnS, CaF 2 , MgF 2 and quartz window sizes need to be limited to considerably smaller sizes. Detailed simulations of the local radiation power load distribution demonstrate that by careful design the load on individual optical components can be considerably reduced. A vacuum test chamber, equipped with a vacuum compatible IR heater has been build. In this chamber a low cost, easily exchangeable window design using Helicoflex gaskets on either side of a 60 mm exposed diameter quartz window have been successfully tested over 70 heat cycles up to a maximum temperature of 450 o C at power loads of 15 kW/m 2 . The design proved to be water and

  9. 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

  10. Evolution of the stellar-to-dark matter relation: Separating star-forming and passive galaxies from z = 1 to 0

    Energy Technology Data Exchange (ETDEWEB)

    Tinker, Jeremy L. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Leauthaud, Alexie; Bundy, Kevin [Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), Todai Institutes for Advanced Study, the University of Tokyo, Kashiwa 277-8583 (Japan); George, Matthew R. [Department of Astronomy, University of California, and Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Behroozi, Peter; Wechsler, Risa H. [Kavli Institute for Particle Astrophysics and Cosmology, Physics Department, Stanford University, and SLAC National Accelerator Laboratory, Stanford, CA 94305 (United States); Massey, Richard [Institute for Computational Cosmology, Durham University, South Road, Durham, DH1 3LE (United Kingdom); Rhodes, Jason, E-mail: jeremy.tinker@nyu.edu [California Institute of Technology, MC 350-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

    2013-12-01

    We use measurements of the stellar mass function, galaxy clustering, and galaxy-galaxy lensing within the COSMOS survey to constrain the stellar-to-halo mass relation (SHMR) of star forming and quiescent galaxies over the redshift range z = [0.2, 1.0]. For massive galaxies, M {sub *} ≳ 10{sup 10.6} M {sub ☉}, our results indicate that star-forming galaxies grow proportionately as fast as their dark matter halos while quiescent galaxies are outpaced by dark matter growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their star formation. Our analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z = 1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M {sub *} ∼ 10{sup 10} M {sub ☉}, the fraction of central galaxies on the red sequence increases by a factor of 10 over our redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. We define a 'migration rate' to the red sequence as the time derivative of the passive galaxy abundances. We find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z = 1 to z = 0. These results imply that the efficiency of quenching star formation for centrals is increasing with cosmic time, while the mechanisms that quench the star formation of satellite galaxies in groups and clusters is losing efficiency.

  11. Gamma ray heating rates due to chromium isotopes in stellar core during late stages of high mass stars (>10M⊙

    Directory of Open Access Journals (Sweden)

    Nabi Jameel-Un

    2017-01-01

    Full Text Available Gamma ray heating rates are thought to play a crucial role during the pre-supernova stage of high mass stars. Gamma ray heating rates, due to β±-decay and electron (positron capture on chromium isotopes, are calculated using proton-neutron quasiparticle random phase approximation theory. The electron capture significantly affects the lepton fraction (Ye and accelerates the core contraction. The gamma rays emitted as a result of weak processes heat the core and tend to hinder the cooling and contraction due to electron capture and neutrino emission. The emitted gamma rays tend to produce enormous entropy and set the convection to play its role at this stage. The gamma heating rates, on 50-60Cr, are calculated for the density range 10 < ρ (g.cm-3 < 1011 and temperature range 107 < T (K < 3.0×1010.

  12. 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...

  13. STAR CLUSTER PROPERTIES IN TWO LEGUS GALAXIES COMPUTED WITH STOCHASTIC STELLAR POPULATION SYNTHESIS MODELS

    International Nuclear Information System (INIS)

    Krumholz, Mark R.; Adamo, Angela; Fumagalli, Michele; Wofford, Aida; Calzetti, Daniela; Grasha, Kathryn; Lee, Janice C.; Whitmore, Bradley C.; Bright, Stacey N.; Ubeda, Leonardo; Gouliermis, Dimitrios A.; Kim, Hwihyun; Nair, Preethi; Ryon, Jenna E.; Smith, Linda J.; Thilker, David; Zackrisson, Erik

    2015-01-01

    We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar

  14. 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.

  15. 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.

  16. Disks around young stellar objects

    Indian Academy of Sciences (India)

    Keywords. Star formation; young stellar objects; circumstellar disks; exoplanets. Abstract. By 1939, when Chandrasekhar's classic monograph on the theory of Stellar Structure was published, although the need for recent star formation was fully acknowledged, no one had yet recognized an object that could be called a star ...

  17. 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.

  18. The ACS LCID project. X. the star formation history of IC 1613: Revisiting the over-cooling problem

    Energy Technology Data Exchange (ETDEWEB)

    Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Hidalgo, Sebastian L.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio, E-mail: skillman@astro.umn.edu, E-mail: shidalgo@iac.es, E-mail: monelli@iac.es, E-mail: carme@iac.es, E-mail: aparicio@iac.es [Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Canary Islands (Spain); and others

    2014-05-01

    We present an analysis of the star formation history (SFH) of a field near the half-light radius in the Local Group dwarf irregular galaxy IC 1613 based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. Our observations reach the oldest main sequence turn-off, allowing a time resolution at the oldest ages of ∼1 Gyr. Our analysis shows that the SFH of the observed field in IC 1613 is consistent with being constant over the entire lifetime of the galaxy. These observations rule out an early dominant episode of star formation in IC 1613. We compare the SFH of IC 1613 with expectations from cosmological models. Since most of the mass is in place at early times for low-mass halos, a naive expectation is that most of the star formation should have taken place at early times. Models in which star formation follows mass accretion result in too many stars formed early and gas mass fractions that are too low today (the 'over-cooling problem'). The depth of the present photometry of IC 1613 shows that, at a resolution of ∼1 Gyr, the star formation rate is consistent with being constant, at even the earliest times, which is difficult to achieve in models where star formation follows mass assembly.

  19. 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.

  20. 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 becaus...

  1. Variability in stellar granulation and convective blueshift with spectral type and magnetic activity . II. From young to old main-sequence K-G-F stars

    Science.gov (United States)

    Meunier, N.; Mignon, L.; Lagrange, A.-M.

    2017-11-01

    Context. The inhibition of small-scale convection in the Sun dominates the long-term radial velocity (RV) variability: it therefore has a critical effect on light exoplanet detectability using RV techniques. Aims: We here extend our previous analysis of stellar convective blueshift and its dependence on magnetic activity to a larger sample of stars in order to extend the Teff range, to study the impact of other stellar properties, and finally to improve the comparison between observed RV jitter and expected RV variations. Methods: We estimate a differential velocity shift for Fe and Ti lines of different depths and derive an absolute convective blueshift using the Sun as a reference for a sample of 360 F7-K4 stars with different properties (age, Teff, metallicity). Results: We confirm the strong variation in convective blueshift with Teff and its dependence on (as shown in the line list in Paper I) activity level. Although we do not observe a significant effect of age or cyclic activity, stars with a higher metallicity tend to have a lower convective blueshift, with a larger effect than expected from numerical simulations. Finally, we estimate that for 71% of the stars in our sample the RV and Log R' _HK variations are compatible with the effect of activity on convection, as observed in the solar case, while for the other stars, other sources (such as binarity or companions) must be invoked to explain the large RV variations. We also confirm a relationship between Log R' _HK and metallicity, which may affect discussions of the possible relationship between metallicity and exoplanets, as RV surveys are biased toward low Log R' _HK and possibly toward high-metallicity stars. Conclusions: We conclude that activity and metallicity strongly affect the small-scale convection levels in stars in the F7-K4 range, with a lower amplitude for the lower mass stars and a larger amplitude for low-metallicity stars. Full Table A.1 is only available at the CDS via anonymous ftp to

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

    NARCIS (Netherlands)

    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.

    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

  3. 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.

  4. Aperture synthesis imaging of the carbon AGB star R Sculptoris. Detection of a complex structure and a dominating spot on the stellar disk

    Science.gov (United States)

    Wittkowski, M.; Hofmann, K.-H.; Höfner, S.; Le Bouquin, J. B.; Nowotny, W.; Paladini, C.; Young, J.; Berger, J.-P.; Brunner, M.; de Gregorio-Monsalvo, I.; Eriksson, K.; Hron, J.; Humphreys, E. M. L.; Lindqvist, M.; Maercker, M.; Mohamed, S.; Olofsson, H.; Ramstedt, S.; Weigelt, G.

    2017-05-01

    Aims: We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris (R Scl). Methods: We employ medium spectral resolution K-band interferometry obtained with the instrument AMBER at the Very Large Telescope Interferometer (VLTI) and H-band low spectral resolution interferometric imaging observations obtained with the VLTI instrument PIONIER. We compare our data to a recent grid of dynamic atmosphere and wind models. We compare derived fundamental parameters to stellar evolution models. Results: The visibility data indicate a broadly circular resolved stellar disk with a complex substructure. The observed AMBER squared visibility values show drops at the positions of CO and CN bands, indicating that these lines form in extended layers above the photosphere. The AMBER visibility values are best fit by a model without a wind. The PIONIER data are consistent with the same model. We obtain a Rosseland angular diameter of 8.9 ± 0.3 mas, corresponding to a Rosseland radius of 355 ± 55 R⊙, an effective temperature of 2640 ± 80 K, and a luminosity of log L/L⊙ = 3.74 ± 0.18. These parameters match evolutionary tracks of initial mass 1.5 ± 0.5 M⊙ and current mass 1.3 ± 0.7 M⊙. The reconstructed PIONIER images exhibit a complex structure within the stellar disk including a dominant bright spot located at the western part of the stellar disk. The spot has an H-band peak intensity of 40% to 60% above the average intensity of the limb-darkening-corrected stellar disk. The contrast between the minimum and maximum intensity on the stellar disk is about 1:2.5. Conclusions: Our observations are broadly consistent with predictions by dynamic atmosphere and wind models, although models with wind appear to have a circumstellar envelope that is too extended compared to our observations. The detected complex structure within the stellar disk is most likely caused by giant convection cells, resulting in large-scale shock fronts

  5. CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses

    Energy Technology Data Exchange (ETDEWEB)

    Lamarche, C.; Stacey, G.; Riechers, D.; Vishwas, A. [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Brisbin, D. [Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Avenida Ejército 441, 8370191 Santiago (Chile); Ferkinhoff, C. [Department of Physics, Winona State University, Winona, MN, 55987 (United States); Hailey-Dunsheath, S. [California Institute of Technology, Mail Code 301-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Nikola, T.; Spoon, H. [Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853 (United States); Sharon, C. E., E-mail: cjl272@cornell.edu [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON L85-4M1 (Canada)

    2017-02-10

    We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2–1) and [N ii] 205 μ m lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ∼6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2–1) line, down to a level twelve times lower than the expected value for star-forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated throughout much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, although we argue it is unlikely, that the ensemble of fine-structure lines is emitted from the region heated by the AGN.

  6. MOIRCS DEEP SURVEY. VIII. EVOLUTION OF STAR FORMATION ACTIVITY AS A FUNCTION OF STELLAR MASS IN GALAXIES SINCE z ∼ 3

    International Nuclear Information System (INIS)

    Kajisawa, M.; Ichikawa, T.; Yamada, T.; Akiyama, M.; Uchimoto, Y. K.; Yoshikawa, T.; Onodera, M.

    2010-01-01

    We study the evolution of star formation activity of galaxies at 0.5 9.5-10 M sun even at z ∼ 3. We estimated star formation rates (SFRs) of the sample with two indicators, namely, the Spitzer/MIPS 24 μm flux and the rest-frame 2800 A luminosity. The SFR distribution at a fixed M star shifts to higher values with increasing redshift at 0.5 1. We found galaxies at 2.5 -1 . Galaxies in the low-SSFR group have SSFRs of ∼0.5-1.0 Gyr -1 , while the high-SSFR population shows ∼10 Gyr -1 . The cosmic SFR density (SFRD) is dominated by galaxies with M star = 10 10-11 M sun at 0.5 star = 10 11-11.5 M sun shows a strong evolution at z>1 and becomes significant at z ∼ 3, especially in the case with the SFR based on MIPS 24 μm. In galaxies with M star = 10 10-11.5 M sun , those with a relatively narrow range of SSFR (∼<1 dex) dominates the cosmic SFRD at 0.5 < z < 3.5. The SSFR of galaxies that dominate the SFRD systematically increases with redshift. At 2.5 < z < 3.5, the high-SSFR population, which is relatively small in number, dominates the SFRD. Major star formation in the universe at higher redshift seems to be associated with a more rapid growth of stellar mass of galaxies.

  7. 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.)

  8. From the Milky Way to differing galaxy environments: filling critical gaps in our knowledge of star formation and its interplay with dust, and in stellar and galaxy evolution.

    Science.gov (United States)

    Bianchi, Luciana

    2018-01-01

    Rest-frame UV, uniquely sensitive to luminous, short-lived hot massive stars, trace and age-date star formation across galaxies, and is very sensitive to dust, whose properties and presence are closely connected to star formation.With wide f-o-v and deep sensitivity in two broad filters,FUV and NUV,GALEX delivered the first comprehensive UV view of large nearby galaxies, and of the universe to z~2 (e.g.,Bianchi 2014 ApSS 354,103), detected star formation at the lowest rates, in environments where it was not seen before and not expected (e.g. Bianchi 2011 ApSS 335,51; Thilker+2009 Nature 457,990;2007 ApJS 173,538), triggering a new era of investigations with HST and large ground-based telescopes. New instrument technology and modeling capabilities make it now possible and compelling to solve standing issues. The scant UV filters available (esp. FUV) and the wide gap in resolution and f-o-v between GALEX and HST leaves old and new questions open. A chief limitation is degeneracies between physical parameters of stellar populations (age/SFR) and hot stars, and dust (e.g. Bianchi+ 2014 JASR 53,928).We show sample model simulations for filter optimization to provide critical measurements for the science objectives. We also demonstrate how adequate FUV+NUV filters, and resolution, allow us to move from speculative interpretation of UV data to unbiased physical characterization of young stellar populations and dust, using new data from UVIT, which, though smaller than CETUS, has better resolution and filter coverage than GALEX.Also, our understanding of galaxy chemical enrichment is limited by critical gaps in stellar evolution; GALEX surveys enabled the first unbiased census of the Milky Way hot-WD population (Bianchi+2011 MNRAS, 411,2770), which we complement with SDSS, Pan-STARRS, and Gaia data to fill such gaps (Bianchi et al.2018, ApSS). Such objects in CETUS fields (deeper exposures, more filters, and the first UV MOS) will be much better characterized, enabling

  9. Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood

    Science.gov (United States)

    Bensby, T.; Feltzing, S.; Oey, M. S.

    2014-02-01

    Aims: The aim of this paper is to explore and map the age and abundance structure of the stars in the nearby Galactic disk. Methods: We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot (kinematically) be associated with either the thin disk or the thick disk. The determination of stellar parameters and elemental abundances is based on a standard analysis using equivalent widths and one-dimensional, plane-parallel model atmospheres calculated under the assumption of local thermodynamical equilibrium (LTE). The spectra have high resolution (R = 40 000-110 000) and high signal-to-noise (S/N = 150-300) and were obtained with the FEROS spectrograph on the ESO 1.5 m and 2.2 m telescopes, the SOFIN and FIES spectrographs on the Nordic Optical Telescope, the UVES spectrograph on the ESO Very Large Telescope, the HARPS spectrograph on the ESO 3.6 m telescope, and the MIKE spectrograph on the Magellan Clay telescope. The abundances from individual Fe i lines were were corrected for non-LTE effects in every step of the analysis. Results: We present stellar parameters, stellar ages, kinematical parameters, orbital parameters, and detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 714 nearby F and G dwarf stars. Our data show that there is an old and α-enhanced disk population, and a younger and less α-enhanced disk population. While they overlap greatly in metallicity between -0.7 < [Fe/H] ≲ +0.1, they show a bimodal distribution in [α/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff ≲ 5400 K) are discarded, showing that it is

  10. A PUBLIC CATALOG OF STELLAR MASSES, STAR FORMATION AND METALLICITY HISTORIES, AND DUST CONTENT FROM THE SLOAN DIGITAL SKY SURVEY USING VESPA

    International Nuclear Information System (INIS)

    Tojeiro, Rita; Wilkins, Stephen; Heavens, Alan F.; Panter, Ben; Jimenez, Raul

    2009-01-01

    We applied the VESPA algorithm to the Sloan Digital Sky Survey final data release of the Main Galaxies and Luminous Red Galaxies samples. The result is a catalog of stellar masses, detailed star formation and metallicity histories and dust content of nearly 800,000 galaxies. We make the catalog public via a T-SQL database, which is described in detail in this paper. We present the results using a range of stellar population and dust models, and will continue to update the catalog as new and improved models are made public. We also present a brief exploration of the catalog, and show that the quantities derived are robust: luminous red galaxies can be described by one to three populations, whereas a main galaxy sample galaxy needs on average two to five; red galaxies are older and less dusty; the dust values we recover are well correlated with measured Balmer decrements and star formation rates are also in agreement with previous measurements. We find that whereas some derived quantities are robust to the choice of modelling, many are still not.

  11. The search for multiple populations in Magellanic Cloud Clusters IV: Coeval multiple stellar populations in the young star cluster NGC 1978

    Science.gov (United States)

    Martocchia, S.; Niederhofer, F.; Dalessandro, E.; Bastian, N.; Kacharov, N.; Usher, C.; Cabrera-Ziri, I.; Lardo, C.; Cassisi, S.; Geisler, D.; Hilker, M.; Hollyhead, K.; Kozhurina-Platais, V.; Larsen, S.; Mackey, D.; Mucciarelli, A.; Platais, I.; Salaris, M.

    2018-04-01

    We have recently shown that the ˜2 Gyr old Large Magellanic Cloud star cluster NGC 1978 hosts multiple populations in terms of star-to-star abundance variations in [N/Fe]. These can be seen as a splitting or spread in the sub-giant and red giant branches (SGB and RGB) when certain photometric filter combinations are used. Due to its relative youth, NGC 1978 can be used to place stringent limits on whether multiple bursts of star-formation have taken place within the cluster, as predicted by some models for the origin of multiple populations. We carry out two distinct analyses to test whether multiple star-formation epochs have occurred within NGC 1978. First, we use UV CMDs to select stars from the first and second population along the SGB, and then compare their positions in optical CMDs, where the morphology is dominantly controlled by age as opposed to multiple population effects. We find that the two populations are indistinguishable, with age differences of 1 ± 20 Myr between them. This is in tension with predictions from the AGB scenario for the origin of multiple populations. Second, we estimate the broadness of the main sequence turnoff (MSTO) of NGC 1978 and we report that it is consistent with the observational errors. We find an upper limit of ˜65 Myr on the age spread in the MSTO of NGC 1978. This finding is in conflict with the age spread scenario as origin of the extendend MSTO in intermediate age clusters, while it fully supports predictions from the stellar rotation model.

  12. UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. II. PHOTOMETRIC REDSHIFTS, STELLAR MASSES, AND STAR FORMATION RATES

    International Nuclear Information System (INIS)

    Barro, G.; Perez-Gonzalez, P. G.; Gallego, J.; Villar, V.; Zamorano, J.; Ashby, M. L. N.; Kajisawa, M.; Yamada, T.; Miyazaki, S.

    2011-01-01

    Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 μm selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] ≤ 23.75 (85% completeness level of the IRAC survey) over 0.48 deg 2 . The typical photometric redshift accuracy is Δz/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 μm data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z ∼> 1.5 observed when only MIPS 24 μm data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

  13. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Konstantopoulos, I. S. [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Maybhate, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Charlton, J. C.; Gronwall, C. [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Fedotov, K.; Desjardins, T. D.; Gallagher, S. C. [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada); Durrell, P. R. [Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555 (United States); Mulchaey, J. S. [Carnegie Observatories, Pasadena, CA 91101 (United States); English, J. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Walker, L. M.; Johnson, K. E. [Department of Astronomy, University of Virginia, P.O. Box 3813, Charlottesville, VA 22904 (United States); Tzanavaris, P., E-mail: iraklis@aao.gov.au [Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2013-06-20

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  14. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    International Nuclear Information System (INIS)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  15. BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups—isochronal age determination using magnetic evolutionary models

    Energy Technology Data Exchange (ETDEWEB)

    Malo, Lison; Doyon, René; Albert, Loïc; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Riedel, Adric, E-mail: malo@cfht.hawaii.edu, E-mail: doyon@astro.umontreal.ca [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

    2014-09-01

    Based on high-resolution optical spectra obtained with ESPaDOnS at Canada-France-Hawaii Telescope, we determine fundamental parameters (T {sub eff}, R, L {sub bol}, log g, and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of Malo et al., which takes into account the position, proper motion, magnitude, color, radial velocity, and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth magnetic evolutionary models and field stars with the goal of constraining the age of our candidates. We find that, in general, low-mass stars in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main-sequence stars. The Dartmouth magnetic evolutionary models show a good fit to observations of field K and M stars, assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of the β Pictoris moving group, we have re-examined the age inconsistency problem between lithium depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increases the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear lithium depletion boundary from which an age of 26 ± 3 Myr is derived, consistent with previous age estimates based on this method.

  16. Calibrating Stellar Population Models in the Near-IR: Implications Due to the Presence of Carbon–Rich AGB Stars

    NARCIS (Netherlands)

    Lyubenova, M.; Kuntschner, H.; Rejbuka, M.; Silva, D. R.; Kissler-Patig, M.; Tacconi-Garman, L. E.; Larsen, S.S.|info:eu-repo/dai/nl/304833347

    2011-01-01

    We present our near-IR integrated spectral library of six globular clusters in the LMC and compare the data with existing stellar populations models. We find good agreement between models and data in the case of old, metal-poor clusters, while for intermediate-age and more metal-rich clusters we

  17. A Framework for Finding and Interpreting Stellar CMEs

    Science.gov (United States)

    Osten, Rachel A.; Wolk, Scott J.

    2017-10-01

    The astrophysical study of mass loss, both steady-state and transient, on the cool half of the HR diagram has implications both for the star itself and the conditions created around the star that can be hospitable or inimical to supporting life. Stellar coronal mass ejections (CMEs) have not been conclusively detected, despite the ubiquity with which their radiative counterparts in an eruptive event (flares) have been. 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. Finally I will describe recent results using observations at low radio frequencies to detect stellar coronal mass ejections, and give updates on prospects using future facilities to make headway in this important area.

  18. Stars, Manuscripts, and Astrolabes-The Stellar Constellations in a Group of Medieval Manuscripts between Latin Literature and a New Science of the Stars

    Science.gov (United States)

    Metzger, W.

    2011-06-01

    The European Middle Ages inherited star names and constellations from Roman antiquity, mostly via Latin literary texts. When, from the 11th century onwards, Arabic texts and instruments became available, figures and vocabulary at first where not compatible with this tradition. The example of an excerpt from Pseudo-Hyginus De Astronomia shows, how a Roman text on the constellations was revised and supplemented with the names of the astrolabe-stars to combine the two different traditions.

  19. Response of atmospheric biomarkers to NO(x)-induced photochemistry generated by stellar cosmic rays for earth-like planets in the habitable zone of M dwarf stars.

    Science.gov (United States)

    Grenfell, John Lee; Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A Beate C; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-12-01

    Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N(2)), which leads to production of nitrogen oxides (NO(x)) in the planetary atmosphere, hence affecting biomarkers such as ozone (O(3)). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NO(x) production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O(3) formation proceeds via the reaction O+O(2)+M→O(3)+M. At high NO(x) abundances, the O atoms arise mainly from NO(2) photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O(2)). For the flaring case, O(3) is mainly destroyed via direct titration, NO+O(3)→NO(2)+O(2), and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O(3), Rayleigh scattering by the main atmospheric gases (O(2), N(2), and CO(2)) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O(3) survived all the stellar-activity scenarios considered except for the strong

  20. 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.

  1. 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.

  2. 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

  3. High Resolution X-ray Spectroscopy and Star Formation: HETG Observations of the Pre-Main Sequence Stellar Cluster IC 348

    Science.gov (United States)

    Principe, David; Huenemoerder, David P.; Schulz, Norbert; Kastner, Joel H.; Weintraub, David; Preibisch, Thomas

    2018-01-01

    We present Chandra High Energy Transmission Grating (HETG) observations of the ∼3 Myr old pre-main sequence (pre-MS) stellar cluster IC 348. With 400-500 cluster members at a distance of ∼300 pc, IC 348 is an ideal target to observe a large number of X-ray sources in a single pointing and is thus an extremely efficient use of Chandra-HETG. High resolution X-ray spectroscopy offers a means to investigate detailed spectral characteristic of X-ray emitting plasmas and their surrounding environments. We present preliminary results where we compare X-ray spectral signatures (e.g., luminosity, temperature, column density, abundance) of the X-ray brightest pre-MS stars in IC 348 with spectral type, multiwavelength signatures of accretion, and the presence of circumstellar disks at multiple stages of pre-MS stellar evolution. Assuming all IC 348 members formed from the same primordial molecular cloud, any disparity between coronal abundances of individual members, as constrained by the identification and strength of emission lines, will constrain the source(s) of coronal chemical evolution at a stage of pre-MS evolution vital to the formation of planets.

  4. Stars

    CERN Document Server

    Hansen, Grace

    2017-01-01

    This title will cover how stars form, different types of stars, their lifecycle, and the most important star to us--the Sun! Aligned to Common Core Standards and correlated to state standards. Abdo Kids Jumbo is an imprint of Abdo Kids, a division of ABDO.

  5. Probing the Extraordinary Ends of Ordinary Stars: White Dwarf Seismology with the Whole Earth Telescope

    OpenAIRE

    Kawaler, Steven D.

    1995-01-01

    During the final evolution of most stars, they shed their outer skin and expose their core of the hot ashes of nuclear burning. As these hot and very dense cores cool into white dwarf stars, they go through episodes of multiperiodic, nonradial g-mode pulsation. The tools of stellar seismology allow us to use the pulsation spectra as powerful probes into the deep interiors of these stars. Progress in white dwarf seismology has required significant international cooperation, since another conse...

  6. 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.

  7. Momentum and energy balance in late-type stellar winds

    Science.gov (United States)

    Macgregor, K. B.

    1981-01-01

    Observations at ultraviolet and X-ray wavelengths indicate that the classical picture of a static stellar atmosphere containing a radiative equilibrium temperature distribution is inapplicable to the majority of late type stars. Mass loss and the presence of atmospheric regions characterized by gas temperatures in excess of the stellar effective temperature appear to be almost ubiquitous throughout the HR diagram. Evidence pertaining to the thermal and dynamical structure of the outer envelopes of cool stars is summarized. These results are compared with the predictions of several theoretical models which were proposed to account for mass loss from latetype stars. Models in which the outflow is thermally radiatively, or wave driven are considered for identification of the physical processes responsible for the observed wind properties. The observed variation of both the wind, thermal and dynamical structure as one proceeds from the supergiant branch toward the main sequence in the cool portion of the HR diagram give consideration to potential mechanisms for heating and cooling the flow from low gravity stars.

  8. Dynamical evolution of a young stellar aggregate in the presence of a massive shell of gas using N-body simulations

    Science.gov (United States)

    Hasan, Priya; Hasan, S. N.

    We study secondary star formation in an expanding shell about a stellar agregate using n-body simulations. We use the (Ahmad-Cohen) Aarseth code for the n-body simulations to study the dynamical effects of interactions of an older generation of stars with a randomly forming second generation of stars in a aggregate. The observational effects of these interactions will be described in detail and discussed. We also show that the dynamics of the young stellar aggregate depends upon the local star formation efficiency(SFE). The young stellar aggregate can produce a gravitationally bound cluster if the expansion velocity of the shell is slow enough even when the local value of the SFE is as low as 10%. This occurs as a result of dynamical cooling effect which forces some of the newborn stars to form an open cluster.

  9. A Snapshot Imaging Survey of Spitzer-selected Young Stellar Objects in Nearby Star Formation Regions*.t23

    Science.gov (United States)

    Stapelfeldt, Karl

    2015-10-01

    Young circumstellar disks are the dusty reservoirs in which planetary systems may eventually form. Previous HST imaging surveys have spatially resolved about twenty circumstellar disks around young stars in nearby molecular clouds. Providing key measurements of disk inclinations, outer radii, asymmetries, vertical thicknesses, and dust properties, these observations have supplied valuable constraints on theories of star and planet formation. Most of this prior work was based on source identifications made 30 years ago by the IRAS survey. With its improved sensitivity and spatial resolution, the Spitzer Space Telescope identified numerous new members of nearby star-forming regions that are optically visible, not yet observed with HST, and which possess infrared excess > 40 mJy at 24 microns (5 times fainter than the IRAS survey 25 micron sensitivity). This group of objects consists of low mass stars, young brown dwarfs, transition disks, and edge-on disks that obscure their central sources. We propose a high dynamic range ACS snapshot survey of this lower-luminosity young star population. Our goals are (1) to determine the frequency of disk detections in scattered light; (2) to measure disk sizes, internal structures, and constituent dust properties in order to test theories of protoplanetary disk evolution; (3) to identify the nearly edge-on systems which are particularly favorable for studies of disk geometry; and (4) to discover faint substellar companion objects. This survey will extend previous HST young star imaging of protoplanetary environments from a solar mass down to the substellar limit, revealing their nature and frequency in the galaxy.

  10. 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.

  11. Computer simulations of close encounters between binary and single stars: the effect of the impact velocity and the stellar masses

    International Nuclear Information System (INIS)

    Fullerton, L.W.; Hills, J.G.

    1982-01-01

    A total of 45 760 simulated encounters between binary and single stars were run to study the effect of impact velocity and the masses of the three stars on the outcome of the collisions. Letting α be the kinetic energy of impact in units of the minimum kinetic energy required to break up the binary, we find that the crossover point between hard binaries (tightly bound binaries which increase their binding energies in the collisions) and soft binaries (more loosely bound binaries which decrease their binding energies in collisions) occurs at αapprox. =0.5 if the impacting single star is equal to or less massive than the binary components and occurs at αapprox. =10 if its mass is three or more times that of the binary components. This bimodal behavior of the crossover point is even more clearly defined when we find its location in terms of the impact velocity V/sub f/ , expressed in units of the original mean orbital speed V/sub o/ of the binary. We find that the crossover point occurs at V/sub f//V/sub o/ approx. =0.6 when the mass of the impacting star is equal to or less than that of the more massive binary component, and it occurs at V/sub f//V/sub o/ approx. =1.9 when its mass is three or more times greater than that of this binary component. The probability that the binary will be broken up in the encounter depends greatly on the mass of the impacting single star relative to that of the binary components, as well as on the impact velocity. If the single-star mass equals or exceeds that of the individual binary components, there is an interval of impact velocity over which all the binaries are broken up in encounters at the zero-impact parameter. This interval grows as the mass of the impacting single star increases. If the impacting star is less massive than the binary components, then the maximum probability of dissociation drops dramatically

  12. THE HABITABLE ZONES OF PRE-MAIN-SEQUENCE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, Ramses M.; Kaltenegger, Lisa [Institute for Pale Blue Dots, Cornell University, Ithaca, NY (United States)

    2014-12-20

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  13. Mixing in massive stellar mergers

    NARCIS (Netherlands)

    Gaburov, E.; jr. Lombardi, J.C.; Portegies Zwart, S.

    2008-01-01

    The early evolution of dense star clusters is possibly dominated by close interactions between stars, and physical collisions between stars may occur quite frequently. Simulating a stellar collision event can be an intensive numerical task, as detailed calculations of this process require

  14. The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

    Science.gov (United States)

    King, Ashley L.; Walton, Dominic J.; Miller, Jon M.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fabian, Andy C.; Furst, Felix; Hailey, Charles J.; hide

    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, a* = 0.985(+0.005/-0.014) (1 sigma 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 report the clear detection of an absorption feature at 7.03 +/- 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log xi = 3.6(+0.2/-0.3) and is dominated by He-like Fe xxv, the wind has a velocity of v/c = 0.043(+0.002/-0.007) (12900(+600/-2100) km s(exp -1)). If the line is instead associated with a more highly ionized gas (log xi = 6.1(+0.7/-0.6)), and is dominated by Fe xxvi, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

  15. Stellar Pulsations and Stellar Evolution: Conflict, Cohabitation, or Symbiosis?

    Science.gov (United States)

    Weiss, Achim

    While the analysis of stellar pulsations allows the determination of current properties of a star, stellar evolution models connect it with its previous history. In many cases results from both methods do not agree. In this review some classical and current cases of disagreement are presented. In some cases these conflicts led to an improvement of the theory of stellar evolution, while in others they still remain unsolved. Some well-known problems of stellar physics are pointed out as well, for which it is hoped that seismology—or in general the analysis of stellar pulsations—will help to resolve them. The limits of this symbiosis will be discussed as well.

  16. Extra-galactic Distances with Massive Stars: The Role of Stellar Variability in the Case of M33

    Energy Technology Data Exchange (ETDEWEB)

    Lee Chien-Hsiu, E-mail: leech@naoj.org [Subaru Telescope, NAOJ, 650 N Aohoku Pl, Hilo, HI 96720 (United States)

    2017-08-01

    In modern cosmology, determining the Hubble constant (H{sub 0}) using a distance ladder to percent level and comparing with the results from the Planck  satellite can shed light on the nature of dark energy, physics of the neutrino, and curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H{sub 0} has be dramatically reduced, from 10% to 2.4%, and with the promise of even reaching 1% in the near future. In this regard, it is fundamentally important to investigate the systematics. This is best done using other good independent distance indicators. One promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants (BSGs). As BSGs are the brightest objects in galaxies, they can probe distances up to 10 Mpc with negligible blending effects. While the FGLR method delivered distance is in good agreement with other distance indicators, it has been shown that this method delivers greater distances in the cases of M33 and NGC 55. Here, we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found that 9 out of 22 BSGs showed variability during the course of 500 days, although with amplitudes as small as 0.05 mag. This suggests that stellar variability plays a negligible role in the FGLR distance determination.

  17. Extra-galactic Distances with Massive Stars: The Role of Stellar Variability in the Case of M33

    Science.gov (United States)

    Lee, Chien-Hsiu

    2017-08-01

    In modern cosmology, determining the Hubble constant (H0) using a distance ladder to percent level and comparing with the results from the Planck satellite can shed light on the nature of dark energy, physics of the neutrino, and curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H0 has be dramatically reduced, from 10% to 2.4%, and with the promise of even reaching 1% in the near future. In this regard, it is fundamentally important to investigate the systematics. This is best done using other good independent distance indicators. One promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants (BSGs). As BSGs are the brightest objects in galaxies, they can probe distances up to 10 Mpc with negligible blending effects. While the FGLR method delivered distance is in good agreement with other distance indicators, it has been shown that this method delivers greater distances in the cases of M33 and NGC 55. Here, we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found that 9 out of 22 BSGs showed variability during the course of 500 days, although with amplitudes as small as 0.05 mag. This suggests that stellar variability plays a negligible role in the FGLR distance determination.

  18. 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.

  19. Stars

    CERN Document Server

    Kukla, Lauren

    2016-01-01

    Climb Aboard! Explore planets and how they are formed! Meet key astronomers! Examine the history of mapping the stars! Investigate red giants, black and white dwarfs, neutron stars, supernovas, and black holes! See an infographic showing our solar system's statistics! Did You Know? facts and a Guidebook of the brightest stars complete your journey. Aligned to Common Core standards and correlated to state standards. Checkerboard Library is an imprint of Abdo Publishing, a division of ABDO.

  20. Tidal effects on stellar activity

    Science.gov (United States)

    Poppenhaeger, K.

    2017-10-01

    The architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. We can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observed in close stellar binary systems. For the exoplanet, tidal interaction can lead to circularization of its orbit and the synchronization of its rotational and orbital period. For the host star, it has long been speculated if significant angular momentum transfer can take place between the planetary orbit and the stellar rotation. In the case of the Earth-Moon system, such tidal interaction has led to an increasing distance between Earth and Moon. For stars with Hot Jupiters, where the orbital period of the exoplanet is typically shorter than the stellar rotation period, one expects a decreasing semimajor axis for the planet and enhanced stellar rotation, leading to increased stellar activity. Also excess turbulence in the stellar convective zone due to rising and subsiding tidal bulges may change the magnetic activity we observe for the host star. I will review recent observational results on stellar activity and tidal interaction in the presence of close-in exoplanets, and discuss the effects of enhanced stellar activity on the exoplanets in such systems.

  1. 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.

  2. Infrared spectroscopy of symbiotic stars and the nature of their cool components

    International Nuclear Information System (INIS)

    Kenyon, S.J.; Gallagher, J.S.

    1983-01-01

    We present low-resolution 2--4 μm spectroscopy of a small sample of symbiotic stars, in an effort to determine if the giant components of these systems fill their Roche Lobes. A [2.35]-[2.2] color index measures the strength of the CO absorption band and provides a useful discriminant of luminosity class among single M-type giants which separates normal giants from supergiants at the same spectral type. Although interpretation of symbiotic spectra is complicated somewhat by their binary nature, our results suggest the late-type components in these systems range from normal red giants to bright asymptotic giants. The possible presence of non-Roche Lobe filling, low-luminosity giants in some symbiotic stars cannot be understood within the framework of existing theories for these interesting objects, and thus may provide important information for understanding mass transfer in binary systems

  3. 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...

  4. Neutron star cooling and the rp process in thermonuclear X-ray bursts

    DEFF Research Database (Denmark)

    Zand, J. J. M. in 't; Visser, M. E. B.; Galloway, D.K.

    2017-01-01

    When the upper layer of an accreting neutron star experiences a thermonuclearrunaway of helium and hydrogen, it exhibits an X-ray burst of a few keV with acool-down phase of typically 1~minute. When there is a surplus of hydrogen,hydrogen fusion is expected to simmer during that same minute due....... This is consistent with a hydrogen deficiency in thesebinaries. We find no clear correlation between the power law and Gaussianlight-curve components....

  5. 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)

  6. Theory of extended stellar atmospheres. II. A grid of static spherical models for O stars and planetary nebula nuclei

    International Nuclear Information System (INIS)

    Kunasz, P.B.; Hummer, D.G.; Mihalas, D.

    1975-01-01

    Spherical static non-LTE model atmospheres are presented for stars with M/M/sub sun/=30 and 60 at various points on their evolutionary tracks, and for some nuclei of planetary nebulae at two points of a modified Harman-Seaton sequence. The method of Mihalas and Hummer was employed, which uses a parametrized radiation force multiplier to simulate the force of radiation arising from the entire line spectrum. However, in the present work the density structure computed in the LTE models was held fixed in the calculation of the corresponding non-LTE models; in addition, the opacity of an ''average light ion'' was taken into account. The temperatures for the non-LTE models are generally lower, at a given depth, than for the corresponding LTE models when T/sub eff/<45,000 K, while the situation is reversed at higher temperatures. The continuous energy distributions are generally flattened by extension. The Lyman jump is in emission for extended models of massive stars, but never for the models of nuclei of planetary nebulae (this is primarily a temperature effect). The Balmer jumps are always in absorption. The Lyman lines are in emission, and the Balmer lines in absorption; He ii lambda4686 comes into emission in the most extended models without hydrogen line pumping, showing that it is an indicator of atmospheric extension. Very severe limb darkening is found for extended models, which have apparent angular sized significantly smaller than expected from the geometrical size of the star. Extensive tables are given of monochromatic magnitudes, continuum jumps and gradients, Stomgren-system colors, monochromatic extensions, and the profiles and equivalent widths of the hydrogen lines for all models, and of the He ii lines for some of the 60 M/sub X/ models

  7. 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.

  8. Estimation of Mass-Loss Rates from Emission Line Profiles in the UV Spectra of Cool Stars

    Science.gov (United States)

    Carpenter, K. G.; Robinson, R. D.; Harper, G. M.

    1999-01-01

    The photon-scattering winds of cool, low-gravity stars (K-M giants and supergiants) produce absorption features in the strong chromospheric emission lines. This provides us with an opportunity to assess important parameters of the wind, including flow and turbulent velocities, the optical depth of the wind above the region of photon creation, and the star's mass-loss rate. We have used the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code along with simple models of the outer atmospheric structure to compute synthetic line profiles for comparison with the observed line profiles. The SEI code has the advantage of being computationally fast and allows a great number of possible wind models to be examined. We therefore use it here to obtain initial first-order estimates of the wind parameters. More sophisticated, but more time-consuming and resource intensive calculations will be performed at a later date, using the SEI-deduced wind parameters as a starting point. A comparison of the profiles over a range of wind velocity laws, turbulence values, and line opacities allows us to constrain the wind parameters, and to estimate the mass-loss rates. We have applied this analysis technique (using lines of Mg II, 0 I, and Fe II) so far to four stars: the normal K5-giant alpha Tau, the hybrid K-giant gamma Dra, the K5 supergiant lambda Vel, and the M-giant gamma Cru. We present in this paper a description of the technique, including the assumptions which go into its use, an assessment of its robustness, and the results of our analysis.

  9. White Dwarf Pulsational Constraints on Stellar Evolution

    Science.gov (United States)

    Dunlap, Bart H.; Clemens, J. Christopher; O'Brien, Patrick C.; Hermes, J. J.; Fuchs, Joshua T.

    2017-01-01

    The complex processes that convert a protostellar cloud into a carbon/oxygen-core white dwarf star are distilled and modeled in state of the art stellar evolution codes. Many of these processes are well-constrained, but several are uncertain or must be parameterized in the models because a complete treatment would be computationally prohibitive—turbulent motions such as convective overshoot cannot, for example, be modeled in 1D. Various free parameters in the models must therefore be calibrated. We will discuss how white dwarf pulsations can inform such calibrations. The results of all prior evolution are cemented into the interiors of white dwarf stars and, so, hidden from view. However, during certain phases of their cooling, pulsations translate the star's evolutionary history into observable surface phenomena. Because the periods of a pulsating white dwarf star depend on an internal structure assembled as it evolved to its final state, white dwarf pulsation periods can be viewed as observable endpoints of stellar evolution. For example, the thickness of the helium layer in a white dwarf directly affects its pulsations; the observed periods are, therefore, a function of the number of thermal pulses during which the star converts helium into core material on the asymptotic giant branch. Because they are also a function of several other significant evolutionary processes, several pulsation modes are necessary to tease all of these apart. Unfortunately, white dwarf pulsators typically do not display enough oscillation modes to constrain stellar evolution. To avoid this limitation, we consider the pulsations of the entire collection of hot pulsating hydrogen-atmosphere white dwarf stars (DAVs). Though any one star may not have sufficient information to place interesting constraints on its evolutionary history, taken together, the stars show a pattern of modes that allows us to test evolutionary models. For an example set of published evolutionary models, we show a

  10. DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR θ CYG, THE BRIGHTEST STAR OBSERVED BY THE KEPLER MISSION

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, J. A. [Los Alamos National Laboratory, XTD-NTA, MS T-082, Los Alamos, NM 87545 (United States); Houdek, G.; Chaplin, W. J.; Antoci, V.; Bedding, T. R.; Huber, D.; Kjeldsen, H. [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Smalley, B. [Astrophysics Group, School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire, ST5 5BG (United Kingdom); Kurtz, D. W. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Mullally, F.; Rowe, J. F. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Bryson, S. T.; Still, M. D. [NASA Ames Research Center, Bldg. 244, MS-244-30, Moffett Field, CA 94035 (United States); Appourchaux, T. [Institut d’Astrophysique Spatiale, Universitè de Paris Sud–CNRS, Batiment 121, F-91405 ORSAY Cedex (France); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Benomar, O. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Garcia, R. A. [Laboratoire AIM, CEA/DRF—CNRS—Univ. Paris Diderot—IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Latham, D. W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Metcalfe, T. S. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); and others

    2016-11-01

    θ Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 (2010 June–September) and subsequently in Quarters 8 and 12–17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000–2700 μ Hz, a large frequency separation of 83.9 ± 0.4 μ Hz, and maximum oscillation amplitude at frequency ν {sub max} = 1829 ± 54 μ Hz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give T {sub eff} = 6697 ± 78 K, radius 1.49 ± 0.03 R {sub ⊙}, [Fe/H] = -0.02 ± 0.06 dex, and log g = 4.23 ± 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35–1.39 M {sub ⊙} and ages of 1.0–1.6 Gyr. θ Cyg’s T {sub eff} and log g place it cooler than the red edge of the γ Doradus instability region established from pre- Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show γ Dor gravity modes driven by the convective blocking mechanism, with frequencies of 1–3 cycles per day (11 to 33 μ Hz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 μ Hz) may be attributable to a faint, possibly background, binary.

  11. The observable properties of cool winds from galaxies, AGN, and star clusters - I. Theoretical framework

    Science.gov (United States)

    Krumholz, Mark R.; Thompson, Todd A.; Ostriker, Eve C.; Martin, Crystal L.

    2017-11-01

    Winds arising from galaxies, star clusters, and active galactic nuclei are crucial players in star and galaxy formation, but it has proven remarkably difficult to use observations of them to determine physical properties of interest, particularly mass fluxes. Much of the difficulty stems from a lack of a theory that links a physically realistic model for winds' density, velocity and covering factors to calculations of light emission and absorption. In this paper we provide such a model. We consider a wind launched from a turbulent region with a range of column densities, derive the differential acceleration of gas as a function of column density, and use this result to compute winds' absorption profiles, emission profiles and emission intensity maps in both optically thin and optically thick species. The model is sufficiently simple that all required computations can be done analytically up to straightforward numerical integrals, rendering it suitable for the problem of deriving physical parameters by fitting models to observed data. We show that our model produces realistic absorption and emission profiles for some example cases, and argue that the most promising methods of deducing mass fluxes are based on combinations of absorption lines of different optical depths, or on combining absorption with measurements of molecular line emission. In the second paper in this series, we expand on these ideas by introducing a set of observational diagnostics that are significantly more robust than those commonly in use, and that can be used to obtain improved estimates of wind properties.

  12. 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.

  13. 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.

  14. A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES

    International Nuclear Information System (INIS)

    Lehmer, B. D.; Jenkins, L. P.; Alexander, D. M.; Goulding, A. D.; Roberts, T. P.; Bauer, F. E.; Brandt, W. N.; Ptak, A.

    2010-01-01

    We present new Chandra observations that complete a sample of seventeen (17) luminous infrared galaxies (LIRGs) with D H ∼ 20 cm -2 . The LIRGs in our sample have total infrared (8-1000 μm) luminosities in the range of L IR ∼ (1-8) x 10 11 L sun . The high-resolution imaging and X-ray spectral information from our Chandra observations allow us to measure separately X-ray contributions from active galactic nuclei and normal galaxy processes (e.g., X-ray binaries and hot gas). We utilized total infrared plus UV luminosities to estimate star formation rates (SFRs) and K-band luminosities and optical colors to estimate stellar masses (M * ) for the sample. Under the assumption that the galaxy-wide 2-10 keV luminosity (L gal HX ) traces the combined emission from high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries, and that the power output from these components is linearly correlated with SFR and M * , respectively, we constrain the relation L gal HX = αM * + βSFR. To achieve this, we construct a Chandra-based data set composed of our new LIRG sample combined with additional samples of less actively star-forming normal galaxies and more powerful LIRGs and ultraluminous infrared galaxies (ULIRGs) from the literature. Using these data, we measure best-fit values of α = (9.05 ± 0.37) x 10 28 erg s -1 M -1 sun and β = (1.62 ± 0.22) x 10 39 erg s -1 (M sun yr -1 ) -1 . This scaling provides a more physically meaningful estimate of L gal HX , with ∼0.1-0.2 dex less scatter, than a direct linear scaling with SFR. Our results suggest that HMXBs dominate the galaxy-wide X-ray emission for galaxies with SFR/M * ∼>5.9 x 10 -11 yr -1 , a factor of ∼2.9 times lower than previous estimates. We find that several of the most powerful LIRGs and ULIRGs, with SFR/M * ∼> 10 -9 yr -1 , appear to be X-ray underluminous with respect to our best-fit relation. We argue that these galaxies are likely to contain X-ray binaries residing in compact star-forming regions

  15. Stellar Chromospheric Activity

    Directory of Open Access Journals (Sweden)

    Hall Jeffrey C.

    2008-03-01

    Full Text Available The Sun, stars similar to it, and many rather dissimilar to it, have chromospheres, regions classically viewed as lying above the brilliant photosphere and characterized by a positive temperature gradient and a marked departure from radiative equilibrium. Stellar chromospheres exhibit a wide range of phenomena collectively called activity, stemming largely from the time evolution of their magnetic fields and the mass flux and transfer of radiation through the complex magnetic topology and the increasingly optically thin plasma of the outer stellar atmosphere. In this review, I will (1 outline the development of our understanding of chromospheric structure from 1960 to the present, (2 discuss the major observational programs and theoretical lines of inquiry, (3 review the origin and nature of both solar and stellar chromospheric activity and its relationship to, and effect on, stellar parameters including total energy output, and (4 summarize the outstanding problems today.

  16. Identification of Stellar Sequences in Various Stellar Systems ...

    Indian Academy of Sciences (India)

    The spatial morphological study of stellar clusters has been carried out through their identified probable members. The field stars decontamination is performed by the statistical cleaning approach (depends on the magnitude and colour of stars within the field and cluster regions). The colour magnitude ratio diagram ...

  17. 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.

  18. 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.

  19. Net Reaction Rate and Neutrino Cooling Rate for the Urca Process in Departure from Chemical Equilibrium in the Crust of Fast-accreting Neutron Stars

    Science.gov (United States)

    Wang, Wei-Hua; Huang, Xi; Zheng, Xiao-Ping

    We discuss the effect of compression on Urca shells in the ocean and crust of accreting neutron stars, especially in superbursting sources. We find that Urca shells may be deviated from chemical equilibrium in neutron stars which accrete at several tenths of the local Eddington accretion rate. The deviation depends on the energy threshold of the parent and daughter nuclei, the transition strength, the temperature, and the local accretion rate. In a typical crust model of accreting neutron stars, the chemical departures range from a few tenths of kBT to tens of kBT for various Urca pairs. If the Urca shell can exist in crusts of accreting neutron stars, compression may enhance the net neutrino cooling rate by a factor of about 1-2 relative to the neutrino emissivity in chemical equilibrium. For some cases, such as Urca pairs with small energy thresholds and/or weak transition strength, the large chemical departure may result in net heating rather than cooling, although the released heat can be small. Strong Urca pairs in the deep crust are hard to be deviated even in neutron stars accreting at the local Eddington accretion rate.

  20. Magnetism of hot stars

    Science.gov (United States)

    Wade, G. A.; Neiner, C.

    2018-01-01

    Strong, stable, and organised magnetic fields are present at the surfaces of a small fraction of OBA stars. These "fossil fields" exhibit uniform characteristics in stars over a tremendous range of stellar mass, age, temperature, and rotation rate. In hot O- and B-type stars, these magnetic fields couple efficiently to the stellar radiatively driven winds, strongly influencing stellar mass loss and rotation. In this article we review the characteristics of the known magnetic hot stars, discuss recent discoveries and insights, and describe recent theoretical progress toward understanding basic field properties and the influence of magnetic fields on hot star evolution.

  1. Improved wavelengths for Fe V and Ni V for analysis of spectra of white dwarf stellar stars

    Science.gov (United States)

    Ward, Jacob; Nave, Gillian

    2015-08-01

    A recent paper by J.C. Berengut et al. tests for a potential variation in the fine-structure constant, α, in the presence of a high gravitational field through spectral analysis of white-dwarf stars. The spectrum of G191-B2B has prominent Fe V and Ni V lines in the vacuum ultraviolet (VUV) region that were used to determine any variation in α via observed shifts in their wavelengths. Although no strong evidence for a variation was found, the authors did find a difference between values obtained for Fe V and Ni V that were indicative of a problem with the laboratory wavelengths. The laboratory wavelengths dominate the uncertainty of the measured variation, so improved values would tighten the constraints on the variation of α.We have re-measured the spectra of Fe V and Ni V spectra in the VUV in order to reduce the wavelength uncertainties and put the two spectra on a consistent wavelength scale. The spectra were produced by a sliding spark light source with electrodes made of invar, an iron nickel alloy. Spectra of Fe V and Ni V were obtained using peak currents of 750-2000 A. The spectra were recorded using the NIST Normal Incidence Vacuum Spectrograph with phosphor image plates and photographic plates as detectors. Wavelengths from 1100 Å to 1800 Å were covered in a single exposure. A spectrum of a Pt/Ne hollow cathode lamp was also recorded for wavelength calibration.The spectra recorded on photographic plates are better resolved than the phosphor image plate spectra and are being measured in two ways. The first measures the positions of the spectral lines on a comparator, traditionally used to measure many archival spectra at NIST. The second uses a commercial image scanner to obtain a digital image of the plate that can be analyzed using line fitting software. Preliminary analysis of these spectra indicates that the literature values of the Fe V and Ni V wavelengths are not on the same scale and differ from our new measurements by up to 0.02 Å in some

  2. Momentum and energy deposition in late-type stellar atmospheres and winds

    Science.gov (United States)

    Hartmann, L.; Macgregor, K. B.

    1980-01-01

    The present study calculates the response of the outer atmospheres of cool low-gravity stars to the passage of the mechanical energy fluxes of solar magnitude in the form of acoustic waves and Alfven waves. It is shown that Alfven waves are efficient in generating outflow, and can account for the order of magnitude of observed mass loss in late-type luminous stars. However, unless these magnetic waves undergo some dissipation within several stellar radii of the surface, the predicted terminal velocities of the resulting stellar winds are far too high. Alfven wave dissipation should give rise to extended warm chromospheres in low-gravity late-type stars, a prediction which can be observationally tested.

  3. Evolved stars at high angular resolution: present and future

    Science.gov (United States)

    Paladini, Claudia

    2016-08-01

    The late evolutionary stages of stellar evolution are a key ingredient for our understanding in many fields of astrophysics, including stellar evolution and the enrichment of the interstellar medium (ISM) via stellar yields. Already the first interferometric campaigns identified evolved stars as the primary targets because of their extended and partially optically thin atmospheres, and the brightness in the infrared. Interferometric studies spanning different wavelength ranges, from visual to mid-infrared, have greatly increased our knowledge of the complex atmospheres of these objects where different dynamic processes are at play. In less than two decades this technique went from measuring simple diameters to produce the first images of stellar surfaces. By scanning the extended atmospheres we constrained theoretical models, learnt about molecular stratification, dust formation, and stellar winds, and there is still a lot to be done. In this contribution I will review the recent results that optical/infrared interferometry has made on our current understanding of cool evolved stars. The presentation will focus on asymptotic giant branch stars, and red supergiants. I will discuss the challenges of image reconstruction, and highlight how this field of research will benefit from the synergy of the current interferometric instrument(s) with the second generation VLTI facilities GRAVITY and MATISSE. Finally I will conclude with a short introspection on applications of a visible interferometer and of the the Planet Formation Imager (PFI) to the field of evolved stars.

  4. Strong far-infrared cooling lines, peculiar CO kinematics, and possible star-formation suppression in Hickson compact group 57

    Energy Technology Data Exchange (ETDEWEB)

    Alatalo, K.; Appleton, P. N.; Ogle, P. M.; Rich, J. A.; Xu, C. K. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Lisenfeld, U. [Departamento de Física Teórica y del Cosmos, Universidad de Granada, E-18071 Granada (Spain); Bitsakis, T. [NASA Herschel Science Center, IPAC, California Institute of Technology, Pasadena, CA 91125 (United States); Guillard, P. [Institut d' Astrophysique Spatiale, Université Paris-Sud XI, F-91405 Orsay Cedex (France); Charmandaris, V. [Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR-15236 Penteli (Greece); Cluver, M.; Jarrett, T. [Astrophysics Cosmology and Gravity Centre, Dept of Astronomy, University of Cape Town, Private Bag X3, Rondebosch, 7701, Republic of South Africa (South Africa); Dopita, M. A.; Kewley, L. J. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Freeland, E. [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Rasmussen, J. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Verdes-Montenegro, L. [Departamento Astronomía Extragaláctica, Instituto Astrofísica Andalucía (CSIC), Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Yun, M., E-mail: kalatalo@ipac.caltech.edu [University of Massachusetts, Astronomy Department, Amherst, MA 01003 (United States)

    2014-11-10

    We present [C II] and [O I] observations from Herschel and CO(1-0) maps from the Combined Array for Research in Millimeter Astronomy (CARMA) of the Hickson compact group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG 57a has been previously shown to contain enhanced quantities of warm molecular hydrogen consistent with shock or turbulent heating. Our observations show that HCG 57d has strong [C II] emission compared to L {sub FIR} and weak CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies at the upper end of the normal distribution of the [C II]/CO and [C II]/FIR ratios, and its far-infrared (FIR) cooling supports a low-density, warm, diffuse gas that falls close to the boundary of acceptable models of a photon-dominated region. However, the power radiated in the [C II] and warm H{sub 2} emissions have similar magnitudes, as seen in other shock-dominated systems and predicted by recent models. We suggest that shock heating of the [C II] is a viable alternative to photoelectric heating in violently disturbed, diffuse gas. The existence of shocks is also consistent with the peculiar CO kinematics in the galaxy, indicating that highly noncircular motions are present. These kinematically disturbed CO regions also show evidence of suppressed star formation, falling a factor of 10-30 below normal galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar properties of both galaxies are consistent with a highly dissipative, off-center collisional encounter between HCG 57d and 57a, creating ring-like morphologies in both systems. Highly dissipative gas-on-gas collisions may be more common in dense groups because of the likelihood of repeated multiple encounters. The possibility of shock-induced star-formation suppression may explain why a subset of these HCG galaxies has been found previously to fall in the mid-infrared green valley.

  5. Strong far-infrared cooling lines, peculiar CO kinematics, and possible star-formation suppression in Hickson compact group 57

    International Nuclear Information System (INIS)

    Alatalo, K.; Appleton, P. N.; Ogle, P. M.; Rich, J. A.; Xu, C. K.; Lisenfeld, U.; Bitsakis, T.; Guillard, P.; Charmandaris, V.; Cluver, M.; Jarrett, T.; Dopita, M. A.; Kewley, L. J.; Freeland, E.; Rasmussen, J.; Verdes-Montenegro, L.; Yun, M.

    2014-01-01

    We present [C II] and [O I] observations from Herschel and CO(1-0) maps from the Combined Array for Research in Millimeter Astronomy (CARMA) of the Hickson compact group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG 57a has been previously shown to contain enhanced quantities of warm molecular hydrogen consistent with shock or turbulent heating. Our observations show that HCG 57d has strong [C II] emission compared to L FIR and weak CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies at the upper end of the normal distribution of the [C II]/CO and [C II]/FIR ratios, and its far-infrared (FIR) cooling supports a low-density, warm, diffuse gas that falls close to the boundary of acceptable models of a photon-dominated region. However, the power radiated in the [C II] and warm H 2 emissions have similar magnitudes, as seen in other shock-dominated systems and predicted by recent models. We suggest that shock heating of the [C II] is a viable alternative to photoelectric heating in violently disturbed, diffuse gas. The existence of shocks is also consistent with the peculiar CO kinematics in the galaxy, indicating that highly noncircular motions are present. These kinematically disturbed CO regions also show evidence of suppressed star formation, falling a factor of 10-30 below normal galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar properties of both galaxies are consistent with a highly dissipative, off-center collisional encounter between HCG 57d and 57a, creating ring-like morphologies in both systems. Highly dissipative gas-on-gas collisions may be more common in dense groups because of the likelihood of repeated multiple encounters. The possibility of shock-induced star-formation suppression may explain why a subset of these HCG galaxies has been found previously to fall in the mid-infrared green valley.

  6. Stellar Structure and Evolution: An Introduction

    Science.gov (United States)

    Jeffery, C. Simon

    The synthesis of new elements takes place inside stars. How do stars evolve and distribute this creation to the universe at large? This article starts with the observables that the theory of stellar evolution aims to reproduce, and gives a quick overview of what that theory predicts (Sects. 2-3). It presents the equations governing stellar structure and evolution (Sects. 4-6) and the physics of stellar interiors (Sects. 7-9). Approximate and numerical methods for their solution are outlined (Sects. 10-11) and the general results of stellar structure and evolution are discussed (Sects. 12-13). The structure and evolution of horizontal-branch stars, hydrogen-deficient stars and other stellar remnants are also considered (Sects. 14-15).

  7. 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.

  8. Stellar Astrophysics with Arcus

    Science.gov (United States)

    Brickhouse, Nancy S.; Huenemoerder, David P.; Wolk, Scott; Schulz, Norbert; Foster, Adam; Brenneman, Laura; Poppenhaeger, Katja; Arcus Team

    2018-01-01

    The Arcus mission is now in Phase A of the NASA Medium-Class Explorer competition. We present here the Arcus science case for stellar astrophysics. With spectral resolving power of at least 2500 and effective area greater than 400 cm^2, Arcus will measure new diagnostic lines, e.g. for H- and He-like ions of oxygen and other elements. Weak dielectronic recombination lines will provide sensitive measurements of temperature to test stellar coronal heating models. Arcus will also resolve the coronal and accretion line components in young accreting stars, allowing detailed studies of accretion shocks and their post-shock behavior. Arcus can resolve line shapes and variability in hot star winds to study inhomogeneities and dynamics of wind structure. Such profiles will provide an independent measure of mass loss rates, for which theoretical and observational discrepancies can reach an order of magnitude. Arcus will also study exoplanet atmospheres through X-ray absorption, determing their extent and composition.

  9. 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)

  10. Non-extensive thermodynamics and neutron star properties

    Energy Technology Data Exchange (ETDEWEB)

    Menezes, Debora P. [Universidade Federal de Santa Catarina, Departamento de Fisica - CFM -, Florianopolis (Brazil); Deppman, Airton [Universidade de Sao Paulo, Instituto de Fisica, Sao Paulo (Brazil); Megias, Eugenio [Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut), Munich (Germany); Universitat Autonoma de Barcelona, Grup de Fisica Teorica and IFAE, Departament de Fisica, Barcelona (Spain); Castro, Luis B. [Universidade Federal do Maranhao, Departamento de Fisica, Sao Luis (Brazil)

    2015-12-15

    In the present work we apply non-extensive statistics to obtain equations of state suitable to describe stellar matter and verify its effects on microscopic and macroscopic quantities. Two snapshots of the star evolution are considered and the direct Urca process is investigated with two different parameter sets. q-values are chosen as 1.05 and 1.14. The equations of state are only slightly modified, but the effects are enough to produce stars with slightly higher maximum masses. The onsets of the constituents are more strongly affected and the internal stellar temperature decreases with the increase of the q-value, with consequences on the strangeness and cooling rates of the stars. (orig.)

  11. Stellar astrophysics

    International Nuclear Information System (INIS)

    1987-01-01

    A number of studies in the field of steller astrophysics were undertaken by the South African Astronomical Observatory in 1986. These studies included; evolutionary effects on the surface abundances of an early-type supergiant; hydrogen deficient stars; t tauri stars; rotational modulation and flares on RS CVn and BY Dra stars; carbon and heavy element stars, and slow variability and circumstellar shells of red variable stars. 4 figs

  12. Dynamical evolution of spherical stellar systems

    International Nuclear Information System (INIS)

    Lee, H.M.

    1986-01-01

    The dynamical effect of heavy mass stars formed out of successive mergers among tidally captured binaries of evolution of spherical stellar systems is investigated. To maximize such effect assumed all tidally captured systems become mergers. Stellar evolution is simulated by computing mean age of mass group and applying death rate as function of mean age. For stellar systems with N = 10 5-6 , combined effect of three body binary heating among heavy mass stars and stellar evolution provides energy to drive post collapse expansion; long-term evolution is dominated by stellar evolution. Long-term behavior of clusters is similar to tidally captured binaries assuming no merger. Observed chemical inhomogeneities among stars in globular clusters may also be explained by stellar mergers. Three-body heating is important in small-N systems, while stellar evolution dominates evolution of large N systems. The effect of primordial degenerate stars is investigated in the second study. Very hard binaries composed of degenerate-normal pair form via tidal capture process and moderately hard degenerate-degenerate binaries form via three-body process. If initial degenerate population is large, initial core-collapse phase may be approximated as collapse of degenerate star. Three-body binaries among degenerate stars eventually provide enough energy to stop collapse and cause reexpansion

  13. The Stellar-Solar Connection

    Science.gov (United States)

    Ayres, T. R.

    2004-05-01

    Many solar-stellar astronomers believe that the solar-stellar connection primarily is a one-way street: the exquisitely detailed studies of the solar surface, interior, and heliosphere strongly mold our views of the distant, unresolved stars. Perhaps many solar physicists have gone so far as to adopt the myopic view that stellar astronomy, by and large, is merely sponging up the fabulous insights from ever deeper examinations of our local star, but the ``dark side'' is not really capable of returning the favor. What could we possibly learn from the stars, that we don't already know from much better observations of the Sun? In my Introduction to this Topical Session, I will discuss two broad issues: (1) the present divergence between solar and stellar physics (driven by the different goals and tools of the two disciplines); and (2) the diversity of stars in the H-R diagram, to help inform our understanding of solar processes. Today, there are observations of stars that greatly exceed the quality of analogous solar measurements: e.g., HST/STIS UV echelle spectra of Alpha Cen A; Chandra transmission grating spectra of solar-type stars; and only recently have we obtained a definitive understanding of the Sun's soft X-ray luminosity in the key ROSAT/PSPC band. The lack of equivalent solar observations hinders practical applications of the solar-stellar connection. On the more informative side, the evolutionary paths of other stars can be quite different from the Sun's, with potentially dramatic influences on phenomena such as magnetic activity. Equally important, examples of Sun-like stars can be found at all stages of evolution, from proplyds to red giants, in the volume of nearby space out to 500 pc. In short, the solar-stellar connection need not be a one-way street, but rather a powerful tool to explore solar processes within the broader context of stars and stellar evolution. This work was supported by NASA grant NAG5-13058.

  14. YOUNG STELLAR CLUSTERS WITH A SCHUSTER MASS DISTRIBUTION. I. STATIONARY WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Palous, Jan; Wuensch, Richard; Hueyotl-Zahuantitla, Filiberto [Astronomical Institute, Academy of Sciences of the Czech Republic, Bocni II 1401-2a, Prague (Czech Republic); Martinez-Gonzalez, Sergio; Silich, Sergiy; Tenorio-Tagle, Guillermo, E-mail: palous@ig.cas.cz [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico)

    2013-08-01

    Hydrodynamic models for spherically symmetric winds driven by young stellar clusters with a generalized Schuster stellar density profile are explored. For this we use both semi-analytic models and one-dimensional numerical simulations. We determine the properties of quasi-adiabatic and radiative stationary winds and define the radius at which the flow turns from subsonic to supersonic for all stellar density distributions. Strongly radiative winds significantly diminish their terminal speed and thus their mechanical luminosity is strongly reduced. This also reduces their potential negative feedback into their host galaxy interstellar medium. The critical luminosity above which radiative cooling becomes dominant within the clusters, leading to thermal instabilities which make the winds non-stationary, is determined, and its dependence on the star cluster density profile, core radius, and half-mass radius is discussed.

  15. 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.

  16. The SOHO-Stellar Connection

    Science.gov (United States)

    Ayres, Thomas R.

    1999-01-01

    I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath

  17. Close encounters between star-planet systems and stellar intruders. II. Effect of the mass and impact velocity of the intruder

    International Nuclear Information System (INIS)

    Hills, J.G.; Dissly, R.W.

    1989-01-01

    Results are reported from over 300,000 simulations of encounters between a planet-star binary system and intruders whose masses range from 0.1 to 100 times the mass of the home star of the planet-star system. These calculations were done at a large number of collision velocities and impact parameters. Cross sections for dissociation, for exchange collisions, for changing the orbital energy, and for changing the orbital eccentricity were determined. 16 refs

  18. Pulsating stars

    CERN Document Server

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  19. Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way

    Science.gov (United States)

    Bensby, T.; Feltzing, S.; Gould, A.; Yee, J. C.; Johnson, J. A.; Asplund, M.; Meléndez, J.; Lucatello, S.; Howes, L. M.; McWilliam, A.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.; Kozłowski, S.; Pietrukowicz, P.; Skowron, J.; Mróz, P.; Pawlak, M.; Abe, F.; Asakura, Y.; Bhattacharya, A.; Bond, I. A.; Bennett, D. P.; Hirao, Y.; Nagakane, M.; Koshimoto, N.; Sumi, T.; Suzuki, D.; Tristram, P. J.

    2017-09-01

    We present a detailed elemental abundance study of 90 F and G dwarf, turn-off, and subgiant stars in the Galactic bulge. Based on high-resolution spectra acquired during gravitational microlensing events, stellar ages and abundances for 11 elements (Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. Four main findings are presented: (1) a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, + 0.12, + 0.41; (2) ahigh fraction of intermediate-age to young stars where at [Fe/H] > 0 more than 35% are younger than 8 Gyr, and for [Fe/H] ≲ -0.5 most stars are 10 Gyr or older; (3) several episodes of significant star formation in the bulge has been identified: 3, 6, 8, and 11 Gyr ago; (4) tentatively the "knee" in the α-element abundance trends of the sub-solar metallicity bulge is located at a slightly higher [Fe/H] than in the local thick disk. These findings show that the Galactic bulge has complex age and abundance properties that appear to be tightly connected to the main Galactic stellar populations. In particular, the peaks in the metallicity distribution, the star formation episodes, and the abundance trends, show similarities with the properties of the Galactic thin and thick disks. At the same time, the star formation rate appears to have been slightly faster in the bulge than in the local thick disk, which most likely is an indication of the denser stellar environment closer to the Galactic centre. There are also additional components not seen outside the bulge region, and that most likely can be associated with the Galactic bar. Our results strengthen the observational evidence that support the idea of a secular origin for the Galactic bulge, formed out of the other main Galactic stellar populations present in the central regions of our Galaxy. Additionally, our analysis of this enlarged sample suggests that the (V-I)0 colour of the bulge red clump should be revised to 1.09. Based on data obtained with the

  20. Stellar Masses

    Indian Academy of Sciences (India)

    later stages of evolution into a red giant differs considerably. It may lead to the formation of a white dwarf via a planetary nebula phase (for stars like the Sun) or the formation of a neutron star via a supernova explosion (for massive stars). The exact course is decided by the mass again. The energy produced is proportional to ...

  1. Stellar Masses

    Indian Academy of Sciences (India)

    brightness of the star. If we could keep all the stars at the same distance, the apparent magnitude itself can give a measure of the intrinsic brightness. This measurement by hypothetically keep- ing the stars at a distance of 10 parsecl is called the absolute magnitude. The Sun, if moved to that distance would have a.

  2. The Stellar Observations Network Group - first results

    DEFF Research Database (Denmark)

    Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard, Joergen

    SONG - the Stellar Observations Network Group is a Danish-led project set to design and build a global network of 1-m telescopes to carry out detailed studies of solar-like stars using asteroseismology and to discover and characterise exo-planets and their star system. Here we present more than 100...... of individual modes over many orders in the frequency spectrum, leading to studies of rotation, convection, near-surface effects, core structure using mixed modes and stellar activity....

  3. Cool half of the H-R diagram in soft X-rays

    International Nuclear Information System (INIS)

    Ayres, T.R.; Linsky, J.L.; Vaiana, G.S.; Golub, L.; Rosner, R.

    1981-01-01

    We report results of an Einstein Guest Observing program to map the occurrence of soft x-ray emission, which is a signature of hot stellar coronae (T>10 6 K), in the cool half of the Hertzsprung Russell (H-R) diagram. We detect X-rays from F--M dwarfs and late F through early K giants, but not from the cooler giants, other than the spectroscopic binary epsilon Car (K0 II+B), or from any supergiants, other than Canopus (F0IB--II). The empirical separation of the cool half of the H-R diagram into a region where stellar soft X-ray emission is a common phenomenon, and a region where hot coronae are rare, if present at all among single stars, is similar to that found previously by Linsky and Haisch for C IV lambdalambda1548,1551 emission (Troughly-equal10 5 K) and by Stencel and Mullan for the onset of rapid mass loss in strong, cool (T 4 K) stellar winds. We discuss the energy balance in the outer atmospheres of the coronal stars, the likely absorption of X-ray emission by cool winds in the ''hybrid-spectrum'' supergiants, a rotation-activity connection among the G dwarfs, and possible evolutionary origins of the structure seen in the cool half of the X-ray H-R diagram

  4. Stellar Structure and Evolution

    CERN Document Server

    Kippenhahn, Rudolf; Weiss, Achim

    2013-01-01

    This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

  5. The magnetic strip(s) in the advanced phases of stellar evolution. Theoretical convective turnover timescale and Rossby number for low- and intermediate-mass stars up to the AGB at various metallicities

    Science.gov (United States)

    Charbonnel, C.; Decressin, T.; Lagarde, N.; Gallet, F.; Palacios, A.; Aurière, M.; Konstantinova-Antova, R.; Mathis, S.; Anderson, R. I.; Dintrans, B.

    2017-09-01

    Context. Recent spectropolarimetric observations of otherwise ordinary (in terms e.g. of surface rotation and chemical properties) G, K, and M giants have revealed localized magnetic strips in the Hertzsprung-Russell diagram coincident with the regions where the first dredge-up and core helium burning occur. Aims: We seek to understand the origin of magnetic fields in such late-type giant stars, which is currently unexplained. In analogy with late-type dwarf stars, we focus primarily on parameters known to influence the generation of magnetic fields in the outer convective envelope. Methods: We compute the classical dynamo parameters along the evolutionary tracks of low- and intermediate-mass stars at various metallicities using stellar models that have been extensively tested by spectroscopic and asteroseismic observations. Specifically, these include convective turnover timescales and convective Rossby numbers, computed from the pre-main sequence (PMS) to the tip of the red giant branch (RGB) or the early asymptotic giant branch (AGB) phase. To investigate the effects of the very extended outer convective envelope, we compute these parameters both for the entire convective envelope and locally, that is, at different depths within the envelope. We also compute the turnover timescales and corresponding Rossby numbers for the convective cores of intermediate-mass stars on the main sequence. Results: Our models show that the Rossby number of the convective envelope becomes lower than unity in the well-delimited locations of the Hertzsprung-Russell diagram where magnetic fields have indeed been detected. Conclusions: We show that α - Ω dynamo processes might not be continuously operating, but that they are favored in the stellar convective envelope at two specific moments along the evolution tracks, that is, during the first dredge-up at the base of the RGB and during central helium burning in the helium-burning phase and early-AGB. This general behavior can explain

  6. The First Kepler Observations of the Pulsations of R Coronae Borealis Stars

    Science.gov (United States)

    Clayton, Geoffrey C.; Jeffery, C. Simon; Montiel, Edward; Saio, Hideyuki; Ramsay, Gavin

    2017-01-01

    K2 has opened a new avenue for the detailed study of the pulsations of the R Coronae Borealis (RCB) stars. These observations are key to understanding the evolution of the RCB stars because their masses cannot be accurately estimated by other means. The ~75 days of near continuous, high-precision observations are ideal for our planned analysis of the brightness variations of the RCB stars. We are observing about 15 RCB stars In K2 Fields 7, 9, and 11.These observations will provide a better understanding of the pulsation mechanisms and modes in RCB stars. RCB stars are thought to be ~0.8-0.9 M(Sun) from previous stellar pulsation modeling. These estimated masses agree well with the predicted masses of the merger products of a CO- and a He-WD. Final-flash stars, since they are single white dwarfs, should typically have masses of 0.55-0.6 M(Sun). No cool RCB star, with T(eff) = 5000-7000 K, is known to be a binary so these mass estimates are of great importance to understanding the evolution of these enigmatic stars. RCB stars show periodic or semi-periodic light and radial velocity fluctuations due to both radial and non-radial pulsations. These stars show pulsation periods in the 40-100 d range. These variations are separate from the large declines in brightness caused by dust forming around the star. The pulsations in RCB stars are thought to arise through strange-mode instabilities. Strange modes occur in stars with high luminosity where radiation pressure dominates. RCB stars comprise a peculiar and rare class of stars that offers an excellent opportunity to reveal crucial insights into the advanced stages of stellar evolution.

  7. 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

  8. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    Maximum stellar iron core mass mass of iron into a neutron star. The radius of this highly compressed theoretical sphere may be somewhat smaller than the actual radius of a real spherical mass of iron, just prior to core collapse, because an unstable real spherical mass of iron is likely to achieve the critical density only at its ...

  9. Convection and stellar oscillations

    DEFF Research Database (Denmark)

    Aarslev, Magnus Johan

    2017-01-01

    energy exchange between convection and pulsations, i.e. the modal part of the surface effect. Studying excitation and damping mechanisms requires a non-adiabatic treatment. A major part of my research has been modelling damping rates of red giant stars observed by {\\Kp}. The basis for the non...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them....... However, the effects are barely prominent enough to be distinguishable with today's observational precision. But it does provide means of determining the mixing-length and enables consistent patching. The previously mentioned investigations are based on adiabatic frequency calculations, which neglect...

  10. Neutron Stars : Magnetism vs Gravity

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Neutron Stars : Magnetism vs Gravity. WHY do neutron stars have such strong magnetic fields? Conservation of magnetic flux of the collapsing stellar core. ∫ B.ds (over surface of the star) = constant; Radius of the star collapses from ~ 5x108 to 1x104 metres; Hence, ...

  11. 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

  12. Characterizing Convection in Stellar Atmospheres

    International Nuclear Information System (INIS)

    Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank

    2011-01-01

    We perform 3D radiative hydrodynamic simulations to study the properties of convection in the superadiabatic layer of stars. The simulations show differences in both the stratification and turbulent quantities for different types of stars. We extract turbulent pressure and eddy sizes, as well as the T-τ relation for different stars and find that they are sensitive to the energy flux and gravity. We also show that contrary to what is usually assumed in the field of stellar atmospheres, the structure and gas dynamics of simulations of turbulent atmospheres cannot be parameterized with T eff and log(g) alone.

  13. Pulsations in Subdwarf B Stars

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Subdwarf B stars play a significant role in close binary evolution and in the hot star content of old stellar populations, in particular in giant elliptical galaxies. While the question of their origin poses several problems for stellar evolution theory, one of their most fascinating properties is the presence of ...

  14. 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...

  15. Stellar and Extragalactic Radiation at the Earth's Surface Jean ...

    Indian Academy of Sciences (India)

    ipi × dex (−0.4 mi). (7). We will use these formulae in estimating the stellar and extragalactic contributions. 3. Stellar radiation. We have used the data given by the CDS, Strasbourg for N = 2,552,323 stars. The data are available in tables grouping stars in magnitude intervals of m = 0.25, either in BT or VT magnitudes.

  16. 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.

  17. THE ADVANCED STELLAR COMPASS

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1997-01-01

    The science objective of the Danish Geomagnetic Research Satellite "Ørsted" is to map the magnetic field of the Earth, with a vector precision of a fraction of a nanotesla. This necessitates an attitude reference instrument with a precision of a few arcseconds onboard the satellite. To meet...... this demand the Advanced Stellar Compass (ASC), a fully autonomous miniature star tracker, was developed. This ASC is capable of both solving the "lost in space" problem and determine the attitude with arcseconds precision. The development, principles of operation and instrument autonomy of the ASC...

  18. Ubiquitous time variability of integrated stellar populations

    Science.gov (United States)

    Conroy, Charlie; van Dokkum, Pieter G.; Choi, Jieun

    2015-11-01

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected ‘pixel shimmer’ in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

  19. 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.)

  20. The Ancient stellar population of Leo A.

    NARCIS (Netherlands)

    Saha, Abhijit; Fiorentino, Giuliana; Tolstoy, Eline; Cole, Andrew

    The primary goal of our proposal is the characterisation of the oldest stellar populations in Leo A using the properties of ancient RR Lyrae variable stars as tracers. Well known and long established correlations exist between the periods and luminosities of RR Lyrae variable stars and their ages

  1. Measuring Stellar Rotation Periods with Kepler

    DEFF Research Database (Denmark)

    Nielsen, M. B.; Gizon, L.; Schunker, H.

    2013-01-01

    We measure rotation periods for 12151 stars in the Kepler field, based on photometric variability caused by stellar activity. Our analysis returns stable rotation periods over at least six out of eight quarters of Kepler data. This large sample of stars enables us to study rotation periods...

  2. Stellar Alchemy

    Science.gov (United States)

    Cassé, Michel; Lyle, Translated by Stephen

    2003-08-01

    Preface; 1. Nuclear astrophysics: defence and illustration; 2. Light from atoms, light from the sky; 3. Visions; 4. Contents of the sky: atomic sources and fountains; 5. Nuclear suns; 6. Sociology of stars and clouds; 7. Histories; 8. Ancient stars in the galactic halo; 9. Conclusion; Appendices.

  3. A Vanishing Star Revisited

    Science.gov (United States)

    1999-07-01

    to achieve a reasonable photometric accuracy. However, the eclipse only lasts a few minutes and it would only be possible to exposure and read-out a few, normal exposures from the CCD camera, not enough to fully characterize the light curve at minimum. Reinhold Häfner decided to use another method. By having the telescope perform a controlled change of position on the sky ("drift") during the exposure, the light from NN Ser before, during and after the eclipse will not be registered on the same spot of the camera detector, but rather along a line. He carefully chose a direction in which this line would not cross those of other stars in the neighbourhood of NN Ser . This was ensured by rotating FORS1 to a predetermined position angle. The drift rate was fixed as one pixel (0.20 arcsec) per 3 seconds of time, a compromise between the necessary integration time and desired time resolution that would give the best chance to document the exact shape of the light-curve . In theory, this would then allow the measurement of the intensity along the recorded trail of NN Ser and hence its brightness at any given time during the eclipse. But how deep would the eclipse be? Would the resulting exposure on each pixel at minimum light be long enough to register a measurable signal? Seeing the light from the cool star! ESO PR Photo 30b/99 ESO PR Photo 30b/99 [Preview - JPEG: 400 x 464 pix - 156k] [Normal - JPEG: 800 x 927 pix - 584k] [High-Res - JPEG: 2292 x 2662 pix - 4.1M] ESO PR Photo 30c/99 ESO PR Photo 30c/99 [Preview - JPEG: 472 x 400 pix - 48k] [Normal - JPEG: 943 x 800 pix - 96k] Caption to ESO PR Photo 30b/99 : 18.5-min "drift" exposure with VLT ANTU and FORS1 of the sky field around the variable stellar system NN Ser (indicated with an arrow). The telescope moved 1 pixel (0.20 arcsec) every 3 seconds so that the images of the stars in the field are trailed from left to right. After some minutes, the very deep eclipse of NN Ser begins when the brightness drops dramatically

  4. 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.

  5. Stellar Populations

    NARCIS (Netherlands)

    Peletier, Reynier F.

    2013-01-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on

  6. Stripping a debris disk by close stellar encounters in an open stellar cluster

    Science.gov (United States)

    Lestrade, J.-F.; Morey, E.; Lassus, A.; Phou, N.

    2011-08-01

    A debris disk is a constituent of any planetary system surrounding a main sequence star. We study whether close stellar encounters can disrupt and strip a debris disk of its planetesimals in the expanding open cluster of its birth with a decreasing star number density over 100 Myr. Such stripping would affect the dust production and hence detectability of the disk. We tabulated the fractions of planetesimals stripped off during stellar flybys of miss distances between 100 and 1000 AU and for several mass ratios of the central to passing stars. We then estimated the numbers of close stellar encounters over the lifetime of several expanding open clusters characterized by their initial star densities. We found that a standard disk, with inner and outer radii of 40 and 100 AU, suffers no loss of planetesimals over 100 Myr around a star born in a common embedded cluster with star density ≤1000 pc-3. In contrast, we found that such a disk is severely depleted of its planetesimals around a star born in an Orion-type cluster where the star density is >20 000 pc-3. In this environment, a disk loses >97% of its planetesimals around an M-dwarf, >63% around a solar-type star, and >42% around an A-dwarf, over 100 Myr. We roughly estimate that two-thirds of the stars may be born in such high star density clusters. This might explain in part why fewer debris disks are observed around lower mass stars.

  7. CHARACTERIZING THE COOL KOIs. III. KOI 961: A SMALL STAR WITH LARGE PROPER MOTION AND THREE SMALL PLANETS

    Energy Technology Data Exchange (ETDEWEB)

    Muirhead, Philip S.; Johnson, John Asher; Morton, Timothy D.; Pineda, John Sebastian; Bottom, Michael; Crepp, Justin R.; Kirby, Evan N. [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Apps, Kevin [75B Cheyne Walk, Surrey, RH6 7LR (United Kingdom); Carter, Joshua A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Fabrycky, Daniel C.; Hamren, Katherine [UCO/Lick, University of California, Santa Cruz, CA 95064 (United States); Rojas-Ayala, Barbara [Astrophysics Department, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Schlawin, Everett; Covey, Kevin R. [Department of Astronomy, Cornell University, 122 Sciences Drive, Ithaca, NY 14583 (United States); Stassun, Keivan G.; Pepper, Joshua; Hebb, Leslie [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Howard, Andrew W.; Isaacson, Howard T.; Marcy, Geoffrey W., E-mail: philm@astro.caltech.edu [Astronomy Department, University of California, Berkeley, CA 94720 (United States); and others

    2012-03-10

    We characterize the star KOI 961, an M dwarf with transit signals indicative of three short-period exoplanets discovered by the Kepler mission. We proceed by comparing KOI 961 to Barnard's Star, a nearby, well-characterized mid-M dwarf. We compare colors, optical and near-infrared spectra, and find remarkable agreement between the two, implying similar effective temperatures and metallicities. Both are metal-poor compared to the Solar neighborhood, have low projected rotational velocity, high absolute radial velocity, large proper motion, and no quiescent H{alpha} emission-all of which are consistent with being old M dwarfs. We combine empirical measurements of Barnard's Star and expectations from evolutionary isochrones to estimate KOI 961's mass (0.13 {+-} 0.05 M{sub Sun }), radius (0.17 {+-} 0.04 R{sub Sun }), and luminosity (2.40 Multiplication-Sign 10{sup -3.0{+-}0.3} L{sub Sun }). We calculate KOI 961's distance (38.7 {+-} 6.3 pc) and space motions, which, like Barnard's Star, are consistent with a high scale-height population in the Milky Way. We perform an independent multi-transit fit to the public Kepler light curve and significantly revise the transit parameters for the three planets. We calculate the false-positive probability for each planet candidate, and find a less than 1% chance that any one of the transiting signals is due to a background or hierarchical eclipsing binary, validating the planetary nature of the transits. The best-fitting radii for all three planets are less than 1 R{sub Circled-Plus }, with KOI 961.03 being Mars-sized (R{sub P} = 0.57 {+-} 0.18 R{sub Circled-Plus }), and they represent some of the smallest exoplanets detected to date.

  8. LAMOST views δ Scuti pulsating stars

    Science.gov (United States)

    Qian, S.-B.; Li, L.-J.; He, J.-J.; Zhang, J.; Zhu, L.-Y.; Han, Z.-T.

    2018-03-01

    About 766 δ Scuti stars were observed by LAMOST by 2017 June 16. Stellar atmospheric parameters of 525 variables were determined, while spectral types were obtained for all samples. In the paper, those spectroscopic data are catalogued. We detect a group of 131 unusual and cool variable stars (UCVs) that are distinguished from the normal δ Scuti stars (NDSTs). On the H-R diagram and the log g-T diagram, the UCVs are far beyond the red edge of pulsational instability trip. Their effective temperatures are lower than 6700 K with periods in the range from 0.09 to 0.22 d. NDSTs have metallicity close to that of the Sun as expected, while UCVs are slightly metal poor than NDSTs. The two peaks on the distributions of the period and stellar atmospheric parameters are all caused by the existence of UCVs. When those UCVs are excluded, it is discovered that the effective temperature, the gravitational acceleration, and the metallicity all are correlated with the pulsating period for NDSTs and their physical properties and evolutionary states are discussed. Detection of those UCVs indicates that about 25 per cent of the known δ Scuti stars may be misclassified. However, if some of them are confirmed to be pulsating stars, they will be a new-type pulsator and their investigations will shed light on theoretical instability domains and on the theories of interacting between the pulsation and the convection of solar-type stars. Meanwhile, 88 δ Scuti stars are detected to be the candidates of binary or multiple systems.

  9. 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.

  10. STAR-H2: a battery-type lead-cooled fast reactor for hydrogen manufacture in a sustainable hierarchical hub-spoke energy infrastructure

    International Nuclear Information System (INIS)

    Wade, D.C.; Doctor, R. D.; Peddicord, K.L.

    2003-01-01

    The Secure Transportable Autonomous Reactor for Hydrogen production STAR-H2 is designed to fit into a sustainable global, mid-21st century hierarchical hub-spoke nuclear energy supply architecture based on nuclear fuel, hydrogen, and electricity energy carriers and having favorable energy security, ecological and nonproliferation features. It will produce hydrogen, oxygen and potable water to service cities and their surrounding regions under an assumed electrical generation network based on fuel cells and microturbines and an assumed transportation sector using hydrogen fueled vehicles. STAR-H2 is a long refueling interval (Battery) turnkey heat supply reactor intended for production of hydrogen by thermochemical water cracking. The reactor is a Pb-cooled, mixed U-TRU-Nitride-fueled, fast spectrum reactor delivering 400 MW th of heat at 800degC core outlet temperature. The primary coolant circulates by natural circulation; the 400 MW th heat rating is set by dual requirements for natural circulation; the 400 MW th heat rating is set by dual requirements for natural circulation and for rail shippability of the vessel. An intermediate low pressure He loop carries the heat to a Ca-Br thermochemical water cracking cycle for the manufacture of H 2 (and O 2 ). The water cracking cycle rejects heat at 550degC and that heat is used in a supercritical CO 2 Brayton cycle turbogenerator to provide hotel load electricity. A thermal desalinisation plant receives discharge heat at 125degC from the Brayton cycle and the brine provides for ultimate heat rejection from the cascaded thermodynamic cycles. The modified UT-3 cycle used in STAR-H2, called the Ca-Br cycle, operates at atmospheric pressure and 750-725degC, uses solid/gas separation steps and achieves about 44% efficiency. Unlike UT-3, it employs a single-stage HBr-dissociation step based on a plasma chemistry technique operating near ambient conditions. The STAR-H2 power plant will operate on a 20 year refueling interval

  11. Simulations of Magnetic Flux Emergence in Cool, Low-Mass Stars: Toward Linking Dynamo Action with Starspots

    Science.gov (United States)

    Weber, Maria Ann; Browning, Matthew; Nelson, Nicholas

    2018-01-01

    Starspots are windows into a star’s internal dynamo mechanism. However, the manner by which the dynamo-generated magnetic field traverses the stellar interior to emerge at the surface is not especially well understood. Establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos and observed starspot properties. In the solar context, insight into this process has been obtained by assuming the magnetism giving rise to sunspots consists partly of idealized thin flux tubes (TFTs). Here, we present three sets of TFT simulations in rotating spherical shells of convection: one representative of the Sun, the second of a solar-like rapid rotator, and the third of a fully convective M dwarf. Our solar simulations reproduce sunspot observables such as low-latitude emergence, tilting action toward the equator following the Joy’s Law trend, and a phenomenon akin to active longitudes. Further, we compare the evolution of rising flux tubes in our (computationally inexpensive) TFT simulations to buoyant magnetic structures that arise naturally in a unique global simulation of a rapidly rotating Sun. We comment on the role of rapid rotation, the Coriolis force, and external torques imparted by the surrounding convection in establishing the trajectories of the flux tubes across the convection zone. In our fully convective M dwarf simulations, the expected starspot latitudes deviate from the solar trend, favoring significantly poleward latitudes unless the differential rotation is sufficiently prograde or the magnetic field is strongly super-equipartition. Together our work provides a link between dynamo-generated magnetic fields, turbulent convection, and observations of starspots along the lower main sequence.

  12. CU Virginis - The First Stellar Pulsar

    OpenAIRE

    Kellett, Barry J.; Graffagnino, Vito; Bingham, Robert; Muxlow, Tom W. B.; Gunn, Alastair G.

    2007-01-01

    CU Virginis is one of the brightest radio emitting members of the magnetic chemically peculiar (MCP) stars and also one of the fastest rotating. We have now discovered that CU Vir is unique among stellar radio sources in generating a persistent, highly collimated, beam of coherent, 100% polarised, radiation from one of its magnetic poles that sweeps across the Earth every time the star rotates. This makes the star strikingly similar to a pulsar. This similarity is further strengthened by the ...

  13. Collisions in spherical stellar systems

    Energy Technology Data Exchange (ETDEWEB)

    Polyachenko, V.L.; Shukhman, I.G. (AN SSSR, Irkutsk. Sibirskij Inst. Zemnogo Magnetizma Ionosfery i Rasprostraneniya Radiovoln)

    From the set of the equations for the stellar distribution function and for the two-particle correlation in the action- angle variables, by averaging over fast finite motions the general expression for the collisional term of a finite stellar system with ''rare'' Coulomb collisions is obtained. In the case of a spherically symmetrical system with the distribution function f/sub 0/=f/sub 0/(E, L) (E, L being the energy and the angular momentum of a star), the kinetic equation is reduced to the standard form of the two-dimensional Fokker-Planck equations.

  14. Computing experiments on stellar systems

    CERN Document Server

    Bouvier, P

    1972-01-01

    A stellar system being usually conceived, in a first approximation, as a group of point-like stars held together by their own gravitational mutual attraction, one may discriminate between three or four different lines of attack on the problem of the dynamical evolution of such a system. These are the straight-forward integration of the n- body problem, the statistical model description, the Monte Carlo technique, the Boltzmann moment approach. Direct numerical integration can now be applied to the dynamical evolution of star clusters containing up to 500 stars, which includes small to medium open stellar clusters, while statistical and Monte Carlo descriptions are better suited for systems of at least several thousand stars. The overall dynamic evolution of an isolated star cluster is characterized by the formation of a dense core surrounded by an extended halo, with some stars escaping with positive energy. This general feature has been confirmed in all the numerical experiments carried out in the last ten y...

  15. Development of an integrated prestressed-concrete pressure vessel for water-cooled reactors (SBB type 'STERN' (star) with supporting boiler)

    International Nuclear Information System (INIS)

    Jueptner, G.; Kumpf, H.; Molz, G.; Neunert, B.; Seidl, O.

    1976-01-01

    This report goes into the reasons for selecting a 'STERN' (star) vessel configuration for accommodating a complete primary circuit including PWR, this involving the grouping of cylindrical pressure vessels of independent design into a star-shaped configuration with the central vessel housing the reactor core in the middle. This arrangement was made possible by application of the DYWIDAG-radial prestressing process generating controlled annular prestressing using existing presses and by an organic coupling of individual vessels. The liner, heat insulating and cooling system required for each vessel comprises a so-called support boiler, i.e. a hot liner not handicapped by the disadvantages of other systems. The support boiler is placed in the and PCV and has flat floor and cover surfaces. Temperature constraints are reduced to specific design requirements by means of radial gap permitting precise adjustment in conjunction with an axial expanding element comprising a multilayer diaphragm which is supported in operation. A detailed description is given of the PCPV, the support boiler and the cover used in the center vessel as well as of their design, the assembly and construction work is described and a summary presented of the quantities and estimated prices involved. Due to the absence of steam raising facilities adapted to meet the star-shaped configuration requirements, a study of satellite vessels was dispensed with, the design of which is in full accord with that of the center vessel. One part of the report is concerned with the calculation of the center vessel. (orig./HP) [de

  16. 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.

  17. 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.

  18. 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.

  19. The physics of stars

    CERN Document Server

    Phillips, A C

    1999-01-01

    The Physics of Stars, Second Edition, is a concise introduction to the properties of stellar interiors and consequently the structure and evolution of stars. Strongly emphasising the basic physics, simple and uncomplicated theoretical models are used to illustrate clearly the connections between fundamental physics and stellar properties. This text does not intend to be encyclopaedic, rather it tends to focus on the most interesting and important aspects of stellar structure, evolution and nucleosynthesis. In the Second Edition, a new chapter on Helioseismology has been added, along with a list

  20. SUB-KILOPARSEC IMAGING OF COOL MOLECULAR GAS IN TWO STRONGLY LENSED DUSTY, STAR-FORMING GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Spilker, J. S.; Marrone, D. P. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Aravena, M. [Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Béthermin, M.; Breuck, C. de [European Southern Observatory, Karl Schwarzschild Straße 2, D-85748 Garching (Germany); Bothwell, M. S. [Cavendish Laboratory, University of Cambridge, JJ Thompson Ave, Cambridge CB3 0HA (United Kingdom); Carlstrom, J. E. [Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Chapman, S. C.; Rotermund, K. M. [Dalhousie University, Halifax, Nova Scotia (Canada); Collier, J. D.; Galvin, T.; Grieve, K.; O’Brien, A. [University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751 (Australia); Fassnacht, C. D. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Gonzalez, A. H.; Ma, J. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); González-López, J. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Hezaveh, Y. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Malkan, M., E-mail: jspilker@as.arizona.edu [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); and others

    2015-10-01

    We present spatially resolved imaging obtained with the Australia Telescope Compact Array (ATCA) of three CO lines in two high-redshift gravitationally lensed dusty star-forming galaxies, discovered by the South Pole Telescope. Strong lensing allows us to probe the structure and dynamics of the molecular gas in these two objects, at z = 2.78 and z = 5.66, with effective source-plane resolution of less than 1 kpc. We model the lensed emission from multiple CO transitions and the dust continuum in a consistent manner, finding that the cold molecular gas as traced by low-J CO always has a larger half-light radius than the 870 μm dust continuum emission. This size difference leads to up to 50% differences in the magnification factor for the cold gas compared to dust. In the z = 2.78 galaxy, these CO observations confirm that the background source is undergoing a major merger, while the velocity field of the other source is more complex. We use the ATCA CO observations and comparable resolution Atacama Large Millimeter/submillimeter Array dust continuum imaging of the same objects to constrain the CO–H{sub 2} conversion factor with three different procedures, finding good agreement between the methods and values consistent with those found for rapidly star-forming systems. We discuss these galaxies in the context of the star formation—gas mass surface density relation, noting that the change in emitting area with observed CO transition must be accounted for when comparing high-redshift galaxies to their lower redshift counterparts.

  1. 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

  2. The stellar seismology of hot white dwarfs and planetary nebula nuclei

    Science.gov (United States)

    Kawaler, Steven D.

    1987-01-01

    The pulsation properties of hot white dwarfs make it possible to determine their mass, surface composition, rotation, and rate of evolution, and provide constraints on their internal structure. Period spacings are sensitive measures of stellar mass and indicate surface layer structure. Measurement of the rate of period change for these stars provide a way to determine their cooling rates. Attention is also given to how well (or poorly) models of excitation of the pulsations fit within current models of planetary nebula nuclei and hot white dwarfs.

  3. 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| Chile, programme number 097.C-0208(A).

  4. Radiative Feedback from Primordial Protostars and Final Mass of the First Stars

    Science.gov (United States)

    Hosokawa, Takashi; Omukai, Kazuyuki; Yoshida, Naoki; Yorke, Harold W.

    2012-01-01

    In this contribution, we review our efforts toward understanding the typical mass-scale of primordial stars. Our direct numerical simulations show that, in both of Population III.1 and III.2 cases, strong UV stellar radiative feedback terminatesmass accretion onto a protostar.AnHII region formed around the protostar very dynamically expands throughout the gas accreting envelope, which cuts off the gas supply to a circumstellar disk. The disk is exposed to the stellar UV radiation and loses its mass by photoevaporation. The derived final masses are 43 Stellar Mass and 17 Stellar Mass in our fiducial Population III.1 and III.2 cases. Much more massive stars should form in other exceptional conditions. In atomic-cooling halos where H2 molecules are dissociated, for instance, a protostar grows via very rapid mass accretion with the rates M* approx. 0.1 - 1 Stellar Mass/yr. Our newstellar evolution calculations show that the protostar significantly inflates and never contracts to reach the ZAMS stage in this case. Such the "supergiant protostars" have very low UV luminosity, which results in weak radiative feedback against the accretion flow. In the early universe, supermassive stars formed through this process might provide massive seeds of supermassive black holes.

  5. Stellarator physics

    International Nuclear Information System (INIS)

    1990-07-01

    This document consists of the proceedings of the Seventh International Workshop on Stellarators, held in Oak Ridge, Tennessee, USA, 10-14 April, 1989. The document consists of a summary of presentations, an overview of experimental results, and papers presented at the workshop on transport, impurities and divertors, diagnostics, ECH confinement experiments, equilibrium and stability studies, RF heating, confinement, magnetic configurations, and new experiments. Refs, figs and tabs

  6. PREFACE: A Stellar Journey A Stellar Journey

    Science.gov (United States)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  7. New and updated stellar parameters for 71 evolved planet hosts. On the metallicity-giant planet connection

    Science.gov (United States)

    Mortier, A.; Santos, N. C.; Sousa, S. G.; Adibekyan, V. Zh.; Delgado Mena, E.; Tsantaki, M.; Israelian, G.; Mayor, M.

    2013-09-01

    Context. It is still being debated whether the well-known metallicity-giant planet correlation for dwarf stars is also valid for giant stars. For this reason, having precise metallicities is very important. Precise stellar parameters are also crucial to planetary research for several other reasons. Different methods can provide different results that lead to discrepancies in the analysis of planet hosts. Aims: To study the impact of different analyses on the metallicity scale for evolved stars, we compare different iron line lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolved stars with planets. With these new homogeneous parameters, we revisit the metallicity-giant planet connection for evolved stars. Methods: A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performed through the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one built for cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting, using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributions of various different samples of evolved stars and red giants. Results: All parameters compare well using a line list set, designed specifically for cool and solar-like stars to provide more accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for future analysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a bias in giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravity stars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicity enhancement is found for red giants with planets (log g FIES spectrograph at the Nordic Optical Telescope

  8. 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).

  9. 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.

  10. Warm dust around cool stars: field M dwarfs with Wise 12 or 22 μm excess emission

    International Nuclear Information System (INIS)

    Theissen, Christopher A.; West, Andrew A.

    2014-01-01

    Using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70,841) that show IR flux greater than the typical dM photosphere levels at 12 and/or 22 μm, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined spectral energy distributions. Our observed IR fluxes are greater than levels expected from ultracool companions (>3σ). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is <0.1%. Using SDSS spectra we measure surface gravity-dependent features (K, Na, and CaH 3) and find <15% of our sample indicates low surface gravities. Examining tracers of youth (Hα, UV fluxes, and Li absorption), we find <3% of our sample appear young, indicating we are observing a population of field stars ≳1 Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z| ∼ 700 pc and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include (1) collisions of planetary bodies, (2) tidal disruption of planetary bodies, or (3) failed planet formation.

  11. Single stellar populations in the near-infrared. I. Preparation of the IRTF spectral stellar library

    NARCIS (Netherlands)

    Meneses-Goytia, S.; Peletier, R. F.; Trager, S. C.; Falcón-Barroso, J.; Koleva, M.; Vazdekis, A.

    2015-01-01

    We present a detailed study of the stars of the NASA InfraRed Telescope Facility (IRTF) spectral library to understand its full extent and reliability for use with stellar population (SP) modeling. The library consist of 210 stars, with a total of 292 spectra, covering the wavelength range of 0.94

  12. Fifteen years in the high-energy life of the solar-type star HD 81809. XMM-Newton observations of a stellar activity cycle

    Science.gov (United States)

    Orlando, S.; Favata, F.; Micela, G.; Sciortino, S.; Maggio, A.; Schmitt, J. H. M. M.; Robrade, J.; Mittag, M.

    2017-09-01

    Context. The modulation of the activity level of solar-like stars is commonly revealed by cyclic variations in their chromospheric indicators, such as the Ca II H&K S-index, similarly to what is observed in our Sun. However, while the variation of solar activity is also reflected in the cyclical modulation of its coronal X-ray emission, similar behavior has only been discovered in a few stars other than the Sun. Aims: The data set of the long-term XMM-Newton monitoring program of HD 81809 is analyzed to study its X-ray cycle, investigate if the latter is related to the chromospheric cycle, infer the structure of the corona of HD 81809, and explore if the coronal activity of HD 81809 can be ascribed to phenomena similar to solar activity and, therefore, considered an extension of the solar case. Methods: We analyzed the observations of HD 81809 performed with XMM-Newton with a regular cadence of six months from 2001 to 2016, which represents one of the longest available observational baseline ( 15 yr) for a solar-like star with a well-studied chromospheric cycle (with a period of 8 yr). We investigated the modulation of coronal luminosity and temperature and its relation with the chromospheric cycle. We interpreted the data in terms of a mixture of solar-like coronal regions, adopting a method originally proposed to study the Sun as an X-ray star. Results: The observations show a well-defined regular cyclic modulation of the X-ray luminosity that reflects the activity level of HD 81809. The data covers approximately two cycles of coronal activity; the modulation has an amplitude of a factor of 5 (excluding evident flares, as in the June 2002 observation) and a period of 7.3 ± 1.5 yr, which is consistent with that of the chromospheric cycle. We demonstrate that the corona of HD 81809 can be interpreted as an extension of the solar case and can be modeled with a mixture of solar-like coronal regions along the whole cycle. The activity level is mainly determined by

  13. Physics of star formation in galaxies

    CERN Document Server

    Palla, F

    2002-01-01

    Begining with a historical introduction, ""Star Formation: The Early History"", this text then presents two long articles on ""Pre-Main-Sequence Evolution of Stars and Young Clusters"" and ""Observations of Young Stellar Objects"".

  14. Superfluidity and Superconductivity in Neutron Stars

    Indian Academy of Sciences (India)

    Neutron stars, the compact stellar remnants of core-collapse supernova explosions, are unique cosmic laboratories for exploring novel phases of matter under extreme conditions. In particular, the occurrence of superfluidity and superconductivity in neutron stars will be briefly reviewed.

  15. 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.

  16. 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.

  17. Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

    Science.gov (United States)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.; hide

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  18. Dusty supernovae running the thermodynamics of the matter reinserted within young and massive super stellar clusters

    International Nuclear Information System (INIS)

    Tenorio-Tagle, Guillermo; Silich, Sergiy; Martínez-González, Sergio; Muñoz-Tuñón, Casiana; Palouš, Jan; Wünsch, Richard

    2013-01-01

    Following the observational and theoretical evidence that points at core-collapse supernovae (SNe) as major producers of dust, here we calculate the hydrodynamics of the matter reinserted within young and massive super stellar clusters under the assumption of gas and dust radiative cooling. The large SN rate expected in massive clusters allows for a continuous replenishment of dust immersed in the high temperature thermalized reinserted matter and warrants a stationary presence of dust within the cluster volume during the type II SN era. We first show that such a balance determines the range of the dust-to-gas-mass ratio, and thus the dust cooling law. We then search for the critical line that separates stationary cluster winds from the bimodal cases in the cluster mechanical luminosity (or cluster mass) versus cluster size parameter space. In the latter, strong radiative cooling reduces considerably the cluster wind mechanical energy output and affects particularly the cluster central regions, leading to frequent thermal instabilities that diminish the pressure and inhibit the exit of the reinserted matter. Instead, matter accumulates there and is expected to eventually lead to gravitational instabilities and to further stellar formation with the matter reinserted by former massive stars. The main outcome of the calculations is that the critical line is almost two orders of magnitude or more, depending on the assumed value of V A∞ , lower than when only gas radiative cooling is applied. And thus, many massive clusters are predicted to enter the bimodal regime.

  19. 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.

  20. TIDAL DISRUPTIONS IN CIRCUMBINARY DISKS. I. STAR FORMATION, DYNAMICS, AND BINARY EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Amaro-Seoane, Pau; Brem, Patrick [Max Planck Institut fuer Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany); Cuadra, Jorge, E-mail: Pau.Amaro-Seoane@aei.mpg.de, E-mail: Patrick.Brem@aei.mpg.de, E-mail: jcuadra@astro.puc.cl [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, 782-0436 Santiago (Chile)

    2013-02-10

    In our current interpretation of the hierarchical structure of the universe, it is well established that galaxies collide and merge with each other during their lifetimes. If massive black holes (MBHs) reside in galactic centers, we expect them to form binaries in galactic nuclei surrounded by a circumbinary disk. If cooling is efficient enough, the gas in the disk will clump and trigger stellar formation in situ. In this first paper we address the evolution of the binary under the influence of the newly formed stars, which form individually and also clustered. We use smoothed particle hydrodynamics techniques to evolve the gas in the circumbinary disk and to study the phase of star formation. When the amount of gas in the disk is negligible, we further evolve the system with a high-accurate direct-summation N-body code to follow the evolution of the stars, the innermost binary and tidal disruption events (TDEs). For this, we modify the direct N-body code to include (1) treatment of TDEs and (2) 'gas cloud particles' that mimic the gas, so that the stellar clusters do not dissolve when we follow their infall on to the MBHs. We find that the amount of stars disrupted by either infalling stellar clusters or individual stars is as large as 10{sup -4} yr{sup -1} per binary, higher than expected for typical galaxies.

  1. Theoretical velocity structure of long-period variable star photospheres

    International Nuclear Information System (INIS)

    Hill, S.J.; Willson, L.A.

    1979-01-01

    Numerical models for shock waves propagating through atmospheres of cool supergiant stars for a grid of masses and surface gravities have been calculated calculated, assuming spherical symmetry, isothermality, and a periodic piston boundary condition. The results of these models can be restated using parameters derived in Willson and Hill; the reparametrization allows the generalization of these results to arbitrary stellar masses and radii. Applying the theoretical generalization to a variety of observed properties of R Leonis and o Ceti allows the selection of a limited range of probable masses and radii for these stars: Mapprox. =0.8--l.5M/sub sun/,Rapprox. =l.3--2.0 x 10 13 cm for o Cet and M=l.8--4.0M/sub sun/, R=l.7--2.5 x 10 13 cm for R Leo. We conclude that both stars are pulsating in the fundamental mode, with a pulsation constant Qapprox. =Od1

  2. Astrospheres and Solar-like Stellar Winds

    Directory of Open Access Journals (Sweden)

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  3. Stellar X-Ray Polarimetry

    Science.gov (United States)

    Swank, J.

    2011-01-01

    Most of the stellar end-state black holes, pulsars, and white dwarfs that are X-ray sources should have polarized X-ray fluxes. The degree will depend on the relative contributions of the unresolved structures. Fluxes from accretion disks and accretion disk corona may be polarized by scattering. Beams and jets may have contributions of polarized emission in strong magnetic fields. The Gravity and Extreme Magnetism Small Explorer (GEMS) will study the effects on polarization of strong gravity of black holes and strong magnetism of neutron stars. Some part of the flux from compact stars accreting from companion stars has been reflected from the companion, its wind, or accretion streams. Polarization of this component is a potential tool for studying the structure of the gas in these binary systems. Polarization due to scattering can also be present in X-ray emission from white dwarf binaries and binary normal stars such as RS CVn stars and colliding wind sources like Eta Car. Normal late type stars may have polarized flux from coronal flares. But X-ray polarization sensitivity is not at the level needed for single early type stars.

  4. Hydrodynamics and stellar winds an introduction

    CERN Document Server

    Maciel, Walter J

    2014-01-01

    Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

  5. Remarks on stellar clusters

    International Nuclear Information System (INIS)

    Teller, E.

    1985-01-01

    In the following, a few simple remarks on the evolution and properties of stellar clusters will be collected. In particular, globular clusters will be considered. Though details of such clusters are often not known, a few questions can be clarified with the help of primitive arguments. These are:- why are spherical clusters spherical, why do they have high densities, why do they consist of approximately a million stars, how may a black hole of great mass form within them, may they be the origin of gamma-ray bursts, may their invisible remnants account for the missing mass of our galaxy. The available data do not warrant a detailed evaluation. However, it is remarkable that exceedingly simple models can shed some light on the questions enumerated above. (author)

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. ON THE FATE OF THE MATTER REINSERTED WITHIN YOUNG NUCLEAR STELLAR CLUSTERS

    International Nuclear Information System (INIS)

    Hueyotl-Zahuantitla, Filiberto; Palouš, Jan; Wünsch, Richard; Tenorio-Tagle, Guillermo; Silich, Sergiy

    2013-01-01

    This paper presents a hydrodynamical model describing the evolution of the gas reinserted by stars within a rotating young nuclear star cluster (NSC). We explicitly consider the impact of the stellar component on the flow by means of a uniform insertion of mass and energy within the stellar cluster. The model includes the gravity force of the stellar component and a central supermassive black hole (SMBH), and accounts for the heating from the central source of radiation and the radiative cooling of the thermalized gas. By using a set of parameters typical for NSCs and SMBHs in Seyfert galaxies, our simulations show that a filamentary/clumpy structure is formed in the inner part of the cluster. This 'torus' is Compton-thick and covers a large fraction of the sky (as seen from the SMBH). In the outer parts of the cluster a powerful wind is produced that inhibits the infall of matter from larger scales and thus the NSC-SMBH interplay occurs in isolation.

  11. ON THE FATE OF THE MATTER REINSERTED WITHIN YOUNG NUCLEAR STELLAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Hueyotl-Zahuantitla, Filiberto; Palous, Jan; Wuensch, Richard [Astronomical Institute, Academy of Sciences of the Czech Republic, Bocni II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, Guillermo; Silich, Sergiy, E-mail: filibert@asu.cas.cz [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico)

    2013-04-01

    This paper presents a hydrodynamical model describing the evolution of the gas reinserted by stars within a rotating young nuclear star cluster (NSC). We explicitly consider the impact of the stellar component on the flow by means of a uniform insertion of mass and energy within the stellar cluster. The model includes the gravity force of the stellar component and a central supermassive black hole (SMBH), and accounts for the heating from the central source of radiation and the radiative cooling of the thermalized gas. By using a set of parameters typical for NSCs and SMBHs in Seyfert galaxies, our simulations show that a filamentary/clumpy structure is formed in the inner part of the cluster. This 'torus' is Compton-thick and covers a large fraction of the sky (as seen from the SMBH). In the outer parts of the cluster a powerful wind is produced that inhibits the infall of matter from larger scales and thus the NSC-SMBH interplay occurs in isolation.

  12. New Observational Evidence of Flash Mixing on the White Dwarf Cooling Curve

    Science.gov (United States)

    Brown, T. M.; Lanz, T.; Sweigart, A. V.; Cracraft, Misty; Hubeny, Ivan; Landsman, W. B.

    2011-01-01

    Blue hook stars are a class of subluminous extreme horizontal branch stars that were discovered in UV images of the massive globular clusters w Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium-core flash on the white dwarf cooling curve. This "flash mixing" produces hotter-than-normal EHB stars with atmospheres significantly enhanced in helium and carbon. The larger bolometric correction, combined with the decrease in hydrogen opacity, makes these stars appear sub luminous in the optical and UV. Flash mixing is more likely to occur in stars born with a high helium abundance, due to their lower mass at the main sequence turnoff. For this reason, the phenomenon is more common in those massive globular clusters that show evidence for secondary populations enhanced in helium. However, a high helium abundance does not, by itself, explain the presence of blue hook stars in massive globular clusters. Here, we present new observational evidence for flash mixing, using recent HST observations. These include UV color-magnitude diagrams of six massive globular clusters and far-UV spectroscopy of hot subdwarfs in one of these clusters (NGC 2808).

  13. 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.

  14. BRITE-Constellation: Nanosatellites for precision photometry of bright stars

    Science.gov (United States)

    Weiss, W. W.; Moffat, A. F. J.; Schwarzenberg-Czerny, A.; Koudelka, O. F.; Grant, C. C.; Zee, R. E.; Kuschnig, R.; Mochnacki, St.; Rucinski, S. M.; Matthews, J. M.; Orleański, P.; Pamyatnykh, A. A.; Pigulski, A.; Alves, J.; Guedel, M.; Handler, G.; Wade, G. A.; Scholtz, A. L.; Scholtz

    2014-02-01

    will be selected is shown in Fig. 1. This sample falls into two principal classes of stars: (1) Hot luminous H-burning stars (O to F stars). Analyses of OB star variability have the potential to help solve two outstanding problems: the sizes of convective (mixed) cores in massive stars and the influence of rapid rotation on their structure and evolution. (2) Cool luminous stars (AGB stars, cool giants and cool supergiants). Measurements of the time scales involved in surface granulation and differential rotation will constrain turbulent convection models. Mass loss from these stars (especially the massive supernova progenitors) is a major contributor to the evolution of the interstellar medium, so in a sense, this sample dominates cosmic ``ecology'' in terms of future generations of star formation. The massive stars are believed to share many characteristics of the lower mass range of the first generation of stars ever formed (although the original examples are of course long gone). BRITE observations will also be used to detect some Jupiter- and even Neptune-sized planets around bright host stars via transits, as expected on the basis of statistics from the Kepler exoplanet mission. Detecting planets around such very bright stars will greatly facilitate their subsequent characterization. BRITE will also use surface spots to investigate stellar rotation. The following Table summarizes launch and orbit parameters of BRITE-Constellation components. The full version of this paper describing in more detail BRITE-Constellation will be published separately in a journal. The symposium presentation is available at http://iaus301.astro.uni.wroc.pl/program.php

  15. 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

  16. 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

  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. Establishing a relation between the mass and the spin of stellar-mass black holes.

    Science.gov (United States)

    Banerjee, Indrani; Mukhopadhyay, Banibrata

    2013-08-09

    Stellar mass black holes (SMBHs), forming by the core collapse of very massive, rapidly rotating stars, are expected to exhibit a high density accretion disk around them developed from the spinning mantle of the collapsing star. A wide class of such disks, due to their high density and temperature, are effective emitters of neutrinos and hence called neutrino cooled disks. Tracking the physics relating the observed (neutrino) luminosity to the mass, spin of black holes (BHs) and the accretion rate (M) of such disks, here we establish a correlation between the spin and mass of SMBHs at their formation stage. Our work shows that spinning BHs are more massive than nonspinning BHs for a given M. However, slowly spinning BHs can turn out to be more massive than spinning BHs if M at their formation stage was higher compared to faster spinning BHs.

  19. Neutron stars, magnetic fields, and gravitational waves

    International Nuclear Information System (INIS)

    Lamb, F.K.

    2001-01-01

    The r-modes of rapidly spinning young neutron stars have recently attracted attention as a promising source of detectable gravitational radiation. These neutron stars are expected to have magnetic fields ∼ 10 12 G. The r-mode velocity perturbation causes differential motion of the fluid in the star; this is a kinematic effect. In addition, the radiation-reaction associated with emission of gravitational radiation by r-waves drives additional differential fluid motions; this is a dynamic effect. These differential fluid motions distort the magnetic fields of neutron stars and may therefore play an important role in determining the structure of neutron star magnetic fields. If the stellar field is ∼ 10 16 (Ω/Ω B ) G or stronger, the usual r-modes are no longer normal modes of the star; here Ω and Ω B are the angular velocities of the star and at which mass shedding occurs. Much weaker magnetic fields can prevent gravitational radiation from amplifying the r-modes or damp existing r-mode oscillations on a relatively short timescale by extracting energy from the modes faster than gravitational wave emission can pump energy into them. The onset of proton superconductivity in the cores of newly formed magnetic neutron stars typically increases the effect on the r-modes of the magnetic field in the core by many orders of magnitude. Once the core has become superconducting, magnetic fields of the order of 10 12 G or greater are usually sufficient to damp r-modes that have been excited by emission of gravitational radiation and to suppress any further emission. A rapid drop in the strength of r-mode gravitational radiation from young neutron stars may therefore signal the onset of superconductivity in the core and provide a lower bound on the strength of the magnetic field there. Hence, measurements of r-mode gravitational waves from newly formed neutron stars may provide valuable diagnostic information about magnetic field strengths, cooling processes, and the

  20. 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.

  1. Stellar population gradients in isolated, local group dwarf galaxies

    Directory of Open Access Journals (Sweden)

    Hidalgo S.L.

    2012-02-01

    Full Text Available We discuss the detailed star formation as a function of radius that we have derived for the LCID galaxies, with particular emphasis on the stellar populations gradient and the effect of the UV-background.

  2. Evolution of stars and galaxies

    International Nuclear Information System (INIS)

    Baade, W.

    1975-01-01

    Transcriptions of recorded lectures given by the author have been edited into book form. Topics covered include: historical introduction, classification of galaxies; observation of galaxies; photography of galaxies; the andromeda nebula, spiral structure; dust and gas in galaxies; outline of stellar evolution; the distances to the galaxies; galactic clusters; stellar associations; the T Tauri stars; globular clusters: color-magnitude diagrams; spectra of population II stars; variable stars in globular clusters; elliptical galaxies; irregular galaxies and star formation; the magellanic clouds; the andromeda nebula, photometry; evolution of galaxies; the structure of the galaxy; the galactic nucleus; the galactic disk; and kinematics and evolution of the galaxy. 27 tables, 26 figures

  3. Observational Effects of Strange Stars

    OpenAIRE

    Lu, T.

    1998-01-01

    In this talk, after briefly reviewing some historical remarks concerning strange stars, the achievements in physics and dynamical behavior of strange stars are discussed. Especially, various observational effects in distinguishing strange stars from neutron stars such as mechanical effects, cooling effects, phase transition and related interesting phenomena are stressed.

  4. STELLAR MASS DEPENDENT DISK DISPERSAL

    International Nuclear Information System (INIS)

    Kennedy, Grant M.; Kenyon, Scott J.

    2009-01-01

    We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

  5. Advanced Stellar Compass, SAC-C, Interface Control Document

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Betto, Maurizio; Riis, Troels

    Interface Control Document for the Advanced Stellar Compass for the SAC-C satellite. The SAC-C is Argentine, Danish and NASA satellite. On the SAC-C satellite there are a simplified version of the Ørsted instrumentation platform. The Advanced Stellar Compass is a improved version of the Ørsted Star...... Imager. This document descibes the interface between the Advanced Stellar Compass and OBDH, the size of the DPU and the Camera etc....

  6. Dynamic collapses of relativistic degenerate stellar cores and radiation pressure dominated stellar interiors

    Science.gov (United States)

    Shi, Chun-Hui; Lou, Yu-Qing

    2018-04-01

    We investigate and explore self-similar dynamic radial collapses of relativistic degenerate stellar cores (RDSCs) and radiation pressure dominated stellar interiors (RPDSIs) of spherical symmetry by invoking a conventional polytropic (CP) equation of state (EoS) with a constant polytropic index γ = 4 / 3 and by allowing free-fall non-zero RDSC or RPDSI surface mass density and pressure due to their sustained physical contact with the outer surrounding stellar envelopes also in contraction. Irrespective of the physical triggering mechanisms (including, e.g., photodissociation, electron-positron pair instability, general relativistic instability etc.) for initiating such a self-similar dynamically collapsing RDSC or RPDSI embedded within a massive star, a very massive star (VMS) or a supermassive star (SMS) in contraction and by comparing with the Schwarzschild radii associated with their corresponding RDSC/RPDSI masses, the emergence of central black holes in a wide mass range appears inevitable during such RDSC/RPDSI dynamic collapses inside massive stars, VMSs, and SMSs, respectively. Radial pulsations of progenitor cores or during a stellar core collapse may well leave imprints onto collapsing RDSCs/RPDSIs towards their self-similar dynamic evolution. Massive neutron stars may form during dynamic collapses of RDSC inside massive stars in contraction under proper conditions.

  7. Binary Populations and Stellar Dynamics in Young Clusters

    Science.gov (United States)

    Vanbeveren, D.; Belkus, H.; Van Bever, J.; Mennekens, N.

    2008-06-01

    We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, η Car, ζ Pup, γ2 Velorum and WR 140.

  8. The Advanced Stellar Compass onboard the Oersted satellite

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Eisenman, Allan R.; Liebe, Carl Christian

    1997-01-01

    In 1997 the first Danish satellite will be launched. The primarily scientific objective of the satellite is to map the magnetic field of the Earth. The attitude of the satellite is determined by an advanced stellar compass (star tracker). An advanced stellar compass consists of a CCD camera conne...

  9. Spotting Stellar Activity Cycles in Gaia Astrometry

    Science.gov (United States)

    Morris, Brett M.; Agol, Eric; Davenport, James R. A.; Hawley, Suzanne L.

    2018-03-01

    Astrometry from Gaia will measure the positions of stellar photometric centroids to unprecedented precision. We show that the precision of Gaia astrometry is sufficient to detect starspot-induced centroid jitter for nearby stars in the Tycho-Gaia Astrometric Solution (TGAS) sample with magnetic activity similar to the young G-star KIC 7174505 or the active M4 dwarf GJ 1243, but is insufficient to measure centroid jitter for stars with Sun-like spot distributions. We simulate Gaia observations of stars with 10 year activity cycles to search for evidence of activity cycles, and find that Gaia astrometry alone likely can not detect activity cycles for stars in the TGAS sample, even if they have spot distributions like KIC 7174505. We review the activity of the nearby low-mass stars in the TGAS sample for which we anticipate significant detections of spot-induced jitter.

  10. 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

  11. HUBBLE SPIES BROWN DWARFS IN NEARBY STELLAR NURSERY

    Science.gov (United States)

    2002-01-01

    Probing deep within a neighborhood stellar nursery, NASA's Hubble Space Telescope uncovered a swarm of newborn brown dwarfs. The orbiting observatory's near-infrared camera revealed about 50 of these objects throughout the Orion Nebula's Trapezium cluster [image at right], about 1,500 light-years from Earth. Appearing like glistening precious stones surrounding a setting of sparkling diamonds, more than 300 fledgling stars and brown dwarfs surround the brightest, most massive stars [center of picture] in Hubble's view of the Trapezium cluster's central region. All of the celestial objects in the Trapezium were born together in this hotbed of star formation. The cluster is named for the trapezoidal alignment of those central massive stars. Brown dwarfs are gaseous objects with masses so low that their cores never become hot enough to fuse hydrogen, the thermonuclear fuel stars like the Sun need to shine steadily. Instead, these gaseous objects fade and cool as they grow older. Brown dwarfs around the age of the Sun (5 billion years old) are very cool and dim, and therefore are difficult for telescopes to find. The brown dwarfs discovered in the Trapezium, however, are youngsters (1 million years old). So they're still hot and bright, and easier to see. This finding, along with observations from ground-based telescopes, is further evidence that brown dwarfs, once considered exotic objects, are nearly as abundant as stars. The image and results appear in the Sept. 20 issue of the Astrophysical Journal. The brown dwarfs are too dim to be seen in a visible-light image taken by the Hubble telescope's Wide Field and Planetary Camera 2 [picture at left]. This view also doesn't show the assemblage of infant stars seen in the near-infrared image. That's because the young stars are embedded in dense clouds of dust and gas. The Hubble telescope's near-infrared camera, the Near Infrared Camera and Multi-Object Spectrometer, penetrated those clouds to capture a view of those

  12. 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.

  13. Microlensing and the physics of stellar atmospheres

    NARCIS (Netherlands)

    Sackett, PD; Menzies, JW; Sackett, PD

    2001-01-01

    The simple physics of microlensing provides a well understood tool with which to probe the atmospheres of distant stars in the Galaxy and Local Group with high magnification and resolution. Recent results in measuring stellar surface structure through broad band photometry and spectroscopy of high

  14. Evolution and seismic tools for stellar astrophysics

    CERN Document Server

    Monteiro, Mario JPFG

    2008-01-01

    A collection of articles published by the journal "Astrophysics and Space Science, Volume 316, Number 1-4", August 2008. This work covers 10 evolution codes and 9 oscillation codes. It is suitable for researchers and research students working on the modeling of stars and on the implementation of seismic test of stellar models.

  15. The resolved stellar population of Leo A

    NARCIS (Netherlands)

    Tolstoy, E

    1996-01-01

    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 Ha filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an

  16. On the collapse of iron stellar cores

    International Nuclear Information System (INIS)

    Barkat, Z.; Rakavy, G.; Reiss, Y.; Wilson, J.R.

    1975-01-01

    The collapse of iron stellar cores is investigated to see whether the outward shock produced by the bounce at neutron star density is sufficient to burn appreciable amounts of the envelope around the iron core. Several models were tried, and in all cases no appreciable burn took place; hence no explosion results from the collapse of these models

  17. ON THE EXTREME POSITIVE STAR FORMATION FEEDBACK CONDITION IN SCUBA SOURCES

    International Nuclear Information System (INIS)

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Hueyotl-Zahuantitla, Filiberto; Munoz-Tunon, Casiana; Wuensch, Richard; Palous, Jan

    2010-01-01

    We present a detailed study of the hydrodynamics of the matter reinserted by massive stars via stellar winds and supernovae explosions in young assembling galaxies. We show that the interplay between the thermalization of the kinetic energy provided by massive stars, radiative cooling of the thermalized plasma, and the gravitational pull of the host galaxy lead to three different hydrodynamic regimes. These are: (1) the quasi-adiabatic supergalactic winds; (2) the bimodal flows, with mass accumulation in the central zones and gas expulsion from the outer zones of the assembling galaxy; and (3) the gravitationally bound regime, for which all of the gas returned by massive stars remains bound to the host galaxy and is likely to be reprocessed into further generations of stars. Which of the three possible solutions takes place depends on the mass of the star-forming region, its mechanical luminosity (or star formation rate), and its size. The model predicts that massive assembling galaxies with large star formation rates similar to those detected in Submillimeter Common-User Bolometric Array sources (∼1000 M sun yr -1 ) are likely to evolve in a positive star formation feedback condition, either in the bimodal or in the gravitationally bound regime. This implies that star formation in these sources may have little impact on the intergalactic medium and result instead into a fast interstellar matter enrichment, as observed in high redshift quasars.

  18. 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.

  19. Magnetic fields of chemically peculiar and related stars. III. Main results of 2016 and analysis of closest perspectives

    Science.gov (United States)

    Romanyuk, I. I.

    2017-07-01

    We have analyzed more than 90 papers in the area "Magnetic fields and physical parameters of chemically peculiar and related stars," published mainly in 2016. The main results of the period under survey are as follows. The search for new magnetic stars continued.Many measurements weremade at the 6-m BTA telescope of the SAO RAS, new data on stellar magnetism in the OrionOB1 association were obtained. A systematic study ofmagnetic fields of stars with large anomalies in the energy distribution in the continuum was started. New data on ultra-slowmagnetic rotators—chemically peculiar stars with rotation periods of years and decades are obtained. Successful observations on the search for new magnetic stars are performed among the objects of the southern sky in Chile at the FORS2 VLT spectropolarimeter. A new direction was developed, namely, the study of binarymagnetic stars. Depending on the mass-distance ratio between the components, interaction with the magnetosphere and, possibly, magnetic braking may occur. The study of the details of this process is important for the theory of formation of stellar magnetic fields. The search for large-scale, but weak magnetic fields (magnitude of unities and tens of G) in non-CP stars is ongoing. Such fields are found in Am stars. No fields were found in the classical Be stars. Cool stars of various types were studied in detail. They manifested magnetic fields of a complex structure. Their mapping was performed, changes in the topology of the field were found at timescales of several years. Spectral and photometric variability was studied. Dozens of new potentially magnetic stars are discovered as a result of the ASAS-3, SuperWASP, Stereo and Kepler surveys. High-accuracy observations of rapidly oscillating stars were performed with the BRITE nanosatellite.Work continued on the studies of magnetic and photometric variability of white dwarfs. Finally, an overview of several papers on exoplanets, related with the subject of our

  20. Characterizing stellar and exoplanetary environments

    CERN Document Server

    Khodachenko, Maxim

    2015-01-01

    In this book an international group of specialists discusses studies of exoplanets subjected to extreme stellar radiation and plasma conditions. It is shown that such studies will help us to understand how terrestrial planets and their atmospheres, including the early Venus, Earth and Mars, evolved during the host star’s active early phase. The book presents an analysis of findings from Hubble Space Telescope observations of transiting exoplanets, as well as applications of advanced numerical models for characterizing the upper atmosphere structure and stellar environments of exoplanets. The authors also address detections of atoms and molecules in the atmosphere of “hot Jupiters” by NASA’s Spitzer telescope. The observational and theoretical investigations and discoveries presented are both timely and important in the context of the next generation of space telescopes. 
 The book is divided into four main parts, grouping chapters on exoplanet host star radiation and plasma environments, exoplanet u...

  1. 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

  2. A Hot Jupiter for Breakfast? Early Stellar Ingestion of Planets May Be Common

    Science.gov (United States)

    Matsakos, Titos; Königl, Arieh

    2015-08-01

    Models of planet formation and evolution predict that giant planets form efficiently in protoplanetary disks, that most of these migrate rapidly to the disk’s inner edge, and that, if the arriving planet’s mass is ≲ Jupiter’s mass, then it could remain stranded near that radius. We argue that such planets would be ingested by tidal interaction with the host star on a timescale ≲ 1 Gyr, and that, in the case of a solar-type host, this would cause the stellar spin to approach the direction of the ingested planet’s orbital axis even if the two were initially highly misaligned. Primordially misaligned stars whose effective temperatures are ≳ 6250 K cannot be realigned in this way because, in contrast with solar-type hosts, their angular momenta are typically higher than the orbital angular momentum of the ingested planet as a result of inefficient magnetic braking and of a comparatively large moment of inertia. Hot Jupiters located farther out from the star can contribute to this process, but their effect is weaker because the tidal interaction strength decreases rapidly with increasing semimajor axis. We demonstrate that, if ∼ 50% of planetary systems harbored a stranded hot Jupiter, this scenario can in principle account for (1) the good alignment exhibited by planets around cool stars irrespective of the planet’s mass or orbital period, (2) the prevalence of misaligned planets around hot stars, (3) the apparent upper bound on the mass of hot Jupiters on retrograde orbits, and (4) the inverse correlation between stellar spin periods and hot-Jupiter masses.

  3. Alaska Athabascan stellar astronomy

    Science.gov (United States)

    Cannon, Christopher M.

    2014-01-01

    Stellar astronomy is a fundamental component of Alaska Athabascan cultures that facilitates time-reckoning, navigation, weather forecasting, and cosmology. Evidence from the linguistic record suggests that a group of stars corresponding to the Big Dipper is the only widely attested constellation across the Northern Athabascan languages. However, instruction from expert Athabascan consultants shows that the correlation of these names with the Big Dipper is only partial. In Alaska Gwich'in, Ahtna, and Upper Tanana languages the Big Dipper is identified as one part of a much larger circumpolar humanoid constellation that spans more than 133 degrees across the sky. The Big Dipper is identified as a tail, while the other remaining asterisms within the humanoid constellation are named using other body part terms. The concept of a whole-sky humanoid constellation provides a single unifying system for mapping the night sky, and the reliance on body-part metaphors renders the system highly mnemonic. By recognizing one part of the constellation the stargazer is immediately able to identify the remaining parts based on an existing mental map of the human body. The circumpolar position of a whole-sky constellation yields a highly functional system tha