WorldWideScience

Sample records for intermediate mass stars

  1. Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

    Science.gov (United States)

    Lundquist, Michael; Kobulnicky, Henry

    2018-01-01

    The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

  2. Rotation and magnetism in intermediate-mass stars

    Science.gov (United States)

    Quentin, Léo G.; Tout, Christopher A.

    2018-06-01

    Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to 20 000 G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than 109 G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a 3 M_{⊙} star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result, the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.

  3. Constraining the Population of Small Close-in Planets Around Evolved Intermediate Mass Stars

    Science.gov (United States)

    Medina, Amber; Johnson, John Asher

    2018-01-01

    Intermediate mass stars ( > 1.3 M_Sun) have high occurrence rates of Jupiter mass planets in predominately long period orbits (~1.0 AU). There is a prominent planet gap, known as the ‘Planet Desert’, for low mass planets (Super-Earth, Neptune) < 0.5 AU from subgiants, the evolved counterpart to intermediate mass stars. Thus far, using current radial velocity methods, we have not been able to detect short period planets around subgiants due to noise from p-mode oscillations perhaps mimicking radial velocity signals (~5 m/s) in this planetary regime. Here we present techniques and preliminary results with regards to finding low mass, short period planets around subgiants and its implications for the Planet Desert.

  4. Characterizing Intermediate-Mass, Pre-Main-Sequence Stars via X-Ray Emision

    Science.gov (United States)

    Haze Nunez, Evan; Povich, Matthew Samuel; Binder, Breanna Arlene; Broos, Patrick; Townsley, Leisa K.

    2018-01-01

    The X-ray emission from intermediate-mass, pre-main-sequence stars (IMPS) can provide useful constraints on the ages of very young (${getting power from the gravitational contraction of the star. Main-sequence late-B and A-type stars are not expected to be strong X-ray emitters, because they lack the both strong winds of more massive stars and the magneto-coronal activity of lower-mass stars. There is, however, mounting evidence that IMPS are powerful intrinsic x-ray emitters during their convection-dominated early evolution, before the development and rapid growth of a radiation zone. We present our prime candidates for intrinsic, coronal X-ray emission from IMPS identified in the Chandra Carina Complex Project. The Carina massive star-forming complex is of special interest due to the wide variation of star formation stages within the region. Candidate IMPS were identified using infrared spectral energy distribution (SED) models. X-ray properties, including thermal plasma temperatures and absorption-corrected fluxes, were derived from XSPEC fits performed using absorption ($N_{H}$) constrained by the extinction values returned by the infrared SED fits. We find that IMPS have systematically higher X-ray luminosities compared to their lower-mass cousins, the TTauri stars.This work is supported by the National Science Foundation under grant CAREER-1454334 and by NASA through Chandra Award 18200040.

  5. Evolving ONe WD+He star systems to intermediate-mass binary pulsars

    Science.gov (United States)

    Liu, D.; Wang, B.; Chen, W.; Zuo, Z.; Han, Z.

    2018-06-01

    It has been suggested that accretion-induced collapse (AIC) is a non-negligible path for the formation of the observed neutron stars (NSs). An ONe white dwarf (WD) that accretes material from a He star may experience AIC process and eventually produce intermediate-mass binary pulsars (IMBPs), named as the ONe WD+He star scenario. Note that previous studies can only account for part of the observed IMBPs with short orbital periods. In this work, we investigate the evolution of about 900 ONe WD+He star binaries to explore the distribution of IMBPs. We found that the ONe WD+He star scenario could form IMBPs including pulsars with 5-340 ms spin periods and 0.75-1.38 M_{⊙} WD companions, in which the orbital periods range from 0.04 to 900 d. Compared with the 20 observed IMBPs, this scenario can cover the parameters of 13 sources in the final orbital period-WD mass plane and the Corbet diagram, most of which have short orbital periods. We found that the ONe WD+He star scenario can explain almost all the observed IMBPs with short orbital periods. This work can well match the observed parameters of PSR J1802-2124 (one of the two precisely observed IMBPs), providing a possible evolutional path for its formation. We also speculate that the compact companion of HD 49798 (a hydrogen depleted sdO6 star) may be not a NS based on this work.

  6. Transitional Disks Associated with Intermediate-Mass Stars: Results of the SEEDS YSO Survey

    Science.gov (United States)

    Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.; hide

    2014-01-01

    Protoplanetary disks are where planets form, grow, and migrate to produce the diversity of exoplanet systems we observe in mature systems. Disks where this process has advanced to the stage of gap opening, and in some cases central cavity formation, have been termed pre-transitional and transitional disks in the hope that they represent intermediate steps toward planetary system formation. Recent reviews have focussed on disks where the star is of solar or sub-solar mass. In contrast to the sub-millimeter where cleared central cavities predominate, at H-band some T Tauri star transitional disks resemble primordial disks in having no indication of clearing, some show a break in the radial surface brightness profile at the inner edge of the outer disk, while others have partially to fully cleared gaps or central cavities. Recently, the Meeus Group I Herbig stars, intermediate-mass PMS stars with IR spectral energy distributions often interpreted as flared disks, have been proposed to have transitional and pre-transitional disks similar to those associated with solar-mass PMS stars, based on thermal-IR imaging, and sub-millimeter interferometry. We have investigated their appearance in scattered light as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS), obtaining H-band polarimetric imagery of 10 intermediate-mass stars with Meeus Group I disks. Augmented by other disks with imagery in the literature, the sample is now sufficiently large to explore how these disks are similar to and differ from T Tauri star disks. The disk morphologies seen in the Tauri disks are also found for the intermediate-mass star disks, but additional phenomena are found; a hallmark of these disks is remarkable individuality and diversity which does not simply correlate with disk mass or stellar properties, including age, including spiral arms in remnant envelopes, arms in the disk, asymmetrically and potentially variably shadowed outer disks, gaps, and one disk

  7. Protoplanetary disks around intermediate-mass stars: the asset of imaging in the mid-infrared

    International Nuclear Information System (INIS)

    Doucet, Coralie

    2006-01-01

    The accrued efficiency of the instruments in many wavelengths has allowed to show that most young stellar objects were surrounded by circumstellar matter distributed in a disk. Direct imaging of such systems is very difficult because of their narrow angular size and their weak luminosity in comparison with the star. Nowadays, 50 % of low-mass pre-main sequence stars, i.e. T Tauri stars, are surrounded by a disk. This proportion is less obvious for intermediate-mass stars, like Herbig Ae stars, that are less numerous and whose direct disk detection is more difficult. Until now, only the interpretation of the Spectral Energy Distribution (SED) of such objects allows to have access to the geometry of the disk. But the solutions are degenerated and several parameters fit the same SED. It is essential to have direct images of the objects, the only evidence of the presence of disks. This PhD allows to show that mid-infrared imaging could rise a part of the degeneracy of the disk's parameters linked to the fit of the SED for several objects and gives constraints on the minimum external radius and inclination of the disk. We present a new observation mode with VISIR, the mid-infrared imager and spectrometer on the VLT (ESO, Chile): the so-called BURST mode. This mode allows to reach the diffraction limit of the telescope. Thanks to mid-infrared imaging with this instrument, we were able, for the first time, to have access to the geometry of a disk (flared structure) around a massive star that was, until now, only deduced from the SED modelling. (author) [fr

  8. A MULTIPLICITY CENSUS OF INTERMEDIATE-MASS STARS IN SCORPIUS-CENTAURUS

    International Nuclear Information System (INIS)

    Janson, Markus; Lafrenière, David; Jayawardhana, Ray; Bonavita, Mariangela; Girard, Julien H.; Brandeker, Alexis; Gizis, John E.

    2013-01-01

    Stellar multiplicity properties have been studied for the lowest and the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here, we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen-burning limit which we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0.''1-5.''0 of 21% ± 4%. Depending on the adopted semimajor axis distribution, our results imply a total multiplicity in the range of ∼60%-80%, which further supports the known trend of a smooth continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco-Cen region

  9. Jetted tidal disruptions of stars as a flag of intermediate mass black holes at high redshifts

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    Fialkov, Anastasia; Loeb, Abraham

    2017-11-01

    Tidal disruption events (TDEs) of stars by single or binary supermassive black holes (SMBHs) brighten galactic nuclei and reveal a population of otherwise dormant black holes. Adopting event rates from the literature, we aim to establish general trends in the redshift evolution of the TDE number counts and their observable signals. We pay particular attention to (I) jetted TDEs whose luminosity is boosted by relativistic beaming and (II) TDEs around binary black holes. We show that the brightest (jetted) TDEs are expected to be produced by massive black hole binaries if the occupancy of intermediate mass black holes (IMBHs) in low-mass galaxies is high. The same binary population will also provide gravitational wave sources for the evolved Laser Interferometer Space Antenna. In addition, we find that the shape of the X-ray luminosity function of TDEs strongly depends on the occupancy of IMBHs and could be used to constrain scenarios of SMBH formation. Finally, we make predictions for the expected number of TDEs observed by future X-ray telescopes finding that a 50 times more sensitive instrument than the Burst Alert Telescope (BAT) on board the Swift satellite is expected to trigger ˜10 times more events than BAT, while 6-20 TDEs are expected in each deep field observed by a telescope 50 times more sensitive than the Chandra X-ray Observatory if the occupation fraction of IMBHs is high. Because of their long decay times, high-redshift TDEs can be mistaken for fixed point sources in deep field surveys and targeted observations of the same deep field with year-long intervals could reveal TDEs.

  10. Intermediate-mass Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions

    Science.gov (United States)

    Katsuda, Satoru; Morii, Mikio; Janka, Hans-Thomas; Wongwathanarat, Annop; Nakamura, Ko; Kotake, Kei; Mori, Koji; Müller, Ewald; Takiwaki, Tomoya; Tanaka, Masaomi; Tominaga, Nozomu; Tsunemi, Hiroshi

    2018-03-01

    The birth properties of neutron stars (NSs) yield important information about the still-debated physical processes that trigger the explosion as well as on intrinsic neutron-star physics. These properties include the high space velocities of young neutron stars with average values of several 100 km s‑1, with an underlying “kick” mechanism that is not fully clarified. There are two competing possibilities that could accelerate NSs during their birth: anisotropic ejection of either stellar debris or neutrinos. Here we present new evidence from X-ray measurements that chemical elements between silicon and calcium in six young gaseous supernova remnants are preferentially expelled opposite to the direction of neutron star motion. There is no correlation between the kick velocities and magnetic field strengths of these neutron stars. Our results support a hydrodynamic origin of neutron-star kicks connected to asymmetric explosive mass ejection, and they conflict with neutron-star acceleration scenarios that invoke anisotropic neutrino emission caused by particle and nuclear physics in combination with very strong neutron-star magnetic fields.

  11. CHEMICAL COMPOSITION OF INTERMEDIATE-MASS STAR MEMBERS OF THE M6 (NGC 6405) OPEN CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Kılıçoğlu, T.; Albayrak, B. [Ankara University, Faculty of Science, Department of Astronomy and Space Sciences, 06100, Tandoğan, Ankara (Turkey); Monier, R. [LESIA, UMR 8109, Observatoire de Paris Meudon, Place J. Janssen, Meudon (France); Richer, J. [Département de physique, Université de Montréal, 2900, Boulevard Edouard-Montpetit, Montréal QC, H3C 3J7 (Canada); Fossati, L., E-mail: tkilicoglu@ankara.edu.tr, E-mail: balbayrak@ankara.edu.tr, E-mail: Richard.Monier@obspm.fr, E-mail: Jacques.Richer@umontreal.ca, E-mail: lfossati@astro.uni-bonn.de [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121, Bonn (Germany)

    2016-03-15

    We present here the first abundance analysis of 44 late B-, A-, and F-type members of the young open cluster M6 (NGC 6405, age about 75 Myr). Low- and medium-resolution spectra, covering the 4500–5840 Å wavelength range, were obtained using the FLAMES/GIRAFFE spectrograph attached to the ESO Very Large Telescopes. We determined the atmospheric parameters using calibrations of the Geneva photometry and by adjusting the H{sub β} profiles to synthetic ones. The abundances of up to 20 chemical elements, from helium to mercury, were derived for 19 late B, 16 A, and 9 F stars by iteratively adjusting synthetic spectra to the observations. We also derived a mean cluster metallicity of [Fe/H] = 0.07 ± 0.03 dex from the iron abundances of the F-type stars. We find that for most chemical elements, the normal late B- and A-type stars exhibit larger star-to-star abundance variations than the F-type stars probably because of the faster rotation of the B and A stars. The abundances of C, O, Mg, Si, and Sc appear to be anticorrelated with that of Fe, while the opposite holds for the abundances of Ca, Ti, Cr, Mn, Ni, Y, and Ba as expected if radiative diffusion is efficient in the envelopes of these stars. In the course of this analysis, we discovered five new peculiar stars: one mild Am, one Am, and one Fm star (HD 318091, CD-32 13109, GSC 07380-01211, CP1), one HgMn star (HD 318126, CP3), and one He-weak P-rich (HD 318101, CP4) star. We also discovered a new spectroscopic binary, most likely a SB2. We performed a detailed modeling of HD 318101, the new He-weak P-rich CP star, using the Montréal stellar evolution code XEVOL which self-consistently treats all particle transport processes. Although the overall abundance pattern of this star is properly reproduced, we find that detailed abundances (in particular the high P excess) resisted modeling attempts even when a range of turbulence profiles and mass-loss rates were considered. Solutions are proposed which are

  12. Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array

    Science.gov (United States)

    White, T. R.; Huber, D.; Mann, A. W.; Casagrande, L.; Grunblatt, S. K.; Justesen, A. B.; Silva Aguirre, V.; Bedding, T. R.; Ireland, M. J.; Schaefer, G. H.; Tuthill, P. G.

    2018-04-01

    Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass (˜ 1.5 M⊙) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis (5.12±0.16 R⊙, 4949±58 K), 24 Sextantis (5.49±0.18 R⊙, 4908±65 K), κ Coronae Borealis (4.77±0.07 R⊙, 4870±47 K), HR 6817 (4.45±0.08 R⊙, 5013±59 K), and HR 8641 (4.91±0.12 R⊙, 4950±68 K). We find disagreements of typically 15 % in angular diameter and ˜ 200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly (˜ 15 %) lower masses than generally reported in the literature.

  13. Observational tests of convective core overshooting in stars of intermediate to high mass in the Galaxy

    Science.gov (United States)

    Stothers, Richard B.

    1991-01-01

    This study presents the results of 14 tests for the presence of convective overshooting in large convecting stellar cores for stars with masses of 4-17 solar masses which are members of detached close binary systems and of open clusters in the Galaxy. A large body of theoretical and observational data is scrutinized and subjected to averaging in order to minimize accidental and systematic errors. A conservative upper limit of d/HP less than 0.4 is found from at least four tests, as well as a tighter upper limit of d/HP less than 0.2 from one good test that is subject to only mild restrictions and is based on the maximum observed effective temperature of evolved blue supergiants. It is concluded that any current uncertainty about the distance scale for these stars is unimportant in conducting the present tests for convective core overshooting. The correct effective temperature scale for the B0.5-B2 stars is almost certainly close to one of the proposed hot scales.

  14. A luminous X-ray outburst from an intermediate-mass black hole in an off-centre star cluster

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    Lin, Dacheng; Strader, Jay; Carrasco, Eleazar R.; Page, Dany; Romanowsky, Aaron J.; Homan, Jeroen; Irwin, Jimmy A.; Remillard, Ronald A.; Godet, Olivier; Webb, Natalie A.; Baumgardt, Holger; Wijnands, Rudy; Barret, Didier; Duc, Pierre-Alain; Brodie, Jean P.; Gwyn, Stephen D. J.

    2018-06-01

    A unique signature for the presence of massive black holes in very dense stellar regions is occasional giant-amplitude outbursts of multi-wavelength radiation from tidal disruption and subsequent accretion of stars that make a close approach to the black holes1. Previous strong tidal disruption event (TDE) candidates were all associated with the centres of largely isolated galaxies2-6. Here, we report the discovery of a luminous X-ray outburst from a massive star cluster at a projected distance of 12.5 kpc from the centre of a large lenticular galaxy. The luminosity peaked at 1043 erg s-1 and decayed systematically over 10 years, approximately following a trend that supports the identification of the event as a TDE. The X-ray spectra were all very soft, with emission confined to be ≲3.0 keV, and could be described with a standard thermal disk. The disk cooled significantly as the luminosity decreased—a key thermal-state signature often observed in accreting stellar-mass black holes. This thermal-state signature, coupled with very high luminosities, ultrasoft X-ray spectra and the characteristic power-law evolution of the light curve, provides strong evidence that the source contains an intermediate-mass black hole with a mass tens of thousand times that of the solar mass. This event demonstrates that one of the most effective means of detecting intermediate-mass black holes is through X-ray flares from TDEs in star clusters.

  15. Burn out or fade away? On the X-ray and magnetic death of intermediate mass stars

    Energy Technology Data Exchange (ETDEWEB)

    Drake, Jeremy J.; Kashyap, Vinay; Günther, H. Moritz; Wright, Nicholas J. [Smithsonian Astrophysical Observatory, MS-3, 60 Garden Street, Cambridge, MA 02138 (United States); Braithwaite, Jonathan, E-mail: jdrake@cfa.harvard.edu [Argelander Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany)

    2014-05-10

    The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L{sub X} ≤ 1.3 × 10{sup 27} erg s{sup –1}. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10{sup 25} erg s{sup –1}. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

  16. Evolution, Nucleosynthesis, and Yields of AGB Stars at Different Metallicities. III. Intermediate-mass Models, Revised Low-mass Models, and the ph-FRUITY Interface

    Science.gov (United States)

    Cristallo, S.; Straniero, O.; Piersanti, L.; Gobrecht, D.

    2015-08-01

    We present a new set of models for intermediate-mass asymptotic giant branch (AGB) stars (4.0, 5.0, and 6.0 M⊙) at different metallicities (-2.15 ≤ [Fe/H] ≤ +0.15). This set integrates the existing models for low-mass AGB stars (1.3 ≤ M/M⊙ ≤ 3.0) already included in the FRUITY database. We describe the physical and chemical evolution of the computed models from the main sequence up to the end of the AGB phase. Due to less efficient third dredge up episodes, models with large core masses show modest surface enhancements. This effect is due to the fact that the interpulse phases are short and, therefore, thermal pulses (TPs) are weak. Moreover, the high temperature at the base of the convective envelope prevents it from deeply penetrating the underlying radiative layers. Depending on the initial stellar mass, the heavy element nucleosynthesis is dominated by different neutron sources. In particular, the s-process distributions of the more massive models are dominated by the 22Ne(α,n)25Mg reaction, which is efficiently activated during TPs. At low metallicities, our models undergo hot bottom burning and hot third dredge up. We compare our theoretical final core masses to available white dwarf observations. Moreover, we quantify the influence intermediate-mass models have on the carbon star luminosity function. Finally, we present the upgrade of the FRUITY web interface, which now also includes the physical quantities of the TP-AGB phase for all of the models included in the database (ph-FRUITY).

  17. EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF AGB STARS AT DIFFERENT METALLICITIES. III. INTERMEDIATE-MASS MODELS, REVISED LOW-MASS MODELS, AND THE pH-FRUITY INTERFACE

    Energy Technology Data Exchange (ETDEWEB)

    Cristallo, S.; Straniero, O.; Piersanti, L.; Gobrecht, D. [INAF-Osservatorio Astronomico di Collurania, I-64100 Teramo (Italy)

    2015-08-15

    We present a new set of models for intermediate-mass asymptotic giant branch (AGB) stars (4.0, 5.0, and 6.0 M{sub ⊙}) at different metallicities (−2.15 ≤ [Fe/H] ≤ +0.15). This set integrates the existing models for low-mass AGB stars (1.3 ≤ M/M{sub ⊙} ≤ 3.0) already included in the FRUITY database. We describe the physical and chemical evolution of the computed models from the main sequence up to the end of the AGB phase. Due to less efficient third dredge up episodes, models with large core masses show modest surface enhancements. This effect is due to the fact that the interpulse phases are short and, therefore, thermal pulses (TPs) are weak. Moreover, the high temperature at the base of the convective envelope prevents it from deeply penetrating the underlying radiative layers. Depending on the initial stellar mass, the heavy element nucleosynthesis is dominated by different neutron sources. In particular, the s-process distributions of the more massive models are dominated by the {sup 22}Ne(α,n){sup 25}Mg reaction, which is efficiently activated during TPs. At low metallicities, our models undergo hot bottom burning and hot third dredge up. We compare our theoretical final core masses to available white dwarf observations. Moreover, we quantify the influence intermediate-mass models have on the carbon star luminosity function. Finally, we present the upgrade of the FRUITY web interface, which now also includes the physical quantities of the TP-AGB phase for all of the models included in the database (ph-FRUITY)

  18. Wandering off the centre: a characterization of the random motion of intermediate-mass black holes in star clusters

    Science.gov (United States)

    de Vita, Ruggero; Trenti, Michele; MacLeod, Morgan

    2018-04-01

    Despite recent observational efforts, unequivocal signs for the presence of intermediate-mass black holes (IMBHs) in globular clusters (GCs) have not been found yet. Especially when the presence of IMBHs is constrained through dynamical modelling of stellar kinematics, it is fundamental to account for the displacement that the IMBH might have with respect to the GC centre. In this paper, we analyse the IMBH wandering around the stellar density centre using a set of realistic direct N-body simulations of star cluster evolution. Guided by the simulation results, we develop a basic yet accurate model that can be used to estimate the average IMBH radial displacement (〈rbh〉) in terms of structural quantities as the core radius (rc), mass (Mc), and velocity dispersion (σc), in addition to the average stellar mass (mc) and the IMBH mass (Mbh). The model can be expressed by the equation /r_c=A(m_c/M_bh)^α [σ _c^2r_c/(GM_c)]^β, in which the free parameters A, α, and β are calculated through comparison with the numerical results on the IMBH displacement. The model is then applied to Galactic GCs, finding that for an IMBH mass equal to 0.1 per cent of the GC mass, the typical expected displacement of a putative IMBH is around 1 arcsec for most Galactic GCs, but IMBHs can wander to larger angular distances in some objects, including a prediction of a 2.5 arcsec displacement for NGC 5139 (ω Cen), and >10 arcsec for NGC5053, NGC6366, and ARP2.

  19. Abundances in Planetary Nebulae: an Autopsy of Low and Intermediate Mass Stars

    Science.gov (United States)

    Buell, James Francis

    In this work we report on the results of synthetic thermally pulsing asymptotic giant branch models (TP-AGB) and compare the results to the abundance ratios in a sample of planetary nebulae. We use updated the input parameters for mass-loss, the stellar luminosity, and dredge-up. We calculated models with masses between 0.8 solar masses and 8 solar masses. We also calculated models with (Fe/H) between -2.5 and 0.3. The effect of the first, second, and third dredge-up as well as hot-bottom burning are reported on. The analysis of a sample of Galactic bulge and disk planetary nebulae is also reported on.

  20. L1188: A Promising Candidate for Cloud–Cloud Collisions Triggering the Formation of Low- and Intermediate-mass Stars

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Yan; Fang, Min; Mao, Ruiqing; Zhang, Shaobo; Wang, Yuan; Su, Yang; Chen, Xuepeng; Yang, Ji; Wang, Hongchi; Lu, Dengrong, E-mail: ygong@pmo.ac.cn [Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing (China)

    2017-01-20

    We present a new large-scale (2° × 2°) simultaneous {sup 12}CO, {sup 13}CO, and C{sup 18}O (J = 1–0) mapping of L1188 with the Purple Mountain Observatory 13.7 m telescope. Our observations have revealed that L1188 consists of two nearly orthogonal filamentary molecular clouds at two clearly separated velocities. Toward the intersection showing large velocity spreads, we find several bridging features connecting the two clouds in velocity, and an open arc structure that exhibits high excitation temperatures, enhanced {sup 12}CO and {sup 13}CO emission, and broad {sup 12}CO line wings. This agrees with the scenario that the two clouds are colliding with each other. The distribution of young stellar object (YSO) candidates implies an enhancement of star formation in the intersection of the two clouds. We suggest that a cloud–cloud collision happened in L1188 about 1 Myr ago, possibly triggering the formation of low- and intermediate-mass YSOs in the intersection.

  1. Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

    Energy Technology Data Exchange (ETDEWEB)

    Juárez, Carmen; Girart, Josep M. [Institut de Ciències de l’Espai, (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, S/N, E-08193 Cerdanyola del Vallès, Catalonia (Spain); Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090, Morelia, Michoacán (Mexico); Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 10617, Taiwan (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping, E-mail: juarez@ice.cat [School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 (China)

    2017-07-20

    We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s{sup −1}, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

  2. Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

    International Nuclear Information System (INIS)

    Juárez, Carmen; Girart, Josep M.; Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier; Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab; Zhang, Qizhou; Qiu, Keping

    2017-01-01

    We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s −1 , converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

  3. EVOLUTION OF INTERMEDIATE-MASS X-RAY BINARIES DRIVEN BY THE MAGNETIC BRAKING OF AP/BP STARS. I. ULTRACOMPACT X-RAY BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wen-Cong [School of Physics and Electrical Information, Shangqiu Normal University, Shangqiu 476000 (China); Podsiadlowski, Philipp, E-mail: chenwc@pku.edu.cn [Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom)

    2016-10-20

    It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40–60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100–10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10{sup −5}, the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10{sup −3}, and 10{sup −5}, respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is ≳2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.

  4. Intermediate-Mass Black Holes

    Science.gov (United States)

    Miller, M. Coleman; Colbert, E. J. M.

    2004-01-01

    The mathematical simplicity of black holes, combined with their links to some of the most energetic events in the universe, means that black holes are key objects for fundamental physics and astrophysics. Until recently, it was generally believed that black holes in nature appear in two broad mass ranges: stellar-mass (M~3 20 M⊙), which are produced by the core collapse of massive stars, and supermassive (M~106 1010 M⊙), which are found in the centers of galaxies and are produced by a still uncertain combination of processes. In the last few years, however, evidence has accumulated for an intermediate-mass class of black holes, with M~102 104 M⊙. If such objects exist they have important implications for the dynamics of stellar clusters, the formation of supermassive black holes, and the production and detection of gravitational waves. We review the evidence for intermediate-mass black holes and discuss future observational and theoretical work that will help clarify numerous outstanding questions about these objects.

  5. URCA neutrino-loss rates under conditions found in the carbon-oxygen cores of intermediate-mass stars

    International Nuclear Information System (INIS)

    Iben, I. Jr.

    1978-01-01

    In the hope of uncovering additional Urca-active nuclei that might appear during carbon burning in the electron-degenerate carbon-oxygen core of an asymptotic-branch star and avert a thermonuclear runaway, a nuclear-reaction matrix connecting 244 nuclear species has been constructed. Analytic expressions for rates of all relevant β-transitions are also presented and used. It is shown that in matter which is composed initially of elements in a solar-system distribution and which has undergone first complete hydrogen burning and then complete helium burning, neutrino-loss rates due to 11 Urca pairs either rival or exceed neutrino losses predicted by the charge- and neutral-current theories of weak interactions. Most remarkably, no new Urca pairs of any consequence appear as a result of several thousand reactions that are allowed to occur during carbon burning. The dominant Urca-loss rates are still due to the pairs 21 F- 21 Ne, 23 Ne- 23 Na, 25 Na- 25 Mg, and 25 Ne- 25 Na, as in matter containing a solar-system distribution of elements that has undergone prior processing during hydrogen- and helium-burning phases. The abundances of these Urca-active pairs are enhanced by one to three orders of magnitude as a consequence of carbon-burning reactions

  6. 2D and 3D Models of Convective Turbulence and Oscillations in Intermediate-Mass Main-Sequence Stars

    Science.gov (United States)

    Guzik, Joyce Ann; Morgan, Taylor H.; Nelson, Nicholas J.; Lovekin, Catherine; Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander

    2015-08-01

    We present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the sun, using three separate approaches: 1) Applying the spherical 3D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid gamma Dor/delta Sct variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive g modes; 2) Using the 3D planar ‘StellarBox’ radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 3) Applying the ROTORC 2D stellar evolution and dynamics code to calculate evolution with a variety of initial rotation rates and extents of core convective overshooting. The nonradial adiabatic pulsation frequencies of these nonspherical models will be calculated using the 2D pulsation code NRO of Clement. We will present new insights into gamma Dor and delta Sct pulsations gained by multidimensional modeling compared to 1D model expectations.

  7. Very low mass stars

    International Nuclear Information System (INIS)

    Liebert, J.; Probst, R.G.

    1987-01-01

    This paper discusses several theoretical and observational topics involved in discovering and analyzing very low mass stellar objects below about 0.3 M circle, as well as their likely extension into the substellar range. The authors hereafter refer to these two classes of objects as VLM stars and brown dwarfs, respectively; collectively, they are called VLM objects. The authors outline recent theoretical work on low-mass stellar interiors and atmospheres, the determination of the hydrogen-burning mass limit, important dynamical evidence bearing on the expected numbers of such objects, and the expectations for such objects from star-formation theory. They focus on the properties of substellar objects near the stellar mass limit. Observational techniques used to discover and analyze VLM objects are summarized

  8. Mass loss from S stars

    International Nuclear Information System (INIS)

    Jura, M.

    1988-01-01

    The mass-loss process in S stars is studied using 65 S stars from the listing of Wing and Yorka (1977). The role of pulsations in the mass-loss process is examined. It is detected that stars with larger mass-loss rates have a greater amplitude of pulsations. The dust-to-gas ratio for the S stars is estimated as 0.002 and the average mass-loss rate is about 6 x 10 to the -8th solar masses/yr. Some of the properties of the S stars, such as scale height, surface density, and lifetime, are measured. It is determined that scale height is 200 pc; the total duration of the S star phase is greater than or equal to 30,000 yr; and the stars inject 3 x 10 to the -6th solar masses/sq kpc yr into the interstellar medium. 46 references

  9. Orbital circularisation of white dwarfs and the formation of gravitational radiation sources in star clusters containing an intermediate mass black hole

    OpenAIRE

    Ivanov, P. B.; Papaloizou, J. C. B.

    2007-01-01

    (abbreviated) We consider how tight binaries consisting of a super-massive black hole of mass $M=10^{3}-10^{4}M_{\\odot}$ and a white dwarf can be formed in a globular cluster. We point out that a major fraction of white dwarfs tidally captured by the black hole may be destroyed by tidal inflation during ongoing circularisation, and the formation of tight binaries is inhibited. However, some stars may survive being spun up to high rotation rates. Then the energy loss through gravitational wave...

  10. On the production of He, C, and N by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances

    Science.gov (United States)

    Henry, R. B. C.; Stephenson, B. G.; Miller Bertolami, M. M.; Kwitter, K. B.; Balick, B.

    2018-01-01

    The primary goal of this paper is to make a direct comparison between the measured and model-predicted abundances of He, C, and N in a sample of 35 well-observed Galactic planetary nebulae (PNe). All observations, data reductions, and abundance determinations were performed in house to ensure maximum homogeneity. Progenitor star masses (M ≤ 4 M⊙) were inferred using two published sets of post-asymptotic giant branch model tracks and L and Teff values. We conclude the following: (1) the mean values of N/O across the progenitor mass range exceeds the solar value, indicating significant N enrichment in the majority of our objects; (2) the onset of hot bottom burning appears to begin around 2 M⊙, i.e. lower than ∼5 M⊙ implied by theory; (3) most of our objects show a clear He enrichment, as expected from dredge-up episodes; (4) the average sample C/O value is 1.23, consistent with the effects of third dredge up; and (5) model grids used to compare to observations successfully span the distribution over metallicity space of all C/O and many He/H data points but mostly fail to do so in the case of N/O. The evident enrichment of N in PN and the general discrepancy between the observed and model-predicted N/O abundance ratios signal the need for extra mixing as an effect of rotation and/or thermohaline mixing in the models. The unexpectedly high N enrichment that is implied here for low-mass stars, if confirmed, will likely impact our conclusions about the source of N in the Universe.

  11. RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S4G IRAC 3.6 AND 4.5 μm IMAGES. I. CORRECTING FOR CONTAMINATION BY POLYCYCLIC AROMATIC HYDROCARBONS, HOT DUST, AND INTERMEDIATE-AGE STARS

    International Nuclear Information System (INIS)

    Meidt, Sharon E.; Schinnerer, Eva; Knapen, Johan H.; Bosma, Albert; Athanassoula, E.; Sheth, Kartik; Muñoz-Mateos, Juan-Carlos; Buta, Ronald J.; Zaritsky, Dennis; Hinz, Joannah L.; Skibba, Ramin A.; Laurikainen, Eija; Salo, Heikki; Elmegreen, Debra; Elmegreen, Bruce G.; Gadotti, Dimitri A.; Regan, Michael; Ho, Luis C.; Madore, Barry F.; Gil de Paz, Armando

    2012-01-01

    With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 μm images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 μm bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 μm, which is dominated by the broad PAH feature. Using the measured 3.6 μm/8 μm ratio to select individual contaminants, we find that hot dust and PAHs together contribute between ∼5% and 15% to the integrated light at 3.6 μm, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information

  12. Low-mass stars with mass loss and low-luminosity carbon star formation

    International Nuclear Information System (INIS)

    Boothroyd, A.I.

    1987-01-01

    The effects of large carbon enrichments in static stellar envelopes were investigated, using new Los Alamos opacities (including low-temperature carbon and molecular opacities) and including carbon ionizations. To search for the production of low-mass,low-luminosity carbon stars, detailed stellar evolutionary computations were carried out for a grid of low-mass stars of two different metallicities. The stars were evolved from the main sequence through all intermediate stages and through helium-shell flashes on the asymptotic giant branch. The effects of the latest nuclear reaction rates, the new Los Alamos opacities, Reimers-type wind mass loss, and detailed treatment of convection and semi-convection were investigated. Two low-luminosity carbon stars were achieved, in excellent agreement with observations. Conditions favoring dredge-up (and thus carbon-star production) include a reasonably large convective mixing length, low metallicity, relatively large envelope mass, and high flash strength. Mass loss was of major importance, tending to oppose dredge-up; the total mass-loss amounts inferred from observations suffice to prevent formation of high-mass, high-luminosity carbon stars

  13. 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

  14. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    International Nuclear Information System (INIS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-01-01

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  15. Mass loss from Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Willis, A.J.

    1982-01-01

    Recent results relating to the stellar winds and mass loss rates of the WR stars are reviewed, emphasising new data and their interpretation acquired at UV, IR and Radio wavelengths. The subject is discussed under the headings: physical and chemical properties of WR stars (effective temperatures and radiative luminosities; masses; chemical abundances); velocity, ionisation and excitation structure of WR winds; mass loss rates of WR stars; mass loss properties of WR stars in the LMC; comparisons with theoretical models of mass loss; ring nebulae around WR stars; conclusions. (author)

  16. The neutron star mass distribution

    Energy Technology Data Exchange (ETDEWEB)

    Kiziltan, Bülent [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kottas, Athanasios; De Yoreo, Maria [Department of Applied Mathematics and Statistics, University of California, Santa Cruz, CA 95064 (United States); Thorsett, Stephen E., E-mail: bkiziltan@cfa.harvard.edu [Department of Astronomy and Astrophysics, University of California and UCO/Lick Observatory, Santa Cruz, CA 95064 (United States)

    2013-11-20

    In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double NS and NS-white dwarf (WD) systems show consistent respective peaks at 1.33 M {sub ☉} and 1.55 M {sub ☉}, suggesting significant mass accretion (Δm ≈ 0.22 M {sub ☉}) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ∼2.1 M {sub ☉} for NSs with WD companions, which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M {sub ☉} limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare supermassive NSs is possible.

  17. High mass planets and low mass stars

    International Nuclear Information System (INIS)

    Stevenson, D.J.

    1986-01-01

    The paper on theoretical models of brown dwarf stars was presented to the workshop on ''Astrophysics of brown dwarfs'', Virginia, USA, 1985. The ingredients in the models i.e. equation of state, entropy and the infrared opacity are described. An analytical model is developed which is based on a polytrope (n = 3/4) but which neglects thermonuclear reactions. The model forms the basis of scaling laws for luminosity, mass, opacity and age. Complicating factors in brown dwarf evolution are also discussed. (U.K.)

  18. Evolutionary effects of mass loss in low-mass stars

    International Nuclear Information System (INIS)

    Renzini, A.

    1981-01-01

    The effects of mass loss on the evolution of low-mass stars (actual mass smaller than 1.4 solar masses) are reviewed. The case of globular cluster stars is discussed in some detail, and it is shown that evolutionary theory sets quite precise limits to the mass-loss rate in population II red giants. The effects of mass loss on the final evolutionary stages of stars producing white dwarfs is also discussed. In particular, the interaction of the wind from the hot central star with the surrounding planetary nebula is considered. Finally, the problem of the origin of hydrogen-deficient stars is briefly discussed. (Auth.)

  19. DENIS, 2MASS and VLM stars

    Science.gov (United States)

    Reid, Neill

    1994-01-01

    To a first approximation, every star is an M dwarf - but there are still considerable gaps in our understanding of these stars, particularly in the space density of the lowest mass stars. Fortunately, the 2 micrometer sky surveys are likely to change this state of affairs. In this paper, I review briefly the likely impact of these surveys.

  20. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    Science.gov (United States)

    2010-07-01

    Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters - millions of times more luminous than the Sun, losing weight through very powerful winds - may provide an answer to the question "how massive can stars be?" A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613). The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun. In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as

  1. 2MASS Identifications for Galactic OB Stars

    OpenAIRE

    Reed, B. Cameron

    2007-01-01

    Cross-identifications for 14,574 intrinsically luminous galactic stars (mostly OB stars) to objects in the 2MASS survey have been determined using a search box of +/-0.0015 degrees (+/- 5.4 arcsec) in both RA and Dec. Instructions on obtaining the relevant files can be obtained at othello.alma.edu/~reed/OB-2MASS.doc.

  2. ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS

    International Nuclear Information System (INIS)

    Özel, Feryal; Psaltis, Dimitrios; Santos Villarreal, Antonio; Narayan, Ramesh

    2012-01-01

    We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M ☉ and a dispersion of 0.24 M ☉ . These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand, double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M ☉ , but with a dispersion of only 0.05 M ☉ . Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M ☉ and a dispersion of 0.2 M ☉ , consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed ∼2 M ☉ suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

  3. Neutrino mass as the probe of intermediate mass scales

    International Nuclear Information System (INIS)

    Senjanovic, G.

    1980-01-01

    A discussion of the calculability of neutrino mass is presented. The possibility of neutrinos being either Dirac or Majorana particles is analyzed in detail. Arguments are offered in favor of the Majorana case: the smallness of neutrino mass is linked to the maximality of parity violation in weak interactions. It is shown how the measured value of neutrino mass would probe the existence of an intermediate mass scale, presumably in the TeV region, at which parity is supposed to become a good symmetry. Experimental consequences of the proposed scheme are discussed, in particular the neutrino-less double β decay, where observation would provide a crucial test of the model, and rare muon decays such as μ → eγ and μ → ee anti e. Finally, the embedding of this model in an O(10) grand unified theory is analyzed, with the emphasis on the implications for intermediate mass scales that it offers. It is concluded that the proposed scheme provides a distinct and testable alternative for understanding the smallness of neutrino mass. 4 figures

  4. Neutrino mass as the probe of intermediate mass scales

    Energy Technology Data Exchange (ETDEWEB)

    Senjanovic, G.

    1980-01-01

    A discussion of the calculability of neutrino mass is presented. The possibility of neutrinos being either Dirac or Majorana particles is analyzed in detail. Arguments are offered in favor of the Majorana case: the smallness of neutrino mass is linked to the maximality of parity violation in weak interactions. It is shown how the measured value of neutrino mass would probe the existence of an intermediate mass scale, presumably in the TeV region, at which parity is supposed to become a good symmetry. Experimental consequences of the proposed scheme are discussed, in particular the neutrino-less double ..beta.. decay, where observation would provide a crucial test of the model, and rare muon decays such as ..mu.. ..-->.. e..gamma.. and ..mu.. ..-->.. ee anti e. Finally, the embedding of this model in an O(10) grand unified theory is analyzed, with the emphasis on the implications for intermediate mass scales that it offers. It is concluded that the proposed scheme provides a distinct and testable alternative for understanding the smallness of neutrino mass. 4 figures.

  5. Mass-Radius diagram for compact stars

    International Nuclear Information System (INIS)

    Carvalho, G A; Jr, R M Marinho; Malheiro, M

    2015-01-01

    The compact stars represent the final stage in the evolution of ordinary stars, they are formed when a star ceases its nuclear fuel, in this point the process that sustain its stability will stop. After this, the internal pressure can no longer stand the gravitational force and the star colapses [2]. In this work we investigate the structure of these stars which are described by the equations of Tolman-Openheimer-Volkof (TOV) [1]. These equations show us how the pressure varies with the mass and radius of the star. We consider the TOV equations for both relativistic and non-relativistic cases. In the case of compact stars (white dwarfs and neutron stars) the internal pressure that balances the gravitational pressure is essentialy the pressure coming from the degeneracy of fermions. To have solved the TOV equations we need a equation of state that shows how this internal pressure is related to the energy density or mass density. Instead of using politropic equations of state we have solved the equations numericaly using the exact relativistic energy equation for the model of fermion gas at zero temperature. We obtain results for the mass-radius relation for white dwarfs and we compared with the results obtained using the politropic equations of state. In addition we discussed a good fit for the mass-radius relation. (paper)

  6. Missing mass from low-luminosity stars

    International Nuclear Information System (INIS)

    Hawkins, M.R.S.

    1986-01-01

    Results from a deep photometric survey for low-luminosity stars show a turnup to the luminosity function at faint magnitudes, and reopen the possibility that the missing mass in the solar neighbourhood is made up of stars after all. (author)

  7. Rotational velocities of low-mass stars

    International Nuclear Information System (INIS)

    Stauffer, J.B.; Hartmann, L.W.; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA)

    1986-01-01

    The rotational velocities of stars provide important clues to how stars form and evolve. Yet until recently, studies of stellar rotation were limited to stars more massive than the sun. This is beginning to change, and an observational outline of the rotational velocity evolution of stars less massive than the sun can now be provided. Low-mass stars rotate slowly during the early stages of premain-sequence evolution, and spin up as they contract to the main sequence. This spin-up culminates in a brief period of very rapid rotation at an age of order 50 million years. Physical interpretation of this increase in rotation and the subsequent main-sequence spin-down are complicated by the possibility of differential internal rotation. The observed rapidity of spin-down among G dwarfs suggests that initially only the outer convective envelopes of these stars are slowed. The data suggest an intrinsic spread in angular momentum among young stars of the same mass and age, a spread which is apparently minimized by the angular-momentum loss mechanism in old low-mass stars. 83 references

  8. Star Formation in low mass galaxies

    Science.gov (United States)

    Mehta, Vihang

    2018-01-01

    Our current hierarchical view of the universe asserts that the large galaxies we see today grew via mergers of numerous smaller galaxies. As evidenced by recent literature, the collective impact of these low mass galaxies on the universe is more substantial than previously thought. Studying the growth and evolution of these low mass galaxies is critical to our understanding of the universe as a whole. Star formation is one of the most important ongoing processes in galaxies. Forming stars is fundamental to the growth of a galaxy. One of the main goals of my thesis is to analyze the star formation in these low mass galaxies at different redshifts.Using the Hubble UltraViolet Ultra Deep Field (UVUDF), I investigate the star formation in galaxies at the peak of the cosmic star formation history using the ultraviolet (UV) light as a star formation indicator. Particularly, I measure the UV luminosity function (LF) to probe the volume-averaged star formation properties of galaxies at these redshifts. The depth of the UVUDF is ideal for a direct measurement of the faint end slope of the UV LF. This redshift range also provides a unique opportunity to directly compare UV to the "gold standard" of star formation indicators, namely the Hα nebular emission line. A joint analysis of the UV and Hα LFs suggests that, on average, the star formation histories in low mass galaxies (~109 M⊙) are more bursty compared to their higher mass counterparts at these redshifts.Complementary to the analysis of the average star formation properties of the bulk galaxy population, I investigate the details of star formation in some very bursty galaxies at lower redshifts selected from Spitzer Large Area Survey with Hyper-Suprime Cam (SPLASH). Using a broadband color-excess selection technique, I identify a sample of low redshift galaxies with bright nebular emission lines in the Subaru-XMM Deep Field (SXDF) from the SPLASH-SXDF catalog. These galaxies are highly star forming and have

  9. Spectroscopic Observations of Nearby Low Mass Stars

    Science.gov (United States)

    Vican, Laura; Zuckerman, B. M.; Rodriguez, D.

    2014-01-01

    Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity. By cross-correlating the GALEX Catalog with the WISE and 2MASS Point Source Catalogs, we have identified more than 2,000 stars whose UV excesses suggest ages in the 10-100 Myr range. We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2,000 stars spectroscopically. We measured the equivalent width of lithium at 6708 A absorption and H-alpha emission lines. Out of a total of 122 stars observed with the Kast grating spectrometer, we find that roughly 10% have strong lithium absorption features. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars. In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile. This submission presents work for the GALNYSS project and should be linked to abstracts submitted by David Rodriguez, Laura Vican, and Joel Kastner.

  10. Intermediate mass distribution of the dual resonance pomeron

    International Nuclear Information System (INIS)

    Chiu, C.B.; Matsuda, S.

    1978-01-01

    The intermediate mass distribution of the dual resonance pomeron is determined at the one-loop level and it is shown that the mass distribution obtained is remarkably similar to a suitably defined mass distribution in the dual multiperipheral model. Thus it is suggestive to identify the intermediate states of the dual resonance pomeron with multiperipheral processes. (Auth.)

  11. The Metallicity Evolution of Low Mass Galaxies: New Contraints at Intermediate Redshift

    Science.gov (United States)

    Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

    2013-01-01

    We present abundance measurements from 26 emission-line-selected galaxies at z approx. 0.6-0.7. By reaching stellar masses as low as 10(exp 8) M stellar mass, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 10(exp 9)M stellar mass. For the portion of our sample above M is greater than 10(exp 9)M (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M* relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation.We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

  12. Mass-loss rates of cool stars

    Science.gov (United States)

    Katrien Els Decin, Leen

    2015-08-01

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

  13. PROTOPLANETARY DISK MASSES FROM STARS TO BROWN DWARFS

    International Nuclear Information System (INIS)

    Mohanty, Subhanjoy; Mortlock, Daniel; Greaves, Jane; Pascucci, Ilaria; Apai, Daniel; Scholz, Aleks; Thompson, Mark; Lodato, Giuseppe; Looper, Dagny

    2013-01-01

    We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ∼100 AU for intermediate-mass stars, solar types, and VLMS, and ∼20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ∼ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly

  14. Olivier Chesneau's Work on Low Mass Stars

    Science.gov (United States)

    Lagadec, E.

    2015-12-01

    During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.

  15. Explosion of a low mass neutron star

    International Nuclear Information System (INIS)

    Blinnikov, S.I.; Imshennik, V.S.; Nadyozhin, D.K.; Novikov, I.D.; Polnarev, A.G.; AN SSSR, Moscow. Fizicheskij Inst.); Perevodchikova, T.V.

    1990-01-01

    The hydrodynamical disruption of a low mass neutron star is investigated for the case when the stellar mass becomes smaller than the minimum value, M min ≅0.1 M sun . The final phase of the process is shown to proceed explosively, leading to an expansion of all the star, with a kinetic energy of 4.8 MeV per nucleon. The results of calculations are virtually independent of the way in which the neutron star mass goes down below M min (mass exchange in a close binary stellar system, nucleon decay, or some effective mass loss due to a hypothetical decrease of the gravitational constant). The neutron star disruption is followed by a short (0.01-0.1 s) burst of thermal hard X-rays and soft gamma-rays (kT=10-100 keV) with a subsequent much more prolonged tail of radiation induced by decays of long-lived radioactive nuclides. Some fraction of the explosion energy may be emitted in the form of neutrinos. (orig.)

  16. VizieR Online Data Catalog: Adiabatic mass loss in binary stars. II. (Ge+, 2015)

    Science.gov (United States)

    Ge, H.; Webbink, R. F.; Chen, X.; Han, Z.

    2016-02-01

    In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z=0.02) of mass 0.10M⊙-100M⊙ from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio qad (throughout this paper, we follow the convention of defining the binary mass ratio as q{equiv}Mdonor/Maccretor) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, qad plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with qad declining with decreasing mass, and asymptotically approaching qad=2/3, appropriate to a classical isentropic n=3/2 polytrope. Our calculated qad values agree well with the behavior of time-dependent models by Chen & Han (2003MNRAS.341..662C) of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass

  17. POPULATION PARAMETERS OF INTERMEDIATE-AGE STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD. II. NEW INSIGHTS FROM EXTENDED MAIN-SEQUENCE TURNOFFS IN SEVEN STAR CLUSTERS

    International Nuclear Information System (INIS)

    Goudfrooij, Paul; Kozhurina-Platais, Vera; Puzia, Thomas H.; Chandar, Rupali

    2011-01-01

    We discuss new photometry from high-resolution images of seven intermediate-age (1-2 Gyr) star clusters in the Large Magellanic Cloud taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. We fit color-magnitude diagrams (CMDs) with several different sets of theoretical isochrones and determine systematic uncertainties for population parameters when derived using any one set of isochrones. The cluster CMDs show several interesting features, including extended main-sequence turnoff (MSTO) regions, narrow red giant branches, and clear sequences of unresolved binary stars. We show that the extended MSTOs are not caused by photometric uncertainties, contamination by field stars, or the presence of binary stars. Enhanced helium abundances in a fraction of cluster stars are also ruled out as the reason for the extended MSTOs. Quantitative comparisons with simulations indicate that the MSTO regions are better described by a spread in ages than by a bimodal age distribution, although we cannot formally rule out the latter for the three lowest-mass clusters in our sample (which have masses lower than ∼3 x 10 4 M sun ). This conclusion differs from that of some previous works which suggested that the age distribution in massive clusters in our sample is bimodal. This suggests that any secondary star formation occurred in an extended fashion rather than through short bursts. We discuss these results in the context of the nature of multiple stellar populations in star clusters.

  18. White dwarfs: connection with masses of the parent stars

    International Nuclear Information System (INIS)

    Amnuel', P.R.; Guseinov, O.Kh.; Novruzova, Kh.I.; Rustamov, Yu.S.

    1988-01-01

    A relationship between the mass of a white dwarf and the mass of the parent star on the main sequence is established. The white dwarf birth-rate matches the birth-rate (death-rate) of main sequence stars

  19. First stars. II. Evolution with mass loss

    Czech Academy of Sciences Publication Activity Database

    Bahena, David; Hadrava, Petr

    2012-01-01

    Roč. 337, č. 2 (2012), s. 651-663 ISSN 0004-640X R&D Projects: GA MŠk(CZ) LC506; GA ČR GA202/09/0772 Institutional research plan: CEZ:AV0Z10030501 Keywords : first stars * evolution * mass loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 2.064, year: 2012

  20. Low-Mass Stars and Their Companions

    Science.gov (United States)

    Montet, Benjamin Tyler

    In this thesis, I present seven studies aimed towards better understanding the demographics and physical properties of M dwarfs and their companions. These studies focus in turn on planetary, brown dwarf, and stellar companions to M dwarfs. I begin with an analysis of radial velocity and transit timing analyses of multi-transiting planetary systems, finding that if both signals are measured to sufficiently high precision the stellar and planetary masses can be measured to a high precision, eliminating a need for stellar models which may have systematic errors. I then combine long-term radial velocity monitoring and a direct imaging campaign to measure the occurrence rate of giant planets around M dwarfs. I find that 6.5 +/- 3.0% of M dwarfs host a Jupiter mass or larger planet within 20 AU, with a strong dependence on stellar metallicity. I then present two papers analyzing the LHS 6343 system, which contains a widely separated M dwarf binary (AB). Star A hosts a transiting brown dwarf (LHS 6343 C) with a 12.7 day period. By combining radial velocity data with transit photometry, I am able to measure the mass and radius of the brown dwarf to 2% precision, the most precise measurement of a brown dwarf to date. I then analyze four secondary eclipses of the LHS 6343 AC system as observed by Spitzer in order to measure the luminosity of the brown dwarf in both Spitzer bandpasses. I find the brown dwarf is consistent with theoretical models of an 1100 K T dwarf at an age of 5 Gyr and empirical observations of field T5-6 dwarfs with temperatures of 1070 +/- 130 K. This is the first non-inflated brown dwarf with a measured mass, radius, and multi-band photometry, making it an ideal test of evolutionary models of field brown dwarfs. Next, I present the results of an astrometric and radial velocity campaign to measure the orbit and masses of both stars in the GJ 3305 AB system, an M+M binary comoving with 51 Eridani, a more massive star with a directly imaged planetary

  1. RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS-PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Bowler, Brendan P.; Johnson, John Asher; Liu, Michael C.; Marcy, Geoffrey W.; Peek, Kathryn M. G.; Henry, Gregory W.; Fischer, Debra A.; Clubb, Kelsey I.; Reffert, Sabine; Schwab, Christian; Lowe, Thomas B.

    2010-01-01

    We present an analysis of ∼5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 ∼ * /M sun ∼ +9 -8 %, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M Jup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M α P β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (∼50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.

  2. Bump masses for BL Her stars

    International Nuclear Information System (INIS)

    Davis, C.G.

    1982-01-01

    The masses of classical Cepheids can be determined by using the phase of the Hertzsprung bump on the light or velocity curve, Cox-Stewart opacities, and nonlinear pulsation theory. The fact that these bump masses are some 60% lower than the evolutionary masses raises some questions about this approach. In support of our method, we calculate the light curve for BL Her, a population II Cepheid, with an observed bump on the declining portion of its light curve. The nonlinear hydrodynamic model we use (Davis and Davison - 1978) resolves the light curve by dynamic zoning and allows us the opportunity to make a direct comparison of the calculated light curve to the observations, using a prescribed mass, luminosity and effective temperature. The parameters for BL Her are from a linear model (Hodson, Cox, and King - 1982) that has nearly the correct period (1./sup d/2) and the correct period ratio from resonance theory (π 2 /π 0 = 0.53) for a bump to appear on the declining portion of the light curve as observed. These parameters are: M = 0.55 M, L = 95.0 L, and T/sub eff/ = 6500 K. This mass is near the evolutionary mass as described by Schwartzschild and Haerm (1970). The model results agree well with the observations and the color-T/sub eff/ relation has the same slope as that observed for RR Lyrae stars by the Oke, Giver and Searle (1965) relationship

  3. Coronal Diagnostics of Intermediate Activity Star XI Boo A

    Science.gov (United States)

    Drake, Jeremy

    2005-01-01

    The analysis of Xi Boo A proved difficult to adapt to our line-by-line approach because of the strong wings of the RGS instrumental profile, as has been detailed in earlier reports. While progress was also delayed because of problems in using SAS v4, we succeeded in the past year or so to bring the analysis to conclusion. Abundances have been derived using both EPIC and RGS data, confirming earlier EUVE findings of a mild solar-like FIP effect, though with some evidence of a turn-up in abundances of elements with higher FIP. Plasma densities appear normal for a moderately active stellar corona. Xi Boo A nicely bridges the gap between the very active stars and stars like the Sun, and it indeed does appear that these are the stars in which the solar-like FIP effects begins to change to the "inverse FIP" type of effect seen in the very active stars. Probing this divide was the main goal of the proposal. These results are in the process of being prepared for publication, though we have not decided the target journal as yet.

  4. Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars

    Science.gov (United States)

    Bowler, Brendan P.; Johnson, John Asher; Marcy, Geoffrey W.; Henry, Gregory W.; Peek, Kathryn M. G.; Fischer, Debra A.; Clubb, Kelsey I.; Liu, Michael C.; Reffert, Sabine; Schwab, Christian; Lowe, Thomas B.

    2010-01-01

    We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 lsim M */M sunlsim 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26+9 -8%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M Jup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN vprop M α P β dlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets. Based on observations obtained at the Lick Observatory, which is operated by the University of California.

  5. Starless Clumps and the Earliest Phases of High-mass Star Formation in the Milky Way

    Science.gov (United States)

    Svoboda, Brian

    2018-01-01

    High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I report on observational studies of dense starless clump candidates (SCCs) that show no signatures of star formation activity. I identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyze their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, I study the 12 most high-mass SCCs within 5 kpc using ALMA. I report previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation effeciency in this sample, these observational facts are consistent with models where high-mass stars form from intially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump.

  6. Effects of mass loss on the evolution of massive stars. I. Main-sequence evolution

    International Nuclear Information System (INIS)

    Dearborn, D.S.P.; Blake, J.B.; Hainebach, K.L.; Schramm, D.N.

    1978-01-01

    The effect of mass loss on the evolution and surface composition of massive stars during main-sequence evolution are examined. While some details of the evolutionary track depend on the formula used for the mass loss, the results appear most sensitive to the total mass removed during the main-sequence lifetime. It was found that low mass-loss rates have very little effect on the evolution of a star; the track is slightly subluminous, but the lifetime is almost unaffected. High rates of mass loss lead to a hot, high-luminosity stellar model with a helium core surrounded by a hydrogen-deficient (Xapprox.0.1) envelope. The main-sequence lifetime is extended by a factor of 2--3. These models may be identified with Wolf-Rayet stars. Between these mass-loss extremes are intermediate models which appear as OBN stars on the main sequence. The mass-loss rates required for significant observable effects range from 8 x 10 -7 to 10 -5 M/sub sun/ yr -1 , depending on the initial stellar mass. It is found that observationally consistent mass-loss rates for stars with M> or =30 M/sub sun/ may be sufficiently high that these stars lose mass on a time scale more rapidly than their main-sequence core evolution time. This result implies that the helium cores resulting from the main-sequence evolution of these massive stars may all be very similar to that of a star of Mapprox.30 M/sub sun/ regardless of the zero-age mass

  7. The coupling between pulsation and mass loss in massive stars

    OpenAIRE

    Townsend, Rich

    2007-01-01

    To what extent can pulsational instabilities resolve the mass-loss problem of massive stars? How important is pulsation in structuring and modulating the winds of these stars? What role does pulsation play in redistributing angular momentum in massive stars? Although I cannot offer answers to these questions, I hope at the very least to explain how they come to be asked.

  8. Early-type galaxies at intermediate redshift observed with Hubble space telescope WFC3: perspectives on recent star formation

    Energy Technology Data Exchange (ETDEWEB)

    Rutkowski, Michael J. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Jeong, Hyunjin; Yi, Sukyoung K. [Department of Astronomy, Yonsei University 134, Shinchon-dong, Sudaemun-gu, Seoul 120-179 (Korea, Republic of); Cohen, Seth H.; Windhorst, Rogier A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Kaviraj, Sugata [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Ryan, Russell E. Jr.; Koekemoer, Anton [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Hathi, Nimish P. [Aix Marseille Université, CNRS, LAM, UMR 7326, F-13388, Marseille (France); Dopita, Michael A. [Research School of Physics and Astronomy, The Australian National University, Canberra, ACT 2611 (Australia)

    2014-12-01

    We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one- and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (∼40%) are likely to have experienced a minor (f{sub YC} ≲ 10% of stellar mass) burst of recent (t{sub YC} ≲ 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 10{sup 10.5} M {sub ☉}) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.

  9. Search for Gravitational Waves from Intermediate Mass Binary Black Holes

    Science.gov (United States)

    Blackburn, L.; Camp, J. B.; Cannizzo, J.; Stroeer, A. S.

    2012-01-01

    We present the results of a weakly modeled burst search for gravitational waves from mergers of non-spinning intermediate mass black holes (IMBH) in the total mass range 100-450 solar Mass and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the IMBH mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 solar Mass , for non-spinning sources, the rate density upper limit is 0.13 per Mpc(exp 3) per Myr at the 90% confidence level.

  10. Massive stars with mass loss: Evolution, nucleosynthesis, and astrophysical implications

    International Nuclear Information System (INIS)

    Prantzos, N.

    1986-06-01

    Evolution and nucleosynthesis of mass loss WR stars is studied, particularly evolution of stars with initial mass between 50 and 100 solar masses, during combustion of H and He. A semi-empirical mass loss formalism, the Roxburgh criterion for convection, and nuclear data are used. Composition of the stellar surface and ejecta (and ejecta contribution to cosmic ray composition) are derived. The contribution of these stars to s elements in our solar system is shown. Their production of 26 Al is compared to the quantity in the galaxy. Gamma ray emission at 1.8 MeV from the decay of this radionuclide is estimated in galactic longitude. The stars evolve as 0 and 0f stars during H combustion and spend 20% of their He combustion period as WN stars and 80% as WC-W0. Evolution always occurs in the blue part of the HR diagram, and satisfies observational constraints on its upper part [fr

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

    Science.gov (United States)

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

    2018-01-01

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

  12. The masses of retired A stars with asteroseismology

    DEFF Research Database (Denmark)

    North, Thomas S. H.; Campante, Tiago L.; Miglio, Andrea

    2017-01-01

    We investigate the masses of 'retired A stars' using asteroseismic detections on seven low-luminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overes...

  13. Evidence for mass loss at moderate to high velocity in Be stars

    Science.gov (United States)

    Snow, T. P., Jr.; Marlborough, J. M.

    1976-01-01

    Ultraviolet spectra of intermediate resolution have been obtained with Copernicus for 12 objects classified as Be or shell stars and for 19 additional early B dwarfs. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si IV doublet at 1400 A, indicating the presence in some cases of outflowing material with maximum velocities of nearly 1000 km/s. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5; the only objects later than B0.5 which show this effect are Be or shell stars. Among the stars considered, there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the ultraviolet flux from B1-B2 dwarfs is sufficient to drive high-velocity stellar winds only if rotational effects reduce the effective gravity near the equator. The mass-loss rate for one of the most active Be stars, 59 Cyg, is crudely estimated to be one billionth or one ten-billionth of a solar mass per year. The data suggest that the extended atmospheres associated with Be-star phenomena may be formed by mass ejection.

  14. SEQUENTIAL STAR FORMATION IN RCW 34: A SPECTROSCOPIC CENSUS OF THE STELLAR CONTENT OF HIGH-MASS STAR-FORMING REGIONS

    International Nuclear Information System (INIS)

    Bik, A.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Puga, E.; Waters, L.B.F.M.; Waelkens, Ch.; Horrobin, M.; Kaper, L.; De Koter, A.; Van den Ancker, M.; Comeron, F.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; Thi, W. F.

    2010-01-01

    In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M sun ) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H 2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is

  15. Examining the Center: Positions, Dominance, and Star Formation Rates of Most Massive Group Galaxies at Intermediate Redshift

    Science.gov (United States)

    Connelly, Jennifer L.; Parker, Laura C.; McGee, Sean; Mulchaey, John S.; Finoguenov, Alexis; Balogh, Michael; Wilman, David; Group Environment Evolution Collaboration

    2015-01-01

    The group environment is believed to be the stage for many galaxy transformations, helping evolve blue star-forming galaxies to red passive ones. In local studies of galaxy clusters, the central member is usually a single dominant giant galaxy at the center of the potential with little star formation thought to be the result of galaxy mergers. In nearby groups, a range of morphologies and star formation rates are observed and the formation history is less clear. Further, the position and dominance of the central galaxy cannot be assumed in groups, which are less massive and evolved than clusters. To understand the connections between global group properties and properties of the central group galaxy at intermediate redshift, we examine galaxy groups from the Group Environment and Evolution Collaboration (GEEC) catalog, including both optically- and X-ray-selected groups at redshift z~0.4. The sample is diverse, containing a range in overall mass and evolutionary state. The number of groups is significant, membership is notably complete, and measurements span the IR to the UV allowing the properties of the members to be connected to those of the host groups. Having investigated trends in the global group properties previously, including mass and velocity substructure, we turn our attention now to the galaxy populations, focusing on the central regions of these systems. The most massive and second most massive group galaxies are identified by their stellar mass. The positions of the most massive galaxies (MMGs) are determined with respect to both the luminosity-weighted and X-ray center. Star formation rates are used to explore the fraction of passive/quiescent versus star-forming MMGs and the dominance of the MMGs in our group sample is also tested. Determinations of these characteristics and trends constitute the important first steps toward a detailed understanding of the relationships between the properties of host groups and their most massive galaxies and the

  16. Observational constraints on neutron star masses and radii

    Energy Technology Data Exchange (ETDEWEB)

    Coleman Miller, M. [University of Maryland, Department of Astronomy and Joint Space-Science Institute, College Park, MD (United States); Lamb, Frederick K. [University of Illinois at Urbana-Champaign, Center for Theoretical Astrophysics and Department of Physics, Urbana, IL (United States); University of Illinois at Urbana-Champaign, Department of Astronomy, Urbana, IL (United States)

    2016-03-15

    Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star - black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method. (orig.)

  17. Mass loss by stars on the asymptotic giant branch

    International Nuclear Information System (INIS)

    Frantsman, Yu.L.

    1986-01-01

    The theoretical populations of white dwarfs and carbon stars were generated for Salpeter initial mass function and constant stellar birth rate history. The effect of very strong mass loss on the mass distribution of white dwarfs and luminosity distribution of carbon stars is discussed and the results are compared with observations. This comparison suggested that a signioficant mass loss by stars on the asymptotic giant branch occurs besides stellar wind and planetary nebulae ejection. Thus it is possible to explain the absence of carbon stars with Msub(bol) 1.0 Msub(sun). The luminosity of asymptotic giant branch stars in the globular clusters of the Magellanic Clouds appears to be a very good indicator of the age

  18. Neutron star formation in theoretical supernovae. Low mass stars and white dwarfs

    International Nuclear Information System (INIS)

    Nomoto, K.

    1986-01-01

    The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. The conditions for which neutron stars form from accretion-induced collapse of white dwarfs in clsoe binary systems is also examined

  19. Evidence for mass loss at moderate to high velocity in Be stars

    International Nuclear Information System (INIS)

    Snow, T.P. Jr.; Marlborough, J.M.

    1976-01-01

    Ultraviolet spectra of intermediate resolution have been obtained with Copernicus of 12 objects classified as Be or shell stars, and 19 additional early B dwarfs. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si iv doublet at 1400 A, indicating the presence in some cases of outflowing material with maximum velocities of nearly 1000 km s -1 . Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5; the only objects later than B0.5 which show this effect are Be or shell stars. Among the stars considered there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the ultraviolet flux from B1-B2 dwarfs is sufficient to drive high-velocity stellar winds only if rotation effects reduce the effective gravity near the equator. The mass loss rate for one of the most active Be stars, 59 Cyg, is crudely estimated to be 10 -10 --10 -9 M/sub sun/ yr -1 . The data are suggestive that the extended atmospheres associated with Be star phenomena may be formed by mass ejection

  20. PULSATION-TRIGGERED MASS LOSS FROM AGB STARS: THE 60 DAY CRITICAL PERIOD

    International Nuclear Information System (INIS)

    McDonald, I.; Zijlstra, A. A.

    2016-01-01

    Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to the first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ∼10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ∼300 days.

  1. Searching for intermediate-mass black holes via optical variability

    Science.gov (United States)

    Adler-Levine, Ryan; Moran, Edward C.; Kay, Laura

    2018-01-01

    A handful of nearby dwarf galaxies with intermediate-mass black holes (IMBHs) in their nuclei display significant optical variability on short timescales. To investigate whether dwarf galaxy AGNs as a class exhibit similar variability, we have monitored a sample of low-mass galaxies that possess spectroscopically confirmed type 1 AGNs. However, because of the variations in seeing, focus, and guiding errors that occur in images taken at different epochs, analyses based on aperture photometry are ineffective. We have thus developed a new method for matching point-spread functions in images that permits use of image subtraction photometry techniques. Applying this method to our photometric data, we have confirmed that several galaxies with IMBHs are indeed variable, which suggests that variability can be used to search for IMBHs in low-mass galaxies whose emission-line properties are ambiguous.

  2. Surveying Low-Mass Star Formation with the Submillimeter Array

    Science.gov (United States)

    Dunham, Michael

    2018-01-01

    Large astronomical surveys yield important statistical information that can’t be derived from single-object and small-number surveys. In this talk I will review two recent surveys in low-mass star formation undertaken by the Submillimeter Array (SMA): a millimeter continuum survey of disks surrounding variably accreting young stars, and a complete continuum and molecular line survey of all protostars in the nearby Perseus Molecular Cloud. I will highlight several new insights into the processes by which low-mass stars gain their mass that have resulted from the statistical power of these surveys.

  3. Mass loss rates of OB stars derived from infrared observations

    International Nuclear Information System (INIS)

    Tanzi, E.G.; Tarenghi, M.; Panagia, N.

    1981-01-01

    In this paper the authors report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types. 37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined independently by various authors for stars in common. Their data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity. (Auth.)

  4. The Mass-Ratio Distribution of Visual Binary Stars

    NARCIS (Netherlands)

    Hogeveen, S.J.

    1990-01-01

    The selection effects that govern the observations of Visual Binary Stars are in- vestigated, in order to obtain a realistic statistical distribution of the mass-ratio q = Msec=Mprim. To this end a numerical simulation programme has been developed, which `generates' binary stars and `looks' at

  5. The luminosity and mass functions of the Pleiades: low-mass stars and brown dwarfs

    International Nuclear Information System (INIS)

    Hambly, N.C.; Jameson, R.F.

    1991-01-01

    COSMOS measurements of R and I Schmidt plates are used to determine the luminosity function and hence mass function of the Pleiades open cluster. Star counts are made in the cluster and the field star contribution, measured outside the cluster, is subtracted. A lower limit of 30 brown dwarfs is found; the mass function is flat at the lowest masses. (author)

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

    Science.gov (United States)

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

    2008-10-01

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

  7. Star Formation in Taurus: Preliminary Results from 2MASS

    Science.gov (United States)

    Beichman, C. A.; Jarrett, T.

    1993-01-01

    Data with the 2MASS prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from IRAS observations to contain a number of very young solar type stars.

  8. Tidal disruption of white dwarfs by intermediate mass black holes

    Directory of Open Access Journals (Sweden)

    Bode T.

    2012-12-01

    Full Text Available Modeling ultra-close encounters between a white dwarf and a spinning, intermediate mass black hole requires a full general relativistic treatment of gravity. This paper summarizes results from such a study. Our results show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole spin. On the other hand, the late-time accretion onto the black hole follows the same decay, Ṁ ∝  t−5/3, estimated from Newtonian gravity disruption studies. The spectrum of the fallback material peaks in the soft X-rays and sustains Eddington luminosity for 1–3 yrs after the disruption. The orientation of the black hole spin has also a profound effect on how the outflowing debris obscures the central region. The disruption produces a burst of gravitational radiation with characteristic frequencies of ∼3.2 Hz and strain amplitudes of ∼10−18 for galactic intermediate mass black holes.

  9. The early evolution of stars and planets with varying mass

    International Nuclear Information System (INIS)

    Bhattacharjee, S.K.

    1980-09-01

    In this thesis some aspects of stellar and planetary evolution with varying mass are examined. It is divided into two sections. The first section deals with the evolution of stars in the pre-main-sequence phase with mass accretion while in the second section we discuss the spin angular momentum of the planets with mass loss. (author)

  10. Evolution of the Black Hole Mass Function in Star Clusters from Multiple Mergers

    Science.gov (United States)

    Christian, Pierre; Mocz, Philip; Loeb, Abraham

    2018-05-01

    We investigate the effects of black hole (BH) mergers in star clusters on the black hole mass function (BHMF). As BHs are not produced in pair-instability supernovae, it is suggested that there is a dearth of high-mass stellar BHs. This dearth generates a gap in the upper end of the BHMF. Meanwhile, parameter fitting of X-ray binaries suggests the existence of a gap in the mass function under 5 solar masses. We show, through evolving a coagulation equation, that BH mergers can appreciably fill the upper mass gap, and that the lower mass gap generates potentially observable features at larger mass scales. We also explore the importance of ejections in such systems and whether dynamical clusters can be formation sites of intermediate-mass BH seeds.

  11. 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.

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

    Directory of Open Access Journals (Sweden)

    Lee Chang-Hwan

    2018-01-01

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

  13. New Light on Dark Stars Red Dwarfs, Low-Mass Stars, Brown Dwarfs

    CERN Document Server

    Reid, I. Neill

    2005-01-01

    There has been very considerable progress in research into low-mass stars, brown dwarfs and extrasolar planets during the past few years, particularly since the fist edtion of this book was published in 2000. In this new edtion the authors present a comprehensive review of both the astrophysical nature of individual red dwarf and brown dwarf stars and their collective statistical properties as an important Galactic stellar population. Chapters dealing with the observational properies of low-mass dwarfs, the stellar mass function and extrasolar planets have been completely revised. Other chapters have been significantly revised and updated as appropriate, including important new material on observational techniques, stellar acivity, the Galactic halo and field star surveys. The authors detail the many discoveries of new brown dwarfs and extrasolar planets made since publication of the first edition of the book and provide a state-of-the-art review of our current knowledge of very low-mass stars, brown dwarfs a...

  14. Rotating neutron stars with exotic cores: masses, radii, stability

    Energy Technology Data Exchange (ETDEWEB)

    Haensel, P.; Bejger, M.; Fortin, M.; Zdunik, L. [Polish Academy of Sciences, N. Copernicus Astronomical Center, Warszawa (Poland)

    2016-03-15

    A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716Hz) and the maximum measured mass (2M {sub CircleDot}). The present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered. (orig.)

  15. On the Maximum Mass of Accreting Primordial Supermassive Stars

    Energy Technology Data Exchange (ETDEWEB)

    Woods, T. E.; Heger, Alexander [Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800 (Australia); Whalen, Daniel J. [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth PO1 3FX (United Kingdom); Haemmerlé, Lionel; Klessen, Ralf S. [Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische. Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

    2017-06-10

    Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z ∼ 6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution, and collapse of accreting, non-rotating supermassive stars under accretion rates of 0.01–10 M {sub ⊙} yr{sup −1} using the stellar evolution code Kepler . Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000–330,000 M {sub ⊙} for accretion rates of 0.1–10 M {sub ⊙} yr{sup −1}, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.

  16. Calculations of mass and moment of inertia for neutron stars

    International Nuclear Information System (INIS)

    Moelnvik, T.; Oestgaard, E.

    1985-01-01

    Masses and moments of inertia for slowly-rotating neutron stars are calculated from the Tolman-Oppenheimer-Volkoff equations and various equations of state for neutron-star matter. We have also obtained pressure and density as a function of the distance from the centre of the star. Generally, two different equations of state are applied for particle densities n>0.47 fm -3 and n -3 . The maximum mass is, in our calculations for all equations of state except for the unrealistic non-relativistic ideal Fermi gas, given by 1.50 Msub(sun) 44 gxcm 2 45 gxcm 2 , which also seem to agree very well with 'experimental results'. The radius of the star corresponding to maximum mass and maximum moment of inertia is given by 8.2 km< R<10.0 km, but a smaller central density rhosub(c) will give a larger radius. (orig.)

  17. Star Masses and Star-Planet Distances for Earth-like Habitability.

    Science.gov (United States)

    Waltham, David

    2017-01-01

    This paper presents statistical estimates for the location and duration of habitable zones (HZs) around stars of different mass. The approach is based upon the assumption that Earth's location, and the Sun's mass, should not be highly atypical of inhabited planets. The results support climate-model-based estimates for the location of the Sun's HZ except models giving a present-day outer-edge beyond 1.64 AU. The statistical approach also demonstrates that there is a habitability issue for stars smaller than 0.65 solar masses since, otherwise, Earth would be an extremely atypical inhabited world. It is difficult to remove this anomaly using the assumption that poor habitability of planets orbiting low-mass stars results from unfavorable radiation regimes either before, or after, their stars enter the main sequence. However, the anomaly is well explained if poor habitability results from tidal locking of planets in the HZs of small stars. The expected host-star mass for planets with intelligent life then has a 95% confidence range of 0.78 M ⊙ planets with at least simple life is 0.57 M ⊙  < M < 1.64 M ⊙ . Key Words: Habitability-Habitable zone-Anthropic-Red dwarfs-Initial mass function. Astrobiology 17, 61-77.

  18. AN INCREASE IN THE MASS OF PLANETARY SYSTEMS AROUND LOWER-MASS STARS

    Energy Technology Data Exchange (ETDEWEB)

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel, E-mail: mulders@lpl.arizona.edu [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States)

    2015-12-01

    Trends in the planet population with host star mass provide an avenue to constrain planet formation theories. We derive the planet radius distribution function for Kepler stars of different spectral types, sampling a range in host star masses. We find that M dwarf stars have 3.5 times more small planets (1.0–2.8 R{sub ⨁}) than main-sequence FGK stars, but two times fewer Neptune-sized and larger (>2.8 R{sub ⨁}) planets. We find no systematic trend in the planet size distribution between spectral types F, G, and K to explain the increasing occurrence rates. Taking into account the mass–radius relationship and heavy-element mass of observed exoplanets, and assuming those are independent of spectral type, we derive the inventory of the heavy-element mass locked up in exoplanets at short orbits. The overall higher planet occurrence rates around M stars are not consistent with the redistribution of the same mass into more, smaller planets. At the orbital periods and planet radii where Kepler observations are complete for all spectral types, the average heavy-element mass locked up in exoplanets increases roughly inversely with stellar mass from 4 M{sub ⨁} in F stars to 5 M{sub ⨁} in G and K stars to 7 M{sub ⨁} in M stars. This trend stands in stark contrast with observed protoplanetary disk masses that decrease toward lower mass stars, and provides a challenge for current planet formation models. Neither models of in situ formation nor migration of fully formed planets are consistent with these results. Instead, these results are indicative of large-scale inward migration of planetary building blocks—either through type-I migration or radial drift of dust grains—that is more efficient for lower mass stars, but does not result in significantly larger or smaller planets.

  19. AN INCREASE IN THE MASS OF PLANETARY SYSTEMS AROUND LOWER-MASS STARS

    International Nuclear Information System (INIS)

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

    2015-01-01

    Trends in the planet population with host star mass provide an avenue to constrain planet formation theories. We derive the planet radius distribution function for Kepler stars of different spectral types, sampling a range in host star masses. We find that M dwarf stars have 3.5 times more small planets (1.0–2.8 R ⨁ ) than main-sequence FGK stars, but two times fewer Neptune-sized and larger (>2.8 R ⨁ ) planets. We find no systematic trend in the planet size distribution between spectral types F, G, and K to explain the increasing occurrence rates. Taking into account the mass–radius relationship and heavy-element mass of observed exoplanets, and assuming those are independent of spectral type, we derive the inventory of the heavy-element mass locked up in exoplanets at short orbits. The overall higher planet occurrence rates around M stars are not consistent with the redistribution of the same mass into more, smaller planets. At the orbital periods and planet radii where Kepler observations are complete for all spectral types, the average heavy-element mass locked up in exoplanets increases roughly inversely with stellar mass from 4 M ⨁ in F stars to 5 M ⨁ in G and K stars to 7 M ⨁ in M stars. This trend stands in stark contrast with observed protoplanetary disk masses that decrease toward lower mass stars, and provides a challenge for current planet formation models. Neither models of in situ formation nor migration of fully formed planets are consistent with these results. Instead, these results are indicative of large-scale inward migration of planetary building blocks—either through type-I migration or radial drift of dust grains—that is more efficient for lower mass stars, but does not result in significantly larger or smaller planets

  20. Fundmental Parameters of Low-Mass Stars, Brown Dwarfs, and Planets

    Science.gov (United States)

    Montet, Benjamin; Johnson, John A.; Bowler, Brendan; Shkolnik, Evgenya

    2016-01-01

    Despite advances in evolutionary models of low-mass stars and brown dwarfs, these models remain poorly constrained by observations. In order to test these predictions directly, masses of individual stars must be measured and combined with broadband photometry and medium-resolution spectroscopy to probe stellar atmospheres. I will present results from an astrometric and spectroscopic survey of low-mass pre-main sequence binary stars to measure individual dynamical masses and compare to model predictions. This is the first systematic test of a large number of stellar systems of intermediate age between young star-forming regions and old field stars. Stars in our sample are members of the Tuc-Hor, AB Doradus, and beta Pictoris moving groups, the last of which includes GJ 3305 AB, the wide binary companion to the imaged exoplanet host 51 Eri. I will also present results of Spitzer observations of secondary eclipses of LHS 6343 C, a T dwarf transiting one member of an M+M binary in the Kepler field. By combining these data with Kepler photometry and radial velocity observations, we can measure the luminosity, mass, and radius of the brown dwarf. This is the first non-inflated brown dwarf for which all three of these parameters have been measured, providing the first benchmark to test model predictions of the masses and radii of field T dwarfs. I will discuss these results in the context of K2 and TESS, which will find additional benchmark transiting brown dwarfs over the course of their missions, including a description of the first planet catalog developed from K2 data and a program to search for transiting planets around mid-M dwarfs.

  1. Evolution of Mass Functions of Coeval Stars through Wind Mass Loss and Binary Interactions

    NARCIS (Netherlands)

    Schneider, F.R.N.; Izzard, R.G.; Langer, N.; de Mink, S.E.

    2015-01-01

    Accurate determinations of stellar mass functions and ages of stellar populations are crucial to much of astrophysics. We analyze the evolution of stellar mass functions of coeval main-sequence stars, including all relevant aspects of single and binary star evolution. We show that the slope of the

  2. THE INTERMEDIATE NEUTRON-CAPTURE PROCESS AND CARBON-ENHANCED METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Hampel, Melanie [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); Lugaro, Maria [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest (Hungary); Meyer, Bradley S., E-mail: mhampel@lsw.uni-heidelberg.de [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States)

    2016-11-10

    Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium, respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP- s / r stars, which show both Ba and Eu enrichment, are particularly puzzling, since the s and the r processes require neutron densities that are more than ten orders of magnitude apart and, hence, are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP- s / r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterized by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from 10{sup 7}–10{sup 15} cm{sup -3}. With respect to the classical s process resulting from neutron densities on the lowest side of this range, neutron densities on the highest side result in abundance patterns, which show an increased production of heavy s -process and r -process elements, but similar abundances of the light s -process elements. Such high values of n may occur in the thermal pulses of asymptotic giant branch stars due to proton ingestion episodes. Comparison to the surface abundances of 20 CEMP- s / r stars shows that our modeled i -process abundances successfully reproduce observed abundance patterns, which could not be previously explained by s -process nucleosynthesis. Because the i -process models fit the abundances of CEMP- s / r stars so well, we propose that this class should be renamed as CEMP- i .

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

    Directory of Open Access Journals (Sweden)

    Salaris M.

    2013-03-01

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

  4. FEEDBACK EFFECTS ON LOW-MASS STAR FORMATION

    International Nuclear Information System (INIS)

    Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.; Fisher, Robert T.

    2012-01-01

    Protostellar feedback, both radiation and bipolar outflows, dramatically affects the fragmentation and mass accretion from star-forming cores. We use ORION, an adaptive mesh refinement gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud in the presence of protostellar feedback. We present results of the first simulations of a star-forming cluster that include both radiative transfer and protostellar outflows. We run four simulations to isolate the individual effects of radiation feedback and outflow feedback as well as the combination of the two. We find that outflows reduce protostellar masses and accretion rates each by a factor of three and therefore reduce protostellar luminosities by an order of magnitude. This means that, while radiation feedback suppresses fragmentation, outflows render protostellar radiation largely irrelevant for low-mass star formation above a mass scale of 0.05 M ☉ . We find initial fragmentation of our cloud at half the global Jeans length, around 0.1 pc. With insufficient protostellar radiation to stop it, these 0.1 pc cores fragment repeatedly, forming typically 10 stars each. The accretion rate in these stars scales with mass as predicted from core accretion models that include both thermal and turbulent motions; the accretion rate does not appear to be consistent with either competitive accretion or accretion from an isothermal sphere. We find that protostellar outflows do not significantly affect the overall cloud dynamics, in the absence of magnetic fields, due to their small opening angles and poor coupling to the dense gas. The outflows reduce the mass from the cores by 2/3, giving a core to star efficiency, ε core ≅ 1/3. The simulations are also able to reproduce many observation of local star-forming regions. Our simulation with radiation and outflows reproduces the observed protostellar luminosity function. All of the simulations can reproduce observed core mass

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

    NARCIS (Netherlands)

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

    2014-01-01

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

  6. Modeling The GRB Host Galaxy Mass Distribution: Are GRBs Unbiased Tracers of Star Formation?

    Energy Technology Data Exchange (ETDEWEB)

    Kocevski, Daniel; /KIPAC, Menlo Park; West, Andrew A.; /UC, Berkeley, Astron. Dept. /MIT, MKI; Modjaz, Maryam; /UC, Berkeley, Astron. Dept.

    2009-08-03

    We model the mass distribution of long gamma-ray burst (GRB) host galaxies given recent results suggesting that GRBs occur in low metallicity environments. By utilizing measurements of the redshift evolution of the mass-metallicity (M-Z) relationship for galaxies, along with a sharp host metallicity cut-off suggested by Modjaz and collaborators, we estimate an upper limit on the stellar mass of a galaxy that can efficiently produce a GRB as a function of redshift. By employing consistent abundance indicators, we find that sub-solar metallicity cut-offs effectively limit GRBs to low stellar mass spirals and dwarf galaxies at low redshift. At higher redshifts, as the average metallicity of galaxies in the Universe falls, the mass range of galaxies capable of hosting a GRB broadens, with an upper bound approaching the mass of even the largest spiral galaxies. We compare these predicted limits to the growing number of published GRB host masses and find that extremely low metallicity cut-offs of 0.1 to 0.5 Z{sub {circle_dot}} are effectively ruled out by a large number of intermediate mass galaxies at low redshift. A mass function that includes a smooth decrease in the efficiency of producing GRBs in galaxies of metallicity above 12+log(O/H){sub KK04} = 8.7 can, however, accommodate a majority of the measured host galaxy masses. We find that at z {approx} 1, the peak in the observed GRB host mass distribution is inconsistent with the expected peak in the mass of galaxies harboring most of the star formation. This suggests that GRBs are metallicity biased tracers of star formation at low and intermediate redshifts, although our model predicts that this bias should disappear at higher redshifts due to the evolving metallicity content of the universe.

  7. MODELING THE GRB HOST GALAXY MASS DISTRIBUTION: ARE GRBs UNBIASED TRACERS OF STAR FORMATION?

    International Nuclear Information System (INIS)

    Kocevski, Daniel; West, Andrew A.; Modjaz, Maryam

    2009-01-01

    We model the mass distribution of long gamma-ray burst (GRB) host galaxies given recent results suggesting that GRBs occur in low-metallicity environments. By utilizing measurements of the redshift evolution of the mass-metallicity relationship for galaxies, along with a sharp host metallicity cutoff suggested by Modjaz and collaborators, we estimate an upper limit on the stellar mass of a galaxy that can efficiently produce a GRB as a function of redshift. By employing consistent abundance indicators, we find that subsolar metallicity cutoffs effectively limit GRBs to low-stellar mass spirals and dwarf galaxies at low redshift. At higher redshifts, as the average metallicity of galaxies in the Universe falls, the mass range of galaxies capable of hosting a GRB broadens, with an upper bound approaching the mass of even the largest spiral galaxies. We compare these predicted limits to the growing number of published GRB host masses and find that extremely low-metallicity cutoffs of 0.1 to 0.5 Z sun are effectively ruled out by a large number of intermediate mass galaxies at low redshift. A mass function that includes a smooth decrease in the efficiency of producing GRBs in galaxies of metallicity above 12+log(O/H) KK04 = 8.7 can, however, accommodate a majority of the measured host galaxy masses. We find that at z ∼ 1, the peak in the observed GRB host mass distribution is inconsistent with the expected peak in the mass of galaxies harboring most of the star formation. This suggests that GRBs are metallicity-biased tracers of star formation at low and intermediate redshifts, although our model predicts that this bias should disappear at higher redshifts due to the evolving metallicity content of the universe.

  8. Formation of primordial supermassive stars by rapid mass accretion

    Energy Technology Data Exchange (ETDEWEB)

    Hosokawa, Takashi; Yoshida, Naoki [Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033 (Japan); Yorke, Harold W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Inayoshi, Kohei; Omukai, Kazuyuki, E-mail: takashi.hosokawa@phys.s.u-tokyo.ac.jp, E-mail: hosokwtk@gmail.com [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2013-12-01

    Supermassive stars (SMSs) forming via very rapid mass accretion ( M-dot {sub ∗}≳0.1 M{sub ⊙} yr{sup −1}) could be precursors of supermassive black holes observed beyond a redshift of about six. Extending our previous work, here we study the evolution of primordial stars growing under such rapid mass accretion until the stellar mass reaches 10{sup 4–5} M {sub ☉}. Our stellar evolution calculations show that a star becomes supermassive while passing through the 'supergiant protostar' stage, whereby the star has a very bloated envelope and a contracting inner core. The stellar radius increases monotonically with the stellar mass until ≅ 100 AU for M {sub *} ≳ 10{sup 4} M {sub ☉}, after which the star begins to slowly contract. Because of the large radius, the effective temperature is always less than 10{sup 4} K during rapid accretion. The accreting material is thus almost completely transparent to the stellar radiation. Only for M {sub *} ≳ 10{sup 5} M {sub ☉} can stellar UV feedback operate and disturb the mass accretion flow. We also examine the pulsation stability of accreting SMSs, showing that the pulsation-driven mass loss does not prevent stellar mass growth. Observational signatures of bloated SMSs should be detectable with future observational facilities such as the James Webb Space Telescope. Our results predict that an inner core of the accreting SMS should suffer from the general relativistic instability soon after the stellar mass exceeds 10{sup 5} M {sub ☉}. An extremely massive black hole should form after the collapse of the inner core.

  9. Evolution of a 30 solar mass star: the interplay of nuclear burning and mass loss

    International Nuclear Information System (INIS)

    Falk, H.J.; Mitalas, R.

    1981-01-01

    Evolutionary tracks for a 30 solar mass star with various mass loss rates (MLR) were evolved to core He exhaustion. The 'overluminosity' of mass losing (ML) stars is explained in terms of the well known mass-luminosity (M-L) law. A critical ZAMS MLR above which mass loss leads to evolution to fainter luminosities is derived. Two tracks showed reversals in their direction of evolution across the HR diagram. These have been shown to be a consequence of mass loss dominating over the effects of the shell source. An analytic criterion for this condition has been derived. (Auth.)

  10. FORMALDEHYDE MASERS: EXCLUSIVE TRACERS OF HIGH-MASS STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Araya, E. D.; Brown, J. E. [Western Illinois University, Physics Department, 1 University Circle, Macomb, IL 61455 (United States); Olmi, L. [INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Ortiz, J. Morales [University of Puerto Rico, Río Piedras Campus, Physical Sciences Department, P.O. Box 23323, San Juan, PR 00931 (United States); Hofner, P.; Creech-Eakman, M. J. [New Mexico Institute of Mining and Technology, Physics Department, 801 Leroy Place, Socorro, NM 87801 (United States); Kurtz, S. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, 58089 Morelia, Michoacán (Mexico); Linz, H. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)

    2015-11-15

    The detection of four formaldehyde (H{sub 2}CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H{sub 2}CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H{sub 2}CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H{sub 2}CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H{sub 2}CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH{sub 3}OH masers. We detected a new 6 cm H{sub 2}CO emission line in G32.74−0.07. This work provides further evidence that supports an exclusive association between H{sub 2}CO masers and young regions of high-mass star formation. Furthermore, we detected H{sub 2}CO absorption toward all Hi-GAL sources, and toward 24 low-mass star-forming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH{sub 3}OH (5005 MHz), and CH{sub 2}NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.

  11. Slope of the mass function of low-mass stars

    International Nuclear Information System (INIS)

    Malkov, O.Yu.

    1987-01-01

    It is shown that the modern method of obtaining the initial mass function contains a number of a uncertainties that can have a significant effect on the slope of the function in the low-mass section (m < m**). The influence of changes of the mass-luminosity relation, the scale of bolometric corrections, and the luminosity function on the form of the mass function is considered. The effect of photometrically unresolved binaries is also discussed. Some quantitative estimates are made, and it is shown that the slope of the initial mass function in the low-mass section can vary in wide ranges

  12. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    International Nuclear Information System (INIS)

    Harwit, Martin; Brisbin, Drew

    2015-01-01

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10 9 to 6 × 10 10 M ☉ . This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established

  13. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    Energy Technology Data Exchange (ETDEWEB)

    Harwit, Martin; Brisbin, Drew, E-mail: harwit@verizon.net [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)

    2015-02-20

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10{sup 9} to 6 × 10{sup 10} M {sub ☉}. This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established.

  14. Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and δ Scuti stars

    Directory of Open Access Journals (Sweden)

    Arias J.P.Sánchez

    2017-01-01

    Full Text Available We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification.

  15. Age determination of 15 old to intermediate-age small Magellanic cloud star clusters

    International Nuclear Information System (INIS)

    Parisi, M. C.; Clariá, J. J.; Piatti, A. E.; Geisler, D.; Leiton, R.; Carraro, G.; Costa, E.; Grocholski, A. J.; Sarajedini, A.

    2014-01-01

    We present color-magnitude diagrams in the V and I bands for 15 star clusters in the Small Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT, Chile). We selected these clusters from our previous work, wherein we derived cluster radial velocities and metallicities from calcium II infrared triplet (CaT) spectra also taken with the VLT. We discovered that the ages of six of our clusters have been appreciably underestimated by previous studies, which used comparatively small telescopes, graphically illustrating the need for large apertures to obtain reliable ages of old and intermediate-age SMC star clusters. In particular, three of these clusters, L4, L6, and L110, turn out to be among the oldest SMC clusters known, with ages of 7.9 ± 1.1, 8.7 ± 1.2, and 7.6 ± 1.0 Gyr, respectively, helping to fill a possible 'SMC cluster age gap'. Using the current ages and metallicities from Parisi et al., we analyze the age distribution, age gradient, and age-metallicity relation (AMR) of a sample of SMC clusters measured homogeneously. There is a suggestion of bimodality in the age distribution but it does not show a constant slope for the first 4 Gyr, and we find no evidence for an age gradient. Due to the improved ages of our cluster sample, we find that our AMR is now better represented in the intermediate/old period than we had derived in Parisi et al., where we simply took ages available in the literature. Additionally, clusters younger than ∼4 Gyr now show better agreement with the bursting model of Pagel and Tautvaišienė, but we confirm that this model is not a good representation of the AMR during the intermediate/old period. A more complicated model is needed to explain the SMC chemical evolution in that period.

  16. The Mass-dependent Star Formation Histories of Disk Galaxies: Infall Model Versus Observations

    Science.gov (United States)

    Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.

    2010-10-01

    We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time tp . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M *, the model adopting a late infall-peak time tp results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we "construct" a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time tp and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M * ~ M * at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.

  17. The role of rotation in the evolution of massive stars losing mass

    International Nuclear Information System (INIS)

    Sreenivasan, S.R.; Wilson, W.J.F.

    1979-01-01

    The role of differential and solid body rotation in the evolution of massive stars undergoing mass loss is discussed. The implications for Of, WR, β Cephei stars and shell stars are brought out. (Auth.)

  18. Accreting Millisecond Pulsars: Neutron Star Masses and Radii

    Science.gov (United States)

    Strohmayer, Tod

    2004-01-01

    High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

  19. Carcass mass gains of steers grazing star grass, with different ...

    African Journals Online (AJOL)

    Carcass mass gains of steers grazing dryland Cynodon aethiopicus cv. No. 2 Star grass pastures during the growing season were determined for each of 16 treatments comprising four levels of nitrogen fertilisation in combination with four overlapping sets of stocking rates. The treatments were repeated over four growing ...

  20. High-mass stars in Milky Way clusters

    Science.gov (United States)

    Negueruela, Ignacio

    2017-11-01

    Young open clusters are our laboratories for studying high-mass star formation and evolution. Unfortunately, the information that they provide is difficult to interpret, and sometimes contradictory. In this contribution, I present a few examples of the uncertainties that we face when confronting observations with theoretical models and our own assumptions.

  1. 30 Doradus: The Low-Mass Stars

    Science.gov (United States)

    Zinnecker, H.; Brandl, B.; Brandner, W.; Moneti, A.; Hunter, D.

    We have obtained HST/NICMOS H-band images of the central 1'x1' field around the R136 starburst cluster in the 30 Doradus HII region, in an attempt to reveal the presence (or absence) of a low-mass stellar population (M VIH 3-colour image of the central 30" x 30" area. The result clearly shows unexpected patches of extinction, with one patch only about 5" from the cluster core.

  2. Observations of low mass stars in clusters: some constraints and puzzles for stellar evolution theory

    International Nuclear Information System (INIS)

    Cannon, R.D.

    1984-01-01

    The author attempts to: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars; and (ii) point out some problem areas where observations and theory do not seem to agree very well. He concentrates on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase are considered. (Auth.)

  3. AGE DETERMINATION OF SIX INTERMEDIATE-AGE SMALL MAGELLANIC CLOUD STAR CLUSTERS WITH HST/ACS

    International Nuclear Information System (INIS)

    Glatt, Katharina; Kayser, Andrea; Grebel, Eva K.; Sabbi, Elena; Gallagher, John S. III; Harbeck, Daniel; Nota, Antonella; Sirianni, Marco; Clementini, Gisella; Tosi, Monica; Koch, Andreas; Da Costa, Gary

    2008-01-01

    We present a photometric analysis of the star clusters Lindsay 1, Kron 3, NGC 339, NGC 416, Lindsay 38, and NGC 419 in the Small Magellanic Cloud (SMC), observed with the Hubble Space Telescope Advanced Camera for Surveys (ACS) in the F555W and F814W filters. Our color-magnitude diagrams (CMDs) extend ∼3.5 mag deeper than the main-sequence turnoff points, deeper than any previous data. Cluster ages were derived using three different isochrone models: Padova, Teramo, and Dartmouth, which are all available in the ACS photometric system. Fitting observed ridgelines for each cluster, we provide a homogeneous and unique set of low-metallicity, single-age fiducial isochrones. The cluster CMDs are best approximated by the Dartmouth isochrones for all clusters, except for NGC 419 where the Padova isochrones provided the best fit. Using Dartmouth isochrones we derive ages of 7.5 ± 0.5 Gyr (Lindsay 1), 6.5 ± 0.5 Gyr (Kron 3), 6 ± 0.5 Gyr (NGC 339), 6 ± 0.5 Gyr (NGC 416), and 6.5 ± 0.5 Gyr (Lindsay 38). The CMD of NGC 419 shows several main-sequence turnoffs, which belong to the cluster and to the SMC field. We thus derive an age range of 1.2-1.6 Gyr for NGC 419. We confirm that the SMC contains several intermediate-age populous star clusters with ages unlike those of the Large Magellanic Cloud and the Milky Way. Interestingly, our intermediate-age star clusters have a metallicity spread of ∼0.6 dex, which demonstrates that the SMC does not have a smooth, monotonic age-metallicity relation. We find an indication for centrally-concentrated blue straggler star candidates in NGC 416, while these are not present for the other clusters. Using the red clump magnitudes, we find that the closest cluster, NGC 419 (∼50 kpc), and the farthest cluster, Lindsay 38 (∼67 kpc), have a relative distance of ∼17 kpc, which confirms the large depth of the SMC. The three oldest SMC clusters (NGC 121, Lindsay 1, and Kron 3) lie in the northwestern part of the SMC, while the youngest

  4. Maximum Mass of Hybrid Stars in the Quark Bag Model

    Science.gov (United States)

    Alaverdyan, G. B.; Vartanyan, Yu. L.

    2017-12-01

    The effect of model parameters in the equation of state for quark matter on the magnitude of the maximum mass of hybrid stars is examined. Quark matter is described in terms of the extended MIT bag model including corrections for one-gluon exchange. For nucleon matter in the range of densities corresponding to the phase transition, a relativistic equation of state is used that is calculated with two-particle correlations taken into account based on using the Bonn meson-exchange potential. The Maxwell construction is used to calculate the characteristics of the first order phase transition and it is shown that for a fixed value of the strong interaction constant αs, the baryon concentrations of the coexisting phases grow monotonically as the bag constant B increases. It is shown that for a fixed value of the strong interaction constant αs, the maximum mass of a hybrid star increases as the bag constant B decreases. For a given value of the bag parameter B, the maximum mass rises as the strong interaction constant αs increases. It is shown that the configurations of hybrid stars with maximum masses equal to or exceeding the mass of the currently known most massive pulsar are possible for values of the strong interaction constant αs > 0.6 and sufficiently low values of the bag constant.

  5. Ages of evolved low mass stars: Central stars of planetary nebulae and white dwarfs

    Directory of Open Access Journals (Sweden)

    Costa R.D.D.

    2013-03-01

    Full Text Available We have developed several methods to estimate the ages of central stars of planetary nebulae (CSPN, which are based either on observed nebular properties or on data from the stars themselves. Our goal is to derive the age distribution of these stars and compare the results with empirical distributions for CSPN and white dwarfs. We have initially developed three methods based on nebular abundances, using (i an age-metallicity relation which is also a function of the galactocentric distance; (ii an age-metallicity relation obtained for the galactic disk, and (iii the central star masses derived from the observed nitrogen abundances. In this work we present two new, more accurate methods, which are based on kinematic properties: (I in this method, the expected rotation velocities of the nebulae around the galactic centre at their galactocentric distances are compared with the predicted values for the galactic rotation curve, and the differences are attributed to the different ages of the evolved stars; (II we determine directly the U, V, W, velocity components of the stars, as well as the velocity dispersions, and use the dispersion-age relation by the Geneva-Copenhagen survey. These methods were applied to two large samples of galactic CSPN. We conclude that most CSPN in the galactic disk have ages under 5 Gyr, and that the age distribution is peaked around 1 to 3 Gyr.

  6. Production of intermediate-mass dileptons in relativistic heavy ion collisions

    International Nuclear Information System (INIS)

    Kvasnikova, Ioulia; Gale, Charles; Kumar Srivastava, Dinesh

    2002-01-01

    The production of intermediate-mass dileptons in ultrarelativistic nuclear collisions at SPS energies is studied. The acceptance and detector resolution inherent to measurements by the NA50 experimental collaboration are accurately modeled. The measured centrality dependence of the intermediate mass lepton pair excess is also addressed

  7. A Tidal Disruption Event in a Nearby Galaxy Hosting an Intermediate Mass Black Hole

    Science.gov (United States)

    Donato, D; Cenko, S. B.; Covino, S.; Troja, E.; Pursimo, T.; Cheung, C. C.; Fox, O.; Kutyrev, A.; Campana, S.; Fugazza, D.; hide

    2014-01-01

    We report the serendipitous discovery of a bright point source flare in the Abell cluster A1795 with archival EUVE and Chandra observations. Assuming the EUVE emission is associated with the Chandra source, the X-ray 0.5-7 kiloelectronvolt flux declined by a factor of approximately 2300 over a time span of 6 years, following a power-law decay with index approximately equal to 2.44 plus or minus 0.40. The Chandra data alone vary by a factor of approximately 20. The spectrum is well fit by a blackbody with a constant temperature of kiloteslas approximately equal to 0.09 kiloelectronvolts (approximately equal to 10 (sup 6) Kelvin). The flare is spatially coincident with the nuclear region of a faint, inactive galaxy with a photometric redshift consistent at the 1 sigma level with the cluster (redshift = 0.062476).We argue that these properties are indicative of a tidal disruption of a star by a black hole (BH) with log(M (sub BH) / M (sub 1 solar mass)) approximately equal to 5.5 plus or minus 0.5. If so, such a discovery indicates that tidal disruption flares may be used to probe BHs in the intermediate mass range, which are very difficult to study by other means.

  8. Kinematic and spatial distributions of barium stars - are the barium stars and Am stars related?

    International Nuclear Information System (INIS)

    Hakkila, J.

    1989-01-01

    The possibility of an evolutionary link between Am stars and barium stars is considered, and an examination of previous data suggests that barium star precursors are main-sequence stars of intermediate mass, are most likely A and/or F dwarfs, and are intermediate-mass binaries with close to intermediate orbital separations. The possible role of mass transfer in the later development of Am systems is explored. Mass transfer and loss from systems with a range of masses and orbital separations may explain such statistical peculiarities of barium stars as the large dispersion in absolute magnitude, the large range of elemental abundances from star to star, and the small number of stars with large peculiar velocities. 93 refs

  9. An unstable truth: how massive stars get their mass

    Science.gov (United States)

    Rosen, Anna L.; Krumholz, Mark R.; McKee, Christopher F.; Klein, Richard I.

    2016-12-01

    The pressure exerted by massive stars' radiation fields is an important mechanism regulating their formation. Detailed simulation of massive star formation therefore requires an accurate treatment of radiation. However, all published simulations have either used a diffusion approximation of limited validity; have only been able to simulate a single star fixed in space, thereby suppressing potentially important instabilities; or did not provide adequate resolution at locations where instabilities may develop. To remedy this, we have developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform 3D radiation-hydrodynamic simulations of the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channelled to the stellar system via gravitational and Rayleigh-Taylor (RT) instabilities, in agreement with previous results using stars capable of moving, but in disagreement with methods where the star is held fixed or with simulations that do not adequately resolve the development of RT instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of instability, but does not suppress it entirely provided the edges of radiation-dominated bubbles are adequately resolved. Instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. Our results suggest that RT features should be present around accreting massive stars throughout their formation.

  10. A super-Earth transiting a nearby low-mass star.

    Science.gov (United States)

    Charbonneau, David; Berta, Zachory K; Irwin, Jonathan; Burke, Christopher J; Nutzman, Philip; Buchhave, Lars A; Lovis, Christophe; Bonfils, Xavier; Latham, David W; Udry, Stéphane; Murray-Clay, Ruth A; Holman, Matthew J; Falco, Emilio E; Winn, Joshua N; Queloz, Didier; Pepe, Francesco; Mayor, Michel; Delfosse, Xavier; Forveille, Thierry

    2009-12-17

    A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. Because such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-star radius ratio is relatively large, nearby small stars have been surveyed intensively. Doppler studies and microlensing have uncovered a population of planets with minimum masses of 1.9-10 times the Earth's mass (M[symbol:see text]), called super-Earths. The first constraint on the bulk composition of this novel class of planets was afforded by CoRoT-7b (refs 8, 9), but the distance and size of its star preclude atmospheric studies in the foreseeable future. Here we report observations of the transiting planet GJ 1214b, which has a mass of 6.55M[symbol:see text]), and a radius 2.68 times Earth's radius (R[symbol:see text]), indicating that it is intermediate in stature between Earth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history. The star is small and only 13 parsecs away, so the planetary atmosphere is amenable to study with current observatories.

  11. Converging on the Initial Mass Function of Stars

    International Nuclear Information System (INIS)

    Federrath, Christoph; Krumholz, Mark; Hopkins, Philip F.

    2017-01-01

    Understanding the origin of stellar masses—the initial mass function (IMF)— remains one of the most challenging problems in astrophysics. The IMF is a key ingredient for simulations of galaxy formation and evolution, and is used to calibrate star formation relations in extra-galactic observations. Modeling the IMF directly in hydrodynamical simulations has been attempted in several previous studies, but the most important processes that control the IMF remain poorly understood. This is because predicting the IMF from direct hydrodynamical simulations involves complex physics such as turbulence, magnetic fields, radiation feedback and mechanical feedback, all of which are difficult to model and the methods used have limitations in terms of accuracy and computational efficiency. Moreover, a physical interpretation of the simulated IMFs requires a numerically converged solution at high resolution, which has so far not been convincingly demonstrated. Here we present a resolution study of star cluster formation aimed at producing a converged IMF. We compare a set of magnetohydrodynamical (MHD) adaptive-mesh-refinement simulations with three different implementations of the thermodynamics of the gas: 1) with an isothermal equation of state (EOS), 2) with a polytropic EOS, and 3) with a simple stellar heating feedback model. We show that in the simulations with an isothermal or polytropic EOS, the number of stars and their mass distributions depend on the numerical resolution. By contrast, the simulations that employ the simple radiative feedback module demonstrate convergence in the number of stars formed and in their IMFs. (paper)

  12. Gravitational Waves and Intermediate-mass Black Hole Retention in Globular Clusters

    Science.gov (United States)

    Fragione, Giacomo; Ginsburg, Idan; Kocsis, Bence

    2018-04-01

    The recent discovery of gravitational waves (GWs) has opened new horizons for physics. Current and upcoming missions, such as LIGO, VIRGO, KAGRA, and LISA, promise to shed light on black holes of every size from stellar mass (SBH) sizes up to supermassive black holes. The intermediate-mass black hole (IMBH) family has not been detected beyond any reasonable doubt. Recent analyses suggest observational evidence for the presence of IMBHs in the centers of two Galactic globular clusters (GCs). In this paper, we investigate the possibility that GCs were born with a central IMBH, which undergoes repeated merger events with SBHs in the cluster core. By means of a semi-analytical method, we follow the evolution of the primordial cluster population in the galactic potential and the mergers of the binary IMBH-SBH systems. Our models predict ≈1000 IMBHs within 1 kpc from the galactic center and show that the IMBH-SBH merger rate density changes from { \\mathcal R }≈ 1000 Gpc‑3 yr‑1 beyond z ≈ 2 to { \\mathcal R }≈ 1{--}10 Gpc‑3 yr‑1 at z ≈ 0. The rates at low redshifts may be significantly higher if young massive star clusters host IMBHs. The merger rates are dominated by IMBHs with masses between 103 and 104 M ⊙. Currently, there are no LIGO/VIRGO upper limits for GW sources in this mass range, but our results show that at design sensitivity, these instruments will detect IMBH-SBH mergers in the coming years. LISA and the Einstein Telescope will be best suited to detect these events. The inspirals of IMBH-SBH systems may also generate an unresolved GW background.

  13. Intermediate coupling vibrational descriptions of odd mass gold isotopes

    CERN Document Server

    Vieu, C; Paar, V

    1976-01-01

    The theoretical analysis of /sup 193-195/Au levels is semi qualitatively performed in the frame of the intermediate coupling vibrational models of Kisslinger-Sorensen and Alaga. From the comparison between the experimental data and the corresponding predictions of the two models, conclusions are drawn on the influence of the clusters and broken pairs.

  14. Neutrino diffusion and mass ejection in protoneutron stars

    International Nuclear Information System (INIS)

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

    2010-01-01

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

  15. Study of the mass-luminosity in binary stars

    International Nuclear Information System (INIS)

    Gimenez, A.; Zamorano, J.

    1986-01-01

    The results of a study of the mass-luminosity relation for main-sequence stars are presented as obtained from the latest data provided by the analysis of eclipsing and visual binary systems. The derived numerical values are discussed in light of their practical use and possible parametrizations indicated by internal structure homologous models. Finally, the astrophysical significance of our results is evaluated and they are compared to available theoretical models. (author)

  16. Restrictions on the masses and coupling constants of excited intermediate bosons

    International Nuclear Information System (INIS)

    Kaidalov, A.B.; Nogteva, A.V.

    1985-01-01

    The properties of the intermediate bosons are discussed in the framework of composite models which include not only the W +- and Z 0 bosons but also their excited states with large masses. The influence of the excited states on the values of the masses of the W +- and Z 0 bosons is investigated. Restrictions on the masses and coupling constants of the excited intermediate bosons are obtained

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

    Science.gov (United States)

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

    2014-02-01

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

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-02-10

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

  20. 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

  1. A PRECISE MASS MEASUREMENT OF THE INTERMEDIATE-MASS BINARY PULSAR PSR J1802 - 2124

    International Nuclear Information System (INIS)

    Ferdman, R. D.; Cognard, I.; Desvignes, G.; Theureau, G.; Stairs, I. H.; Kramer, M.; McLaughlin, M. A.; Lorimer, D. R.; Nice, D. J.; Manchester, R. N.; Hobbs, G.; Lyne, A. G.; Faulkner, A.; Camilo, F.; Possenti, A.; Demorest, P. B.; Backer, D. C.

    2010-01-01

    PSR J1802 - 2124 is a 12.6 ms pulsar in a 16.8 hr binary orbit with a relatively massive white dwarf (WD) companion. These properties make it a member of the intermediate-mass class of binary pulsar (IMBP) systems. We have been timing this pulsar since its discovery in 2002. Concentrated observations at the Green Bank Telescope, augmented with data from the Parkes and Nancay observatories, have allowed us to determine the general relativistic Shapiro delay. This has yielded pulsar and WD mass measurements of 1.24 ± 0.11 M sun and 0.78 ± 0.04 M sun (68% confidence), respectively. The low mass of the pulsar, the high mass of the WD companion, the short orbital period, and the pulsar spin period may be explained by the system having gone through a common-envelope phase in its evolution. We argue that selection effects may contribute to the relatively small number of known IMBPs.

  2. Mass distribution and evolutionary scheme for central stars of planetary nebulae

    International Nuclear Information System (INIS)

    Heap, S.R.; Augensen, H.J.; Widener Univ., Chester, PA)

    1987-01-01

    IUE data and a distance measuring method that considered central stars in optically thick nebulae were used to examine mass distributions of planetary nebulae. Other data such as spectral type, spatial and kinematic characteristics, etc., were studied to derive relationships between population type and mass distribution. A central star mass range of at least 0.55 solar mass was obtained. Stars with masses of at least 0.64 solar mass, concentrated in the galactic disk, originated from 1.5 solar mass stars. Low mass nuclei originated in old disk or halo populations and evolved from 1.0 solar mass objects. A mass-loss parameter value of 1/3 was calculated for red giants, implying that white dwarfs evolve from stars of under 5 solar masses. Mass distributions around planetary nuclei were concluded to follow patterns associated with the individual mass. 75 references

  3. Washington photometry of 14 intermediate-age to old star clusters in the Small Magellanic Cloud

    Science.gov (United States)

    Piatti, Andrés E.; Clariá, Juan J.; Bica, Eduardo; Geisler, Doug; Ahumada, Andrea V.; Girardi, Léo

    2011-10-01

    We present CCD photometry in the Washington system C, T1 and T2 passbands down to T1˜ 23 in the fields of L3, L28, HW 66, L100, HW 79, IC 1708, L106, L108, L109, NGC 643, L112, HW 84, HW 85 and HW 86, 14 Small Magellanic Cloud (SMC) clusters, most of them poorly studied objects. We measured T1 magnitudes and C-T1 and T1-T2 colours for a total of 213 516 stars spread throughout cluster areas of 14.7 × 14.7 arcmin2 each. We carried out an in-depth analysis of the field star contamination of the colour-magnitude diagrams (CMDs) and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the (T1, C-T1) CMDs, as well as from the δ(T1) index and the standard giant branch procedure, we derived ages and metallicities for the cluster sample. With the exception of IC 1708, a relatively metal-poor Hyades-age cluster, the remaining 13 objects are between intermediate and old age (from 1.0 to 6.3 Gyr), their [Fe/H] values ranging from -1.4 to -0.7 dex. By combining these results with others available in the literature, we compiled a sample of 43 well-known SMC clusters older than 1 Gyr, with which we produced a revised age distribution. We found that the present clusters' age distribution reveals two primary excesses of clusters at t˜ 2 and 5 Gyr, which engraves the SMC with clear signs of enhanced formation episodes at both ages. In addition, we found that from the birth of the SMC cluster system until approximately the first 4 Gyr of its lifetime, the cluster formation resembles that of a constant formation rate scenario.

  4. New light on dark stars red dwarfs, low-mass stars, brown dwarfs

    CERN Document Server

    Reid, I Neill

    2000-01-01

    Perhaps the most common question that a child asks when he or she sees the night sky from a dark site for the first time is: 'How many stars are there?' This happens to be a question which has exercised the intellectual skills of many astronomers over the course of most of the last century, including, for the last two decades, one of the authors of this text. Until recently, the most accurate answer was 'We are not certain, but there is a good chance that almost all of them are M dwarfs. ' Within the last three years, results from new sky-surveys - particularly the first deep surveys at near­ infrared wavelengths - have provided a breakthrough in this subject, solidifying our census of the lowest-mass stars and identifying large numbers of the hitherto almost mythical substellar-mass brown dwarfs. These extremely low-luminosity objects are the central subjects of this book, and the subtitle should be interpreted accordingly. The expression 'low-mass stars' carries a wide range of meanings in the astronomical...

  5. Star formation and mass assembly in high redshift galaxies

    Science.gov (United States)

    Santini, P.; Fontana, A.; Grazian, A.; Salimbeni, S.; Fiore, F.; Fontanot, F.; Boutsia, K.; Castellano, M.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Menci, N.; Nonino, M.; Paris, D.; Pentericci, L.; Vanzella, E.

    2009-09-01

    Aims: The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results: We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at z>0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to ≃ 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z≃ 2, massive galaxies are actively star-forming, with a median {SFR} ≃ 300 M_⊙ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions: The analysis of the SFR density and the SSFR seems to support the downsizing scenario, according to which high mass galaxies

  6. A tidal disruption event in a nearby galaxy hosting an intermediate mass black hole

    Energy Technology Data Exchange (ETDEWEB)

    Donato, D.; Troja, E. [CRESST and Astroparticle Physics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States); Cenko, S. B.; Fox, O. [Astrophysics Science Division, NASA/GSFC, Mail Code 661, Greenbelt, MD 20771 (United States); Covino, S. [INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (Italy); Pursimo, T. [Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma (Spain); Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States); Kutyrev, A. [Observational Cosmology Laboratory, NASA/GSFC, 8800 Greenbelt Road, Greenbelt, MD 20771-2400 (United States); Campana, S.; Fugazza, D. [Joint Space Science Institute, University of Maryland, College Park, MD 20742 (United States); Landt, H. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Butler, N. R., E-mail: davide.donato-1@nasa.gov [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States)

    2014-02-01

    We report the serendipitous discovery of a bright point source flare in the Abell cluster A1795 with archival EUVE and Chandra observations. Assuming the EUVE emission is associated with the Chandra source, the X-ray 0.5-7 keV flux declined by a factor of ∼2300 over a time span of 6 yr, following a power-law decay with index ∼2.44 ± 0.40. The Chandra data alone vary by a factor of ∼20. The spectrum is well fit by a blackbody with a constant temperature of kT ∼ 0.09 keV (∼10{sup 6} K). The flare is spatially coincident with the nuclear region of a faint, inactive galaxy with a photometric redshift consistent at the 1σ level with the cluster (z = 0.062476). We argue that these properties are indicative of a tidal disruption of a star by a black hole (BH) with log (M {sub BH}/M {sub ☉}) ∼ 5.5 ± 0.5. If so, such a discovery indicates that tidal disruption flares may be used to probe BHs in the intermediate mass range, which are very difficult to study by other means.

  7. A tidal disruption event in a nearby galaxy hosting an intermediate mass black hole

    International Nuclear Information System (INIS)

    Donato, D.; Troja, E.; Cenko, S. B.; Fox, O.; Covino, S.; Pursimo, T.; Cheung, C. C.; Kutyrev, A.; Campana, S.; Fugazza, D.; Landt, H.; Butler, N. R.

    2014-01-01

    We report the serendipitous discovery of a bright point source flare in the Abell cluster A1795 with archival EUVE and Chandra observations. Assuming the EUVE emission is associated with the Chandra source, the X-ray 0.5-7 keV flux declined by a factor of ∼2300 over a time span of 6 yr, following a power-law decay with index ∼2.44 ± 0.40. The Chandra data alone vary by a factor of ∼20. The spectrum is well fit by a blackbody with a constant temperature of kT ∼ 0.09 keV (∼10 6 K). The flare is spatially coincident with the nuclear region of a faint, inactive galaxy with a photometric redshift consistent at the 1σ level with the cluster (z = 0.062476). We argue that these properties are indicative of a tidal disruption of a star by a black hole (BH) with log (M BH /M ☉ ) ∼ 5.5 ± 0.5. If so, such a discovery indicates that tidal disruption flares may be used to probe BHs in the intermediate mass range, which are very difficult to study by other means.

  8. Prompt emission from tidal disruptions of white dwarfs by intermediate mass black holes

    Directory of Open Access Journals (Sweden)

    Laguna P.

    2012-12-01

    Full Text Available We present a qualitative picture of prompt emission from tidal disruptions of white dwarfs (WD by intermediate mass black holes (IMBH. The smaller size of an IMBH compared to a supermassive black hole and a smaller tidal radius of a WD disruption lead to a very fast event with high peak luminosity. Magnetic field is generated in situ following the tidal disruption, which leads to effective accretion. Since large-scale magnetic field is also produced, geometrically thick super-Eddington inflow leads to a relativistic jet. The dense jet possesses a photosphere, which emits quasi-thermal radiation in soft X-rays. The source can be classified as a long low-luminosity gamma-ray burst (ll-GRB. Tidal compression of a WD causes nuclear ignition, which is observable as an accompanying supernova. We suggest that GRB060218 and SN2006aj is such a pair of ll-GRB and supernova. We argue that in a flux-limited sample the disruptions of WDs by IMBHs are more frequent then the disruptions of other stars by IMBHs.

  9. The initial mass function for very low mass stars in the Hyades

    International Nuclear Information System (INIS)

    Hubbard, W.B.; Burrows, A.; Lunine, J.I.

    1990-01-01

    Theoretical luminosity functions at various evolutionary ages for stars and substellar objects (brown dwarfs), spanning the mass range from 0.03 to 0.2 solar mass is computed. These functions constrain the distribution of very low mass objects in a star cluster of known age. Calculations with a 1988-1989 survey of faint members of the Hyades cluster by Leggett and Hawkins (1988, 1989), a cluster whose age is 6 x 10 to the 8th yr are compared. The comparison shows that the survey does not reach sufficiently low luminosities to reveal brown dwarfs. A strong constraint on the initial mass function (IMF) for very low mass stars in the Hyades is obtained and it is inferred that its IMF does not increase with decreasing mass for the mass interval investigated here. Results imply at most a moderate contribution from brown dwarfs to the cluster mass, and to the Galaxy's mass if the Hyades are representative of the Galaxy as a whole. 10 refs

  10. Advanced evolution of a 15 solar mass star

    International Nuclear Information System (INIS)

    Endal, A.S.

    1974-01-01

    The evolution of a 15 solar mass star has been followed from the zero-age main sequence to the neon-ignition phase by use of the Henyey method for solving the equations of quasi-hydrostatic evolution. The detailed results of nucleosynthesis during carbon burning were calculated by a second-order, backwards-differencing scheme, with the effects of convection included in an approximate manner. The results of the evolution calculations and of the nucleosynthesis calculations are described and a detailed analysis of the effects of convection on nucleosynthesis is presented. The quiescent nature of evolution through the hydrogen, helium, and carbon burning stages is confirmed. Comparison with previous studies of the post-carbon burning evolution of massive stars shows that calculations in which degeneracy is neglected will not yield realistic results

  11. A Multiwavelength Approach to the Star Formation Rate Estimation in Galaxies at Intermediate Redshifts

    Science.gov (United States)

    Cardiel, N.; Elbaz, D.; Schiavon, R. P.; Willmer, C. N. A.; Koo, D. C.; Phillips, A. C.; Gallego, J.

    2003-02-01

    We use a sample of seven starburst galaxies at intermediate redshifts (z~0.4 and 0.8) with observations ranging from the observed ultraviolet to 1.4 GHz, to compare the star formation rate (SFR) estimators that are used in the different wavelength regimes. We find that extinction-corrected Hα underestimates the SFR, and the degree of this underestimation increases with the infrared luminosity of the galaxies. Galaxies with very different levels of dust extinction as measured with SFRIR/SFR(Hα, uncorrected for extinction) present a similar attenuation A[Hα], as if the Balmer lines probed a different region of the galaxy than the one responsible for the bulk of the IR luminosity for large SFRs. In addition, SFR estimates derived from [O II] λ3727 match very well those inferred from Hα after applying the metallicity correction derived from local galaxies. SFRs estimated from the UV luminosities show a dichotomic behavior, similar to that previously reported by other authors in galaxies at zfinancial support of the W. M. Keck Foundation. Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based in part on observations with the Infrared Space Observatory (ISO), an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, Netherlands, and United Kingdom) with the participation of ISAS and NASA.

  12. Radio Observations of Ultra-Luminous X-Ray Sources ---Microblazars or Intermediate-Mass Black Holes?---

    Science.gov (United States)

    Körding, E.; Colbert, E.; Falcke, H.

    In recent years Ultra-Luminous X-Ray sources (ULXs) received wide attention, however, their true nature is not yet understood. Many explanations have been suggested, including intermediate-mass black holes, super-Eddington accretion flows, anisotropic emission, and relativistic beaming of microquasars. We model the logN-logS distribution of ULXs assuming that each neutron star or black hole XRB can be described by an accretion disk plus jet model, where the jet is relativistically beamed. The distribution can be either fit by intermediate-mass black holes or by stellar mass black holes with mildly relativistic jets. Even though the jet is intrinsically weaker than the accretion disk, relativistic beaming can in the latter approach lead to the high fluxes observed. To further explore the possibility of microblazars contributing to the ULX phenomenon, we have embarked on a radio-monitoring study of ULXs in nearby galaxies with the VLA. However, up to now no radio flare has been detected. Using the radio/X-ray correlation the upper limits on the radio flux can be converted into upper limits for the black hole masses of MBH ≲ 10^3 M⊙.

  13. THE STAR FORMATION HISTORIES OF RED-SEQUENCE GALAXIES, MASS-TO-LIGHT RATIOS AND THE FUNDAMENTAL PLANE

    International Nuclear Information System (INIS)

    Allanson, Steven P.; Hudson, Michael J.; Smith, Russell J.; Lucey, John R.

    2009-01-01

    This paper addresses the challenge of understanding the typical star formation histories of red-sequence galaxies, using linestrength indices and mass-to-light ratios as complementary constraints on their stellar age distribution. We first construct simple parametric models of the star formation history that bracket a range of scenarios, and fit these models to the linestrength indices of low-redshift cluster red-sequence galaxies. For giant galaxies, we confirm the downsizing trend, i.e., the stellar populations are younger, on average, for lower σ galaxies. We find, however, that this trend flattens or reverses at σ ∼ -1 . We then compare predicted stellar mass-to-light ratios with dynamical mass-to-light ratios derived from the fundamental plane (FP), or by the SAURON group. For galaxies with σ ∼ 70 km s -1 , models with a late 'frosting' of young stars and models with exponential star formation histories have stellar mass-to-light ratios that are larger than observed dynamical mass-to-light ratios by factors of 1.7 and 1.4, respectively, and so are rejected. The single stellar population (SSP) model is consistent with the FP, and requires a modest amount of dark matter (between 20% and 30%) to account for the difference between stellar and dynamical mass-to-light ratios. A model in which star formation was 'quenched' at intermediate ages is also consistent with the observations, although in this case less dark matter is required for low mass galaxies. We also find that the contribution of stellar populations to the 'tilt' of the fundamental plane is highly dependent on the assumed star formation history: for the SSP model, the tilt of the FP is driven primarily by stellar-population effects. For a quenched model, two-thirds of the tilt is due to stellar populations and only one-third is due to dark matter or non-homology.

  14. Radio Detections During Two State Transitions of the Intermediate-Mass Black Hole HLX-1

    Science.gov (United States)

    Webb, Natalie; Cseh, David; Lenc, Emil; Godet, Olivier; Barret, Didier; Corbel, Stephane; Farrell, Sean; Fender, Robert; Gehrels, Neil; Heywood, Ian

    2012-01-01

    Relativistic jets are streams of plasma moving at appreciable fractions of the speed of light. They have been observed from stellar-mass black holes (approx. 3 to 20 solar masses) as well as supermassive black holes (approx.. 10(exp 6) to 10(exp 9) Solar Mass) found in the centers of most galaxies. Jets should also be produced by intermediate-mass black holes (approx. 10(exp 2) to 10(exp 5) Solar Mass), although evidence for this third class of black hole has, until recently, been weak. We report the detection of transient radio emission at the location of the intermediate-mass black hole candidate ESO 243-49 HLX-1, which is consistent with a discrete jet ejection event. These observations also allow us to refine the mass estimate of the black hole to be between approx. 9 × 10(exp 3) Solar Mass and approx. 9 × 10(exp 4) Solar Mass.

  15. Prospects for detection of intermediate-mass black holes in globular clusters using integrated-light spectroscopy

    Science.gov (United States)

    de Vita, R.; Trenti, M.; Bianchini, P.; Askar, A.; Giersz, M.; van de Ven, G.

    2017-06-01

    The detection of intermediate-mass black holes (IMBHs) in Galactic globular clusters (GCs) has so far been controversial. In order to characterize the effectiveness of integrated-light spectroscopy through integral field units, we analyse realistic mock data generated from state-of-the-art Monte Carlo simulations of GCs with a central IMBH, considering different setups and conditions varying IMBH mass, cluster distance and accuracy in determination of the centre. The mock observations are modelled with isotropic Jeans models to assess the success rate in identifying the IMBH presence, which we find to be primarily dependent on IMBH mass. However, even for an IMBH of considerable mass (3 per cent of the total GC mass), the analysis does not yield conclusive results in one out of five cases, because of shot noise due to bright stars close to the IMBH line of sight. This stochastic variability in the modelling outcome grows with decreasing BH mass, with approximately three failures out of four for IMBHs with 0.1 per cent of total GC mass. Finally, we find that our analysis is generally unable to exclude at 68 per cent confidence an IMBH with mass of 103 M⊙ in snapshots without a central BH. Interestingly, our results are not sensitive to GC distance within 5-20 kpc, nor to misidentification of the GC centre by less than 2 arcsec (<20 per cent of the core radius). These findings highlight the value of ground-based integral field spectroscopy for large GC surveys, where systematic failures can be accounted for, but stress the importance of discrete kinematic measurements that are less affected by stochasticity induced by bright stars.

  16. INTERMEDIATE-MASS HOT CORES AT {approx}500 AU: DISKS OR OUTFLOWS?

    Energy Technology Data Exchange (ETDEWEB)

    Palau, Aina; Girart, Josep M. [Institut de Ciencies de l' Espai (CSIC-IEEC), Campus UAB-Facultat de Ciencies, Torre C5-parell 2, 08193 Bellaterra, Catalunya (Spain); Fuente, Asuncion; Alonso-Albi, Tomas [Observatorio Astronomico Nacional, P.O. Box 112, 28803 Alcala de Henares, Madrid (Spain); Fontani, Francesco; Sanchez-Monge, Alvaro [Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Firenze (Italy); Boissier, Jeremie [Istituto di Radioastronomia, INAF, Via Gobetti 101, Bologna (Italy); Pietu, Vincent; Neri, Roberto [IRAM, 300 Rue de la piscine, 38406 Saint Martin d' Heres (France); Busquet, Gemma [Istituto di Fisica dello Spazio Interplanetario, INAF, Area di Recerca di Tor Vergata, Via Fosso Cavaliere 100, 00133 Roma (Italy); Estalella, Robert [Departament d' Astronomia i Meteorologia (IEEC-UB), Institut Ciencies Cosmos, Universitat Barcelona, Marti Franques 1, 08028 Barcelona (Spain); Zapata, Luis A. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, P.O. Box 3-72, 58090 Morelia, Michoacan (Mexico); Zhang, Qizhou; Ho, Paul T. P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Audard, Marc, E-mail: palau@ieec.uab.es [Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix (Switzerland)

    2011-12-20

    Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS 22198+6336 and AFGL 5142, reveal the presence of several complex organic molecules at {approx}500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH{sub 3}CH{sub 2}OH, (CH{sub 2}OH){sub 2}, CH{sub 3}COCH{sub 3}, and CH{sub 3}OH, with, additionally, CH{sub 3}CHO, CH{sub 3}OD, and HCOOD for IRAS 22198+6336, and C{sub 6}H and O{sup 13}CS for AFGL 5142. The emission of complex molecules is resolved down to sizes of {approx}300 and {approx}600 AU, for IRAS 22198+6336 and AFGL 5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as is usually found. This is especially clear for the case of IRAS 22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass {approx}> 4 M{sub Sun }. As for AFGL 5142, the hot core emission is resolved into two elongated cores separated {approx}1800 AU. A detailed comparison of the complex molecule peaks to the new CO (2-1) data and H{sub 2}O maser data from the literature suggests also that for AFGL 5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.

  17. INTERMEDIATE-MASS HOT CORES AT ∼500 AU: DISKS OR OUTFLOWS?

    International Nuclear Information System (INIS)

    Palau, Aina; Girart, Josep M.; Fuente, Asunción; Alonso-Albi, Tomás; Fontani, Francesco; Sánchez-Monge, Álvaro; Boissier, Jérémie; Piétu, Vincent; Neri, Roberto; Busquet, Gemma; Estalella, Robert; Zapata, Luis A.; Zhang, Qizhou; Ho, Paul T. P.; Audard, Marc

    2011-01-01

    Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS 22198+6336 and AFGL 5142, reveal the presence of several complex organic molecules at ∼500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH 3 CH 2 OH, (CH 2 OH) 2 , CH 3 COCH 3 , and CH 3 OH, with, additionally, CH 3 CHO, CH 3 OD, and HCOOD for IRAS 22198+6336, and C 6 H and O 13 CS for AFGL 5142. The emission of complex molecules is resolved down to sizes of ∼300 and ∼600 AU, for IRAS 22198+6336 and AFGL 5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as is usually found. This is especially clear for the case of IRAS 22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass ∼> 4 M ☉ . As for AFGL 5142, the hot core emission is resolved into two elongated cores separated ∼1800 AU. A detailed comparison of the complex molecule peaks to the new CO (2-1) data and H 2 O maser data from the literature suggests also that for AFGL 5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.

  18. CONSTRAINTS OF THE PHYSICS OF LOW-MASS AGB STARS FROM CH AND CEMP STARS

    Energy Technology Data Exchange (ETDEWEB)

    Cristallo, S.; Piersanti, L.; Gobrecht, D. [INAF—Osservatorio Astronomico di Teramo, I-64100 (Italy); Karinkuzhi, D.; Goswami, A. [Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India)

    2016-12-20

    We analyze a set of published elemental abundances from a sample of CH stars which are based on high resolution spectral analysis of ELODIE and SUBARU/HDS spectra. All the elemental abundances were derived from local thermodynamic equilibrium analysis using model atmospheres, and thus they represent the largest homogeneous abundance data available for CH stars to date. For this reason, we can use the set to constrain the physics and the nucleosynthesis occurring in low mass asymptotic giant branch (AGB) s.tars. CH stars have been polluted in the past from an already extinct AGB companion and thus show s-process enriched surfaces. We discuss the effects induced on the surface AGB s-process distributions by different prescriptions for convection and rotation. Our reference theoretical FRUITY set fits only part of the observations. Moreover, the s-process observational spread for a fixed metallicity cannot be reproduced. At [Fe/H] > −1, a good fit is found when rotation and a different treatment of the inner border of the convective envelope are simultaneously taken into account. In order to increase the statistics at low metallicities, we include in our analysis a selected number of CEMP stars and, therefore, we compute additional AGB models down to [Fe/H] = −2.85. Our theoretical models are unable to attain the large [hs/ls] ratios characterizing the surfaces of those objects. We speculate on the reasons for such a discrepancy, discussing the possibility that the observed distribution is a result of a proton mixing episode leading to a very high neutron density (the so-called i-process).

  19. Characterization of the Praesepe star cluster by photometry and proper motions with 2MASS, PPMXL, and Pan-STARRS

    Energy Technology Data Exchange (ETDEWEB)

    Wang, P. F.; Chen, W. P. [Department of Physics, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan (China); Lin, C. C.; Huang, C. K.; Panwar, N.; Lee, C. H. [Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan (China); Pandey, A. K. [Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263129 (India); Tsai, M. F.; Tang, C.-H. [Department of Computer Science and Information Engineering, National Central University, 300 Jhongda Road, Jhongli 32001, Taiwan (China); Goldman, B. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Heasley, J. N.; Hodapp, K. W.; Huber, M. E.; Jedicke, R.; Kaiser, N. [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Draper, P. W. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Grav, T. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); and others

    2014-03-20

    Membership identification is the first step in determining the properties of a star cluster. Low-mass members in particular could be used to trace the dynamical history, such as mass segregation, stellar evaporation, or tidal stripping, of a star cluster in its Galactic environment. We identified member candidates of the intermediate-age Praesepe cluster (M44) with stellar masses ∼0.11-2.4 M {sub ☉}, using Panoramic Survey Telescope And Rapid Response System and Two Micron All Sky Survey photometry, and PPMXL proper motions. Within a sky area of 3° radius, 1040 candidates are identified, of which 96 are new inclusions. Using the same set of selection criteria on field stars, an estimated false positive rate of 16% was determined, suggesting that 872 of the candidates are true members. This most complete and reliable membership list allows us to favor the BT-Settl model over other stellar models. The cluster shows a distinct binary track above the main sequence, with a binary frequency of 20%-40%, and a high occurrence rate of similar mass pairs. The mass function is consistent with that of the disk population but shows a deficit of members below 0.3 solar masses. A clear mass segregation is evidenced, with the lowest-mass members in our sample being evaporated from this disintegrating cluster.

  20. Synchrotron photoionization mass spectrometry study of intermediates in fuel-rich 1,2-dimethoxyethane flame

    International Nuclear Information System (INIS)

    Lin, Z. K.; Han, D. L.; Li, S. F.; Li, Y. Y.; Yuan, T.

    2009-01-01

    Intermediates in a fuel-rich premixed laminar 1,2-dimethoxyethane (DME) flame are studied by molecular beam mass spectrometry combined with tunable synchrotron vacuum ultraviolet photoionization. About 30 intermediate species are identified in the present work, and their mole fraction profiles are evaluated. The experimental results show that the formations of intermediates, both hydrocarbons and oxygenated hydrocarbons, are closely linked to the structure of fuel, which is consistent with the previous reports. Species produced from H atom abstraction and beta scission of DME usually have much higher concentrations than others. The oxygen atoms in DME are considered to act as partitions of the primary intermediates; therefore farther reactions among these primary intermediates are difficult to occur, resulting in absence of most large intermediate species.

  1. Evolution of massive stars with mass loss: surface abundances

    International Nuclear Information System (INIS)

    Greggio, L.

    1984-01-01

    The location of theoretical stellar models in the upper part of the Hertzsprung-Russell diagram depends on a variety of poorly understood physical processes which may occur during the evolution of massive stars. The comparison between theoretical predictions and observations of the surface chemical composition of these objects can help in understanding their evolution and to set more stringent limits to the mentioned parameters. To this end, evolutionary sequences corresponding to 20, 40 and 60 solar masses have been computed up to core He exhaustion, following in detail the abundance variations of CNO, Ne and Mg isotopes. (Auth.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-10

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

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

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

    Science.gov (United States)

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

    2014-01-01

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

  5. Low-energy consequences of superstring-inspired models with intermediate-mass scales

    International Nuclear Information System (INIS)

    Gabbiani, F.

    1987-01-01

    The phenomenological consequences of implementing intermediate-mass scales in E 6 superstring-inspired models are discussed. Starting from a suitable Calabi-Yau compactification with b 1,1 >1, one gets, after Hosotani breaking, the rank r=5 gauge group SU(3) C x SU(2) L x U(1) Y x U(1) E , that is broken at an intermediate-mass scale down to the standard-model group. The analysis of both the intermediate and the electroweak breaking is performed in the two cases Λ c = M x and Λ c x , where Λ c is the scale at which the hidden sector gauginos condensate. It is performed quantitatively the minimization of the low-energy effective potential and the renormalization group analysis, yielding a viable set of mass spectra and confirming the reliability of the intermediate-breaking scheme

  6. A NEW CLASS OF GAMMA-RAY BURSTS FROM STELLAR DISRUPTIONS BY INTERMEDIATE-MASS BLACK HOLES

    International Nuclear Information System (INIS)

    Gao, H.; Lu, Y.; Zhang, S. N.

    2010-01-01

    It has been argued that the long gamma-ray burst (GRB) of GRB 060614 without an associated supernova (SN) has challenged the current classification and fuel model for long GRBs, and thus a tidal disruption model has been proposed to account for such an event. Since it is difficult to detect SNe for long GRBs at high redshift, the absence of an SN association cannot be regarded as the solid criterion for a new classification of long GRBs similar to GRB 060614, called GRB 060614-type bursts. Fortunately, we now know that there is an obvious periodic substructure observed in the prompt light curve of GRB 060614. We thus use such periodic substructure as a potential criterion to categorize some long GRBs into a new class of bursts, which might have been fueled by an intermediate-mass black hole (IMBH) gulping a star, rather than a massive star collapsing to form a black hole. Therefore, the second criterion to recognize for this new class of bursts is whether they fit the tidal disruption model. From a total of 328 Swift GRBs with accurately measured durations and without SN association, we find 25 GRBs satisfying the criteria for GRB 060614-type bursts: seven of them are with known redshifts and 18 with unknown redshifts. These new bursts are ∼6% of the total Swift GRBs, which are clustered into two subclasses: Type I and Type II with considerably different viscous parameters of accretion disks formed by tidally disrupting their different progenitor stars. We suggest that the two different kinds of progenitors are solar-type stars and white dwarfs: the progenitors for four Type I bursts with viscous parameter of around 0.1 are solar-type stars, and the progenitors for 21 Type II bursts with viscous parameter of around 0.3 are white dwarfs. The potential applications of this new class of GRBs as cosmic standard candles are discussed briefly.

  7. Mass distributions in nucleon-induced fission at intermediate energies

    CERN Document Server

    Duijvestijn, M C; Hambsch, F J

    2001-01-01

    Temperature-dependent fission barriers and fission-fragment mass distributions are calculated in the framework of the multimodal random neck-rupture model (MM-RNRM). It is shown how the distinction between the different fission modes disappears at higher excitation energies, due to the melting of shell effects. The fission-fragment mass yield calculations are coupled to the nuclear reaction code ALICE-91, which takes into account the competition between the other reaction channels and fission. With the combination of the temperature-dependent MM-RNRM and ALICE-91 nucleon-induced fission is investigated at energies between 10 and 200 MeV for nuclei varying from Au to Am. (72 refs).

  8. for the internal rotation evolution of low-mass stars

    Directory of Open Access Journals (Sweden)

    Pinçon Charly

    2017-01-01

    Full Text Available Due to the space-borne missions CoRoT and Kepler, noteworthy breakthroughs have been made in our understanding of stellar evolution, and in particular about the angular momentum redistribution in stellar interiors. Indeed, the high-precision seismic data provide with the measurement of the mean core rotation rate for thousands of low-mass stars from the subgiant branch to the red giant branch. All these observations exhibit much lower core rotation rates than expected by current stellar evolution codes and they emphasize the need for an additional transport process. In this framework, internal gravity waves (herefater, IGW could play a signifivative role since they are known to be able to transport angular momentum. In this work, we estimate the effciency of the transport by the IGW that are generated by penetrative convection at the interface between the convective and the radiative regions. As a first step, this study is based on the comparison between the timescale for the waves to modify a given rotation profile and the contraction/expansion timescale throughout the radiative zone of 1.3M⊙ stellar models. We show that IGW, on their own, are ineffcient to slow down the core rotation of stars on the red giant branch, where the radiative damping becomes strong enough and prevent the IGW from reaching the innermost layers. However, we find that IGW generated by penetrative convection could effciently modify the core rotation of subgiant stars as soon as the amplitude of the radial differential rotation between the core and the base of the convective zone is high enough, with typical values close to the observed rotation rates in these stars. This result argues for the necessity to account for IGW generated by penetrative convection in stellar modeling and in the angular momentum redistribution issue.

  9. High-mass Star Formation and Its Initial Conditions

    Science.gov (United States)

    Zhang, C. P.

    2017-11-01

    In this thesis, we present four works on the infrared dark clouds, fragmentation and deuteration of compact and cold cores, hyper-compact (HC) HII regions, and infrared dust bubbles, respectively. They are not only the products of early high-mass star formation, but reflect different evolutionary sequences of high-mass star formation. (1) Using the IRAM (Institut de Radioastronomie Millimétrique) 30 m telescope, we obtained HCO^+, HNC, N_2^+, and C^{18}O emission in six IRDCs (infrared dark clouds), and study their dynamics, stability, temperature, and density. (2) Fragmentation at the earliest phases is an important process of massive star formation. Eight massive precluster clumps (G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71) were selected from the SCUBA (submillimetre Common-User Bolometer Array) 850 μm and 450 μm data. The VLA (Very Large Array) at 1.3 cm, PbBI at 3.5 mm and 1.3 mm, APEX (Atacama Pathfinder Experiment telescope) at 870 μm observations were followed up, and archival infrared data at 4.5 μm, 8.0 μm, 24 μm, and 70 μm were combined to study the fragmentation and evolution of these clumps. We explored the habitats of the massive clumps at large scale, cores/condensations at small scale, and the fragmentation process at different wavelengths. Star formation in these eight clumps may have been triggered by the UC (ultra-compact) HII regions nearby. (3) The formation of hyper-compact (HC) HII regions is an important stage in massive star formation. We present high angular resolution observations carried out with the SMA (Submillimeter Array) and the VLA (Very Large Array) toward the HC HII region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected a total of about 25 transitions of 8 different species and their isotopologues (CO, CH_3CN, SO_2, CH_3CCH, OCS, CS, H30α/38β, and NH_{3}). G35.58-0.03 consists of an HC HII core with electron temperature Te* ≥ 5500 K, emission measure EM ≈ 1.9×10^{9} pc

  10. The dwarfs beyond: The stellar-to-halo mass relation for a new sample of intermediate redshift low-mass galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Sarah H.; Ellis, Richard S.; Newman, Andrew B. [California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 (United States); Benson, Andrew, E-mail: smiller@astro.caltech.edu [Carnegie Observatories, 813 Santa Barbara St, Pasadena, CA 91101 (United States)

    2014-02-20

    A number of recent challenges to the standard ΛCDM paradigm relate to discrepancies that arise in comparing the abundance and kinematics of local dwarf galaxies with the predictions of numerical simulations. Such arguments rely heavily on the assumption that the Local Volume's dwarf and satellite galaxies form a representative distribution in terms of their stellar-to-halo mass ratios. To address this question, we present new, deep spectroscopy using DEIMOS on Keck for 82 low-mass (10{sup 7}-10{sup 9} M {sub ☉}), star-forming galaxies at intermediate redshift (0.2 < z < 1). For 50% of these we are able to determine resolved rotation curves using nebular emission lines and thereby construct the stellar mass Tully-Fisher relation to masses as low as 10{sup 7} M {sub ☉}. Using scaling relations determined from weak lensing data, we convert this to a stellar-to-halo mass relation for comparison with abundance matching predictions. We find a discrepancy between our observations and the predictions from abundance matching in the sense that we observe 3-12 times more stellar mass at a given halo mass. We suggest possible reasons for this discrepancy, as well as improved tests for the future.

  11. Low-mass stars in globular clusters. III. The mass function of 47 Tucanae.

    Science.gov (United States)

    de Marchi, G.; Paresce, F.

    1995-12-01

    We have used the WFPC2 on board HST to investigate the stellar population in a field located 4'6 E of the center of the globular cluster 47 Tuc (NGC 104), close to the half-mass radius, through wide band imaging at 606 and 812nm. A total of ~3000 stars are accurately classified by two-color photometry to form a color-magnitude diagram extending down to a limiting magnitude m_814_=~m_I_=~24. A rich cluster main sequence is detected spanning the range from m_814_=~18 through m_814_=~23, where it spreads considerably due to the increasing photometric uncertainty and galaxy contamination. A secondary sequence of objects is also detected, parallel to the main sequence, as expected for a population of binary stars. The measured binary fraction in the range 195%. The main sequence luminosity function obtained from the observed CMD increases with decreasing luminosity following a power-law trend with index α=~0.15 in the range 5crowding. On the basis of the available mass-luminosity relation for this metallicity, the resultant mass function shows a power-law increase in numbers for decreasing masses in the range 0.8-0.3Msun_ with a slope α=~1.5, but then flattens out in the 0.3-0.15Msun_ range. The comparison of the mass function of 47 Tuc with that of NGC 6397 (Paper I) and of M 15 (Paper II), previously investigated with the same instrumentation, suggests that the stellar population near the half-mass radius of these clusters should not be very sensitive to either internal or externally-driven dynamical processes. The difference between their mass functions could then be attributed to metallicity, reflecting an intrinsic difference in their initial mass functions, unless mass-segregation is stronger in 47 Tuc than in the other two clusters. This latter circumstance could be due, for instance, to the large number of binaries discovered in 47 Tuc. In all cases, however, the mass function is found to flatten below 0.3Msun_ and the flattening is most likely an intrinsic

  12. Mass-radius relation for magnetized strange quark stars

    CERN Document Server

    Martinez, A Perez; Paret, D Manreza

    2010-01-01

    We review the stability of magnetized strange quark matter (MSQM) within the phenomenological MIT bag model, taking into account the variation of the relevant input parameters, namely, the strange quark mass, baryon density, magnetic field and bag parameter. A comparison with magnetized asymmetric quark matter in $\\beta$-equilibrium as well as with strange quark matter (SQM) is presented. We obtain that the energy per baryon for MSQM decreases as the magnetic field increases, and its minimum value at vanishing pressure is lower than the value found for SQM, which implies that MSQM is more stable than non-magnetized SQM. The mass-radius relation for magnetized strange quark stars is also obtained in this framework.

  13. Low-mass Stars with Extreme Mid-Infrared Excesses: Potential Signatures of Planetary Collisions

    Science.gov (United States)

    Theissen, Christopher; West, Andrew

    2018-01-01

    I investigate the occurrence of extreme mid-infrared (MIR) excesses, a tracer of large amounts of dust orbiting stars, in low-mass stellar systems. Extreme MIR excesses, defined as an excess IR luminosity greater than 1% of the stellar luminosity (LIR/L* ≥ 0.01), have previously only been observed around a small number of solar-mass (M⊙) stars. The origin of this excess has been hypothesized to be massive amounts of orbiting dust, created by collisions between terrestrial planets or large planetesimals. Until recently, there was a dearth of low-mass (M* ≤ 0.6M⊙) stars exhibiting extreme MIR excesses, even though low-mass stars are ubiquitous (~70% of all stars), and known to host multiple terrestrial planets (≥ 3 planets per star).I combine the spectroscopic sample of low-mass stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 (70,841 stars) with MIR photometry from the Wide-field Infrared Survey Explorer (WISE), to locate stars exhibiting extreme MIR excesses. I find the occurrence frequency of low-mass field stars (stars with ages ≥ 1 Gyr) exhibiting extreme MIR excesses is much larger than that for higher-mass field stars (0.41 ± 0.03% versus 0.00067 ± 0.00033%, respectively).In addition, I build a larger sample of low-mass stars based on stellar colors and proper motions using SDSS, WISE, and the Two-Micron All-Sky Survey (8,735,004 stars). I also build a galactic model to simulate stellar counts and kinematics to estimate the number of stars missing from my sample. I perform a larger, more complete study of low-mass stars exhibiting extreme MIR excesses, and find a lower occurrence frequency (0.020 ± 0.001%) than found in the spectroscopic sample but that is still orders of magnitude larger than that for higher-mass stars. I find a slight trend for redder stars (lower-mass stars) to exhibit a higher occurrence frequency of extreme MIR excesses, as well as a lower frequency with increased stellar age. These samples probe important

  14. Rotation of the Mass Donors in High-mass X-ray Binaries and Symbiotic Stars

    Directory of Open Access Journals (Sweden)

    K. Stoyanov

    2015-02-01

    Full Text Available Our aim is to investigate the tidal interaction in High-mass X-ray Binaries and Symbiotic stars in order to determine in which objects the rotation of the mass donors is synchronized or pseudosynchronized with the orbital motion of the compact companion. We find that the Be/X-ray binaries are not synchronized and the orbital periods of the systems are greater than the rotational periods of the mass donors. The giant and supergiant High-mass X-ray binaries and symbiotic stars are close to synchronization. We compare the rotation of mass donors in symbiotics with the projected rotational velocities of field giants and find that the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. We find that the projected rotational velocity of the red giant in symbiotic star MWC 560 is v sin i= 8.2±1.5 km.s−1, and estimate its rotational period to be Prot<>/sub = 144 - 306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68 − 0.82.

  15. Asteroseismology of white dwarf stars

    OpenAIRE

    Córsico, A. H.

    2014-01-01

    Most of low- and intermediate-mass stars that populate the Universe will end their lives as white dwarf stars. These ancient stellar remnants have encrypted inside a precious record of the evolutionary history of the progenitor stars, providing a wealth of information about the evolution of stars, star formation, and the age of a variety of stellar populations, such as our Galaxy and open and globular clusters. While some information like surface chemical composition, temperature and gravity ...

  16. A population of relic intermediate-mass black holes in the halo of the Milky Way

    International Nuclear Information System (INIS)

    Rashkov, Valery; Madau, Piero

    2014-01-01

    If 'seed' central black holes were common in the subgalactic building blocks that merged to form present-day massive galaxies, then relic intermediate-mass black holes (IMBHs) should be present in the Galactic bulge and halo. We use a particle tagging technique to dynamically populate the N-body Via Lactea II high-resolution simulation with black holes, and assess the size, properties, and detectability of the leftover population. The method assigns a black hole to the most tightly bound central particle of each subhalo at infall according to an extrapolation of the M BH -σ * relation, and self-consistently follows the accretion and disruption of Milky Way progenitor dwarfs and their holes in a cosmological 'live' host from high redshift to today. We show that, depending on the minimum stellar velocity dispersion, σ m , below which central black holes are assumed to be increasingly rare, as many as ∼2000 (σ m = 3 km s –1 ) or as few as ∼70 (σ m = 12 km s –1 ) IMBHs may be left wandering in the halo of the Milky Way today. The fraction of IMBHs forced from their hosts by gravitational recoil is ≲ 20%. We identify two main Galactic subpopulations, 'naked' IMBHs, whose host subhalos were totally destroyed after infall, and 'clothed' IMBHs residing in dark matter satellites that survived tidal stripping. Naked IMBHs typically constitute 40%-50% of the total and are more centrally concentrated. We show that, in the σ m = 12 km s –1 scenario, the clusters of tightly bound stars that should accompany naked IMBHs would be fainter than m V = 16 mag, spatially resolvable, and have proper motions of 0.1-10 mas yr –1 . Their detection may provide an observational tool to constrain the formation history of massive black holes in the early universe.

  17. Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

    International Nuclear Information System (INIS)

    Yu, Jincheng; Puzia, Thomas H.; Lin, Congping; Zhang, Yiwei

    2017-01-01

    We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

  18. Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Jincheng; Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Católica, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22 (Chile); Lin, Congping; Zhang, Yiwei, E-mail: yujc.astro@gmail.com, E-mail: tpuzia@gmail.com, E-mail: congpinglin@gmail.com, E-mail: yiweizhang831129@gmail.com [Center for Mathematical Science, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 4370074 (China)

    2017-05-10

    We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

  19. A VLT/FLAMES STUDY OF THE PECULIAR INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 1846. I. KINEMATICS

    International Nuclear Information System (INIS)

    Mackey, A. D.; Da Costa, G. S.; Yong, D.; Ferguson, A. M. N.

    2013-01-01

    In this paper we present high-resolution VLT/FLAMES observations of red giant stars in the massive intermediate-age Large Magellanic Cloud star cluster NGC 1846, which, on the basis of its extended main-sequence turnoff (EMSTO), possesses an internal age spread of ≈300 Myr. We describe in detail our target selection and data reduction procedures, and construct a sample of 21 stars possessing radial velocities indicating their membership of NGC 1846 at high confidence. We consider high-resolution spectra of the planetary nebula Mo-17, and conclude that this object is also a member of the cluster. Our measured radial velocities allow us to conduct a detailed investigation of the internal kinematics of NGC 1846, the first time this has been done for an EMSTO system. The key result of this work is that the cluster exhibits a significant degree of systemic rotation, of a magnitude comparable to the mean velocity dispersion. Using an extensive suite of Monte Carlo models we demonstrate that, despite our relatively small sample size and the substantial fraction of unresolved binary stars in the cluster, the rotation signal we detect is very likely to be genuine. Our observations are in qualitative agreement with the predictions of simulations modeling the formation of multiple populations of stars in globular clusters, where a dynamically cold, rapidly rotating second generation is a common feature. NGC 1846 is less than one relaxation time old, so any dynamical signatures encoded during its formation ought to remain present.

  20. On p-mode oscillations in stars from 1 solar mass to 2 solar masses

    Science.gov (United States)

    Audard, N.; Provost, J.

    1994-06-01

    The structure of stars more massive than about 1.2 solar masses is characterized by a convective core. We have studied the evolution with age and mass of acoustic frequencies of high radical order n and low degree l for models of stars of 1, 1.5 and 2 solar masses. Using a polynomial approximation for the frequency, the p-mode spectrum can be characterized by derived global asteroseismic coefficients, i.e. the mean separation nu0 is approximately equal to nun, l - nun - 1, l and the small frequency separation Delta nu0, 2 is approximately equal to nun, l = 0 - nun - 1, l = 2. The diagram (nu0, delta nu0, 2/nu0) plotted along the evolutionary tracks would help to separate the effects of age and mass. We study the sensitivity of these coefficients and other observable quantities, like the radius and luminosity, to stellar parameters in the vicinity of 1 solar mass and 2 solar masses; this sensitivity substantially depends on the stellar mass and must be taken into account for asteroseismic calibration of stellar clusters. Considering finally some rapid variations of the internal structure, we show that the second frequency difference delta2 nu = nu(subn, l) - 2 nun - 1, l + nun - 2, l exponent gamma in the He II ionization zone.

  1. Maser Emission Associated with Young High Mass Stars

    Science.gov (United States)

    Mahmoud, Khaled Abdalla Edris

    In this work the maser emission has been used to study the very early stage evolution of the young stars. The maser emission of OH molecule was searched for towards a sample of high mass protostellar objects using the Nançay and GBT telescopes. The sample of objects searched was selected to contain very young forming high mass stars. The results of this survey have been compared with previous H2O and CH3OH masers observations. Then MERLIN has been used to map the OH as well as H2O and CH3OH masers towards one of these sources in high angular resolution. The survey detected OH maser emission towards 63 objects with 37 new detections. There are 56 star forming regions and 7 OH/IR candidates. The detection of OH masers towards 26% of a sample of 217 sources should remove any doubt about the existence of OH maser emission towards these objects of this early evolutionary stage. Nearly half of the detected sources have OH fluxes rates and velocity range support the spatial association of OH and class II CH3OH masers as suggested by Caswell et al. [1995] and modelled by Cragg et al. [2002]. IRAS20126+4104 was mapped in the OH, water and methanol masers using MERLIN. The 1665-MHz OH, 22-GHz H2O and 6.7-GHz CH3OH masers are detected and all originate very close to the central source. The OH and methanol masers appear to trace part of the circumstellar disk around the central source. The positions and velocities of the OH masers are consistent with Keplerian rotation around a central mass of ˜5Msun. The water masers are offset from the OH and CH3OH masers and have significantly changed since they were last observed, but still appear to be associated outflow from the source. All the OH masers components are circular polarized, in some cases reaching 100 percent while some OH components also have low levels of linear polarization. We identified one Zeeman pair and the splitting of this pair indicate the presence of a magnetic field of strength ˜11 mG within ˜0.5" (850 AU

  2. Dust discs around low-mass main-sequence stars

    International Nuclear Information System (INIS)

    Wolstencroft, R.D.; Walker, H.J.

    1988-01-01

    Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars α Lyr, α PsA, β Pic and ε Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The colour, diameter and thickness of the optical image of β Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. (author)

  3. Mass loss of stars on the asymptotic giant branch. Mechanisms, models and measurements

    Science.gov (United States)

    Höfner, Susanne; Olofsson, Hans

    2018-01-01

    As low- and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newly-formed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angular-resolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their wind-forming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angular-resolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building realistic models of wind acceleration and developing a predictive theory of mass loss for AGB stars, which is a crucial ingredient of stellar and galactic chemical evolution models. At present, it is still not fully possible to model all these phenomena from first principles, and to predict the mass-loss rate based on fundamental stellar parameters only. However, much progress has been made

  4. Carbon stars in lmc clusters revisited

    OpenAIRE

    Marigo, Paola; Girardi, Leo Alberto; Chiosi, Cesare

    1996-01-01

    Examining the available data for AGB stars in the Large Magellanic Cloud (LMC) clusters, we address the question about the mass interval of low- and intermediate-mass stars which eventually evolve into carbon stars (C stars) during the TP-AGB phase. We combine the data compiled by Frogel, Mould & Blanco (1990) - near infrared photometry and spectral classification for luminous AGB stars in clusters - with the ages for individual clusters derived from independent methods. The resulting distrib...

  5. An intermediate-mass black hole in the centre of the globular cluster 47 Tucanae.

    Science.gov (United States)

    Kızıltan, Bülent; Baumgardt, Holger; Loeb, Abraham

    2017-02-08

    Intermediate-mass black holes should help us to understand the evolutionary connection between stellar-mass and super-massive black holes. However, the existence of intermediate-mass black holes is still uncertain, and their formation process is therefore unknown. It has long been suspected that black holes with masses 100 to 10,000 times that of the Sun should form and reside in dense stellar systems. Therefore, dedicated observational campaigns have targeted globular clusters for many decades, searching for signatures of these elusive objects. All candidate signatures appear radio-dim and do not have the X-ray to radio flux ratios required for accreting black holes. Based on the lack of an electromagnetic counterpart, upper limits of 2,060 and 470 solar masses have been placed on the mass of a putative black hole in 47 Tucanae (NGC 104) from radio and X-ray observations, respectively. Here we show there is evidence for a central black hole in 47 Tucanae with a mass of solar masses when the dynamical state of the globular cluster is probed with pulsars. The existence of an intermediate-mass black hole in the centre of one of the densest clusters with no detectable electromagnetic counterpart suggests that the black hole is not accreting at a sufficient rate to make it electromagnetically bright and therefore, contrary to expectations, is gas-starved. This intermediate-mass black hole might be a member of an electromagnetically invisible population of black holes that grow into supermassive black holes in galaxies.

  6. Formation and Evolution of Neutron Star Binaries: Masses of Neutron Stars

    Directory of Open Access Journals (Sweden)

    Lee Chang-Hwan

    2012-02-01

    Full Text Available Neutron star (NS is one of the most interesting astrophysical compact objects for hardronic physics. It is believed that the central density of NS can reach several times the normal nuclear matter density (ρ0. Hence, the inner part of NS is the ultimate testing place for the physics of dense matter. Recently, the mass of NS in a NS-white dwarf (WD binary PSR J1614-2230 has been estimated to be 1.97 ± 0.04M๏ [1]. Since this estimate is based on the observed Shapiro delay, it can give the lower limit of the maximum NS mass and rules out many soft equations of state. On the other hand, all the well-measured NS masses in NS-NS binaries are smaller than 1.5M๏. In this work, by introducing the supercritical accretion during the binary evolution, we propose a possibility of forming higher mass NS in NS-WD binaries. In this scenario, the lifetimes of NS and WD progenitors are significantly different, and NS in NS-WD binary can accrete > 0.5M๏ after NS formation during the giant phase of the progenitor of WD. On the other hand, for the binary system with NS and heavier (> 8M๏ giants, the first-born NS will accrete more from the companion and can collapse into black hole. The only way to avoid the supercritical accretion is that the initial masses of progenitors of NS binary should be very close so that they evolve almost at the same time and don’t have time to accrete after NS formation.

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

    Science.gov (United States)

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

    2018-05-01

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

  8. THE MASS-DEPENDENCE OF ANGULAR MOMENTUM EVOLUTION IN SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Baraffe, Isabelle; Chabrier, Gilles; Brun, A. Sacha; Bouvier, Jérôme

    2015-01-01

    To better understand the observed distributions of the rotation rate and magnetic activity of Sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar wind torque on the Rossby number. The torque also contains an empirically derived scaling with stellar mass (and radius), which provides new insight into the mass-dependence of stellar magnetic and wind properties. We demonstrate that this new formulation explains why the lowest mass stars are observed to maintain rapid rotation for much longer than solar-mass stars, and simultaneously why older populations exhibit a sequence of slowly rotating stars, in which the low-mass stars rotate more slowly than solar-mass stars. The model also reproduces some previously unexplained features in the period-mass diagram for the Kepler field, notably: the particular shape of the ''upper envelope'' of the distribution, suggesting that ∼95% of Kepler field stars with measured rotation periods are younger than ∼4 Gyr; and the shape of the ''lower envelope'', corresponding to the location where stars transition between magnetically saturated and unsaturated regimes

  9. THE CONTRIBUTIONS OF INTERACTIVE BINARY STARS TO DOUBLE MAIN-SEQUENCE TURNOFFS AND DUAL RED CLUMP OF INTERMEDIATE-AGE STAR CLUSTERS

    International Nuclear Information System (INIS)

    Yang Wuming; Bi Shaolan; Tian Zhijia; Li Tanda; Liu Kang; Meng Xiangcun

    2011-01-01

    Double or extended main-sequence turnoffs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. The DMSTOs are interpreted as that the cluster has two distinct stellar populations with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolution of a binary-star stellar population. We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended main-sequence turnoff (MSTO) rather than DMSTOs. However, the rest of the main sequence, subgiant branch, and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and mergers.

  10. Using He I λ10830 to Diagnose Mass Flows Around Herbig Ae/Be Stars

    Science.gov (United States)

    Cauley, Paul W.; Johns-Krull, Christopher M.

    2015-01-01

    The pre-main sequence Herbig Ae/Be stars (HAEBES) are the intermediate mass cousins of the low mass T Tauri stars (TTSs). However, it is not clear that the same accretion and mass outflow mechanisms operate identically in both mass regimes. Classical TTSs (CTTSs) accrete material from their disks along stellar magnetic field lines in a scenario called magnetospheric accretion. Magnetospheric accretion requires a strong stellar dipole field in order to truncate the inner gas disk. These fields are either absent or very weak on a large majority of HAEBES, challenging the view that magnetospheric accretion is the dominant accretion mechanism. If magnetospheric accretion does not operate similarly around HAEBES as it does around CTTSs, then strong magnetocentrifugal outflows, which are directly linked to accretion and are ubiquitous around CTTSs, may be driven less efficiently from HAEBE systems. Here we present high resolution spectroscopic observations of the He I λ10830 line in a sample of 48 HAEBES. He I λ10830 is an excellent tracer of both mass infall and outflow which is directly manifested as red and blue-shifted absorption in the profile morphologies. These features, among others, are common in our sample. The occurrence of both red and blue-shifted absorption profiles is less frequent, however, than is found in CTTSs. Statistical contingency tests confirm this difference at a significant level. In addition, we find strong evidence for smaller disk truncation radii in the objects displaying red-shifted absorption profiles. This is expected for HAEBES experiencing magnetospheric accretion based on their large rotation rates and weak magnetic field strengths. Finally, the low incidence of blue-shifted absorption in our sample compared to CTTSs and the complete lack of simultaneous red and blue-shifted absorption features suggests that magnetospheric accretion in HAEBES is less efficient at driving strong outflows. The stellar wind-like outflows that are

  11. On the mass-spectrum relation for the main sequence stars

    International Nuclear Information System (INIS)

    Svechnikov, M.A.; Tajdakova, T.A.

    1984-01-01

    From 240 main-sequence stars with well-determined masses, a new mass-spectrum relation is obtained, which differs appreciably in certain intervals of spectral types from the mass-spectrum relations of Allen and Trimble. The accuracy of mass determination for the components of eclipsing binary systems of different types from their spectra given in the General Catalogue of Variable Stars (3rd edition) and in its supplements is evaluated

  12. Fragment mass distribution of proton-induced spallation reaction with intermediate energy

    International Nuclear Information System (INIS)

    Fan Sheng; Ye Yanlin; Xu Chuncheng; Chen Tao; Sobolevsky, N.M.

    2000-01-01

    The test of part benchmark of SHIELD code is finished. The fragment cross section and mass distribution and excitation function of the residual nuclei from proton-induced spallation reaction on thin Pb target with intermediate energy have been calculated by SHIELD code. And the results are in good agreement with measured data. The fragment mass distribution of the residual nuclei from proton-induced spallation reaction on thick Pb target with incident energy 1.6 GeV have been simulated

  13. Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO

    OpenAIRE

    Abbott, B. P.; Abbott, R.; Adhikari, R. X.; Ananyeva, A.; Anderson, S. B.; Appert, S.; Arai, K.; Araya, M. C.; Barayoga, J. C.; Barish, B. C.; Berger, B. K.; Billingsley, G.; Blackburn, J. K.; Bork, R.; Brooks, A. F.

    2017-01-01

    During their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that...

  14. Measuring Intermediate-Mass Black-Hole Binaries with Advanced Gravitational Wave Detectors.

    Science.gov (United States)

    Veitch, John; Pürrer, Michael; Mandel, Ilya

    2015-10-02

    We perform a systematic study to explore the accuracy with which the parameters of intermediate-mass black-hole binary systems can be measured from their gravitational wave (GW) signatures using second-generation GW detectors. We make use of the most recent reduced-order models containing inspiral, merger, and ringdown signals of aligned-spin effective-one-body waveforms to significantly speed up the calculations. We explore the phenomenology of the measurement accuracies for binaries with total masses between 50M(⊙) and 500M(⊙) and mass ratios between 0.1 and 1. We find that (i) at total masses below ∼200M(⊙), where the signal-to-noise ratio is dominated by the inspiral portion of the signal, the chirp mass parameter can be accurately measured; (ii) at higher masses, the information content is dominated by the ringdown, and total mass is measured more accurately; (iii) the mass of the lower-mass companion is poorly estimated, especially at high total mass and more extreme mass ratios; and (iv) spin cannot be accurately measured for our injection set with nonspinning components. Most importantly, we find that for binaries with nonspinning components at all values of the mass ratio in the considered range and at a network signal-to-noise ratio of 15, analyzed with spin-aligned templates, the presence of an intermediate-mass black hole with mass >100M(⊙) can be confirmed with 95% confidence in any binary that includes a component with a mass of 130M(⊙) or greater.

  15. Necessity of intermediate mass scales in grand unified theories with spontaneously broken CP invariance

    International Nuclear Information System (INIS)

    Senjanovic, G.

    1982-07-01

    It is demonstrated that the spontaneous breakdown of CP invariance in grand unified theories requires the presence of intermediate mass scales. The simplest realization is provided by weakly broken left-right symmetry in the context of SU(2)sub(L) x SU(2)sub(R) x U(1)sub(B-L) model embedded in grand unified theories. (author)

  16. Rotation in moderate-mass pre-main-sequence radiative track G stars

    International Nuclear Information System (INIS)

    Mcnamara, B.

    1990-01-01

    Recent studies suggest that the observed high-mass radiative track velocity histograms for pre-main-sequence stars differ significantly. In the Vogel and Kuhi (1981) study, these stars were found to possess a rather broad distribution of rotational velocities with a moderate peak at low velocities. In contrast, Smith et al. (1983), found a very sharply peaked distribution located at low values of v sin i. The difference in these velocity distributions is shown to be due to inadequate allowance for field stars in the Smith, et al., work. Once these stars are removed, the high-mass velocity distributions of the two regions are remarkably similar. This result suggests that a unique velocity distribution might be used in modeling very young stars. Assuming that the Orion Ic proto-F stars continue to contract in a homologous fashion, their average current rotational velocity is in agreement with that expected for zero-age main sequence F stars. 27 refs

  17. The impact of galaxy geometry and mass evolution on the survival of star clusters

    International Nuclear Information System (INIS)

    Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

    2014-01-01

    Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10 10 M ☉ to 10 × 10 10 M ☉ halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk of identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.

  18. The effect of Livermore OPAL opacities on the evolutionary masses of RR Lyrae stars

    Science.gov (United States)

    Yi, Sukyoung; Lee, Young-Wook; Demarque, Pierre

    1993-01-01

    We have investigated the effect of the new Livermore OPAL opacities on the evolution of horizontal-branch (HB) stars. This work was motivated by the recent stellar pulsation calculations using the new Livermore opacities, which suggest that the masses of double-mode RR Lyrae stars are 0.1-0.2 solar mass larger than those based on earlier opacities. Unlike the pulsation calculations, we find that the effect of opacity change on the evolution of HB stars is not significant. In particular, the effect of the mean masses of RR Lyrae stars is very small, showing a decrease of only 0.01-0.02 solar mass compared to the models based on old Cox-Stewart opacities. Consequently, with the new Livermore OPAL opacities, both the stellar pulsation and evolution models now predict approximately the same masses for the RR Lyrae stars. Our evolutionary models suggest that the mean masses of the RR Lyrae stars are about 0.76 and about 0.71 solar mass for M15 (Oosterhoff group II) and M3 (group I), respectively. If (alpha/Fe) = 0.4, these values are decreased by about 0.03 solar mass. Variations of the mean masses of RR Lyrae stars with HB morphology and metallicity are also presented.

  19. Compact stars with a small electric charge: the limiting radius to mass relation and the maximum mass for incompressible matter

    Energy Technology Data Exchange (ETDEWEB)

    Lemos, Jose P.S.; Lopes, Francisco J.; Quinta, Goncalo [Universidade de Lisboa, UL, Departamento de Fisica, Centro Multidisciplinar de Astrofisica, CENTRA, Instituto Superior Tecnico, IST, Lisbon (Portugal); Zanchin, Vilson T. [Universidade Federal do ABC, Centro de Ciencias Naturais e Humanas, Santo Andre, SP (Brazil)

    2015-02-01

    One of the stiffest equations of state for matter in a compact star is constant energy density and this generates the interior Schwarzschild radius to mass relation and the Misner maximum mass for relativistic compact stars. If dark matter populates the interior of stars, and this matter is supersymmetric or of some other type, some of it possessing a tiny electric charge, there is the possibility that highly compact stars can trap a small but non-negligible electric charge. In this case the radius to mass relation for such compact stars should get modifications. We use an analytical scheme to investigate the limiting radius to mass relation and the maximum mass of relativistic stars made of an incompressible fluid with a small electric charge. The investigation is carried out by using the hydrostatic equilibrium equation, i.e., the Tolman-Oppenheimer-Volkoff (TOV) equation, together with the other equations of structure, with the further hypothesis that the charge distribution is proportional to the energy density. The approach relies on Volkoff and Misner's method to solve the TOV equation. For zero charge one gets the interior Schwarzschild limit, and supposing incompressible boson or fermion matter with constituents with masses of the order of the neutron mass one finds that the maximum mass is the Misner mass. For a small electric charge, our analytical approximating scheme, valid in first order in the star's electric charge, shows that the maximum mass increases relatively to the uncharged case, whereas the minimum possible radius decreases, an expected effect since the new field is repulsive, aiding the pressure to sustain the star against gravitational collapse. (orig.)

  20. MOTION VERIFIED RED STARS (MoVeRS): A CATALOG OF PROPER MOTION SELECTED LOW-MASS STARS FROM WISE, SDSS, AND 2MASS

    Energy Technology Data Exchange (ETDEWEB)

    Theissen, Christopher A.; West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Dhital, Saurav, E-mail: ctheisse@bu.edu [Department of Physical Sciences, Embry-Riddle Aeronautical University, 600 South Clyde Morris Blvd., Daytona Beach, FL 32114 (United States)

    2016-02-15

    We present a photometric catalog of 8,735,004 proper motion selected low-mass stars (KML-spectral types) within the Sloan Digital Sky Survey (SDSS) footprint, from the combined SDSS Data Release 10 (DR10), Two Micron All-Sky Survey (2MASS) point-source catalog (PSC), and Wide-field Infrared Survey Explorer (WISE) AllWISE catalog. Stars were selected using r − i, i − z, r − z, z − J, and z − W1 colors, and SDSS, WISE, and 2MASS astrometry was combined to compute proper motions. The resulting 3,518,150 stars were augmented with proper motions for 5,216,854 earlier type stars from the combined SDSS and United States Naval Observatory B1.0 catalog (USNO-B). We used SDSS+USNO-B proper motions to determine the best criteria for selecting a clean sample of stars. Only stars whose proper motions were greater than their 2σ uncertainty were included. Our Motion Verified Red Stars catalog is available through SDSS CasJobs and VizieR.

  1. The BDNYC database of low-mass stars, brown dwarfs, and planetary mass companions

    Science.gov (United States)

    Cruz, Kelle; Rodriguez, David; Filippazzo, Joseph; Gonzales, Eileen; Faherty, Jacqueline K.; Rice, Emily; BDNYC

    2018-01-01

    We present a web-interface to a database of low-mass stars, brown dwarfs, and planetary mass companions. Users can send SELECT SQL queries to the database, perform searches by coordinates or name, check the database inventory on specified objects, and even plot spectra interactively. The initial version of this database contains information for 198 objects and version 2 will contain over 1000 objects. The database currently includes photometric data from 2MASS, WISE, and Spitzer and version 2 will include a significant portion of the publicly available optical and NIR spectra for brown dwarfs. The database is maintained and curated by the BDNYC research group and we welcome contributions from other researchers via GitHub.

  2. Disk Masses around Solar-mass Stars are Underestimated by CO Observations

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Mo; Evans II, Neal J. [Astronomy Department, University of Texas, 2515 Speedway, Stop C1400, Austin, TX 78712 (United States); Dodson-Robinson, Sarah E. [University of Delaware, Department of Physics and Astronomy, 217 Sharp Lab, Newark, DE 19716 (United States); Willacy, Karen; Turner, Neal J. [Mail Stop 169-506, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

    2017-05-20

    Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H{sub 2} abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a function of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H{sub 2} ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low- J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.

  3. Evolution of thermally pulsing asymptotic giant branch stars. IV. Constraining mass loss and lifetimes of low mass, low metallicity AGB stars

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfield, Philip; Dalcanton, Julianne J.; Weisz, Daniel; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Marigo, Paola [Department of Physics and Astronomy G. Galilei, University of Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Girardi, Léo; Gullieuszik, Marco [Osservatorio Astronomico di Padova—INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Bressan, Alessandro [Astrophysics Sector, SISSA, Via Bonomea 265, I-34136 Trieste (Italy); Dolphin, Andrew [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Aringer, Bernhard [Department of Astrophysics, University of Vienna, Turkenschanzstraße 17, A-1180 Wien (Austria)

    2014-07-20

    The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] ≲ –0.86) galaxies taken from the ACS Nearby Galaxy Survey Treasury sample, using Hubble Space Telescope (HST) photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and red giant branch (RGB) stars, N{sub TP-AGB}/N{sub RGB}, to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories derived from the HST deep optical observations. We test various mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). These comparisons confirm that pre-dust mass loss is important, since models that neglect pre-dust mass loss fail to explain the observed N{sub TP-AGB}/N{sub RGB} ratio or the luminosity functions. In contrast, models with more efficient pre-dust mass loss produce results consistent with observations. We find that for [Fe/H] ≲ –0.86, lower mass TP-AGB stars (M ≲ 1 M{sub ☉}) must have lifetimes of ∼0.5 Myr and higher masses (M ≲ 3 M{sub ☉}) must have lifetimes ≲ 1.2 Myr. In addition, assuming our best-fitting mass-loss prescription, we show that the third dredge-up has no significant effect on TP-AGB lifetimes in this mass and metallicity range.

  4. Strange star candidates revised within a quark model with chiral mass scaling

    Institute of Scientific and Technical Information of China (English)

    Ang Li; Guang-Xiong Peng; Ju-Fu Lu

    2011-01-01

    We calculate the properties of static strange stars using a quark model with chiral mass scaling. The results are characterized by a large maximum mass (~ 1.6 M⊙) and radius (~ 10 km). Together with a broad collection of modern neutron star models, we discuss some recent astrophysical observational data that could shed new light on the possible presence of strange quark matter in compact stars. We conclude that none of the present astrophysical observations can prove or confute the existence of strange stars.

  5. A new direction for dark matter research: intermediate-mass compact halo objects

    Energy Technology Data Exchange (ETDEWEB)

    Chapline, George F. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA (United States); Frampton, Paul H., E-mail: george.chapline@gmail.com, E-mail: paul.h.frampton@gmail.com [15 Summerheights, 29 Water Eaton Road, Oxford OX2 7PG (United Kingdom)

    2016-11-01

    The failure to find evidence for elementary particles that could serve as the constituents of dark matter brings to mind suggestions that dark matter might consist of massive compact objects (MACHOs). In particular, it has recently been argued that MACHOs with masses > 15 M {sub ⊙} may have been prolifically produced at the onset of the big bang. Although a variety of astrophysical signatures for primordial MACHOs with masses in this range have been discussed in the literature, we favor a strategy that uses the potential for magnification of stars outside our galaxy due to gravitational microlensing of these stars by MACHOs in the halo of our galaxy. We point out that the effect of the motion of the Earth on the shape of the micro-lensing brightening curves provides a promising approach to testing over the course of next several years the hypothesis that dark matter consists of massive compact objects.

  6. On the core-mass-shell-luminosity relation for shell-burning stars

    International Nuclear Information System (INIS)

    Jeffery, C.S.; Saint Andrews Univ.

    1988-01-01

    Core-mass-shell-luminosity relations for several types of shell-burning star have been calculated using simultaneous differential equations derived from simple homology approximations. The principal objective of obtaining a mass-luminosity relation for helium giants was achieved. This relation gives substantially higher luminosities than the equivalent relation for H-shell stars with core masses greater than 1 solar mass. The algorithm for calculating mass-luminosity relations in this fashion was investigated in detail. Most of the assumptions regarding the physics in the shell do not play a critical role in determining the core-mass-shell-luminosity relation. The behaviour of the core-mass-core-radius relation for a growing degenerate core as a single unique function of mass and growth rate needs to be defined before a single core-mass-shell-luminosity relation for all H-shell stars can be obtained directly from the homology approximations. (author)

  7. Relation between initial and minimum final white dwarf mass for Population I stars

    Energy Technology Data Exchange (ETDEWEB)

    Mazzitelli, I.; Dantona, F.

    1986-12-01

    The evolutionary paths for Population I stars having initial masses 1, 2.5, 3, 4, and 5 solar masses were computed from the homogeneous main sequence to the onset of the first major thermal pulse to evaluate the minimum mass and the chemical stratification of the remnant white dwarf (WD) associated with each parent mass. The helium flash phase was followed in detail for a 2.5 solar masses star, whereas for the 1 solar mass star the flash was bypassed, and the models at the beginning of the steady central helium burning phase were obtained by means of a scaling procedure upon the properly computed total and core masses. The results show that for a parent ranging between 1-3 solar masses the core mass at the first thermal pulse ranges only from 0.64-0.69 solar mass. If some very fast mass-loss mechanism is triggered in connection with the early stages of the thermal pulse phase, as suggested by the observed deficiency of asymptotic giant branch stars, the relation between final and initial mass is almost flat at least up to an initial mass of 3 solar masses, and the mass spectrum of the WDs is narrow and heavily peaked around 0.65 solar mass. 53 references.

  8. Relation between initial and minimum final white dwarf mass for Population I stars

    International Nuclear Information System (INIS)

    Mazzitelli, I.; Dantona, F.; CNR, Istituto di Astrofisica Spaziale, Frascati; Roma, Osservatorio Astronomico, Rome, Italy)

    1986-01-01

    The evolutionary paths for Population I stars having initial masses 1, 2.5, 3, 4, and 5 solar masses were computed from the homogeneous main sequence to the onset of the first major thermal pulse to evaluate the minimum mass and the chemical stratification of the remnant white dwarf (WD) associated with each parent mass. The helium flash phase was followed in detail for a 2.5 solar masses star, whereas for the 1 solar mass star the flash was bypassed, and the models at the beginning of the steady central helium burning phase were obtained by means of a scaling procedure upon the properly computed total and core masses. The results show that for a parent ranging between 1-3 solar masses the core mass at the first thermal pulse ranges only from 0.64-0.69 solar mass. If some very fast mass-loss mechanism is triggered in connection with the early stages of the thermal pulse phase, as suggested by the observed deficiency of asymptotic giant branch stars, the relation between final and initial mass is almost flat at least up to an initial mass of 3 solar masses, and the mass spectrum of the WDs is narrow and heavily peaked around 0.65 solar mass. 53 references

  9. Critical masses of bare homogeneous spherical UO2-water mixtures at intermediate enrichments

    International Nuclear Information System (INIS)

    Rendon, G.L.; Stratton, W.

    1999-01-01

    Critical masses of bare homogeneous spherical UO 2 -water mixtures at various intermediate fissile enrichments determined by multigroup, transport theory is presented. This work was performed to provide support for particular issues encountered by the nuclear industry when operating in the intermediate enrichment regime, namely, the validation of codes used to set criticality safety limits. Validation is normally performed with a comparison of computational results and applicable experiments. However, this may be difficult in some cases because of the lack of sufficient applicable experiments in the intermediate enrichment range. If a large extension of the area of applicability from an experiment to the desired application exists, then an alternative means for validation must be employed. Ideal interpretations of standard ANSI/ANS 8.1 Section 4.3 (1983) implies that perhaps an independent code and data system may be employed for validation purposes

  10. Black holes evaporation and big mass particle (maximon, intermediate boson) creation in nonstationary universe

    International Nuclear Information System (INIS)

    Man'ko, V.I.; Markov, M.A.

    1984-01-01

    This chapter considers the process of creation of particles with maximally big masses (maximons, intermediate bosons) in the nonstationary Universe within the framework of neutral and charged scalar field theory. The conclusions of the matter creation model for real particles (resonances) and hypothetical particles (maximons, friedmons, intermediate bosons) are analyzed. It is determined that if the mechanism of maximon's creation exists, then these particles must be stable. The maximons could be the final states of decaying black holes. A possible mechanism of cosmic ray creation as a result of ''vacuum'' generation of known unstable particles is discussed. The limits upon the mass and the life time of intermediate bosons are calculated. It is demonstrated that the creation of masses greater than 10 GeV, and with life times less than 10- 24 sec and quantity of elementary particles greater than 100 are in contradiction with the particle creation mechanism and the experimental mass density in the Universe. The formalism of the examined method and its vacuum properties are discussed in an appendix

  11. Deeply inelastic collisions as a source of intermediate mass fragments at E/A = 27 MeV

    International Nuclear Information System (INIS)

    Borderie, B.; Montoya, M.; Rivet, M.F.; Jouan, D.; Cabot, C.; Fuchs, H.; Gardes, D.; Gauvin, H.; Jacquet, D.; Monnet, F.

    1988-01-01

    Intermediate-mass fragments detected in coincidence with heavy residues were measured in 40 Ar induced reactions on Ag at E/A = 27 MeV. From the observed characteristics, it is inferred that intermediate-mass fragments associated with the so-called intermediate-velocity source come mainly from deeply inelastic collisions occurring after or at the same time as preequilibrium particle emission. (orig.)

  12. THE SMALL-SCALE PHYSICAL STRUCTURE AND FRAGMENTATION DIFFERENCE OF TWO EMBEDDED INTERMEDIATE-MASS PROTOSTARS IN ORION

    International Nuclear Information System (INIS)

    Van Kempen, T. A.; Longmore, S. N.; Johnstone, D.; Pillai, T.; Fuente, A.

    2012-01-01

    Intermediate-mass (IM) protostars, the bridge between the very common solar-like protostars and the more massive, but rarer, O and B stars, can only be studied at high physical spatial resolutions in a handful of clouds. In this paper, we present and analyze the continuum results from an observing campaign at the Submillimeter Array (SMA) targeting two well-studied IM protostars in Orion, NGC 2071 and L1641 S3 MMS 1. The extended SMA (eSMA) probes structure at angular resolutions up to 0.''2, revealing protostellar disks on scales of ∼200 AU. Continuum flux measurements on these scales indicate that a significant amount of mass, a few tens of M ☉ , is present. Envelope, stellar, and disk masses are derived using compact, extended, and eSMA configurations and compared against spectral energy distribution fitting models. We hypothesize that fragmentation into three components occurred within NGC 2071 at an early time, when the envelopes were less than 10% of their current masses, e.g., ☉ . No fragmentation occurred for L1641 S3 MMS 1. For NGC 2071, evidence is given that the bulk of the envelope material currently around each source was accreted after the initial fragmentation. In addition, about 30% of the total core mass is not yet associated to one of the three sources. A global accretion model is favored and a potential accretion history of NGC 2071 is presented. It is shown that the relatively low level of fragmentation in NGC 2071 was stifled compared to the expected fragmentation from a Jeans argument. Similarly, the lack of fragmentation in L1641 S3 MMS 1 is likely due to similar arguments.

  13. THE SMALL-SCALE PHYSICAL STRUCTURE AND FRAGMENTATION DIFFERENCE OF TWO EMBEDDED INTERMEDIATE-MASS PROTOSTARS IN ORION

    Energy Technology Data Exchange (ETDEWEB)

    Van Kempen, T. A. [Joint ALMA Offices, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Longmore, S. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Johnstone, D. [National Research Council Canada, Herzberg Institute for Astronomy, 5071 West Saanich Road, Victoria, BC (Canada); Pillai, T. [Caltech, MC 249-17, 1200 East California Blvd, Pasadena, CA 91125 (United States); Fuente, A., E-mail: tkempen@alma.cl [Observatorio Astronomico Nacional (OAN), Apdo. 112, E-28803 Alcala de Henares, Madrid (Spain)

    2012-06-01

    Intermediate-mass (IM) protostars, the bridge between the very common solar-like protostars and the more massive, but rarer, O and B stars, can only be studied at high physical spatial resolutions in a handful of clouds. In this paper, we present and analyze the continuum results from an observing campaign at the Submillimeter Array (SMA) targeting two well-studied IM protostars in Orion, NGC 2071 and L1641 S3 MMS 1. The extended SMA (eSMA) probes structure at angular resolutions up to 0.''2, revealing protostellar disks on scales of {approx}200 AU. Continuum flux measurements on these scales indicate that a significant amount of mass, a few tens of M{sub Sun }, is present. Envelope, stellar, and disk masses are derived using compact, extended, and eSMA configurations and compared against spectral energy distribution fitting models. We hypothesize that fragmentation into three components occurred within NGC 2071 at an early time, when the envelopes were less than 10% of their current masses, e.g., <0.5 M{sub Sun }. No fragmentation occurred for L1641 S3 MMS 1. For NGC 2071, evidence is given that the bulk of the envelope material currently around each source was accreted after the initial fragmentation. In addition, about 30% of the total core mass is not yet associated to one of the three sources. A global accretion model is favored and a potential accretion history of NGC 2071 is presented. It is shown that the relatively low level of fragmentation in NGC 2071 was stifled compared to the expected fragmentation from a Jeans argument. Similarly, the lack of fragmentation in L1641 S3 MMS 1 is likely due to similar arguments.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

  15. Model atmospheres with periodic shocks. [pulsations and mass loss in variable stars

    Science.gov (United States)

    Bowen, G. H.

    1989-01-01

    The pulsation of a long-period variable star generates shock waves which dramatically affect the structure of the star's atmosphere and produce conditions that lead to rapid mass loss. Numerical modeling of atmospheres with periodic shocks is being pursued to study the processes involved and the evolutionary consequences for the stars. It is characteristic of these complex dynamical systems that most effects result from the interaction of various time-dependent processes.

  16. Neutrino masses in the SO(10) model with intermediate stage of the symmetry breaking

    International Nuclear Information System (INIS)

    Svetovoj, V.B.

    1982-01-01

    An effect for the neutrino masses of an intermediate stage in the symmetry spontaneous breaking, different from SU(5), is investigated in some detail for the SO(1O) model. There are two possibilities depending on the composition of the Higgs sector: i) msub(ν) approximately msub(f)(Msub(W)/Msub(1)); ii) msub(ν) approximately msub(f)sub(b)/Msub(1))(M/Msub(1)), where M, M 1 and Msub) are the scales of the breaking of the original SO(10) simmetry, the intermediate symmetry, and the standard SUsub(c)(3)xSUsub(L)(2)xU(1) symmetry, respectively, and msub(f) is a typical fermion mass. It as shown that a Majorana mass of the right neutrino (νsub(R)) of a purely loop origin would result in a too large mass of the usual neutrinos, so a tree-graph contribution to the mass of νsub(R) is necessary. Numerical estimates for the neutrino masses are discussed [ru

  17. Neutrino masses in an SO(10) model with an intermediate stage of symmetry breaking

    International Nuclear Information System (INIS)

    Svetovoi, V.B.

    1982-01-01

    The effect on neutrino masses of an intermediate stage in symmetry breaking different from SU(5) is investigated in detail for the SO(10) model. There are two possibilities depending on the contents of the Higgs sector: i) m/sub ν/approx.m/sub f/(M/sub W//M 1 ); ii) m/sub ν/approx.m/sub f/(M/sub W//M 1 )(M/M 1 ), where M, M 1 and M/sub W/ are the scales of the breaking of the original SO(10) symmetry, the intermediate symmetry, and the standard SU/sub c/(3) x SU/sub L/(2) x U(1) symmetry, respectively, and m/sub f/ is a typical fermion mass. It is shown that a Majorana mass of the right-handed-neutrino (ν/sub R/) of a purely loop origin would result in too large a mass of the usual neutrinos, so a tree-graph contribution to the mass of ν/sub R/ is necessary. Numerical estimates for the neutrino masses are discussed

  18. Measurement of mass distribution of U-235 fission products in the intermediate neutron region

    International Nuclear Information System (INIS)

    Nakagomi, Yoshihiro; Kobayashi, Shohei; Yamamoto, Shuji; Kanno, Ikuo; Wakabayashi, Hiroaki.

    1982-01-01

    The mass distribution and the momentum distribution of U-235 fission products in the intermediate neutron region were measured by using a combination system of the Yayoi intermediate neutron column and an electron linear accelerator. The double energy measurement method was applied. A fission chamber, which consists of an enriched uranium target and two Si surface barrier detectors, was used for the measurement of the neutrons with energy above 1.3 eV. The linear accelerator was operated at the repetition rate of 100 Hz and the pulse width of 10 ns. The data obtained by the two-dimensional pulse height analysis were analyzed by the Schmitt's method. The preliminary results of the mass distribution and the momentum distribution of fission fragments were obtained. (Kato, T.)

  19. Mass return to the interstellar medium from highly-evolved carbon stars

    International Nuclear Information System (INIS)

    Latter, W.B.; Thronson, H.A. Jr.; Hacking, P.; Bally, J.; Black, J.; Bell Telephone Labs. Inc., Holmdel, NJ)

    1986-01-01

    Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated

  20. Constraining the mass and radius of neutron stars in globular clusters

    Science.gov (United States)

    Steiner, A. W.; Heinke, C. O.; Bogdanov, S.; Li, C. K.; Ho, W. C. G.; Bahramian, A.; Han, S.

    2018-05-01

    We analyse observations of eight quiescent low-mass X-ray binaries in globular clusters and combine them to determine the neutron star mass-radius curve and the equation of state of dense matter. We determine the effect that several uncertainties may have on our results, including uncertainties in the distance, the atmosphere composition, the neutron star maximum mass, the neutron star mass distribution, the possible presence of a hotspot on the neutron star surface, and the prior choice for the equation of state of dense matter. The distance uncertainty is implemented in a new Gaussian blurring method that can be directly applied to the probability distribution over mass and radius. We find that the radius of a 1.4 solar mass neutron star is most likely from 10 to 14 km and that tighter constraints are only possible with stronger assumptions about the nature of the neutron stars, the systematics of the observations, or the nature of dense matter. Strong phase transitions in the equation of state are preferred, and in this case, the radius is likely smaller than 12 km. However, radii larger than 12 km are preferred if the neutron stars have uneven temperature distributions.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  2. The 2014-2017 outburst of the young star ASASSN-13db. A time-resolved picture of a very-low-mass star between EXors and FUors

    Science.gov (United States)

    Sicilia-Aguilar, A.; Oprandi, A.; Froebrich, D.; Fang, M.; Prieto, J. L.; Stanek, K.; Scholz, A.; Kochanek, C. S.; Henning, Th.; Gredel, R.; Holoien, T. W.-S.; Rabus, M.; Shappee, B. J.; Billington, S. J.; Campbell-White, J.; Zegmott, T. J.

    2017-11-01

    Context. Accretion outbursts are key elements in star formation. ASASSN-13db is a M5-type star with a protoplanetary disk, the lowest-mass star known to experience accretion outbursts. Since its discovery in 2013, it has experienced two outbursts, the second of which started in November 2014 and lasted until February 2017. Aims: We explore the photometric and spectroscopic behavior of ASASSN-13db during the 2014-2017 outburst. Methods: We use high- and low-resolution spectroscopy and time-resolved photometry from the ASAS-SN survey, the LCOGT and the Beacon Observatory to study the light curve of ASASSN-13db and the dynamical and physical properties of the accretion flow. Results: The 2014-2017 outburst lasted for nearly 800 days. A 4.15 d period in the light curve likely corresponds to rotational modulation of a star with hot spot(s). The spectra show multiple emission lines with variable inverse P-Cygni profiles and a highly variable blue-shifted absorption below the continuum. Line ratios from metallic emission lines (Fe I/Fe II, Ti I/Ti II) suggest temperatures of 5800-6000 K in the accretion flow. Conclusions: Photometrically and spectroscopically, the 2014-2017 event displays an intermediate behavior between EXors and FUors. The accretion rate ([Ṁ]= 1-3 × 10-7 M⊙/yr), about two orders of magnitude higher than the accretion rate in quiescence, is not significantly different from the accretion rate observed in 2013. The absorption features in the spectra suggest that the system is viewed at a high angle and drives a powerful, non-axisymmetric wind, maybe related to magnetic reconnection. The properties of ASASSN-13db suggest that temperatures lower than those for solar-type stars are needed for modeling accretion in very-low-mass systems. Finally, the rotational modulation during the outburst reveals that accretion-related structures settle after the beginning of the outburst and can be relatively stable and long-lived. Our work also demonstrates the power

  3. Hydrogen-antihydrogen oscillations: Signature of intermediate mass scales in GUTs

    Directory of Open Access Journals (Sweden)

    Uptal Sarkar

    1983-01-01

    Full Text Available Hydrogen-antihydrogen oscillations and the double nucleon decay (pp, np and nn into two antileptons are discussed in the context of SO(10, E(6 and SU(16 GUTs. It is shown that the intermediate mass scales of the GUTs concerned govern the amplitude of these processes which are found to compete with the other baryon nonconserving processes in SU(16 GUT.

  4. AGB [asymptotic giant branch]: Star evolution

    International Nuclear Information System (INIS)

    Becker, S.A.

    1987-01-01

    Asymptotic giant branch stars are red supergiant stars of low-to-intermediate mass. This class of stars is of particular interest because many of these stars can have nuclear processed material brought up repeatedly from the deep interior to the surface where it can be observed. A review of recent theoretical and observational work on stars undergoing the asymptotic giant branch phase is presented. 41 refs

  5. Observations of mass loss from OB and Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Barlow, M.J.

    1982-01-01

    In this review, three observationally accessible parameters of the winds of OB and Wolf-Rayet stars are discussed: (1) Terminal velocities, (2) Velocity laws, (3) Mass loss rates. In addition, some discussion of the ionisation structure of the winds is included. In general, only the most recent results for OB stars are mentioned. (Auth.)

  6. A two-solar-mass neutron star measured using Shapiro delay

    NARCIS (Netherlands)

    Demorest, P.B.; Pennucci, T.; Ransom, S.M.; Roberts, M.S.E.; Hessels, J.W.T.

    2010-01-01

    Neutron stars are composed of the densest form of matter known to exist in our Universe, the composition and properties of which are still theoretically uncertain. Measurements of the masses or radii of these objects can strongly constrain the neutron star matter equation of state and rule out

  7. Tracing early evolutionary stages of high-mass star formation with molecular lines

    NARCIS (Netherlands)

    Marseille, M. G.; van der Tak, F. F. S.; Herpin, F.; Jacq, T.

    2010-01-01

    Context. Despite its major role in the evolution of the interstellar medium, the formation of high-mass stars (M >= 10 M(circle dot)) remains poorly understood. Two types of massive star cluster precursors, the so-called massive dense cores (MDCs), have been observed, which differ in terms of their

  8. PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

    Energy Technology Data Exchange (ETDEWEB)

    Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed [California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Shkolnik, Evgenya L.; Flagg, Laura [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Liu, Michael C.; Howard, Andrew W.; Aller, Kimberly M.; Best, William M. J.; Kotson, Michael C.; Baranec, Christoph [Institute for Astronomy, University of Hawai‘i at Mānoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Schlieder, Joshua E. [NASA Postdoctoral Program Fellow, NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States); Mann, Andrew W.; Dupuy, Trent J. [Department of Astronomy, University of Texas at Austin, TX (United States); Hinkley, Sasha [Physics and Astronomy, University of Exeter, EX4 4QL Exeter (United Kingdom); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Johnson, John Asher [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Weinberger, Alycia J. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington, DC 20015 (United States); Allers, Katelyn N. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Herczeg, Gregory J., E-mail: bpbowler@caltech.edu [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871 (China); and others

    2015-06-10

    We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (∼10–100 M{sub Jup}) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 M{sub Jup}) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ∼40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the

  9. PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

    International Nuclear Information System (INIS)

    Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed; Shkolnik, Evgenya L.; Flagg, Laura; Liu, Michael C.; Howard, Andrew W.; Aller, Kimberly M.; Best, William M. J.; Kotson, Michael C.; Baranec, Christoph; Schlieder, Joshua E.; Mann, Andrew W.; Dupuy, Trent J.; Hinkley, Sasha; Crepp, Justin R.; Johnson, John Asher; Weinberger, Alycia J.; Allers, Katelyn N.; Herczeg, Gregory J.

    2015-01-01

    We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (∼10–100 M Jup ) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 M Jup ) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ∼40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest

  10. The convective noise floor for the spectroscopic detection of low mass companions to solar type stars

    Science.gov (United States)

    Deming, D.; Espenak, F.; Jennings, D. E.; Brault, J. W.

    1986-01-01

    The threshold mass for the unambiguous spectroscopic detection of low mass companions to solar type stars is defined here as the time when the maximum acceleration in the stellar radial velocity due to the Doppler reflex of the companion exceeds the apparent acceleration produced by changes in convection. An apparent acceleration of 11 m/s/yr in integrated sunlight was measured using near infrared Fourier transform spectroscopy. This drift in the apparent solar velocity is attributed to a lessening in the magnetic inhibition of granular convection as solar minimum approaches. The threshold mass for spectroscopic detection of companions to a one solar mass star is estimated at below one Jupiter mass.

  11. CHARACTERIZING THE STAR FORMATION OF THE LOW-MASS SHIELD GALAXIES FROM HUBBLE SPACE TELESCOPE IMAGING

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Simones, Jacob E. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street, S.E., Minneapolis, MN 55455 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Haynes, Martha P.; Giovanelli, Riccardo [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Salzer, John J. [Department of Astronomy, Indiana University, 727 East 3rd Street, Bloomington, IN 47405 (United States); Adams, Elizabeth A. K. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7900 AA Dwingeloo (Netherlands); Elson, Ed C. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa); Ott, Jürgen, E-mail: kmcquinn@astro.umn.edu [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)

    2015-03-20

    The Survey of Hi in Extremely Low-mass Dwarfs is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies that populate the faint end of the galaxy luminosity function. The galaxies were selected from the first ∼10% of the Hi Arecibo Legacy Fast ALFA survey based on their low Hi mass and low baryonic mass. Here, we measure the star formation properties from optically resolved stellar populations for 12 galaxies using a color–magnitude diagram fitting technique. We derive lifetime average star formation rates (SFRs), recent SFRs, stellar masses, and gas fractions. Overall, the recent SFRs are comparable to the lifetime SFRs with mean birthrate parameter of 1.4, with a surprisingly narrow standard deviation of 0.7. Two galaxies are classified as dwarf transition galaxies (dTrans). These dTrans systems have star formation and gas properties consistent with the rest of the sample, in agreement with previous results that some dTrans galaxies may simply be low-luminosity dwarf irregulars. We do not find a correlation between the recent star formation activity and the distance to the nearest neighboring galaxy, suggesting that the star formation process is not driven by gravitational interactions, but regulated internally. Further, we find a broadening in the star formation and gas properties (i.e., specific SFRs, stellar masses, and gas fractions) compared to the generally tight correlation found in more massive galaxies. Overall, the star formation and gas properties indicate these very low-mass galaxies host a fluctuating, non-deterministic, and inefficient star formation process.

  12. Observations of Intermediate-mass Black Holes and Ultra-Luminous X-ray sources

    Science.gov (United States)

    Colbert, E. J. M.

    2003-12-01

    I will review various observations that suggest that intermediate-mass black holes (IMBHs) with masses ˜102-104 M⊙ exist in our Universe. I will also discuss some of the limitations of these observations. HST Observations of excess dark mass in globular cluster cores suggest IMBHs may be responsible, and some mass estimates from lensing experiments are nearly in the IMBH range. The intriguing Ultra-Luminous X-ray sources (ULXs, or IXOs) are off-nuclear X-ray point sources with X-ray luminosities LX ≳ 1039 erg s-1. ULXs are typically rare (1 in every 5 galaxies), and the nature of their ultra-luminous emission is currently debated. I will discuss the evidence for IMBHs in some ULXs, and briefly outline some phenomenology. Finally, I will discuss future observations that can be made to search for IMBHs.

  13. Bounds on the mass and the moment of inertia of nonrotating neutron stars

    International Nuclear Information System (INIS)

    Sabbadini, A.G.

    1976-01-01

    Bounds are placed on the mass and the moment of inertia of relativistic, spherical, perfect fluid neutron stars, under minimal assumptions on the equation of state of neutron star matter above nuclear densities. The assumptions are: the pressure p, the density rho, and the derivative dp/d rho are positive. The equation of state is assumed to be known below the density rho 0 = 5 x 10 14 g/cm 3 . The upper bound on the mass of a nonrotating neutron star, under these assumptions, is found to be 5 M/sub solar mass/. Upper and lower bounds on the moment of inertia are derived: for a spherical star of given mass and radius (without assuming a specific equation of state in any density region); for a spherical neutron star of arbitrary mass and radius; for a spherical neutron star of given mass. These bounds are optimum ones, in the sense that there always exists a configuration consistent with the assumptions, having a moment of inertia equal to the bound. Using these results for the moment of inertia, the correction to the upper bound on the mass due to slow rotation is discussed

  14. Mass loss by stars at the stage of the asymptotic giant branch

    International Nuclear Information System (INIS)

    Frantsman, Y.L.

    1986-01-01

    For a given initial stellar mass function, star formation function, and initial chemical composition, distributions have been constructed for stars of the asymptotic giant branch by luminosity, and for white dwarfs by mass, by calculating the approximate evolution of a large number of stars. Variants are calculated with different assumptions about the mass loss in the asymptotic branch. Theory can be reconciled with observation only if it is assumed that at this stage there is also a still large mass loss in addition to the stellar wind and the ejection of a planetary nebula shell. This provides the explanation for the absence in the Magellanic clouds of carbon stars with M /sub bol/ 1.0M /sub ./. The degenerate carbon-oxygen nuclei of stars evolving along the asymptotic giant branch cannot attain the Chandrasekhar limit on account of the great mass loss by the stars. The luminosity of stars of the asymptotic giant branch in the globular clusters of the Magellanic Clouds is a good indicator of the age of the clusters

  15. Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB

    Science.gov (United States)

    Barnes, J. R.; Jeffers, S. V.; Haswell, C. A.; Jones, H. R. A.; Shulyak, D.; Pavlenko, Ya. V.; Jenkins, J. S.

    2017-10-01

    We aim to understand how stellar parameters such as mass and rotation impact the distribution of star-spots on the stellar surface. To this purpose, we have used Doppler imaging to reconstruct the surface brightness distributions of three fully convective M dwarfs with similar rotation rates. We secured high cadence spectral time series observations of the 5.5 au separation binary GJ 65, comprising GJ 65A (M5.5V, Prot = 0.24 d) and GJ 65B (M6V, Prot = 0.23 d). We also present new observations of GJ 791.2A (M4.5V, Prot = 0.31 d). Observations of each star were made on two nights with UVES, covering a wavelength range from 0.64 - 1.03μm. The time series spectra reveal multiple line distortions that we interpret as cool star-spots and which are persistent on both nights suggesting stability on the time-scale of 3 d. Spots are recovered with resolutions down to 8.3° at the equator. The global spot distributions for GJ 791.2A are similar to observations made a year earlier. Similar high latitude and circumpolar spot structure is seen on GJ 791.2A and GJ 65A. However, they are surprisingly absent on GJ 65B, which instead reveals more extensive, larger, spots concentrated at intermediate latitudes. All three stars show small amplitude latitude-dependent rotation that is consistent with solid body rotation. We compare our measurements of differential rotation with previous Doppler imaging studies and discuss the results in the wider context of other observational estimates and recent theoretical predictions.

  16. Initial mass function for early-type stars in starburst galaxies

    International Nuclear Information System (INIS)

    Sekiguchi, K.; Anderson, K.S.

    1987-01-01

    The IMF slope of early-type stars in starburst galaxies is investigated using IUE observations and a technique that utilizes mass-linewidth relations for early-type stars. Fourteen low-resolution IUE spectra of eight starburst galaxies and three H II region galaxies are used to obtain line-strength ratios Si IV(1400 A)/C IV(1550 A). These are compared to model line ratios, and indicate that the average IMF slope for OB stars in these intense star-formation regions is appreciably flatter than that of the solar neighborhood. 46 references

  17. Reconciling mass functions with the star-forming main sequence via mergers

    Science.gov (United States)

    Steinhardt, Charles L.; Yurk, Dominic; Capak, Peter

    2017-06-01

    We combine star formation along the 'main sequence', quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging.

  18. Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars

    Science.gov (United States)

    Jones, M. I.; Jenkins, J. S.; Brahm, R.; Wittenmyer, R. A.; Olivares E., F.; Melo, C. H. F.; Rojo, P.; Jordán, A.; Drass, H.; Butler, R. P.; Wang, L.

    2016-05-01

    Context. Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets. In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. Aims: During the past six years we have conducted a radial velocity follow-up program of 166 giant stars to detect substellar companions and to characterize their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. Methods: We took multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we computed precision radial velocities and derived atmospheric and physical parameters. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we detected the presence of several substellar companions. Results: We present four new planetary systems around the giant stars HIP 8541, HIP 74890, HIP 84056, and HIP 95124. Additionally, we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5-5.9% around stars with [Fe/H] ~ 0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆ ~ 1.0 and 2.1 M⊙, with a maximum of f = 13.0+10.1-4.2% at M⋆ = 2.1 M⊙. Conclusions: We conclude that giant planets are preferentially formed around metal-rich stars. In addition, we conclude that they are more efficiently formed around more massive stars, in the stellar mass range of ~1.0-2.1 M⊙. These observational results confirm previous findings for solar

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

    NARCIS (Netherlands)

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

    2013-01-01

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

  20. Determination of the mass-ratio distribution, I: single-lined spectroscopic binary stars

    NARCIS (Netherlands)

    Hogeveen, S.J.

    1992-01-01

    For single-lined spectroscopic binary stars (sbi), the mass ratio q = Msec=Mprim is calculated from the mass function f(m), which is determined from observations. For statistical investigations of the mass-ratio distribution, the term sin^3 i, that remains in the cubic equation from which q is

  1. Evolution of variable stars

    International Nuclear Information System (INIS)

    Becker, S.A.

    1986-08-01

    Throughout the domain of the H R diagram lie groupings of stars whose luminosity varies with time. These variable stars can be classified based on their observed properties into distinct types such as β Cephei stars, δ Cephei stars, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive star, an intermediate mass star, and a low mass star will be presented. 19 refs., 1 fig., 1 tab

  2. Ultra-luminous X-ray sources and intermediate-mass black holes

    International Nuclear Information System (INIS)

    Cseh, David

    2012-01-01

    More than ten years ago, the discovery of Ultra-luminous X-ray sources (ULXs) has opened up an entirely new field in astrophysics. Many ideas were developed to explain the nature of these sources, like their emission mechanism, mass, and origin, without any strong conclusions. Their discovery boosted the fields of X-ray binaries, accretion physics, stellar evolution, cosmology, black hole formation and growth, due to the concept of intermediate-mass black holes (IMBHs). Since their discovery is related to the domain of X-ray astrophysics, there have been very few studies made in other wavelengths. This thesis focuses on the multiwavelength nature of Ultra-luminous X-ray sources and intermediate-mass black holes from various aspects, which help to overcome some difficulties we face today. First, I investigated the accretion signatures of a putative intermediate-mass black hole in a particular globular cluster. To this purpose, I characterized the nature of the innermost X-ray sources in the cluster. Then I calculated an upper limit on the mass of the black hole by studying possible accretion efficiencies and rates based on the dedicated X-ray and radio observations. The accreting properties of the source was described with standard spherical accretion and in the context of inefficient accretion. Secondly, I attempted to dynamically measure the mass of the black hole in a particular ULX via optical spectroscopy. I discovered that a certain emission line has a broad component that markedly shifts in wavelength. I investigated the possibility whether this line originates in the accretion disk, and thus might trace the orbital motion of the binary system. I also characterized the parameters of the binary system, such as the mass function, possible orbital separation, the size of the line-emitting region, and an upper limit on the mass of the black hole. Then I studied the environment of a number of ULXs that are associated with large-scale optical and radio nebulae. I

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

    Science.gov (United States)

    Suzuki, Takeru K.

    2018-06-01

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

  4. 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.

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

    International Nuclear Information System (INIS)

    Li Zhongmu; Mao Caiyan; Chen Li; Zhang Qian

    2012-01-01

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

  6. Basic calibrations of the photographic RGU system. III - Intermediate and extreme Population II dwarf stars

    Science.gov (United States)

    Buser, R.; Fenkart, R. P.

    1990-11-01

    This paper presents an extended calibration of the color-magnitude and two-color diagrams and the metal-abundance parameter for the intermediate Population II and the extreme halo dwarfs observed in the Basel Palomar-Schmidt RGU three-color photometric surveys of the galaxy. The calibration covers the metallicity range between values +0.50 and -3.00. It is shown that the calibrations presented are sufficiently accurate to be useful for the future analyses of photographic survey data.

  7. Effect of mass loss on the driving of g-modes in B supergiant stars

    Energy Technology Data Exchange (ETDEWEB)

    Godart, Melanie; Noels, Arlette [Institut d' Astrophysique et de Geophysique, Liege (Belgium); Dupret, Marc-Antoine [Observatoire de Paris-Meudon, LESIA (France)], E-mail: Helanie.Godart@ulg.ac.be, E-mail: Arlette.Noels@ulg.ac.be, E-mail: ma.dupret@obspm.fr

    2008-10-15

    MOST has detected p and g-modes in the B supergiant star HD163899. Saio et al. (2006) have explained the driving of g-modes in a post main sequence star by the presence of a convective shell which prevents some modes from entering the damping radiative core. We show that this scenario depends on the evolution of the star, with or without mass loss. If the mass loss rate is high enough, the convective shell disappears and all the g-modes are stable.

  8. Effect of mass loss on the driving of g-modes in B supergiant stars

    International Nuclear Information System (INIS)

    Godart, Melanie; Noels, Arlette; Dupret, Marc-Antoine

    2008-01-01

    MOST has detected p and g-modes in the B supergiant star HD163899. Saio et al. (2006) have explained the driving of g-modes in a post main sequence star by the presence of a convective shell which prevents some modes from entering the damping radiative core. We show that this scenario depends on the evolution of the star, with or without mass loss. If the mass loss rate is high enough, the convective shell disappears and all the g-modes are stable.

  9. Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements

    Science.gov (United States)

    Raithel, Carolyn A.; Sukhbold, Tuguldur; Özel, Feryal

    2018-03-01

    The mass distribution of compact objects provides a fossil record that can be studied to uncover information on the late stages of massive star evolution, the supernova explosion mechanism, and the dense matter equation of state. Observations of neutron star masses indicate a bimodal Gaussian distribution, while the observed black hole mass distribution decays exponentially for stellar-mass black holes. We use these observed distributions to directly confront the predictions of stellar evolution models and the neutrino-driven supernova simulations of Sukhbold et al. We find strong agreement between the black hole and low-mass neutron star distributions created by these simulations and the observations. We show that a large fraction of the stellar envelope must be ejected, either during the formation of stellar-mass black holes or prior to the implosion through tidal stripping due to a binary companion, in order to reproduce the observed black hole mass distribution. We also determine the origins of the bimodal peaks of the neutron star mass distribution, finding that the low-mass peak (centered at ∼1.4 M ⊙) originates from progenitors with M ZAMS ≈ 9–18 M ⊙. The simulations fail to reproduce the observed peak of high-mass neutron stars (centered at ∼1.8 M ⊙) and we explore several possible explanations. We argue that the close agreement between the observed and predicted black hole and low-mass neutron star mass distributions provides new, promising evidence that these stellar evolution and explosion models capture the majority of relevant stellar, nuclear, and explosion physics involved in the formation of compact objects.

  10. Shadow of a Large Disc Casts New Light on the Formation of High Mass Stars

    Science.gov (United States)

    2004-05-01

    : 3815 x 4574 pix - 5.4M] Caption: PR Photo 15a/04 is a reproduction of a three-colour composite of the sky region of M 17, a H II region excited by a cluster of young, hot stars. A large silhouette disc has been found to the south-west of the cluster centre. The area within the indicated square is shown in more detail in PR Photo 15b/04. The present image was obtained with the ISAAC near-infrared instrument at the 8.2-m VLT ANTU telescope at Paranal. In the left photo, the orientation and the scale at the distance of M 17 (7,000 light-years) are indicated, and the main regions are identified. To the right, this beautiful photo is available without text and in full resolution for reproduction purposes. While many details related to the formation and early evolution of low-mass stars like the Sun are now well understood, the basic scenario that leads to the formation of high-mass stars [2] still remains a mystery. Two possible scenarios for the formation of massive stars are currently being studied. In the first, such stars form by accretion of large amounts of circumstellar material; the infall onto the nascent star varies with time. Another possibility is formation by collision (coalescence) of protostars of intermediate masses, increasing the stellar mass in "jumps". In their continuing quest to add more pieces to the puzzle and help providing an answer to this fundamental question, a team of European astronomers [1] used a battery of telescopes, mostly at two of the European Southern Observatory's Chilean sites of La Silla and Paranal, to study in unsurpassed detail the Omega nebula. The Omega nebula, also known as the 17th object in the list of famous French astronomer Charles Messier, i.e. Messier 17 or M 17, is one of the most prominent star forming regions in our Galaxy. It is located at a distance of 7,000 light-years. M 17 is extremely young - in astronomical terms - as witnessed by the presence of a cluster of high-mass stars that ionise the surrounding

  11. An upper bound on Q-star masses

    International Nuclear Information System (INIS)

    Hochron, D.R.; Selipsky, S.B.

    1992-06-01

    Q-stars (the gravitational generalization of Q-balls, strongly bound bulk matter that an appear in field theories of strongly interacting hadrons) are the only known impact objects consistent with the known bulk structure of nuclei and chiral symmetry that evade the Rhoades-Ruffini upper bound of 3.2M circle-dot . Generic bounds are quite weak: M Q-star circle-dot . If, however, we assume that the 1.558 ms pulsar is a Q-star, equilibrium. A stability criteria of rotating fluids place a much stronger upper bound of M c ≤ 5.3M circle-dot on such models under certain special assumptions. This has important implications for heavy compact objects such as Cygnus X-1

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

    Science.gov (United States)

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

    2018-01-01

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

  13. The mass-metallicity relations for gas and stars in star-forming galaxies: strong outflow versus variable IMF

    Science.gov (United States)

    Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Comparat, Johan; Gonzalez-Perez, Violeta; Ventura, Paolo

    2018-02-01

    We investigate the mass-metallicity relations for the gaseous (MZRgas) and stellar components (MZRstar) of local star-forming galaxies based on a representative sample from Sloan Digital Sky Survey Data Release 12. The mass-weighted average stellar metallicities are systematically lower than the gas metallicities. This difference in metallicity increases towards galaxies with lower masses and reaches 0.4-0.8 dex at 109 M⊙ (depending on the gas metallicity calibration). As a result, the MZRstar is much steeper than the MZRgas. The much lower metallicities in stars compared to the gas in low-mass galaxies imply dramatic metallicity evolution with suppressed metal enrichment at early times. The aim of this paper is to explain the observed large difference in gas and stellar metallicity and to infer the origin of the mass-metallicity relations. To this end we develop a galactic chemical evolution model accounting for star formation, gas inflow and outflow. By combining the observed mass-metallicity relation for both gas and stellar components to constrain the models, we find that only two scenarios are able to reproduce the observations. Either strong metal outflow or a steep initial mass function (IMF) slope at early epochs of galaxy evolution is needed. Based on these two scenarios, for the first time we successfully reproduce the observed MZRgas and MZRstar simultaneously, together with other independent observational constraints in the local Universe. Our model also naturally reproduces the flattening of the MZRgas at the high-mass end leaving the MZRstar intact, as seen in observational data.

  14. Coronal mass ejection shock fronts containing the two types of intermediate shocks

    International Nuclear Information System (INIS)

    Steinolfson, R.S.; Hundhausen, A.J.

    1990-01-01

    Numerical solutions of the time-dependent, magnetohydrodynamic (MHD) equations in two dimensions are used to demonstrate the formation of both types of intermediate shocks in a single shock front for physical conditions that are an idealization of those expected to occur in some observed coronal mass ejections. The key to producing such a shock configuration in the simulations is the use of an initial atmosphere containing a magnetic field representative of that in a coronal streamer with open field lines overlying a region of closed field lines. Previous attempts using just open field lines (perpendicular to the surface) produced shock configurations containing just one of the two intermediate shock types. A schematic of such a shock front containing both intermediate shock types has been constructed previously based solely on the known properties of MHD shocks from the Rankine-Hugoniot equations and specific requirements placed on the shock solution at points along the front where the shock normal and upstream magnetic field are aligned. The shock front also contains, at various locations along the front, a hydrodynamic (nonmagnetic) shock, a switch-on shock, and a fast shock in addition to the intermediate shocks. This particular configuration occurs when the shock front speed exceeds the upstream (preshock) intermediate wave speed but is less than a critical speed defined in the paper (equation 1) along at least some portion of the shock front. A distinctive feature of the front is that it is concave upward (away from the surface) near the region where the field in the preshock plasma is normal to the front of near the central portion of the shock front

  15. A Universal Break in the Planet-to-star Mass-ratio Function of Kepler MKG Stars

    Science.gov (United States)

    Pascucci, Ilaria; Mulders, Gijs D.; Gould, Andrew; Fernandes, Rachel

    2018-04-01

    We follow the microlensing approach and quantify the occurrence of Kepler exoplanets as a function of planet-to-star mass ratio, q, rather than planet radius or mass. For planets with radii ∼1–6 R ⊕ and periods law with a break at ∼3 × 10‑5 independent of host type for hosts below 1 M ⊙. These findings indicate that the planet-to-star mass ratio is a more fundamental quantity in planet formation than planet mass. We then compare our results to those from microlensing for which the overwhelming majority satisfies the M host common planet inside the snowline is ∼3–10 times less massive than the one outside. With rocky planets interior to gaseous planets, the solar system broadly follows the combined mass-ratio function inferred from Kepler and microlensing. However, the exoplanet population has a less extreme radial distribution of planetary masses than the solar system. Establishing whether the mass-ratio function beyond the snowline is also host type independent will be crucial to build a comprehensive theory of planet formation.

  16. Mass and age of red giant branch stars observed with LAMOST and Kepler

    Science.gov (United States)

    Wu, Yaqian; Xiang, Maosheng; Bi, Shaolan; Liu, Xiaowei; Yu, Jie; Hon, Marc; Sharma, Sanjib; Li, Tanda; Huang, Yang; Liu, Kang; Zhang, Xianfei; Li, Yaguang; Ge, Zhishuai; Tian, Zhijia; Zhang, Jinghua; Zhang, Jianwei

    2018-04-01

    Obtaining accurate and precise masses and ages for large numbers of giant stars is of great importance for unraveling the assemblage history of the Galaxy. In this paper, we estimate masses and ages of 6940 red giant branch (RGB) stars with asteroseismic parameters deduced from Kepler photometry and stellar atmospheric parameters derived from LAMOST spectra. The typical uncertainties of mass is a few per cent, and that of age is ˜20 per cent. The sample stars reveal two separate sequences in the age-[α/Fe] relation - a high-α sequence with stars older than ˜8 Gyr and a low-α sequence composed of stars with ages ranging from younger than 1 Gyr to older than 11 Gyr. We further investigate the feasibility of deducing ages and masses directly from LAMOST spectra with a machine learning method based on kernel based principal component analysis, taking a sub-sample of these RGB stars as a training data set. We demonstrate that ages thus derived achieve an accuracy of ˜24 per cent. We also explored the feasibility of estimating ages and masses based on the spectroscopically measured carbon and nitrogen abundances. The results are quite satisfactory and significantly improved compared to the previous studies.

  17. Mass loss from OH/IR stars - Models for the infrared emission of circumstellar dust shells

    Science.gov (United States)

    Justtanont, K.; Tielens, A. G. G. M.

    1992-01-01

    The IR emission of a sample of 24 OH/IR stars is modeled, and the properties of circumstellar dust and mass-loss rate of the central star are derived. It is shown that for some sources the observations of the far-IR emission is well fitted with a lambda exp -1 law, while some have a steeper index of 1.5. For a few sources, the presence of circumstellar ice grains is inferred from detailed studies of the observed 10-micron feature. Dust mass-loss rates are determined from detailed studies for all the stars in this sample. They range from 6.0 x 10 exp -10 solar mass/yr for an optically visible Mira to 2.2 x 10 exp -6 solar mass/yr for a heavily obscured OH/IR star. These dust mass-loss rates are compared to those calculated from IRAS photometry using 12-, 25-, and 60-micron fluxes. The dust mass-loss rates are also compared to gas mass-loss rates determined from OH and CO observations. For stars with tenuous shells, a dust-to-gas ratio of 0.001 is obtained.

  18. AN INITIAL MASS FUNCTION FOR INDIVIDUAL STARS IN GALACTIC DISKS. I. CONSTRAINING THE SHAPE OF THE INITIAL MASS FUNCTION

    International Nuclear Information System (INIS)

    Parravano, Antonio; McKee, Christopher F.; Hollenbach, David J.

    2011-01-01

    We derive a semi-empirical galactic initial mass function (IMF) from observational constraints. We assume that the IMF, ψ(m), is a smooth function of the stellar mass m. The mass dependence of the proposed IMF is determined by five parameters: the low-mass slope γ, the high-mass slope -Γ (taken to be -1.35), the characteristic mass m ch (∼ the peak mass of the IMF), and the lower and upper limits on the mass, m l and m u (taken to be 0.004 and 120 M sun , respectively): ψ(m)dln m ∝ m -Γ {1 - exp [- (m/m ch ) γ+Γ ]}dln m. The values of γ and m ch are derived from two integral constraints: (1) the ratio of the number density of stars in the range m = 0.1-0.6 M sun to that in the range m = 0.6-0.8 M sun as inferred from the mass distribution of field stars in the local neighborhood and (2) the ratio of the number of stars in the range m = 0.08-1 M sun to the number of brown dwarfs in the range m = 0.03-0.08 M sun in young clusters. The IMF satisfying the above constraints is characterized by the parameters γ = 0.51 and m ch = 0.35 M sun (which corresponds to a peak mass of 0.27 M sun ). This IMF agrees quite well with the Chabrier IMF for the entire mass range over which we have compared with data, but predicts significantly more stars with masses sun ; we also compare with other IMFs in current use and give a number of important parameters implied by the IMFs.

  19. A Multi-Fiber Spectroscopic Search for Low-mass Young Stars in Orion OB1

    Science.gov (United States)

    Loerincs, Jacqueline; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

    2017-01-01

    We present here results of a low resolution spectroscopic followup of candidate low-mass pre-main sequence stars in the Orion OB1 association. Our targets were selected from the CIDA Variability Survey of Orion (CVSO), and we used the Michigan/Magellan Fiber Spectrograph (M2FS) on the Magellan Clay 6.5m telescope to obtain spectra of 500 candidate T Tauri stars distributed in seven 0.5 deg diameter fields, adding to a total area of ~5.5 deg2. We identify young stars by looking at the distinctive Hα 6563 Å emission and Lithium Li I 6707 Å absorption features characteristic of young low mass pre-main sequence stars. Furthermore, by measuring the strength of their Hα emission lines, confirmed T Tauri stars can be classified as either Classical T Tauris (CTTS) or Weak-line T Tauris (WTTS), which give indication of whether the star is actively accreting material from a gas and dust disk surrounding the star, which may be the precursor of a planetary system. We confirm a total of 90 T Tauri stars, of which 50% are newly identified young members of Orion; out of the 49 new detections,15 are accreting CTTS, and of these all but one are found in the OB1b sub-region. This result is in line with our previous findings that this region is much younger than the more extended Orion OB1a sub-association. The M2FS results add to our growing census of young stars in Orion, that is allowing us to characterize in a systematic and consistent way the distribution of stellar ages across the entire complex, in order to building a complete picture of star formation in this, one of nearest most active sites of star birth.

  20. Symplectic no-core shell-model approach to intermediate-mass nuclei

    Science.gov (United States)

    Tobin, G. K.; Ferriss, M. C.; Launey, K. D.; Dytrych, T.; Draayer, J. P.; Dreyfuss, A. C.; Bahri, C.

    2014-03-01

    We present a microscopic description of nuclei in the intermediate-mass region, including the proximity to the proton drip line, based on a no-core shell model with a schematic many-nucleon long-range interaction with no parameter adjustments. The outcome confirms the essential role played by the symplectic symmetry to inform the interaction and the winnowing of shell-model spaces. We show that it is imperative that model spaces be expanded well beyond the current limits up through 15 major shells to accommodate particle excitations, which appear critical to highly deformed spatial structures and the convergence of associated observables.

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

    Science.gov (United States)

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

    2017-04-01

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

  2. Elemental gas-phase abundances of intermediate redshift type Ia supernova star-forming host galaxies

    Science.gov (United States)

    Moreno-Raya, M. E.; Galbany, L.; López-Sánchez, Á. R.; Mollá, M.; González-Gaitán, S.; Vílchez, J. M.; Carnero, A.

    2018-05-01

    The maximum luminosity of type Ia supernovae (SNe Ia) depends on the oxygen abundance of the regions of the host galaxies, where they explode. This metallicity dependence reduces the dispersion in the Hubble diagram (HD) when included with the traditional two-parameter calibration of SN Ia light-curve parameters and absolute magnitude. In this work, we use empirical calibrations to carefully estimate the oxygen abundance of galaxies hosting SNe Ia from the SDSS-II/SN (Sloan Digital Sky Survey-II Supernova) survey at intermediate redshift by measuring their emission-line intensities. We also derive electronic temperature with the direct method for a small fraction of objects for consistency. We find a trend of decreasing oxygen abundance with increasing redshift for the most massive galaxies. Moreover, we study the dependence of the HD residuals (HR) with galaxy oxygen abundance obtaining a correlation in line with those found in other works. In particular, the HR versus oxygen abundance shows a slope of -0.186 ± 0.123 mag dex-1 (1.52σ) in good agreement with theoretical expectations. This implies smaller distance modulii after corrections for SNe Ia in metal-rich galaxies. Based on our previous results on local SNe Ia, we propose this dependence to be due to the lower luminosity of the SNe Ia produced in more metal-rich environments.

  3. Gamow's calculation of the neutron star's critical mass revised

    International Nuclear Information System (INIS)

    Ludwig, Hendrik; Ruffini, Remo

    2014-01-01

    It has at times been indicated that Landau introduced neutron stars in his classic paper of 1932. This is clearly impossible because the discovery of the neutron by Chadwick was submitted more than one month after Landau's work. Therefore, and according to his calculations, what Landau really did was to study white dwarfs, and the critical mass he obtained clearly matched the value derived by Stoner and later by Chandrasekhar. The birth of the concept of a neutron star is still today unclear. Clearly, in 1934, the work of Baade and Zwicky pointed to neutron stars as originating from supernovae. Oppenheimer in 1939 is also well known to have introduced general relativity (GR) in the study of neutron stars. The aim of this note is to point out that the crucial idea for treating the neutron star has been advanced in Newtonian theory by Gamow. However, this pioneering work was plagued by mistakes. The critical mass he should have obtained was 6.9 M, not the one he declared, namely, 1.5 M. Probably, he was taken to this result by the work of Landau on white dwarfs. We revise Gamow's calculation of the critical mass regarding calculational and conceptual aspects and discuss whether it is justified to consider it the first neutron-star critical mass. We compare Gamow's approach to other early and modern approaches to the problem.

  4. MASS TRANSPORT AND TURBULENCE IN GRAVITATIONALLY UNSTABLE DISK GALAXIES. II. THE EFFECTS OF STAR FORMATION FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Goldbaum, Nathan J. [National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801 (United States); Krumholz, Mark R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2601 (Australia); Forbes, John C., E-mail: ngoldbau@illinois.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2016-08-10

    Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 and leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.

  5. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    Science.gov (United States)

    O. Silva, Hector; Berti, Emanuele; Sotani, Hajime

    2016-03-01

    Compact objects such as neutron stars are ideal astrophysical laboratories to test our understanding of the fundamental interactions in the regime of supranuclear densities, unachievable by terrestrial experiments. Despite recent progress, the description of matter (i.e., the equation of state) at such densities is still debatable. This translates into uncertainties in the bulk properties of neutron stars, masses and radii for instance. Here we will consider low-mass neutron stars. Such stars are expected to carry important information on nuclear matter near the nuclear saturation point. It has recently been shown that the masses and surface redshifts of low-mass neutron stars smoothly depend on simple functions of the central density and of a characteristic parameter η associated with the choice of equation of state. Here we extend these results to slowly-rotating and tidally deformed stars and obtain empirical relations for various quantities, such as the moment of inertia, quadrupole moment and ellipticity, tidal and rotational Love numbers, and rotational apsidal constants. We discuss how these relations might be used to constrain the equation of state by future observations in the electromagnetic and gravitational-wave spectra.

  6. Mass loss of evolved massive stars: the circumstellar environment at high angular resolution

    International Nuclear Information System (INIS)

    Montarges, Miguel

    2014-01-01

    Mass loss of evolved stars is still largely mysterious, despite its importance as the main evolution engine for the chemical composition of the interstellar medium. For red supergiants (RSG), the triggering of the outflow and the mechanism of dust condensation remain unknown. Concerning red giant stars, we still do not know how their mass loss is able to form a bipolar planetary nebula. During my PhD thesis, I observed evolved stars with high angular resolution techniques. They allowed us to study the surface and the close environment of these stars, from where mass loss originates. With near-infrared interferometric observations, I characterized the water vapor and carbon monoxide envelope of the nearby RSG Betelgeuse. I also monitored a hot spot on its surface and analyzed the structure of its convection, as well as that of Antares (another very nearby supergiant) thanks to radiative hydrodynamical simulations. Diffraction-limited imaging techniques (near-infrared adaptive optics, ultraviolet space telescope) allowed me to observe the evolution of inhomogeneities in the circumstellar envelope of Betelgeuse and to discover a circumstellar disk around L2 Puppis, an asymptotic giant branch star. These multi-scale and multi-wavelength observations obtained at several epochs allowed us to monitor the evolution of the structures and to derive information on the dynamics of the stellar environment. With a wider stellar sample expected in the next few years, this observing program will allow a better understanding of the mass loss of evolved stars. (author)

  7. OPTICAL VARIABILITY OF THE ACCRETION DISK AROUND THE INTERMEDIATE-MASS BLACK HOLE ESO 243-49 HLX-1 DURING THE 2012 OUTBURST

    Energy Technology Data Exchange (ETDEWEB)

    Webb, N. A.; Godet, O.; Barret, D. [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); Wiersema, K. [University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Lasota, J.-P. [Institut d' Astrophysique de Paris, UMR 7095, CNRS, UPMC Université Paris 06, 98bis Boulevard Arago, F-75014 Paris (France); Farrell, S. A. [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia); Maccarone, T. J. [Department of Physics, Box 41051, Texas Tech University, Lubbock TX 79409-1051 (United States); Servillat, M., E-mail: natalie.webb@irap.omp.eu [Laboratoire AIM (CEA/DSM/IRFU/SAp, CNRS, Université Paris Diderot), CEA Saclay, Bat. 709, F-91191 Gif-sur-Yvette (France)

    2014-01-01

    We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large Telescope, V-, and R-band) observations of the intermediate-mass black hole candidate HLX-1 before and during the 2012 outburst. We show that the V-band magnitudes vary with time, thus proving that a portion of the observed emission originates in the accretion disk. Using the first quiescent optical observations of HLX-1, we show that the stellar population surrounding HLX-1 is fainter than V ∼ 25.1 and R ∼ 24.2. We show that the optical emission may increase before the X-ray emission consistent with the scenario proposed by Lasota et al. in which the regular outbursts could be related to the passage at periastron of a star circling the intermediate-mass black hole in an eccentric orbit, which triggers mass transfer into a quasi-permanent accretion disk around the black hole. Further, if there is indeed a delay in the X-ray emission we estimate the mass-transfer delivery radius to be ∼10{sup 11} cm.

  8. The Extreme Ultraviolet Flux of Very Low Mass Stars

    Science.gov (United States)

    Drake, Jeremy

    2017-09-01

    The X-ray and EUV emission of stars is vital for understanding the atmospheres and evolution of their planets. The coronae of dwarf stars later than M6 behave differently to those of earlier spectral types and are more X-ray dim and radio bright. Too faint to have been observed by EUVE, their EUV behavior is currently highly uncertain. We propose to observe a small sample of late M dwarfs using the off-axis HRC-S thin Al" filter that is sensitive to EUV emission in the 50-200 A range. The measured fluxes will be used to understand the amount of cooler coronal plasma present, and extend X-ray-EUV flux relations to the latest stellar types.

  9. CONNECTING FLARES AND TRANSIENT MASS-LOSS EVENTS IN MAGNETICALLY ACTIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Osten, Rachel A. [Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218 (United States); Wolk, Scott J., E-mail: osten@stsci.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States)

    2015-08-10

    We explore the ramification of associating the energetics of extreme magnetic reconnection events with transient mass-loss in a stellar analogy with solar eruptive events. We establish energy partitions relative to the total bolometric radiated flare energy for different observed components of stellar flares and show that there is rough agreement for these values with solar flares. We apply an equipartition between the bolometric radiated flare energy and kinetic energy in an accompanying mass ejection, seen in solar eruptive events and expected from reconnection. This allows an integrated flare rate in a particular waveband to be used to estimate the amount of associated transient mass-loss. This approach is supported by a good correspondence between observational flare signatures on high flaring rate stars and the Sun, which suggests a common physical origin. If the frequent and extreme flares that young solar-like stars and low-mass stars experience are accompanied by transient mass-loss in the form of coronal mass ejections, then the cumulative effect of this mass-loss could be large. We find that for young solar-like stars and active M dwarfs, the total mass lost due to transient magnetic eruptions could have significant impacts on disk evolution, and thus planet formation, and also exoplanet habitability.

  10. The evolution of massive stars with mass loss: the H- and the He-burning phases

    International Nuclear Information System (INIS)

    Chieffi, Alessandro; Limongi, Marco

    2010-01-01

    The evolution of a massive star to its final fate is strongly modified by the efficient mass loss episodes it experiences during its lifetime. In the following, we will briefly summarize how the H- and the He- burning phases depend on the adopted mass loss rate.

  11. Mass-loss Rates from Coronal Mass Ejections: A Predictive Theoretical Model for Solar-type Stars

    Energy Technology Data Exchange (ETDEWEB)

    Cranmer, Steven R. [Department of Astrophysical and Planetary Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States)

    2017-05-10

    Coronal mass ejections (CMEs) are eruptive events that cause a solar-type star to shed mass and magnetic flux. CMEs tend to occur together with flares, radio storms, and bursts of energetic particles. On the Sun, CME-related mass loss is roughly an order of magnitude less intense than that of the background solar wind. However, on other types of stars, CMEs have been proposed to carry away much more mass and energy than the time-steady wind. Earlier papers have used observed correlations between solar CMEs and flare energies, in combination with stellar flare observations, to estimate stellar CME rates. This paper sidesteps flares and attempts to calibrate a more fundamental correlation between surface-averaged magnetic fluxes and CME properties. For the Sun, there exists a power-law relationship between the magnetic filling factor and the CME kinetic energy flux, and it is generalized for use on other stars. An example prediction of the time evolution of wind/CME mass-loss rates for a solar-mass star is given. A key result is that for ages younger than about 1 Gyr (i.e., activity levels only slightly higher than the present-day Sun), the CME mass loss exceeds that of the time-steady wind. At younger ages, CMEs carry 10–100 times more mass than the wind, and such high rates may be powerful enough to dispel circumstellar disks and affect the habitability of nearby planets. The cumulative CME mass lost by the young Sun may have been as much as 1% of a solar mass.

  12. 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.

  13. 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.

  14. Detection of X-ray emission from the young low-mass star Rossiter 137B

    Science.gov (United States)

    Vilhu, O.; Linsky, J. L.

    1987-01-01

    Rst 137B, a close M-dwarf companion to the active K-star HD 36705, has been detected in a High Resolution Image in the Einstein Observatory Archive. The X-ray surface fluxes (0.2-4 keV) from both stars are close to the empirical saturation level, F(x)/F(bol) of about 0.001, defined by rapid rotators and very young stars. This supports the earlier results of the youthfulness of the system. This young couple is an excellent subject for studies of dependence of early evolution on stellar mass. Rst 137B is one of the latest spectral types and thus lowest-mass premain-sequence stars yet detected as an X-ray source.

  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. Modulated mass-transfer model for superhumps in SU Ursae Majoris stars

    Science.gov (United States)

    Mineshige, Shin

    1988-01-01

    The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the superhump peaks. The elliptical accretion-disk model with extended vertical disk structure can account for the observed characteristics of superhumps in these stars.

  17. Modulated mass-transfer model for superhumps in SU Ursae Majoris stars

    International Nuclear Information System (INIS)

    Mineshige, S.

    1988-01-01

    The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the superhump peaks. The elliptical accretion-disk model with extended vertical disk structure can account for the observed characteristics of superhumps in these stars. 52 references

  18. Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

    Czech Academy of Sciences Publication Activity Database

    Krtička, J.; Kubát, Jiří

    2014-01-01

    Roč. 567, July (2014), A63/1-A63/7 ISSN 0004-6361 R&D Projects: GA ČR GA13-10589S Grant - others:GA MŠk(CZ) LM2010005 Institutional support: RVO:67985815 Keywords : stars: winds * outflows * stars: mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  19. MASS LOSS IN PRE-MAIN-SEQUENCE STARS VIA CORONAL MASS EJECTIONS AND IMPLICATIONS FOR ANGULAR MOMENTUM LOSS

    Energy Technology Data Exchange (ETDEWEB)

    Aarnio, Alicia N. [Astronomy Department, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Matt, Sean P. [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, F-91191 Gif-sur-Yvette (France); Stassun, Keivan G., E-mail: aarnio@umich.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)

    2012-11-20

    We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log (M {sub CME}[g]) = 0.63 Multiplication-Sign log (E {sub flare}[erg]) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10{sup -12}-10{sup -9} M {sub Sun} yr{sup -1}. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical {approx}1 M {sub Sun} T Tauri star is <10{sup -10} M {sub Sun} yr{sup -1}, the resulting spin-down torque is too small during the first {approx}1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is {approx}> 10{sup -10} M {sub Sun} yr{sup -1}, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.

  20. LP 543-25: A Rare Low-mass Runaway Disk Star

    Science.gov (United States)

    de la Fuente Marcos, Raúl; de la Fuente Marcos, Carlos

    2018-05-01

    LP 543-25 or PSS 544-7 is a high proper-motion star located 458 pc from the Sun in the constellation of Canis Minor; it has been argued that it could be a candidate cannonball star ejected by a star cluster. Here, we revisit the issue of the kinematics of this interesting star using Gaia DR2. The heliocentric Galactic velocity components are (U, V, W) = (206, -289, 30) km/s; the corresponding Galactocentric Galactic velocity components show that LP 543-25 is moving in the Galactic plane and away from the Galactic Center at a rate of nearly 200 km/s, which is compatible with an origin in one of the multiple star clusters that inhabit the inner regions of the Milky Way. LP 543-25 appears to be a member of an elusive class of stars, the low-mass runaway stars. It is perhaps one of the closest and less massive runaway stars identified so far.

  1. 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.

  2. UPDATED MASS SCALING RELATIONS FOR NUCLEAR STAR CLUSTERS AND A COMPARISON TO SUPERMASSIVE BLACK HOLES

    International Nuclear Information System (INIS)

    Scott, Nicholas; Graham, Alister W.

    2013-01-01

    We investigate whether or not nuclear star clusters and supermassive black holes (SMBHs) follow a common set of mass scaling relations with their host galaxy's properties, and hence can be considered to form a single class of central massive object (CMO). We have compiled a large sample of galaxies with measured nuclear star cluster masses and host galaxy properties from the literature and fit log-linear scaling relations. We find that nuclear star cluster mass, M NC , correlates most tightly with the host galaxy's velocity dispersion: log M NC = (2.11 ± 0.31)log (σ/54) + (6.63 ± 0.09), but has a slope dramatically shallower than the relation defined by SMBHs. We find that the nuclear star cluster mass relations involving host galaxy (and spheroid) luminosity and stellar and dynamical mass, intercept with but are in general shallower than the corresponding black hole scaling relations. In particular, M NC ∝M 0.55±0.15 Gal,dyn ; the nuclear cluster mass is not a constant fraction of its host galaxy or spheroid mass. We conclude that nuclear stellar clusters and SMBHs do not form a single family of CMOs.

  3. White dwarf stars exceeding the Chandrasekhar mass limit

    Science.gov (United States)

    Tomaschitz, Roman

    2018-01-01

    The effect of nonlinear ultra-relativistic electron dispersion on the mass-radius relation of high-mass white dwarfs is studied. The dispersion is described by a permeability tensor in the Dirac equation, generated by the ionized high-density stellar matter, which constitutes the neutralizing background of the nearly degenerate electron plasma. The electron dispersion results in a stable mass-radius relation for high-mass white dwarfs, in contrast to a mass limit in the case of vacuum permeabilities. In the ultra-relativistic regime, the dispersion relation is a power law whose amplitude and scaling exponent is inferred from mass and radius estimates of two high-mass white dwarfs, Sirius B and LHS 4033. Evidence for the existence of super-Chandrasekhar mass white dwarfs is provided by several Type Ia supernovae (e.g., SN 2013cv, SN 2003fg, SN 2007if and SN 2009dc), whose mass ejecta exceed the Chandrasekhar limit by up to a factor of two. The dispersive mass-radius relation is used to estimate the radii, central densities, Fermi temperatures, bulk and compression moduli and sound velocities of their white dwarf progenitors.

  4. Bifurcations and Chaos of AN Immersed Cantilever Beam in a Fluid and Carrying AN Intermediate Mass

    Science.gov (United States)

    AL-QAISIA, A. A.; HAMDAN, M. N.

    2002-06-01

    The concern of this work is the local stability and period-doubling bifurcations of the response to a transverse harmonic excitation of a slender cantilever beam partially immersed in a fluid and carrying an intermediate lumped mass. The unimodal form of the non-linear dynamic model describing the beam-mass in-plane large-amplitude flexural vibration, which accounts for axial inertia, non-linear curvature and inextensibility condition, developed in Al-Qaisia et al. (2000Shock and Vibration7 , 179-194), is analyzed and studied for the resonance responses of the first three modes of vibration, using two-term harmonic balance method. Then a consistent second order stability analysis of the associated linearized variational equation is carried out using approximate methods to predict the zones of symmetry breaking leading to period-doubling bifurcation and chaos on the resonance response curves. The results of the present work are verified for selected physical system parameters by numerical simulations using methods of the qualitative theory, and good agreement was obtained between the analytical and numerical results. Also, analytical prediction of the period-doubling bifurcation and chaos boundaries obtained using a period-doubling bifurcation criterion proposed in Al-Qaisia and Hamdan (2001 Journal of Sound and Vibration244, 453-479) are compared with those of computer simulations. In addition, results of the effect of fluid density, fluid depth, mass ratio, mass position and damping on the period-doubling bifurcation diagrams are studies and presented.

  5. The Evolution of High-Mass Star-Forming Cores in the Nessie Nebula

    Science.gov (United States)

    Jackson, James; Rathborne, Jill; Sanhueza, Patricio; Whitaker, John Scott; Camarata, Matthew

    2013-04-01

    We aim to deduce the evolution of the ensemble properties of high-mass star-forming cores within a cluster-forming molecular clump. Two different theories of high-mass star-formation, "competitive accretion" and "monolithic collapse" make very different predictions for this evolution. In "competitive accretion" the clump will contain only low-mass cores in the early phases, and high-mass cores will be found in the later stages. In "monolithic collapse" high-mass cores are found early on, and the mass distribution of the cores will remain essentially unchanged. Both models predict cores to increase in temperature. We can classify evolutionary stage from Spitzer mid-IR images. We choose to study 6 cores in the Nessie nebula that span the complete range of protostellar evolution. Nessie is an ideal laboratory because all the cores are at the same distance and in the same Galactic environment.

  6. Excitation of neutron star oscillations by an orbiting mass

    International Nuclear Information System (INIS)

    Ruoff, J.

    2001-01-01

    In this contribution, I present results from a numerical study of the even-parity gravitational radiation generated from a particle orbiting a neutron star. The investigation is focused on those conditions on the orbital parameters that favor the excitation of w-modes. It is found that, for astrophysically realistic conditions, there is practically no w-mode contribution to the emitted radiation. Only for particles with ultra-relativistic orbital speeds ≥ 0.9c, the w-mode does significantly contribute to the total emitted gravitational energy. To obtain reliable results, a way is presented to construct consistent initial data which contain as little as possible initial radiation. (author)

  7. X-Ray Emission from Active Galactic Nuclei with Intermediate-Mass Black Holes

    Science.gov (United States)

    Dewangan, G. C.; Mathur, S.; Griffiths, R. E.; Rao, A. R.

    2008-12-01

    We present a systematic X-ray study of eight active galactic nuclei (AGNs) with intermediate-mass black holes (MBH ~ 8-95 × 104 M⊙) based on 12 XMM-Newton observations. The sample includes the two prototype AGNs in this class—NGC 4395 and POX 52 and six other AGNs discovered with the Sloan Digitized Sky Survey. These AGNs show some of the strongest X-ray variability, with the normalized excess variances being the largest and the power density break timescales being the shortest observed among radio-quiet AGNs. The excess-variance-luminosity correlation appears to depend on both the BH mass and the Eddington luminosity ratio. The break timescale-black hole mass relations for AGN with IMBHs are consistent with that observed for massive AGNs. We find that the FWHM of the Hβ/Hα line is uncorrelated with the BH mass, but shows strong anticorrelation with the Eddington luminosity ratio. Four AGNs show clear evidence for soft X-ray excess emission (kTin ~ 150-200 eV). X-ray spectra of three other AGNs are consistent with the presence of the soft excess emission. NGC 4395 with lowest L/LEdd lacks the soft excess emission. Evidently small black mass is not the primary driver of strong soft X-ray excess emission from AGNs. The X-ray spectral properties and optical-to-X-ray spectral energy distributions of these AGNs are similar to those of Seyfert 1 galaxies. The observed X-ray/UV properties of AGNs with IMBHs are consistent with these AGNs being low-mass extensions of more massive AGNs, those with high Eddington luminosity ratio looking more like narrow-line Seyfert 1 s and those with low L/LEdd looking more like broad-line Seyfert 1 galaxies.

  8. Limits on runaway growth of intermediate mass black holes from advanced LIGO

    Science.gov (United States)

    Kovetz, Ely D.; Cholis, Ilias; Kamionkowski, Marc; Silk, Joseph

    2018-06-01

    There is growing evidence that intermediate-mass black holes (IMBHs), defined here as having a mass in the range M =500 -105 M⊙ , are present in the dense centers of certain globular clusters (GCs). Gravitational waves from their mergers with other IMBHs or with stellar BHs in the cluster are mostly emitted in frequencies ≲10 Hz , which unfortunately is out of reach for current ground-based observatories such as advanced LIGO (aLIGO). Nevertheless, we show that aLIGO measurements can be used to efficiently probe one of the possible formation mechanisms of IMBHs in GCs, namely a runaway merger process of stellar seed BHs. In this case, aLIGO will be sensitive to the lower-mass rungs of the merger ladder, ranging from the seed BH mass to masses ≳50 - 300 M⊙ , where the background from standard mergers is expected to be very low. Assuming this generic IMBH formation scenario, we calculate the mass functions that correspond to the limiting cases of possible merger trees. Based on estimates for the number density of GCs and taking into account the instrumental sensitivity, we show that current observations do not effectively limit the occupation fraction focc of IMBHs formed by runaway mergers of stellar BHs in GCs. However, we find that if runaway mergers occur steadily throughout the lifetimes of GCs (as opposed to happening mainly early in their lifetimes), then a six-year run of aLIGO at design sensitivity will be able to probe down to focc≲3 % at a 99.9% confidence level, either finding evidence for this formation mechanism, or necessitating others if the fraction of GCs that harbor IMBHs is higher.

  9. Relativistic deflection of background starlight measures the mass of a nearby white dwarf star.

    Science.gov (United States)

    Sahu, Kailash C; Anderson, Jay; Casertano, Stefano; Bond, Howard E; Bergeron, Pierre; Nelan, Edmund P; Pueyo, Laurent; Brown, Thomas M; Bellini, Andrea; Levay, Zoltan G; Sokol, Joshua; Dominik, Martin; Calamida, Annalisa; Kains, Noé; Livio, Mario

    2017-06-09

    Gravitational deflection of starlight around the Sun during the 1919 total solar eclipse provided measurements that confirmed Einstein's general theory of relativity. We have used the Hubble Space Telescope to measure the analogous process of astrometric microlensing caused by a nearby star, the white dwarf Stein 2051 B. As Stein 2051 B passed closely in front of a background star, the background star's position was deflected. Measurement of this deflection at multiple epochs allowed us to determine the mass of Stein 2051 B-the sixth-nearest white dwarf to the Sun-as 0.675 ± 0.051 solar masses. This mass determination provides confirmation of the physics of degenerate matter and lends support to white dwarf evolutionary theory. Copyright © 2017, American Association for the Advancement of Science.

  10. A UV spectroscopic snapshot survey of low-mass stars in the Hyades

    Science.gov (United States)

    Agueros, Marcel

    2017-08-01

    Because of its proximity, the 650-Myr-old Hyades open cluster is a unique resource for exploring the relationship between magnetic activity, rotation, and age in low-mass stars. While the cluster has been largely ignored in UV studies of the dependence of activity on rotation, we now have an extensive and growing set of complementary rotation period, Halpha, and X-ray measurements with which to examine in detail the rotation-activity relation at 650 Myr and to constrain theories of magnetic heating. We propose to measure Mg II line emission, the strongest NUV activity tracer, in COS spectra of 86 Hyads ranging in spectral type from G to M with known rotation periods or currently being observed by K2. These stars form a representative sample of low-mass Hyads with known periods and are a significant addition to, and expansion of, the sample of 20 mainly solar-mass rotators with existing (mostly low-resolution) IUE NUV spectra. The Mg II measurements will contribute significantly to our goal of mapping out the rotation-activity relation star-by-star in this benchmark open cluster. This, in turn, will move us toward an improved understanding of the radiation environment and habitability of the exoplanets we continue to find around low-mass stars.

  11. Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades

    Science.gov (United States)

    Stauffer, John R.; Liebert, James; Giampapa, Mark; Macintosh, Bruce; Reid, Neill; Hamilton, Donald

    1994-01-01

    We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km s(exp -1) for approximately 20 candidate very low mass members of the Hyades and Pleiades clusters. The radial velocities for the Hyades sample suggest that nearly all of these stars are indeed highly probable members of the Hyades. The faintest stars in the Hyades sample have masses of order 0.1 solar mass. We also obtained radial velocities for four candidate very low mass members of the Pleiades and two objects that are candidate BD Pleiads. All of these stars have apparent V magnitudes fainter than the Hyades stars we observed, and the resultant radial velocity accuracy is worse. We believe that the three brighter stars are indeed likely very low mass stellar members of the Pleiades, whereas the status of the two brown dwarf candidates is uncertain. The Hyades stars we have observed and the three Pleiades very low mass stars are the lowest mass members of any open cluster whose membership has been confirmed by radial velocities and whose chromospheric activity has been measured. We see no change in chromospheric activity at the boundary where stars are expected to become fully convective (M approximately equals 0.3 solar mass) in either cluster. In the Pleiades, however, there may be a decrease in chromospheric activity for stars with (V-I)(sub K) greater than 3.5 (M less than or equal to 0.1 solar mass).

  12. The V Band Empirical Mass-Luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, F.; Fu, Y. N.

    2010-01-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determination of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass-luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙. Recently, many relevant data have been accumulated for main sequence stars with larger mass, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weight to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. Compared with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in studies of statistical nature, but also in studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  13. The V-band Empirical Mass-luminosity Relation for Main Sequence Stars

    Science.gov (United States)

    Xia, Fang; Fu, Yan-Ning

    2010-07-01

    Stellar mass is an indispensable parameter in the studies of stellar physics and stellar dynamics. On the one hand, the most reliable way to determine the stellar dynamical mass is via orbital determinations of binaries. On the other hand, however, most stellar masses have to be estimated by using the mass luminosity relation (MLR). Therefore, it is important to obtain the empirical MLR through fitting the data of stellar dynamical mass and luminosity. The effect of metallicity can make this relation disperse in the V-band, but studies show that this is mainly limited to the case when the stellar mass is less than 0.6M⊙ Recently, many relevant data have been accumulated for main sequence stars with larger masses, which make it possible to significantly improve the corresponding MLR. Using a fitting method which can reasonably assign weights to the observational data including two quantities with different dimensions, we obtain a V-band MLR based on the dynamical masses and luminosities of 203 main sequence stars. In comparison with the previous work, the improved MLR is statistically significant, and the relative error of mass estimation reaches about 5%. Therefore, our MLR is useful not only in the studies of statistical nature, but also in the studies of concrete stellar systems, such as the long-term dynamical study and the short-term positioning study of a specific multiple star system.

  14. EVIDENCE FOR AN INTERMEDIATE-MASS BLACK HOLE IN NGC 5408 X-1

    International Nuclear Information System (INIS)

    Strohmayer, Tod E.; Mushotzky, Richard F.

    2009-01-01

    We report the discovery with XMM-Newton of correlated spectral and timing behavior in the ultraluminous X-ray source (ULX) NGC 5408 X-1. An ∼100 ks pointing with XMM/Newton obtained in 2008 January reveals a strong 10 mHz quasi-periodic oscillation (QPO) in the >1 keV flux, as well as flat-topped, band-limited noise breaking to a power law. The energy spectrum is again dominated by two components, a 0.16 keV thermal disk and a power law with an index of ∼2.5. These new measurements, combined with results from our previous 2006 January pointing in which we first detected QPOs, show for the first time in a ULX a pattern of spectral and temporal correlations strongly analogous to that seen in Galactic black hole (BH) sources, but at much higher X-ray luminosity and longer characteristic timescales. We find that the QPO frequency is proportional to the inferred disk flux, while the QPO and broadband noise amplitude (rms) are inversely proportional to the disk flux. Assuming that QPO frequency scales inversely with the BH mass at a given power-law spectral index we derive mass estimates using the observed QPO frequency-spectral index relations from five stellar-mass BH systems with dynamical mass constraints. The results from all sources are consistent with a mass range for NGC 5408 X-1 from 1000 to 9000 M sun . We argue that these are conservative limits, and a more likely range is from 2000 to 5000 M sun . Moreover, the recent relation from Gierlinski et al. that relates the BH mass to the strength of variability at high frequencies (above the break in the power spectrum) is also indicative of such a high mass for NGC 5408 X-1. Importantly, none of the above estimates appears consistent with a BH mass less than ∼1000 M sun for NGC 5408 X-1. We argue that these new findings strongly support the conclusion that NGC 5408 X-1 harbors an intermediate-mass BH.

  15. Intermediate-mass Higgs boson and isosinglet neutral heavy lepton signals at hadron supercolliders

    International Nuclear Information System (INIS)

    Bhattacharya, G.

    1992-01-01

    The signals for the Standard Model intermediate-mass Higgs boson and isosinglet neutral heavy leptons at the forthcoming hadron supercolliders-the Superconducting Super Collider (SSC) and the CERN Large Hadron Collider (LHC), are studied. The author studies inclusive production of the Standard Model Higgs boson in the intermediate-mass region (M W approx-lt m H approx-lt 2M Z ) and its subsequent decay into two on- or off-shell W bosons that decay leptonically. Backgrounds from continuum W pair production and top quark pair production with semileptonic decays are investigated. The author concludes the Higgs boson signal may be observed via the decay H → W*W* → (ell bar v ell ) (bar ell' v' ell ) at the SSC for 145 GeV H approx-lt 2M Z and at the LHC for 150 GeV H approx-lt 2M Z if m t > 150 GeV. The author analyzes the search and discovery potential of isosinglet neutral heavy leptons (NHLs) produced via real or virtual W decay at pp supercolliders. The author considers the signal resulting from the leptonic decay of the NHL, and the two major backgrounds-continuum WZ, Wγ production and t bar tj production, where j is a hadronic jet. The decay patterns of NHL depend on its mass M N , and different search strategies are needed for the two mass regions M N W and M N > M Z . The author finds for m t ≥ 150 (200) GeV the signal is observable for M N ≤ 60 (70) GeV in the mass-region M N W , and up to M N ≅ 110 GeV for M N > M W , at both SSC and LHC. It is shown the non-observance of the signal (with a 4σ statistical significance) in the region M N W could put upper limits on the NHL coupling constants that would be an improvement over the limits obtainable from the CERN Large Electron Positron Collider (LEP I)

  16. An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

    Energy Technology Data Exchange (ETDEWEB)

    Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, Morelia, Michoacán 58089 (Mexico)

    2014-10-01

    We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies are SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

  17. TESTING THE ASTEROSEISMIC MASS SCALE USING METAL-POOR STARS CHARACTERIZED WITH APOGEE AND KEPLER

    Energy Technology Data Exchange (ETDEWEB)

    Epstein, Courtney R.; Johnson, Jennifer A.; Tayar, Jamie; Pinsonneault, Marc [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Elsworth, Yvonne P.; Chaplin, William J. [School of Physics and Astronomy, University of Birmingham, Edgbaston Park Road, West Midlands, Birmingham B15 2TT (United Kingdom); Shetrone, Matthew [McDonald Observatory, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Mosser, Benoît [LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, F-92195 Meudon Cedex (France); Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106-7215 (United States); Silva Aguirre, Víctor [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719, USA and JINA: Joint Institute for Nuclear Astrophysics (United States); Bizyaev, Dmitry [Apache Point Observatory, Sunspot, NM 88349 (United States); Bedding, Timothy R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); García, Rafael A. [Laboratoire AIM, CEA/DSM-CNRS, Universit Paris 7 Diderot, IRFU/SAp, Centre de Saclay, F-91191, Gif-sur-Yvette (France); Pérez, Ana E. García; Hearty, Fred R., E-mail: epstein@astronomy.ohio-state.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2014-04-20

    Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher (<ΔM > =0.17 ± 0.05 M {sub ☉}) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M {sub ☉} level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of ∼100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations.

  18. REFINED NEUTRON STAR MASS DETERMINATIONS FOR SIX ECLIPSING X-RAY PULSAR BINARIES

    International Nuclear Information System (INIS)

    Rawls, Meredith L.; Orosz, Jerome A.; McClintock, Jeffrey E.; Torres, Manuel A. P.; Bailyn, Charles D.; Buxton, Michelle M.

    2011-01-01

    We present an improved method for determining the mass of neutron stars in eclipsing X-ray pulsar binaries and apply the method to six systems, namely, Vela X-1, 4U 1538-52, SMC X-1, LMC X-4, Cen X-3, and Her X-1. In previous studies to determine neutron star mass, the X-ray eclipse duration has been approximated analytically by assuming that the companion star is spherical with an effective Roche lobe radius. We use a numerical code based on Roche geometry with various optimizers to analyze the published data for these systems, which we supplement with new spectroscopic and photometric data for 4U 1538-52. This allows us to model the eclipse duration more accurately and thus calculate an improved value for the neutron star mass. The derived neutron star mass also depends on the assumed Roche lobe filling factor β of the companion star, where β = 1 indicates a completely filled Roche lobe. In previous work a range of β between 0.9 and 1.0 was usually adopted. We use optical ellipsoidal light-curve data to constrain β. We find neutron star masses of 1.77 ± 0.08 M sun for Vela X-1, 0.87 ± 0.07 M sun for 4U 1538-52 (eccentric orbit), 1.00 ± 0.10 M sun for 4U 1538-52 (circular orbit), 1.04 ± 0.09 M sun for SMC X-1, 1.29 ± 0.05 M sun for LMC X-4, 1.49 ± 0.08 M sun for Cen X-3, and 1.07 ± 0.36 M sun for Her X-1. We discuss the limits of the approximations that were used to derive the earlier mass determinations, and we comment on the implications our new masses have for observationally refining the upper and lower bounds of the neutron star mass distribution.

  19. Intermediate-mass black holes in dwarf galaxies out to redshift ˜ 2.4 in the Chandra COSMOS Legacy Survey

    Science.gov (United States)

    Mezcua, M.; Civano, F.; Marchesi, S.; Suh, H.; Fabbiano, G.; Volonteri, M.

    2018-05-01

    We present a sample of 40 AGN in dwarf galaxies at redshifts z ≲ 2.4. The galaxies are drawn from the Chandra COSMOS-Legacy survey as having stellar masses 107 ≤ M* ≤ 3 × 109 M⊙. Most of the dwarf galaxies are star-forming. After removing the contribution from star formation to the X-ray emission, the AGN luminosities of the 40 dwarf galaxies are in the range L0.5-10keV ˜ 1039 - 1044 erg s-1. With 12 sources at z > 0.5, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. The record-holder is cid_1192, at z = 2.39 and with L0.5-10keV ˜ 1044 erg s-1. One of the dwarf galaxies has M* = 6.6 × 107 M⊙ and is the least massive galaxy found so far to host an AGN. All the AGN are of type 2 and consistent with hosting intermediate-mass black holes (BHs) with masses ˜104 - 105 M⊙ and typical Eddington ratios >1%. We also study the evolution, corrected for completeness, of AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to z = 0.7. We find that the AGN fraction for 109 < M* ≤ 3 × 109 M⊙ and LX ˜ 1041 - 1042 erg s-1 is ˜0.4% for z ≤ 0.3 and that it decreases with X-ray luminosity and decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to decrease with redshift, suggesting that AGN in dwarf galaxies evolve differently than those in high-mass galaxies. Mindful of potential caveats, the results seem to favor a direct collapse formation mechanism for the seed BHs in the early Universe.

  20. Spectroscopic and physical parameters of Galactic O-type stars. III. Mass discrepancy and rotational mixing

    Science.gov (United States)

    Markova, N.; Puls, J.; Langer, N.

    2018-05-01

    Context. Massive stars play a key role in the evolution of galaxies and our Universe. Aims: Our goal is to compare observed and predicted properties of single Galactic O stars to identify and constrain uncertain physical parameters and processes in stellar evolution and atmosphere models. Methods: We used a sample of 53 objects of all luminosity classes and with spectral types from O3 to O9.7. For 30 of these, we determined the main photospheric and wind parameters, including projected rotational rates accounting for macroturbulence, and He and N surface abundances, using optical spectroscopy and applying the model atmosphere code FASTWIND. For the remaining objects, similar data from the literature, based on analyses by means of the CMFGEN code, were used instead. The properties of our sample were then compared to published predictions based on two grids of single massive star evolution models that include rotationally induced mixing. Results: Any of the considered model grids face problem in simultaneously reproducing the stellar masses, equatorial gravities, surface abundances, and rotation rates of our sample stars. The spectroscopic masses derived for objects below 30 M⊙ tend to be smaller than the evolutionary ones, no matter which of the two grids have been used as a reference. While this result may indicate the need to improve the model atmosphere calculations (e.g. regarding the treatment of turbulent pressure), our analysis shows that the established mass problem cannot be fully explained in terms of inaccurate parameters obtained by quantitative spectroscopy or inadequate model values of Vrot on the zero age main sequence. Within each luminosity class, we find a close correlation of N surface abundance and luminosity, and a stronger N enrichment in more massive and evolved O stars. Additionally, we also find a correlation of the surface nitrogen and helium abundances. The large number of nitrogen-enriched stars above 30 M⊙ argues for rotationally

  1. N-body modeling of globular clusters: detecting intermediate-mass black holes by non-equipartition in HST proper motions

    Science.gov (United States)

    Trenti, Michele

    2010-09-01

    Intermediate Mass Black Holes {IMBHs} are objects of considerable astrophysical significance. They have been invoked as possible remnants of Population III stars, precursors of supermassive black holes, sources of ultra-luminous X-ray emission, and emitters of gravitational waves. The centers of globular clusters, where they may have formed through runaway collapse of massive stars, may be our best chance of detecting them. HST studies of velocity dispersions have provided tentative evidence, but the measurements are difficult and the results have been disputed. It is thus important to explore and develop additional indicators of the presence of an IMBH in these systems. In a Cycle 16 theory project we focused on the fingerprints of an IMBH derived from HST photometry. We showed that an IMBH leads to a detectable quenching of mass segregation. Analysis of HST-ACS data for NGC 2298 validated the method, and ruled out an IMBH of more than 300 solar masses. We propose here to extend the search for IMBH signatures from photometry to kinematics. The velocity dispersion of stars in collisionally relaxed stellar systems such as globular clusters scales with main sequence mass as sigma m^alpha. A value alpha = -0.5 corresponds to equipartition. Mass-dependent kinematics can now be measured from HST proper motion studies {e.g., alpha = -0.21 for Omega Cen}. Preliminary analysis shows that the value of alpha can be used as indicator of the presence of an IMBH. In fact, the quenching of mass segregation is a result of the degree of equipartition that the system attains. However, detailed numerical simulations are required to quantify this. Therefore we propose {a} to carry out a new, larger set of realistic N-body simulations of star clusters with IMBHs, primordial binaries and stellar evolution to predict in detail the expected kinematic signatures and {b} to compare these predictions to datasets that are {becoming} available. Considerable HST resources have been invested in

  2. Simultaneous, multi-wavelength flare observations of nearby low-mass stars

    Science.gov (United States)

    Thackeray, Beverly; Barclay, Thomas; Quintana, Elisa; Villadsen, Jacqueline; Wofford, Alia; Schlieder, Joshua; Boyd, Patricia

    2018-01-01

    Low-mass stars are the most common stars in the Galaxy and have been targeted in the tens-of-thousands by K2, the re-purposed Kepler mission, as they are prime targets to search for and characterize small, Earth-like planets. Understanding how these fully convective stars drive magnetic activity that manifests as stochastic, short-term brightenings, or flares, provides insight into the prospects of planetary habitability. High energy radiation and energetic particle emission associated with these stars can erode atmospheres, and impact habitability. An innovative campaign to study low mass stars through simultaneous multi-wavelength observations is currently underway with observations ongoing in the X-ray, UV, optical, and radio. I will present early results of our pilot study of the nearby M-Dwarf star Wolf 359 (CN Leo) using K2, SWIFT, and ground based radio observatories, forming a comprehensive picture of flare activity from an M-Dwarf, and discuss the potential impact of these results on exoplanets. "This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE1322106. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation."

  3. NO EVIDENCE FOR INTERMEDIATE-MASS BLACK HOLES IN GLOBULAR CLUSTERS: STRONG CONSTRAINTS FROM THE JVLA

    International Nuclear Information System (INIS)

    Strader, Jay; Chomiuk, Laura; Maccarone, Thomas J.; Miller-Jones, James C. A.; Seth, Anil C.; Heinke, Craig O.; Sivakoff, Gregory R.

    2012-01-01

    With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky Very Large Array radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 μJy beam –1 at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3σ upper limits on IMBHs from 360 to 980 M ☉ . These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (1) IMBHs ∼> 1000 M ☉ are rare in globular clusters or (2) when present, IMBHs accrete in an extraordinarily inefficient manner.

  4. No Evidence for Intermediate-mass Black Holes in Globular Clusters: Strong Constraints from the JVLA

    Science.gov (United States)

    Strader, Jay; Chomiuk, Laura; Maccarone, Thomas J.; Miller-Jones, James C. A.; Seth, Anil C.; Heinke, Craig O.; Sivakoff, Gregory R.

    2012-05-01

    With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky Very Large Array radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 μJy beam-1 at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3σ upper limits on IMBHs from 360 to 980 M ⊙. These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (1) IMBHs >~ 1000 M ⊙ are rare in globular clusters or (2) when present, IMBHs accrete in an extraordinarily inefficient manner.

  5. 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.

  6. Velocity-mass correlation of the O-type stars: model results

    International Nuclear Information System (INIS)

    Stone, R.C.

    1982-01-01

    This paper presents new model results describing the evolution of massive close binaries from their initial ZAMS to post-supernova stages. Unlike the previous conservative study by Stone [Astrophys. J. 232, 520 (1979) (Paper II)], these results allow explicitly for mass loss from the binary system occurring during the core hydrogen- and helium-burning stages of the primary binary star as well as during the Roche lobe overflow. Because of uncertainties in these rates, model results are given for several reasonable choices for these rates. All of the models consistently predict an increasing relation between the peculiar space velocities and masses for runaway OB stars which agrees well with the observed correlations discussed in Stone [Astron. J. 86, 544 (1981) (Paper III)] and also predict a lower limit at Mroughly-equal11M/sub sun/ for the masses of runaway stars, in agreement with the observational limit found by A. Blaauw (Bull. Astron. Inst. Neth. 15, 265, 1961), both of which support the binary-supernova scenario described by van den Heuvel and Heise for the origin of runaway stars. These models also predict that the more massive O stars will produce correspondingly more massive compact remnants, and that most binaries experiencing supernova-induced kick velocities of magnitude V/sub k/> or approx. =300 km s -1 will disrupt following the explosions. The best estimate for this velocity as established from pulsar observations is V/sub k/roughly-equal150 km s -1 , in which case probably only 15% if these binaries will be disrupted by the supernova explosions, and therefore, almost all runaway stars should have either neutron star or black hole companions

  7. Very Low-mass Stars and Brown Dwarfs in Upper Scorpius Using Gaia DR1: Mass Function, Disks, and Kinematics

    Science.gov (United States)

    Cook, Neil J.; Scholz, Aleks; Jayawardhana, Ray

    2017-12-01

    Our understanding of the brown dwarf population in star-forming regions is dependent on knowing distances and proper motions and therefore will be improved through the Gaia space mission. In this paper, we select new samples of very low-mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimized proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early-type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which ˜125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with ˜105 brown dwarfs. We also compile a joint sample from the literature that includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disk fraction among low-mass brown dwarfs (M< 0.05 {M}⊙ ) is substantially higher than in more massive objects, indicating that disks around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for 0.01< M< 0.1 {M}⊙ is consistent with the Kroupa Initial Mass Function. We investigate the possibility that some “proper motion outliers” have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying levels of contamination and completeness.

  8. Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

    Science.gov (United States)

    Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

    2016-03-01

    Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

  9. Properties of evolved mass-losing stars in the Milky Way and variations in the interstellar dust composition

    International Nuclear Information System (INIS)

    Thronson, H.A. Jr.; Latter, W.B.; Black, J.H.; Bally, J.; Hacking, P.; Steward Observatory, Tucson, AZ; AT and T Bell Laboratories, Holmdel, NJ; Cornell Univ., Ithaca, NY; California Institute of Technology, Pasadena)

    1987-01-01

    A large sample of evolved carbon-rich and oxygen-rich objects has been studied using data from the IRAS Point Source Catalog. The number density of infrared-emitting carbon stars shows no variation with Galactocentric radius, while the evolved oxygen star volume density can be well fitted by a given law. A law is given for the number of carbon stars; a total is found in the Galaxy of 48,000 highly evolved oxygen stars. The mass-return rate for all evolved stars is found to be 0.35 solar mass/yr, with a small percentage contribution from carbon stars. The mass-loss rates for both types of stars are dominated by the small number of objects with the smallest rates. A mean lifetime of about 200,000 yr is obtained for both carbon and oxygen stars. Main-sequence stars in the mass range of three to five solar masses are the probable precursors of the carbon stars. 53 references

  10. Correlations of intermediate mass fragments from Fe+Ta, Au, and Th collisions

    International Nuclear Information System (INIS)

    Sangster, T.C.; Begemann-Blaich, M.; Blaich, T.; Britt, H.C.; Hansen, L.F.; Namboodiri, M.N.; Peilert, G.

    1995-01-01

    Charge, velocity, and angular correlations between intermediate mass fragments (IMF) are presented for 50 and 100 MeV/nucleon Fe bombardments of Ta, Au, and Th targets. Correlation functions generated as a function of the relative velocity and the opening angle between two IMF's are qualitatively independent of the projectile energy and target mass and show a suppression at small relative velocities and opening angles due to the Coulomb repulsion between the fragments. The correlations are consistent with IMF's emitted primarily from a highly excited target residue following a rapid preequilibrium cascade. The correlation data are compared to model calculations using the event generator MENEKA and the quantum molecular dynamics (QMD) code with a statistical deexcitation of residual fragments utilizing the multifragmentation code SMM. All data are consistent with a simultaneous multifragmentation at a freeze-out density of 0.1--0.3 times normal nuclear matter density or a more sequential emission with time constant τ≤500 fm/c

  11. The mass-metallicity-star formation rate relation under the STARLIGHT microscope

    Science.gov (United States)

    Schlickmann, M.; Vale Asari, N.; Cid Fernandes, R.; Stasińska, G.

    2014-10-01

    The correlation between stellar mass and gas-phase oxygen abundance (M-Z relation) has been known for decades. The slope and scatter of this trend is strongly dependent on galaxy evolution: Chemical enrichment in a galaxy is driven by its star formation history, which in turn depends on its secular evolution and interaction with other galaxies and intergalactic gas. In last couple of years, the M-Z relation has been studied as a function of a third parameter: the recent star formation rate (SFR) as calibrated by the Hα luminosity, which traces stars formed in the last 10 Myr. This mass-metallicity-SFR relation has been reported to be very tight. This result puts strong constraints on galaxy evolution models in low and high redshifts, informing which models of infall and outflow of gas are acceptable. We explore the mass-metallicity-SFR relation in light of the SDSS-STARLIGHT database put together by our group. We find that we recover similar results as the ones reported by authors who use the MPA/JHU catalogue. We also present some preliminary results exploring the mass-metallicity-SFR relation in a more detailed fashion: starlight recovers a galaxy's full star formation history, and not only its recent SFR.

  12. On the stability and maximum mass of differentially rotating relativistic stars

    Science.gov (United States)

    Weih, Lukas R.; Most, Elias R.; Rezzolla, Luciano

    2018-01-01

    The stability properties of rotating relativistic stars against prompt gravitational collapse to a black hole are rather well understood for uniformly rotating models. This is not the case for differentially rotating neutron stars, which are expected to be produced in catastrophic events such as the merger of binary system of neutron stars or the collapse of a massive stellar core. We consider sequences of differentially rotating equilibrium models using the j-constant law and by combining them with their dynamical evolution, we show that a sufficient stability criterion for differentially rotating neutron stars exists similar to the one of their uniformly rotating counterparts. Namely: along a sequence of constant angular momentum, a dynamical instability sets in for central rest-mass densities slightly below the one of the equilibrium solution at the turning point. In addition, following Breu & Rezzolla, we show that 'quasi-universal' relations can be found when calculating the turning-point mass. In turn, this allows us to compute the maximum mass allowed by differential rotation, Mmax,dr, in terms of the maximum mass of the non-rotating configuration, M_{_TOV}, finding that M_{max, dr} ˜eq (1.54 ± 0.05) M_{_TOV} for all the equations of state we have considered.

  13. Astrophysical parameters of open star clusters using 2MASS JHKs data

    Science.gov (United States)

    Durgapal, Alok; Bisht, Devendra; Yadav, Ramakant Singh

    2018-04-01

    In the present analysis we have estimated the fundamental parameters of two poorly studied open star clusters, namely Teutsch 61 and Czernik 3, using 2MASS JHKs data. We have used the color-magnitude and colour-colour diagrams to determine their fundamental parameters.

  14. RED DWARF DYNAMO RAISES PUZZLE OVER INTERIORS OF LOWEST-MASS STARS

    Science.gov (United States)

    2002-01-01

    NASA's Hubble Space Telescope has uncovered surprising evidence that powerful magnetic fields might exist around the lowest mass stars in the universe, which are near the threshold of stellar burning processes. 'New theories will have to be developed to explain how these strong fields are produced, since conventional models predict that these low mass red dwarfs should have very weak or no magnetic fields,' says Dr. Jeffrey Linsky of the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, Colorado. 'The Hubble observations provide clear evidence that very low mass red dwarf stars must have some form of dynamo to amplify their magnetic fields.' His conclusions are based upon Hubble's detection of a high-temperature outburst, called a flare, on the surface of the extremely small, cool red dwarf star Van Biesbroeck 10 (VB10) also known as Gliese 752B. Stellar flares are caused by intense, twisted magnetic fields that accelerate and contain gasses which are much hotter than a star's surface. Explosive flares are common on the Sun and expected for stars that have internal structures similar to our Sun's. Stars as small as VB10 are predicted to have a simpler internal structure than that of the Sun and so are not expected to generate the electric currents required for magnetic fields that drive flares. Besides leading to a clearer understanding of the interior structure of the smallest red dwarf stars known, these unexpected results might possibly shed light on brown dwarf stars. A brown dwarf is a long-sought class of astronomical object that is too small to shine like a star through nuclear fusion processes, but is too large to be considered a planet. 'Since VB10 is nearly a brown dwarf, it is likely brown dwarfs also have strong magnetic fields,' says Linsky. 'Additional Hubble searches for flares are needed to confirm this prediction.' A QUARTER-MILLION DEGREE TORCH The star VB10 and its companion star Gliese 752A make up a binary system located 19 light

  15. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-09-20

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

  17. RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Dunham, Michael M. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Vorobyov, Eduard I., E-mail: michael.dunham@yale.edu, E-mail: eduard.vorobiev@univie.ac.at [Institute of Astronomy, University of Vienna, Vienna 1180 (Austria)

    2012-03-01

    We determine the observational signatures of protostellar cores by coupling two-dimensional radiative transfer calculations with numerical hydrodynamical simulations that predict accretion rates that both decline with time and feature short-term variability and episodic bursts caused by disk gravitational instability and fragmentation. We calculate the radiative transfer of the collapsing cores throughout the full duration of the collapse, using as inputs the core, disk, protostellar masses, radii, and mass accretion rates predicted by the hydrodynamical simulations. From the resulting spectral energy distributions, we calculate standard observational signatures (L{sub bol}, T{sub bol}, L{sub bol}/L{sub smm}) to directly compare to observations. We show that the accretion process predicted by these models reproduces the full spread of observed protostars in both L{sub bol}-T{sub bol} and L{sub bol}-M{sub core} space, including very low luminosity objects, provides a reasonable match to the observed protostellar luminosity distribution, and resolves the long-standing luminosity problem. These models predict an embedded phase duration shorter than recent observationally determined estimates (0.12 Myr versus 0.44 Myr), and a fraction of total time spent in Stage 0 of 23%, consistent with the range of values determined by observations. On average, the models spend 1.3% of their total time in accretion bursts, during which 5.3% of the final stellar mass accretes, with maximum values being 11.8% and 35.5% for the total time and accreted stellar mass, respectively. Time-averaged models that filter out the accretion variability and bursts do not provide as good of a match to the observed luminosity problem, suggesting that the bursts are required.

  18. Merger of binary neutron stars of unequal mass in full general relativity

    International Nuclear Information System (INIS)

    Shibata, Masaru; Taniguchi, Keisuke; Uryu-bar, Ko-barji

    2003-01-01

    We present results of three dimensional numerical simulations of the merger of unequal-mass binary neutron stars in full general relativity. A Γ-law equation of state P=(Γ-1)ρε is adopted, where P, ρ, ε, and Γ are the pressure, rest mass density, specific internal energy, and the adiabatic constant, respectively. We take Γ=2 and the baryon rest-mass ratio Q M to be in the range 0.85-1. The typical grid size is (633,633,317) for (x,y,z). We improve several implementations since the latest work. In the present code, the radiation reaction of gravitational waves is taken into account with a good accuracy. This fact enables us to follow the coalescence all the way from the late inspiral phase through the merger phase for which the transition is triggered by the radiation reaction. It is found that if the total rest mass of the system is more than ∼1.7 times of the maximum allowed rest mass of spherical neutron stars, a black hole is formed after the merger, irrespective of the mass ratios. The gravitational waveforms and outcomes in the merger of unequal-mass binaries are compared with those in equal-mass binaries. It is found that the disk mass around the so formed black holes increases with decreasing rest-mass ratios and decreases with increasing compactness of neutron stars. The merger process and the gravitational waveforms also depend strongly on the rest-mass ratios even for the range Q M =0.85-1

  19. A M2FS Spectroscopic Study of Low-mass Young Stars in Orion OB1

    Science.gov (United States)

    Kaleida, Catherine C.; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

    2015-01-01

    Surveys of pre-main sequence stars in the ~4-10 Myr range provide a window into the decline of the accretion phase of stars and the formation of planets. Nearby star clusters and stellar associations allow for the study of these young stellar populations all the way down to the lowest mass members. One of the best examples of nearby 4-10 Myr old stellar populations is the Orion OB1 association. The CIDA Variability Survey of Orion OB1 (CVSO - Briceño et al. 2001) has used the variability properties of low-mass pre-main-sequence (PMS) stars to identify hundreds of K and M-type stellar members of the Orion OB1 association, a number of them displaying IR-excess emission and thought to be representative of more evolved disk-bearing young stars. Characterizing these young, low-mass objects using spectroscopy is integral to understanding the accretion phase in young stars. We present preliminary results of a spectroscopic survey of candidate and confirmed Orion OB1 low-mass members taken during November 2014 and February 2014 using the Michigan/Magellan Fiber Spectrograph (M2FS), a PI instrument on the Magellan Clay Telescope (PI: M. Matteo). Target fields located in the off-cloud regions of Orion were identified in the CVSO, and observed using the low and high-resolution modes of M2FS. Both low and high-resolution spectra are needed in order to confirm membership and derive masses, ages, kinematics and accretion properties. Initial analysis of these spectra reveal many new K and M-type members of the Orion OB1 association in these low extinction, off-cloud areas. These are the more evolved siblings of the youngest stars still embedded in the molecular clouds, like those in the Orion Nebula Cluster. With membership and spectroscopic indicators of accretion we are building the most comprehensive stellar census of this association, enabling us to derive a robust estimate of the fraction of young stars still accreting at a various ages, a key constraint for the end of

  20. Light-Time Effect and Mass Transfer in the Triple Star SW Lyncis

    Directory of Open Access Journals (Sweden)

    Chun-Hwey Kim

    1999-06-01

    Full Text Available In this paper all the photoelectric times of minimum for the triple star SW Lyn have been analyzed in terms of light-time e ect due to the third-body and secular period decreases induced by mass transfer process. The light-time orbit determined recently by Ogloza et al.(1998 were modi ed and improved. And it is found that the orbital period of SW Lyn have been decreasing secularly. The third-body revolves around the mass center of triple stars every 5y.77 in a highly eccentric elliptical orbit(e=0.61. The third-body with a minimum mass of 1.13M may be a binary or a white dwarf. The rate of secular period-decrease were obtained as ¡âP/P = -12.45 x 10^-11, implying the mass-transfer from the massive primary star to the secondary. The mass losing rate from the primary were calculated as about 1.24 x 10^-8M /y. It is noticed that the mass-transfer in SW Lyn system is opposite in direction to that deduced from it's Roche geometry by previous investigators.

  1. Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

    Science.gov (United States)

    Meszaros, P.; Rees, M. J.

    1992-01-01

    A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

  2. GW170817: a neutron star merger in a mass-transferring triple system

    Science.gov (United States)

    Chang, Philip; Murray, Norman

    2018-02-01

    The light curve of GW170817 is surprisingly blue and bright. Assuming that the event is a binary neutron star merger, we argue that blueness and brightness of the light curve is the result of ejecta that contains an substantial amount of thermal energy. To achieve this, the ejecta must be reheated at a substantial distance (1-2000 solar radii) from the merger to avoid losing the energy to adiabatic cooling. We show that this reheating can occur if the merger occurs in a hierarchical triple system where the outer star has evolved and filled its Roche lobe. The outer star feeds mass to the inner binary, forming a circumbinary disc, driving the inner binary to merge. Because the outer star fills its Roche lobe, a substantial fraction of the dynamical ejecta collides with the evolved star, reheating the ejecta in the process. We suggest that the process of mass transfer in hierarchical triples tends to form coplanar triple systems such as PSR J0337+1715, and may provide electromagnetic counterparts to binary black hole mergers.

  3. The Masses and Evolutionary State of the Stars in the Dwarf Nova SS Cygni

    Science.gov (United States)

    Bitner, Martin A.; Robinson, Edward L.; Behr, Bradford B.

    2007-06-01

    The dwarf nova SS Cygni is a close binary star consisting of a K star transferring mass to a white dwarf by way of an accretion disk. We have obtained new spectroscopic observations of SS Cyg. Fits of synthetic spectra for Roche lobe-filling stars to the absorption-line spectrum of the K star yield the amplitude of the K star's radial velocity curve and the mass ratio, KK=162.5+/-1.0 km s-1 and q=MK/MWD=0.685+/-0.015. The fits also show that the accretion disk and white dwarf contribute a fraction f=0.535+/-0.075 of the total flux at 5500 Å. Taking the weighted average of our results with previously published results obtained using similar techniques, we find =163.7+/-0.7 km s-1 and =0.683+/-0.012. The orbital light curve of SS Cyg shows an ellipsoidal variation diluted by light from the disk and white dwarf. From an analysis of the ellipsoidal variations, we limit the orbital inclination to the range 45degAustin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

  4. Evidence for a maximum mass cut-off in the neutron star mass distribution and constraints on the equation of state

    Science.gov (United States)

    Alsing, Justin; Silva, Hector O.; Berti, Emanuele

    2018-04-01

    We infer the mass distribution of neutron stars in binary systems using a flexible Gaussian mixture model and use Bayesian model selection to explore evidence for multi-modality and a sharp cut-off in the mass distribution. We find overwhelming evidence for a bimodal distribution, in agreement with previous literature, and report for the first time positive evidence for a sharp cut-off at a maximum neutron star mass. We measure the maximum mass to be 2.0M⊙ sharp cut-off is interpreted as the maximum stable neutron star mass allowed by the equation of state of dense matter, our measurement puts constraints on the equation of state. For a set of realistic equations of state that support >2M⊙ neutron stars, our inference of mmax is able to distinguish between models at odds ratios of up to 12: 1, whilst under a flexible piecewise polytropic equation of state model our maximum mass measurement improves constraints on the pressure at 3 - 7 × the nuclear saturation density by ˜30 - 50% compared to simply requiring mmax > 2M⊙. We obtain a lower bound on the maximum sound speed attained inside the neutron star of c_s^max > 0.63c (99.8%), ruling out c_s^max c/√{3} at high significance. Our constraints on the maximum neutron star mass strengthen the case for neutron star-neutron star mergers as the primary source of short gamma-ray bursts.

  5. Exoplanet dynamics. Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars.

    Science.gov (United States)

    Leconte, Jérémy; Wu, Hanbo; Menou, Kristen; Murray, Norman

    2015-02-06

    Planets in the habitable zone of lower-mass stars are often assumed to be in a state of tidally synchronized rotation, which would considerably affect their putative habitability. Although thermal tides cause Venus to rotate retrogradely, simple scaling arguments tend to attribute this peculiarity to the massive Venusian atmosphere. Using a global climate model, we show that even a relatively thin atmosphere can drive terrestrial planets' rotation away from synchronicity. We derive a more realistic atmospheric tide model that predicts four asynchronous equilibrium spin states, two being stable, when the amplitude of the thermal tide exceeds a threshold that is met for habitable Earth-like planets with a 1-bar atmosphere around stars more massive than ~0.5 to 0.7 solar mass. Thus, many recently discovered terrestrial planets could exhibit asynchronous spin-orbit rotation, even with a thin atmosphere. Copyright © 2015, American Association for the Advancement of Science.

  6. Modeling Type II-P/II-L Supernovae Interacting with Recent Episodic Mass Ejections from Their Presupernova Stars with MESA and SNEC

    Science.gov (United States)

    Das, Sanskriti; Ray, Alak

    2017-12-01

    We show how dense, compact, discrete shells of circumstellar gas immediately outside of red supergiants affect the optical light curves of Type II-P/II-L supernovae (SNe), using the example of SN 2013ej. Earlier efforts in the literature had used an artificial circumstellar medium (CSM) stitched to the surface of an evolved star that had not gone through a phase of late-stage heavy mass loss, which, in essence, is the original source of the CSM. In contrast, we allow enhanced mass-loss rate from the modeled star during the 16O and 28Si burning stages and construct the CSM from the resulting mass-loss history in a self-consistent way. Once such evolved pre-SN stars are exploded, we find that the models with early interaction between the shock and the dense CSM reproduce light curves far better than those without that mass loss and, hence, having no nearby dense CSM. The required explosion energy for the progenitors with a dense CSM is reduced by almost a factor of two compared to those without the CSM. Our model, with a more realistic CSM profile and presupernova and explosion parameters, fits observed data much better throughout the rise, plateau, and radioactive tail phases as compared to previous studies. This points to an intermediate class of supernovae between Type II-P/II-L and Type II-n SNe with the characteristics of simultaneous UV and optical peak, slow decline after peak, and a longer plateau.

  7. HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gruendl, Robert A.; Chu, Y.-H.

    2009-01-01

    background galaxies. A comprehensive search for YSOs in the LMC has also been carried out by the SAGE team and reported by Whitney et al. There are three major differences between these two searches. (1) In the common region of color-magnitude space, ∼850 of our 1172 probable YSOs are missed in the SAGE YSO catalog because their conservative point-source identification criteria have excluded YSOs superposed on complex stellar and interstellar environments. (2) About 20%-30% of the YSOs identified by the SAGE team are sources we classify as background galaxies. (3) The SAGE YSO catalog identifies YSO in parts of color-magnitude space that we excluded and thus contains more evolved or fainter YSOs missed by our analysis. The shortcomings and strengths of both these YSO catalogs should be considered prior to statistical studies of star formation in the LMC. Finally, the mid-infrared luminosity functions in the IRAC bands of our most likely YSO candidates in the LMC can be well described by N(L) ∝ L -1 , which is consistent with the Salpeter initial mass function if a mass-luminosity relation of L ∝ M 2.4 is adopted.

  8. IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 pc. II. DISTANCES, KINEMATICS, AND GROUP MEMBERSHIP

    Energy Technology Data Exchange (ETDEWEB)

    Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Anglada-Escude, Guillem [Institut fuer Astrophysik, Universitaet Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Liu, Michael C.; Bowler, Brendan P. [Institute for Astronomy, University of Hawaii at Manoa 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Weinberger, Alycia J.; Boss, Alan P. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Reid, I. Neill [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Tamura, Motohide, E-mail: shkolnik@lowell.edu [National Astronomical Observatory of Japan, Tokyo (Japan)

    2012-10-10

    We have conducted a kinematic study of 165 young M dwarfs with ages of {approx}<300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of {approx}<25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young ({approx}<3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages {approx}<150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.

  9. THE MASS-INDEPENDENCE OF SPECIFIC STAR FORMATION RATES IN GALACTIC DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Abramson, Louis E.; Gladders, Michael D. [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Kelson, Daniel D.; Dressler, Alan; Oemler, Augustus Jr. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Poggianti, Bianca [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Vulcani, Benedetta, E-mail: labramson@uchicago.edu [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8582 (Japan)

    2014-04-20

    The slope of the star formation rate/stellar mass relation (the SFR {sup M}ain Sequence{sup ;} SFR-M {sub *}) is not quite unity: specific star formation rates (SFR/M {sub *}) are weakly but significantly anti-correlated with M {sub *}. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions—portions of a galaxy not forming stars—with M {sub *}. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFR{sub disk} ≡ SFR/M {sub *,} {sub disk}) reduces the M {sub *} dependence of SF efficiency by ∼0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log sSFR{sub disk}-log M {sub *} to have a slope β{sub disk} in [ – 0.20, 0.00] ± 0.02 (depending on the SFR estimator and Main Sequence definition) for star-forming galaxies with M {sub *} ≥ 10{sup 10} M {sub ☉} and bulge mass-fractions B/T ≲ 0.6, generally consistent with a pure-disk control sample (β{sub control} = –0.05 ± 0.04). That (SFR/M {sub *,} {sub disk}) is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any SFR-M {sub *} relation, including manifestations of ''mass quenching'' (bulge growth), factors shaping the star-forming stellar mass function (uniform dlog M {sub *}/dt for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in SFR(M {sub *}, t)). Our results emphasize the need to treat galaxies as composite systems—not integrated masses—in observational and theoretical work.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  11. Emission - line theoretical profiles for Wolf- Rayet stars with low-mass companions

    International Nuclear Information System (INIS)

    Antokhin, I.I.

    1986-01-01

    Profiles of the resonant line λ 765 A and the subordinate line λ 4058 of N4 have been calculated for a binary system medel consisting of the Wolf-Rayet star and the low-mass companion (possibly, a relativistic object) by means of Sobolev approximation. The equations of statistical equilibrium have been solved for the first 32 levels of N4. Two cases have been considered: 1) detached zone of N5 surrounding the Wolf-Rayet star and the companion; 2) common zone of N5. The criteria for detection of presence of a companion in line profile observations have been formulated

  12. Mass-Individualism: Converse All Stars and the Paradox of Sartorial Sameness

    DEFF Research Database (Denmark)

    Mackinney-Valentin, Maria

    2014-01-01

    . The concept of mass-individualism is used as a vehicle for understanding this paradox that is heightened both by the social value attributed to individuality in much of contemporary Western society and the image of All Stars as a symbol of individuality and self-expression. The concept is seen as part...... of an ambiguous strategy of status representation operating on conditions of fashion democracy. The study is interview-based and focuses on consumers aged seven to 71 in the greater Copenhagen area in which All Stars may be considered a transplanted, American cultural icon. Themes of undercoding and visual...

  13. Neutron Star masses from the Field Correlator Method Equation of State

    Directory of Open Access Journals (Sweden)

    Zappalà D.

    2014-04-01

    Full Text Available We analyse the hadron-quark phase transition in neutron stars by confronting the hadronic Equation of State (EoS obtained according to the microscopic Brueckner-Hartree-Fock many body theory, with the quark matter EoS derived within the Field Correlator Method. In particular, the latter EoS is only parametrized in terms of the gluon condensate and the large distance quark-antiquark potential, so that the comparison of the results of this analysis with the most recent measurements of heavy neutron star masses provides some physical constraints on these two parameters.

  14. SHIELD: The Star Formation Law in Extremely Low-mass Galaxies

    Science.gov (United States)

    Teich, Yaron; McNichols, Andrew; Cannon, John M.; SHIELD Team

    2016-01-01

    The "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD) is a multiwavelength, legacy-class observational study of 12 low-mass dwarf galaxies discovered in Arecibo Legacy Fast ALFA (ALFALFA) survey data products. Here we analyze the relationships between HI and star formation in these systems using multi-configuration, high spatial (~300 pc) and spectral (0.82 - 2.46 km s-1 ch-1) resolution HI observations from the Karl G. Jansky Very Large Array, Hα imaging from the WIYN 3.5m telescope, and archival GALEX far-ultraviolet imaging. We compare the locations and intensities of star formation with the properties of the neutral ISM. We quantify the degree of local co-spatiality between star forming regions and regions of high HI column densities using the Kennicutt-Schmidt (K-S) relation. The values of the K-S index N vary considerably from system to system; because no single galaxy is representative of the sample, we instead focus on the narratives of the individual galaxies and their complex distribution of gaseous and stellar components. At the extremely faint end of the HI mass function, these systems are dominated by stochastic fluctuations in their interstellar media, which governs whether or not they show signs of recent star formation.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College.

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

    Science.gov (United States)

    Morscher, Maggie

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

  16. The Mass Function of Young Star Clusters in the "Antennae" Galaxies.

    Science.gov (United States)

    Zhang; Fall

    1999-12-20

    We determine the mass function of young star clusters in the merging galaxies known as the "Antennae" (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimate the intrinsic luminosity and age, and hence the mass, of each cluster. We find that the mass function of the young star clusters (with ages less, similar160 Myr) is well represented by a power law of the form psi&parl0;M&parr0;~M-2 over the range 104 less, similarM less, similar106 M middle dot in circle. This result may have important implications for our understanding of the origin of globular clusters during the early phases of galactic evolution.

  17. Episodic mass loss from the hydrogen-deficient central star of the planetary nebula Longmore 4

    Energy Technology Data Exchange (ETDEWEB)

    Bond, Howard E., E-mail: heb11@psu.edu [Current address: Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA. (United States)

    2014-09-01

    A spectacular transient mass-loss episode from the extremely hot, hydrogen-deficient central star of the planetary nebula (PN) Longmore 4 (Lo 4) was discovered in 1992 by Werner et al. During that event, the star temporarily changed from its normal PG 1159 spectrum to that of an emission-line low-luminosity early-type Wolf-Rayet [WCE] star. After a few days, Lo 4 reverted to its normal, predominantly absorption-line PG 1159 type. To determine whether such events recur, and if so how often, I monitored the optical spectrum of Lo 4 from early 2003 to early 2012. Out of 81 spectra taken at random dates, 4 of them revealed mass-loss outbursts similar to that seen in 1992. This indicates that the episodes recur approximately every 100 days (if the recurrence rate has been approximately constant and the duration of a typical episode is ∼5 days), and that the star is in a high-mass-loss state about 5% of the time. Since the enhanced stellar wind is hydrogen-deficient, it arises from the photosphere and is unlikely to be related to phenomena such as a binary or planetary companion or infalling dust. I speculate on plausible mechanisms for these unique outbursts, including the possibility that they are related to the non-radial GW Vir-type pulsations exhibited by Lo 4. The central star of the PN NGC 246 has stellar parameters similar to those of Lo 4, and it is also a GW Vir-type pulsator with similar pulsation periods. I obtained 167 spectra of NGC 246 between 2003 and 2011, but no mass ejections were found.

  18. Coincidence measurements of intermediate mass fragments produced in /sup 32/S-induced reactions on Ag at E/A = 22.5 MeV

    International Nuclear Information System (INIS)

    Fields, D.J.; Lynch, W.G.; Nayak, T.K.

    1986-01-01

    Single- and two-particle inclusive cross sections for the production of light nuclei and intermediate mass fragments, 3< or =Z< or =24, were measured at angles well beyond the grazing angle for /sup 32/S-induced reactions on Ag at 720 MeV. Information about fragment multiplicities and reaction dynamics was extracted from measurements of light particles, intermediate mass fragments, and targetlike residues in coincidence with intermediate mass fragments. Incomplete linear momentum transfer and non-compound-particle emission are important features of collisions producing intermediate mass fragments. About half of the incident kinetic energy in these collisions is converted into internal excitation. The mean multiplicity of intermediate mass fragments is of the order of 1. Particle correlations are strongly enhanced in the plane which contains the intermediate mass fragment and the beam axis

  19. Clinical impact of body mass index on prostate biopsy in patients with intermediate PSA levels

    International Nuclear Information System (INIS)

    Sekita, Nobuyuki; Chin, Kensei; Fujimura, Masaaki; Mikami, Kazuo; Suzuki, Hiroyoshi; Kamijima, Shuichi

    2008-01-01

    From April 2005 to September 2007, 480 patients underwent transrectal prostate biopsy at our institution. The clinical data including age, serum prostate specific antigen (PSA) level, prostate volume and body mass index (BMI) were obtained, and the cancer detection rates and pathological findings were evaluated in 305 cases with a PSA concentration of 4.0 to 10.0 ng/ml. Prostate volume was calculated from magnetic resonance imaging (MRI) findings. The 305 patients were categorized according to their BMI into three groups (normal, less than 22 kg/m 2 ; overweight, 22-25 kg/m 2 ; and obese, more than 25 kg/m 2 ). Cancer detection rates and histopathologic findings were compared between the groups. Multivariate logistic regression analysis was also performed. Prostate cancer was detected in 127 patients. No significant differences in BMI were observed between biopsy-positive and biopsy-negative cases (p=0.965), and the detection rates of prostate cancer observed in the three groups were not significantly different. There was a significant association between BMI and the findings of high Gleason score (more than 4+3) (p=0.048). BMI was not a contributory factor of prostate cancer detection for cases with intermediate PSA levels; however, patients with high BMI may have high-grade malignancy features. (author)

  20. Ab initio results for intermediate-mass, open-shell nuclei

    Science.gov (United States)

    Baker, Robert B.; Dytrych, Tomas; Launey, Kristina D.; Draayer, Jerry P.

    2017-01-01

    A theoretical understanding of nuclei in the intermediate-mass region is vital to astrophysical models, especially for nucleosynthesis. Here, we employ the ab initio symmetry-adapted no-core shell model (SA-NCSM) in an effort to push first-principle calculations across the sd-shell region. The ab initio SA-NCSM's advantages come from its ability to control the growth of model spaces by including only physically relevant subspaces, which allows us to explore ultra-large model spaces beyond the reach of other methods. We report on calculations for 19Ne and 20Ne up through 13 harmonic oscillator shells using realistic interactions and discuss the underlying structure as well as implications for various astrophysical reactions. This work was supported by the U.S. NSF (OCI-0904874 and ACI -1516338) and the U.S. DOE (DE-SC0005248), and also benefitted from the Blue Waters sustained-petascale computing project and high performance computing resources provided by LSU.

  1. The low-mass star and sub-stellar populations of the 25 Orionis group

    Science.gov (United States)

    Downes, Juan José; Briceño, César; Mateu, Cecilia; Hernández, Jesús; Vivas, Anna Katherina; Calvet, Nuria; Hartmann, Lee; Petr-Gotzens, Monika G.; Allen, Lori

    2014-10-01

    We present the results of a survey of the low-mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA (Centro de Investigaciones de Astronomía `Francisco J. Duarte', Mérida, Venezuela) Deep Survey of Orion, near-IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low-resolution spectroscopy obtained with Hectospec at the MMT telescope, we selected 1246 photometric candidates to low-mass stars and brown dwarfs with estimated masses within 0.02 ≲ M/M⊙ ≲ 0.8 and spectroscopically confirmed a sample of 77 low-mass stars as new members of the cluster with a mean age of ˜7 Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices α3 = -1.73 ± 0.31 and α2 = 0.68 ± 0.41 in the mass ranges 0.03 ≤ M/M⊙ ≤ 0.08 and 0.08 ≤ M/M⊙ ≤ 0.5, respectively, or a Scalo lognormal function with coefficients m_c=0.21^{+0.02}_{-0.02} and σ = 0.36 ± 0.03 in the mass range 0.03 ≤ M/M⊙ ≤ 0.8. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the east-west elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low-mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low-mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged.

  2. Infrared colours and inferred masses of metal-poor giant stars in the Keplerfield

    Science.gov (United States)

    Casey, A. R.; Kennedy, G. M.; Hartle, T. R.; Schlaufman, Kevin C.

    2018-05-01

    Intrinsically luminous giant stars in the Milky Way are the only potential volume-complete tracers of the distant disk, bulge, and halo. The chemical abundances of metal-poor giants also reflect the compositions of the earliest star-forming regions, providing the initial conditions for the chemical evolution of the Galaxy. However, the intrinsic rarity of metal-poor giants combined with the difficulty of efficiently identifying them with broad-band optical photometry has made it difficult to exploit them for studies of the Milky Way. One long-standing problem is that photometric selections for giant and/or metal-poor stars frequently include a large fraction of metal-rich dwarf contaminants. We re-derive a giant star photometric selection using existing public g-band and narrow-band DDO51photometry obtained in the Keplerfield. Our selection is simple and yields a contamination rate of main-sequence stars of ≲1% and a completeness of about 80 % for giant stars with Teff ≲ 5250 K - subject to the selection function of the spectroscopic surveys used to estimate these rates, and the magnitude range considered (11 ≲ g ≲ 15). While the DDO51filter is known to be sensitive to stellar surface gravity, we further show that the mid-infrared colours of DDO51-selected giants are strongly correlated with spectroscopic metallicity. This extends the infrared metal-poor selection developed by Schlaufman & Casey, demonstrating that the principal contaminants in their selection can be efficiently removed by the photometric separation of dwarfs and giants. This implies that any similarly efficient dwarf/giant discriminant (e.g., Gaiaparallaxes) can be used in conjunction with WISEcolours to select samples of giant stars with high completeness and low contamination. We employ our photometric selection to identify three metal-poor giant candidates in the Keplerfield with global asteroseismic parameters and find that masses inferred for these three stars using standard

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-01

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

  4. The effect of dynamical quark mass on the calculation of a strange quark star's structure

    Institute of Scientific and Technical Information of China (English)

    Gholam Hossein Bordbar; Babak Ziaei

    2012-01-01

    We discuss the dynamical behavior of strange quark matter components,in particular the effects of density dependent quark mass on the equation of state of strange quark matter.The dynamical masses of quarks are computed within the Nambu-Jona-Lasinio model,then we perform strange quark matter calculations employing the MIT bag model with these dynamical masses.For the sake of comparing dynamical mass interaction with QCD quark-quark interaction,we consider the one-gluon-exchange term as the effective interaction between quarks for the MIT bag model.Our dynamical approach illustrates an improvement in the obtained equation of state values.We also investigate the structure of the strange quark star using TolmanOppenheimer-Volkoff equations for all applied models.Our results show that dynamical mass interaction leads to lower values for gravitational mass.

  5. Liquid-vapor phase transition, collective flow and entropy determination from future measurements of intermediate mass fragments

    International Nuclear Information System (INIS)

    Coffin, J.P.

    1991-01-01

    Some global variables reflecting the highly collective character of nuclear matter produced in relativistic heavy-ion collisions are briefly reviewed on the basis of presently available experimental results and of Quantum Statistical Model and Quantum Molecular Dynamic Model predictions relative to intermediate mass fragments. Possible future measurements are suggested. (author) 27 refs., 8 figs

  6. The scenario of two families of compact stars. Pt. 1. Equations of state, mass-radius relations and binary systems

    Energy Technology Data Exchange (ETDEWEB)

    Drago, Alessandro; Pagliara, Giuseppe [Ferrara Univ. (Italy). Dipt. di Fisica e Scienze della Terra; INFN, Ferrara (Italy); Lavagno, Andrea; Pigato, Daniele [Politecnico di Torino (Italy). Dept. of Applied Science and Technology; INFN, Torino (Italy)

    2016-02-15

    We present several arguments which favor the scenario of two coexisting families of compact stars: hadronic stars and quark stars. Besides the well-known hyperon puzzle of the physics of compact stars, a similar puzzle exists also when considering delta resonances. We show that these particles appear at densities close to twice saturation density and must be therefore included in the calculations of the hadronic equation of state. Such an early appearance is strictly related to the value of the L parameter of the symmetry energy that has been found, in recent phenomenological studies, to lie in the range 40 < L < 62 MeV. We discuss also the threshold for the formation of deltas and hyperons for hot and lepton-rich hadronic matter. Similarly to the case of hyperons, also delta resonances cause a softening of the equation of state, which makes it difficult to obtain massive hadronic stars. Quark stars, on the other hand, can reach masses up to 2.75M {sub CircleDot} as predicted by perturbative QCD calculations. We then discuss the observational constraints on the masses and the radii of compact stars. The tension between the precise measurements of high masses and the indications of the existence of very compact stellar objects (with radii of the order of 10 km) is relieved when assuming that very massive compact stars are quark stars and very compact stars are hadronic stars. Finally, we discuss recent interesting measurements of the eccentricities of the orbits of millisecond pulsars in low mass X-ray binaries. The high values of the eccentricities found in some cases could be explained by assuming that the hadronic star, initially present in the binary system, converts to a quark star due to the increase of its central density. (orig.)

  7. Evolution of low-mass stars in the alpha persei cluster

    International Nuclear Information System (INIS)

    Stauffer, J.R.; Hartmann, L.W.; Burnham, J.N.; Jones, B.F.

    1985-01-01

    We present a photometric and spectroscopic study of low-mass members of the α Persei cluster. Now relative proper motions have been obtained for 4000 stars in a 1X2 x 1X2 region of the α Persei open cluster. The survey extends to Vroughly-equal16.5 mag, much fainter than the previous proper motion surveys. Optical photometry and high-dispersion spectroscopy of the possible cluster members from our survey, as well as a set of 10th to 12th magnitude stars from previous surveys, have also been obtained. The new photometry shows an apparent pre-main sequence (PMS), but we cannot yet accurately determine the PMS turn-on point. The faint stars in the cluster have positions in a V versus V-I diagram that are roughly in accord with the 5 x 10 7 yr isochrone derived by VandenBerg et al. In agreement with previous results for the Pleiades cluster, some of the late-type α Persei members are photometric variables, with periods of 1 day or less. Light curves and estimated periods are presented for six of the G and K dwarf members of the cluster. We attribute the periodic light variations to spots on the surfaces of these stars, which are carried around the visible hemisphere by rapid rotation. The photometric periods are consistent with rotational broadening measurements when available. Projected rotational velocities derived from the echelle spectra indicate that nearly 50% of the stars observed that are later than G2 have 25 km s -1 -1 . The large rotational velocities among low-mass stars in young clusters are ascribed to spin-up during contraction to the main sequence

  8. Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

    Science.gov (United States)

    Groenewegen, M. A. T.; Sloan, G. C.

    2018-01-01

    Context. Mass loss is one of the fundamental properties of asymptotic giant branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking. Aims: We aim to investigate mass loss and luminosity in a large sample of evolved stars in several Local Group galaxies with a variety of metalliticies and star-formation histories: the Small and Large Magellanic Cloud, and the Fornax, Carina, and Sculptor dwarf spheroidal galaxies (dSphs). Methods: Dust radiative transfer models are presented for 225 carbon stars and 171 oxygen-rich evolved stars in several Local Group galaxies for which spectra from the Infrared Spectrograph on Spitzer are available. The spectra are complemented with available optical and infrared photometry to construct spectral energy distributions. A minimization procedure was used to determine luminosity and mass-loss rate (MLR). Pulsation periods were derived for a large fraction of the sample based on a re-analysis of existing data. Results: New deep K-band photometry from the VMC survey and multi-epoch data from IRAC (at 4.5 μm) and AllWISE and NEOWISE have allowed us to derive pulsation periods longer than 1000 days for some of the most heavily obscured and reddened objects. We derive (dust) MLRs and luminosities for the entire sample. The estimated MLRs can differ significantly from estimates for the same objects in the literature due to differences in adopted optical constants (up to factors of several) and details in the radiative transfer modelling. Updated parameters for the super-AGB candidate MSX SMC 055 (IRAS 00483-7347) are presented. Its current mass is estimated to be 8.5 ± 1.6 M⊙, suggesting an initial mass well above 8 M⊙ in agreement with estimates based on its large Rubidium abundance. Using synthetic photometry, we present and discuss colour-colour and

  9. A hot Jupiter orbiting a 2-million-year-old solar-mass T Tauri star.

    Science.gov (United States)

    Donati, J F; Moutou, C; Malo, L; Baruteau, C; Yu, L; Hébrard, E; Hussain, G; Alencar, S; Ménard, F; Bouvier, J; Petit, P; Takami, M; Doyon, R; Collier Cameron, A

    2016-06-30

    Hot Jupiters are giant Jupiter-like exoplanets that orbit their host stars 100 times more closely than Jupiter orbits the Sun. These planets presumably form in the outer part of the primordial disk from which both the central star and surrounding planets are born, then migrate inwards and yet avoid falling into their host star. It is, however, unclear whether this occurs early in the lives of hot Jupiters, when they are still embedded within protoplanetary disks, or later, once multiple planets are formed and interact. Although numerous hot Jupiters have been detected around mature Sun-like stars, their existence has not yet been firmly demonstrated for young stars, whose magnetic activity is so intense that it overshadows the radial velocity signal that close-in giant planets can induce. Here we report that the radial velocities of the young star V830 Tau exhibit a sine wave of period 4.93 days and semi-amplitude 75 metres per second, detected with a false-alarm probability of less than 0.03 per cent, after filtering out the magnetic activity plaguing the spectra. We find that this signal is unrelated to the 2.741-day rotation period of V830 Tau and we attribute it to the presence of a planet of mass 0.77 times that of Jupiter, orbiting at a distance of 0.057 astronomical units from the host star. Our result demonstrates that hot Jupiters can migrate inwards in less than two million years, probably as a result of planet–disk interactions.

  10. A planet in a polar orbit of 1.4 solar-mass star

    Directory of Open Access Journals (Sweden)

    Guenther E.W.

    2015-01-01

    Full Text Available Although more than a thousand transiting extrasolar planets have been discovered, only very few of them orbit stars that are more massive than the Sun. The discovery of such planets is interesting, because they have formed in disks that are more massive but had a shorter life time than those of solar-like stars. Studies of planets more massive than the Sun thus tell us how the properties of the proto-planetary disks effect the formation of planets. Another aspect that makes these planets interesting is that they have kept their original orbital inclinations. By studying them we can thus find out whether the orbital axes planets are initially aligned to the stars rotational axes, or not. Here we report on the discovery of a planet of a 1.4 solar-mass star with a period of 5.6 days in a polar orbit made by CoRoT. This new planet thus is one of the few known close-in planets orbiting a star that is substantially more massive than the Sun.

  11. Massive stars evolution with mass-loss. 20-100 M(sun) models

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C; Sreenivasan, S R [Calgary Univ., Alberta (Canada). Dept. of Physics; Nasi, E [Padua Univ. (Italy). Istituto di Astronomia

    1978-02-01

    The evolution of stars with initial masses 20, 30, 40, 60, 80, 100 M(sun) and Population I chemical composition (X = 0.700, Z = 0.02) is calculated, taking into account mass-loss due to stellar winds, from the main sequence up to the early stages of central He-burning. This study incorporates mass-loss rates predicted by the theory of Castor et al. (1975) for the early type phases and a novel way of treating mass-loss rates due to acoustic energy flux driven winds in the later stages analogous to the work of Fusi-Pecci and Renzini (1975a). The results are presented in terms of evolutionary tracks, isochrones, loci of constant mass-loss rates and loci of constant mass in the HR diagram. The effects of mass-loss on the internal structure of the models as well as on the occurrence of semiconvection are also investigated. A detailed comparison of the theoretical predictions and observational results is made and possible implications for O, Of, Wolf-Rayet stars and red supergiants are brought out.

  12. Rotation of Low-mass Stars in Upper Scorpius and ρ Ophiuchus with K2

    Science.gov (United States)

    Rebull, L. M.; Stauffer, J. R.; Cody, A. M.; Hillenbrand, L. A.; David, T. J.; Pinsonneault, M.

    2018-05-01

    We present an analysis of K2 light curves (LCs) for candidate members of the young Upper Sco (USco) association (∼8 Myr) and the neighboring ρ Oph embedded cluster (∼1 Myr). We establish ∼1300 stars as probable members, ∼80% of which are periodic. The phased LCs have a variety of shapes which can be attributed to physical causes ranging from stellar pulsation and stellar rotation to disk-related phenomena. We identify and discuss a number of observed behaviors. The periods are ∼0.2–30 days with a peak near 2 days and the rapid period end nearing breakup velocity. M stars in the young USco region rotate systematically faster than GK stars, a pattern also present in K2 data for the older Pleiades and Praesepe systems. At higher masses (types FGK), the well-defined period–color relationship for slowly rotating stars seen in the Pleiades and Praesepe systems is not yet present in USco. Circumstellar disks are present predominantly among the more slowly rotating M stars in USco, with few disks in the subday rotators. However, M dwarfs with disks rotate faster on average than FGK systems with disks. For four of these disked M dwarfs, we provide direct evidence for disk locking based on the K2 LC morphologies. Our preliminary analysis shows a relatively mass-independent spin-up by a factor of ∼3.5 between USco and the Pleiades, then mass-dependent spin-down between Pleiades and Praesepe.

  13. Consequences of dynamical disruption and mass segregation for the binary frequencies of star clusters

    International Nuclear Information System (INIS)

    Geller, Aaron M.; De Grijs, Richard; Li, Chengyuan; Hurley, Jarrod R.

    2013-01-01

    The massive (13,000-26,000 M ☉ ) and young (15-30 Myr) Large Magellanic Cloud star cluster NGC 1818 reveals an unexpected increasing binary frequency with radius for F-type stars (1.3-2.2 M ☉ ). This is in contrast to many older star clusters that show a decreasing binary frequency with radius. We study this phenomenon with sophisticated N-body modeling, exploring a range of initial conditions, from smooth virialized density distributions to highly substructured and collapsing configurations. We find that many of these models can reproduce the cluster's observed properties, although with a modest preference for substructured initial conditions. Our models produce the observed radial trend in binary frequency through disruption of soft binaries (with semi-major axes, a ≳ 3000 AU), on approximately a crossing time (∼5.4 Myr), preferentially in the cluster core. Mass segregation subsequently causes the binaries to sink toward the core. After roughly one initial half-mass relaxation time (t rh (0) ∼ 340 Myr) the radial binary frequency distribution becomes bimodal, the innermost binaries having already segregated toward the core, leaving a minimum in the radial binary frequency distribution that marches outward with time. After 4-6 t rh (0), the rising distribution in the halo disappears, leaving a radial distribution that rises only toward the core. Thus, both a radial binary frequency distribution that falls toward the core (as observed for NGC 1818) and one that rises toward the core (as for older star clusters) can arise naturally from the same evolutionary sequence owing to binary disruption and mass segregation in rich star clusters.

  14. Neutron star mass limit at 2M{sub ⊙} supports the existence of a CEP

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez-Castillo, D. [JINR Dubna, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); Benic, S. [University of Zagreb, Department of Physics, Zagreb (Croatia); Blaschke, D. [JINR Dubna, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); National Research Nuclear University (MEPhI), Moscow (Russian Federation); University of Wroclaw, Institute of Theoretical Physics, Wroclaw (Poland); Han, Sophia [University of Tennessee, Department of Physics and Astronomy, Knoxville, TN (United States); Oak Ridge National Laboratory, Physics Division, Oak Ridge, TN (United States); Typel, S. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany)

    2016-08-15

    We point out that the very existence of a ''horizontal branch'' in the mass-radius characteristics for neutron stars indicates a strong first-order phase transition and thus supports the existence of a critical endpoint (CEP) of first-order phase transitions in the QCD phase diagram. This branch would sample a sequence of hybrid stars with quark matter core, leading to the endpoint of stable compact star configurations with the highest possible baryon densities. Since we know of the existence of compact stars with 2M{sub ⊙}, this hypothetical branch has to lie in the vicinity of this mass value, if it exists. We report here a correlation between the maximal radius of the horizontal branch and the pressure at the onset of hadron-to-quark matter phase transition, which is likely to be a universal quantity of utmost relevance to the upcoming experiments with heavy-ion collisions at NICA and FAIR. (orig.)

  15. Galaxy Zoo: the dependence of the star formation-stellar mass relation on spiral disc morphology

    Science.gov (United States)

    Willett, Kyle W.; Schawinski, Kevin; Simmons, Brooke D.; Masters, Karen L.; Skibba, Ramin A.; Kaviraj, Sugata; Melvin, Thomas; Wong, O. Ivy; Nichol, Robert C.; Cheung, Edmond; Lintott, Chris J.; Fortson, Lucy

    2015-05-01

    We measure the stellar mass-star formation rate (SFR) relation in star-forming disc galaxies at z ≤ 0.085, using Galaxy Zoo morphologies to examine different populations of spirals as classified by their kiloparsec-scale structure. We examine the number of spiral arms, their relative pitch angle, and the presence of a galactic bar in the disc, and show that both the slope and dispersion of the M⋆-SFR relation is constant when varying all the above parameters. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by ˜0.3 dex; this is significantly smaller than the increase seen in merging systems at z > 1. Of the galaxies lying significantly above the M⋆-SFR relation in the local Universe, more than 50 per cent are mergers. We interpret this as evidence that the spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms or are completely overwhelmed by the combination of outflows and feedback. The arrangement of the star formation can be changed, but the system as a whole regulates itself even in the presence of strong dynamical forcing.

  16. Very Low-Mass Stars with Extremely Low Metallicity in the Milky Way's Halo

    Science.gov (United States)

    Aoki, Wako; Beers, Timothy C.; Suda, Takuma; Honda, Satoshi; Lee, Young Sun

    2016-08-01

    Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] LTE model atmospheres has obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical-abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010), and the other exhibits low abundances of the α-elements and odd-Z elements, suggested to be signatures of the yields of very massive stars (> 100 solar masses; Aoki et al. 2014). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

  17. The origin of the Crab Nebula and the electron capture supernova in 8-10 M solar mass stars

    Science.gov (United States)

    Nomoto, K.

    1981-01-01

    The chemical composition of the Crab Nebula is compared with several presupernova models. The small carbon and oxygen abundances in the helium-rich nebula are consistent with only the presupernova model of the star whose main sequence mass was MMS approximately 8-9.5 M. More massive stars contain too much carbon in the helium layer and smaller mass stars do not leave neutron stars. The progenitor star of the Crab Nebula lost appreciable part of the hydrogen-rich envelope before the hydrogen-rich and helium layers were mixed by convection. Finally it exploded as the electron capture supernova; the O+Ne+Mg core collapsed to form a neutron star and only the extended helium-rich envelope was ejected by the weak shock wave.

  18. EFFICIENT SELECTION AND CLASSIFICATION OF INFRARED EXCESS EMISSION STARS BASED ON AKARI AND 2MASS DATA

    Energy Technology Data Exchange (ETDEWEB)

    Huang Yafang; Li Jinzeng [National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Rector, Travis A. [University of Alaska, 3211 Providence Drive, Anchorage, AK 99508 (United States); Mallamaci, Carlos C., E-mail: ljz@nao.cas.cn [Observatorio Astronomico Felix Aguilar, Universidad Nacional de San Juan (Argentina)

    2013-05-15

    The selection of young stellar objects (YSOs) based on excess emission in the infrared is easily contaminated by post-main-sequence stars and various types of emission line stars with similar properties. We define in this paper stringent criteria for an efficient selection and classification of stellar sources with infrared excess emission based on combined Two Micron All Sky Survey (2MASS) and AKARI colors. First of all, bright dwarfs and giants with known spectral types were selected from the Hipparcos Catalogue and cross-identified with the 2MASS and AKARI Point Source Catalogues to produce the main-sequence and the post-main-sequence tracks, which appear as expected as tight tracks with very small dispersion. However, several of the main-sequence stars indicate excess emission in the color space. Further investigations based on the SIMBAD data help to clarify their nature as classical Be stars, which are found to be located in a well isolated region on each of the color-color (C-C) diagrams. Several kinds of contaminants were then removed based on their distribution in the C-C diagrams. A test sample of Herbig Ae/Be stars and classical T Tauri stars were cross-identified with the 2MASS and AKARI catalogs to define the loci of YSOs with different masses on the C-C diagrams. Well classified Class I and Class II sources were taken as a second test sample to discriminate between various types of YSOs at possibly different evolutionary stages. This helped to define the loci of different types of YSOs and a set of criteria for selecting YSOs based on their colors in the near- and mid-infrared. Candidate YSOs toward IC 1396 indicating excess emission in the near-infrared were employed to verify the validity of the new source selection criteria defined based on C-C diagrams compiled with the 2MASS and AKARI data. Optical spectroscopy and spectral energy distributions of the IC 1396 sample yield a clear identification of the YSOs and further confirm the criteria defined

  19. EFFICIENT SELECTION AND CLASSIFICATION OF INFRARED EXCESS EMISSION STARS BASED ON AKARI AND 2MASS DATA

    International Nuclear Information System (INIS)

    Huang Yafang; Li Jinzeng; Rector, Travis A.; Mallamaci, Carlos C.

    2013-01-01

    The selection of young stellar objects (YSOs) based on excess emission in the infrared is easily contaminated by post-main-sequence stars and various types of emission line stars with similar properties. We define in this paper stringent criteria for an efficient selection and classification of stellar sources with infrared excess emission based on combined Two Micron All Sky Survey (2MASS) and AKARI colors. First of all, bright dwarfs and giants with known spectral types were selected from the Hipparcos Catalogue and cross-identified with the 2MASS and AKARI Point Source Catalogues to produce the main-sequence and the post-main-sequence tracks, which appear as expected as tight tracks with very small dispersion. However, several of the main-sequence stars indicate excess emission in the color space. Further investigations based on the SIMBAD data help to clarify their nature as classical Be stars, which are found to be located in a well isolated region on each of the color-color (C-C) diagrams. Several kinds of contaminants were then removed based on their distribution in the C-C diagrams. A test sample of Herbig Ae/Be stars and classical T Tauri stars were cross-identified with the 2MASS and AKARI catalogs to define the loci of YSOs with different masses on the C-C diagrams. Well classified Class I and Class II sources were taken as a second test sample to discriminate between various types of YSOs at possibly different evolutionary stages. This helped to define the loci of different types of YSOs and a set of criteria for selecting YSOs based on their colors in the near- and mid-infrared. Candidate YSOs toward IC 1396 indicating excess emission in the near-infrared were employed to verify the validity of the new source selection criteria defined based on C-C diagrams compiled with the 2MASS and AKARI data. Optical spectroscopy and spectral energy distributions of the IC 1396 sample yield a clear identification of the YSOs and further confirm the criteria defined

  20. Gravitational wave generated by mass ejection in protoneutron star neutrino burst

    International Nuclear Information System (INIS)

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

    2010-01-01

    In this work we discuss the mechanism of mass ejection in protoneutron stars induced by diffusion of neutrinos. A dynamical calculation is employed in order to determine the amount of matter ejected and the properties of the remnant compact object [1]. The equations of state of this supra-nuclear regime [2] is properly linked with others describing the different sub-nuclear regimes of density [3, 4, 5]. For specified initial configurations of the protoneutron star, we solve numerically the set of equations of motion together with a schematic treatment of the neutrino transport through the dense stellar medium. We investigate the gravitational waves production accompanying the mass ejection induced by the neutrino burst. It is estimated the gravitational wave intensity and the detection of such wave by the existing detector or near future project for this purpose is discussed.

  1. Effect of mass loss on the chemical yields from massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C; Caimmi, R [Padua Univ. (Italy). Istituto di Astronomia

    1979-01-01

    Recent results on the calculation of the chemical yields from massive stars, are rediscussed by taking into account the occurrence of mass loss by stellar wind during the core H- and He-burning phases. The new yields are found to be compatible with the observed distribution of chemical abundances in the solar system, except for He. The net enrichment of several elements over the galaxy's lifetime is found to be consistent with the current estimate of the star formation rate, if we adopt a two phase process of galaxy formation (halodisk). The relative He to heavy element enrichment rate ..delta..Y/..delta..Z turns out to agree with the observational value when mass loss by stellar wind is taken into account.

  2. Binary star statistics: the mass ratio distribution for very wide systems

    International Nuclear Information System (INIS)

    Trimble, V.

    1987-01-01

    The distribution of mass ratios for a sample of common proper motion (CPM) binaries is determined and compared with that of 798 visual binaries (VB's) studied earlier, in hopes of answering the question: Can the member stars of these systems have been drawn at random from the normal initial mass function for single stars? The observed distributions peak strongly toward q = 1.0 for both kinds of systems, but less strongly for the CPM's than for the VB's. Due allowance having been made for assorted observational selection effects, it seems quite probable that the CPM's represent the observed part of a population drawn at random from the normal IMF, while the VB's are much more difficult to interpret that way and could, perhaps, result from a formation mechanism that somewhat favors sytems with roughly equal components. (author)

  3. Neutron-star mass limit in the bimetric theory of gravitation

    International Nuclear Information System (INIS)

    Caporaso, G.; Brecher, K.

    1977-01-01

    The ''neutron''-star upper mass limit is examined in Rosen's bimetric theory of gravitation. An exact solution, approximate scaling law, and numerical integration of the hydrostatic equilibrium equation show the dependence of the mass limit on the assumed equation of state. As in general relativity, that limit varies roughly as 1/√rho 0 , where rho 0 is the density above which the equation of state becomes ''stiff.'' Unlike general relativity, the stiffer the equation of state, the higher the mass limit. For rho 0 = 2 x 10 14 g/cm 3 and P = (rho - rho 0 ) c 2 , we found M/sub max/ = 81M/sub sun/. This mass is consistent with causality and experimental tests of gravitation and nuclear physics. For dp/drho > c 2 it appears that the upper mass limit can become arbitrarily large

  4. Heat and mass transfer analysis intermediate temperature solid oxide fuel cells (IT-SOFC)

    International Nuclear Information System (INIS)

    Timurkutluk, B.; Mat, M. M.; Kaplan, Y.

    2007-01-01

    Solid oxide fuel cells (SOFCs) have been considered as next generation energy conversion system due to their high efficiency, clean and quite operation with fuel flexibility. To date, yittria stabilized zirconia (YSZ) electrolytes have been mainly used for SOFC applications at high temperatures around 1000 degree C because of their high ionic conductivity, chemical stability and good mechanical properties. However, such a high temperature is undesirable for fuel cell operations in the viewpoint of stability. Moreover, high operation temperature necessitates high cost interconnect and seal materials. Thus, the reduction in the operation temperature of SOFCs is one of the key issues in the aspects of the cost reduction and the long term operation without degradation as well as commercialization of the SOFC systems. With the reducing temperature, not only low cost stainless steels and glass materials can be used as interconnect and sealing materials respectively but the manufacturing technology will also extend. Therefore, the design of complex geometrical SOFC component will also be possible. One way to reduce the operation temperature of SOFC is use of an alternative electrolyte material to YSZ showing acceptable properties at intermediate temperatures (600-800 degree C). As being one of IT-SOFC electrolyte materials, gadolinium doped ceria (GDC) has been taken great deals. In this study, a mathematical model for mass and heat transfer for a single cell GDC electrolyte SOFC system was developed and numerical solutions were evaluated. In order to verify the mathematical model, set of experiments were performed by taking species from four different samples randomly and five various temperature measurements. The numerical results reasonably agree with experimental data

  5. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    International Nuclear Information System (INIS)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria; Greenwood, Aaron; Kamp, Inga; Henning, Thomas; Ménard, François; Dent, William R. F.; II, Neal J. Evans

    2017-01-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

  6. EVOLUTIONARY TRACKS OF THE CLIMATE OF EARTH-LIKE PLANETS AROUND DIFFERENT MASS STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kadoya, S.; Tajika, E., E-mail: kadoya@astrobio.k.u-tokyo.ac.jp, E-mail: tajika@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Faculty of Science Bldg. 1 #711, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)

    2016-07-10

    The climatic evolution of the Earth depends strongly on the evolution of the insolation from the Sun and the amount of the greenhouse gasses, especially CO{sub 2} in the atmosphere. Here, we investigate the evolution of the climate of hypothetical Earths around stars whose masses are different from the solar mass with a luminosity evolution model of the stars, a mantle degassing model coupled with a parameterized convection model of the planetary interiors, and an energy balance climate model of the planetary surface. In the habitable zone (HZ), the climate of the planets is initially warm or hot, depending on the orbital semimajor axes. We found that, in the inner HZ, the climate of the planets becomes hotter with time owing to the increase in the luminosity of the central stars, while, in the outer HZ, it becomes colder and eventually globally ice-covered owing to the decrease in the CO{sub 2} degassing rate of the planets. The orbital condition for maintaining the warm climate similar to the present Earth becomes very limited, and more interestingly, the planet orbiting in the outer HZ becomes globally ice-covered after a certain critical age (∼3 Gyr for the hypothetical Earth with standard parameters), irrespective of the mass of the central star. This is because the critical age depends on the evolution of the planets and planetary factors, rather than on the stellar mass. The habitability of the Earth-like planet is shown to be limited with age even though it is orbiting within the HZ.

  7. Effects of strangeness on the mass-radius of neutron stars in MQMC

    International Nuclear Information System (INIS)

    Sahoo, H.S.; Mishra, R.N.; Panda, P.K.; Barik, N.

    2017-01-01

    With the increase of baryon density towards centers of neutron stars, chemical potentials of neutrons become high so that neutrons at Fermi surfaces are changed to hyperons via strangeness non-conserving weak interactions overcoming rest masses of hyperons. In the present attempt we incorporate an additional pair of hidden strange mesons σ∗ and ϕ which couple only to the strange quark and the hyperons of the nuclear matter

  8. Low virial parameters in molecular clouds: Implications for high-mass star formation and magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Kauffmann, Jens; Pillai, Thushara [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Goldsmith, Paul F., E-mail: jens.kauffmann@astro.caltech.edu, E-mail: tpillai@astro.caltech.edu [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Boulevard, Pasadena, CA 91109 (United States)

    2013-12-20

    Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only 'supercritical' cloud fragments are able to collapse and form stars. The virial parameter α = M {sub vir}/M, which compares the virial mass to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by α ≲ 2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters α ≳ 2 prevail in clouds. This would suggest that collapse toward star formation is a gradual and relatively slow process and that magnetic fields are not needed to explain the observed cloud structure. Here, we review a range of very recent observational studies that derive virial parameters <<2 and compile a catalog of 1325 virial parameter estimates. Low values of α are in particular observed for regions of high-mass star formation (HMSF). These observations may argue for a more rapid and violent evolution during collapse. This would enable 'competitive accretion' in HMSF, constrain some models of 'monolithic collapse', and might explain the absence of high-mass starless cores. Alternatively, the data could point at the presence of significant magnetic fields ∼1 mG at high gas densities. We examine to what extent the derived observational properties might be biased by observational or theoretical uncertainties. For a wide range of reasonable parameters, our conclusions appear to be robust with respect to such biases.

  9. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Greenwood, Aaron; Kamp, Inga [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Henning, Thomas [Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg (Germany); Ménard, François [Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble (France); Dent, William R. F. [Department of Engineering, Atacama Large Millimeter/submillimeter Array (ALMA) Santiago Central Offices, Alonso de Córdova 3107, Vitacura, Casilla 763 0355, Santiago (Chile); II, Neal J. Evans, E-mail: equant@lpl.arizona.edu [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States)

    2017-06-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μ m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3–78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature–stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μ m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further.

  10. EVOLUTIONARY TRACKS OF THE CLIMATE OF EARTH-LIKE PLANETS AROUND DIFFERENT MASS STARS

    International Nuclear Information System (INIS)

    Kadoya, S.; Tajika, E.

    2016-01-01

    The climatic evolution of the Earth depends strongly on the evolution of the insolation from the Sun and the amount of the greenhouse gasses, especially CO_2 in the atmosphere. Here, we investigate the evolution of the climate of hypothetical Earths around stars whose masses are different from the solar mass with a luminosity evolution model of the stars, a mantle degassing model coupled with a parameterized convection model of the planetary interiors, and an energy balance climate model of the planetary surface. In the habitable zone (HZ), the climate of the planets is initially warm or hot, depending on the orbital semimajor axes. We found that, in the inner HZ, the climate of the planets becomes hotter with time owing to the increase in the luminosity of the central stars, while, in the outer HZ, it becomes colder and eventually globally ice-covered owing to the decrease in the CO_2 degassing rate of the planets. The orbital condition for maintaining the warm climate similar to the present Earth becomes very limited, and more interestingly, the planet orbiting in the outer HZ becomes globally ice-covered after a certain critical age (∼3 Gyr for the hypothetical Earth with standard parameters), irrespective of the mass of the central star. This is because the critical age depends on the evolution of the planets and planetary factors, rather than on the stellar mass. The habitability of the Earth-like planet is shown to be limited with age even though it is orbiting within the HZ.

  11. Peering through the dust: NuSTAR observations of two first-2MASS red quasars

    DEFF Research Database (Denmark)

    LaMassa, Stephanie M.; Ricarte, Angelo; Glikman, Eilat

    2016-01-01

    through this gas and dust, revealing the properties of circumnuclear obscuration. Here, we present NuSTAR and XMM-Newton/Chandra observations of FIRST-2MASS-selected red quasars F2M 0830+3759 and F2M 1227+3214. We find that though F2M 0830+3759 is moderately obscured (NH,Z = (2.1 ± 0.2) ×  1022 cm−2...

  12. On the mass of rotating stars in Newtonian gravity and GR

    International Nuclear Information System (INIS)

    Reina, Borja; Vera, Raül

    2016-01-01

    We show how the correction to the calculation of the mass in the original relativistic model of a rotating star by Hartle (1967 Astrophys. J. 150 1005–29), found recently by Reina and Vera (2015 Class. Quantum Grav. 32 155008), appears in the Newtonian limit, and that the correcting term is indeed present, albeit hidden, in the original Newtonian approach by Chandrasekhar (1933 Mon. Not. Roy. Astr. Soc. 93 390–406). (note)

  13. HIGH-MASS STAR FORMATION TOWARD SOUTHERN INFRARED BUBBLE S10

    Energy Technology Data Exchange (ETDEWEB)

    Das, Swagat Ranjan; Tej, Anandmayee; Vig, Sarita [Indian Institute of Space Science and Technology, Trivandrum 695547 (India); Ghosh, Swarna K.; Ishwara Chandra, C. H., E-mail: swagat.12@iist.ac.in [National Centre For Radio Astrophysics, Pune 411007 (India)

    2016-11-01

    An investigation in radio and infrared wavelengths of two high-mass star-forming regions toward the southern Galactic bubble S10 is presented here. The two regions under study are associated with the broken bubble S10 and Extended Green Object, G345.99-0.02, respectively. Radio continuum emission mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, is detected toward both of the regions. These regions are estimated to be ionized by early-B- to late-O-type stars. Spitzer GLIMPSE mid-infrared data is used to identify young stellar objects (YSOs) associated with these regions. A Class-I/II-type source, with an estimated mass of 6.2  M {sub ⊙}, lies ∼7″ from the radio peak. Pixel-wise, modified blackbody fits to the thermal dust emission using Herschel far-infrared data is performed to construct dust temperature and column density maps. Eight clumps are detected in the two regions using the 250 μ m image. The masses and linear diameter of these range between ∼300–1600  M {sub ⊙} and 0.2–1.1 pc, respectively, which qualifies them as high-mass star-forming clumps. Modeling of the spectral energy distribution of these clumps indicates the presence of high luminosity, high accretion rate, massive YSOs possibly in the accelerating accretion phase. Furthermore, based on the radio and MIR morphology, the occurrence of a possible bow wave toward the likely ionizing star is explored.

  14. FIRST OBSERVATIONAL SIGNATURE OF ROTATIONAL DECELERATION IN A MASSIVE, INTERMEDIATE-AGE STAR CLUSTER IN THE MAGELLANIC CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Xiaohan [School of Physics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Li, Chengyuan; De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai, E-mail: grijs@pku.edu.cn [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

    2016-07-20

    While the extended main-sequence turnoffs (eMSTOs) found in almost all 1–2 Gyr old star clusters in the Magellanic Clouds are often explained by postulating extended star formation histories (SFHs), the tight subgiant branches (SGBs) seen in some clusters challenge this popular scenario. Puzzlingly, the SGB of the eMSTO cluster NGC 419 is significantly broader at bluer than at redder colors. We carefully assess and confirm the reality of this observational trend. If we would assume that the widths of the features in color–magnitude space were entirely owing to a range in stellar ages, the SFHs of the eMSTO stars and the blue SGB region would be significantly more prolonged than that of the red part of the SGB. This cannot be explained by assuming an internal age spread. We show that rotational deceleration of a population of rapidly rotating stars, a currently hotly debated alternative scenario, naturally explains the observed trend along the SGB. Our analysis shows that a “converging” SGB could be produced if the cluster is mostly composed of rapidly rotating stars that slow down over time owing to the conservation of angular momentum during their evolutionary expansion from main-sequence turnoff stars to red giants.

  15. Evidence for a trophic cascade on rocky reefs following sea star mass mortality in British Columbia

    Directory of Open Access Journals (Sweden)

    Jessica A. Schultz

    2016-04-01

    Full Text Available Echinoderm population collapses, driven by disease outbreaks and climatic events, may be important drivers of population dynamics, ecological shifts and biodiversity. The northeast Pacific recently experienced a mass mortality of sea stars. In Howe Sound, British Columbia, the sunflower star Pycnopodia helianthoides—a previously abundant predator of bottom-dwelling invertebrates—began to show signs of a wasting syndrome in early September 2013, and dense aggregations disappeared from many sites in a matter of weeks. Here, we assess changes in subtidal community composition by comparing the abundance of fish, invertebrates and macroalgae at 20 sites in Howe Sound before and after the 2013 sea star mortality to evaluate evidence for a trophic cascade. We observed changes in the abundance of several species after the sea star mortality, most notably a four-fold increase in the number of green sea urchins, Strongylocentrotus droebachiensis, and a significant decline in kelp cover, which are together consistent with a trophic cascade. Qualitative data on the abundance of sunflower stars and green urchins from a citizen science database show that the patterns of echinoderm abundance detected at our study sites reflected wider local trends. The trophic cascade evident at the scale of Howe Sound was observed at half of the study sites. It remains unclear whether the urchin response was triggered directly, via a reduction in urchin mortality, or indirectly, via a shift in urchin distribution into areas previously occupied by the predatory sea stars. Understanding the ecological implications of sudden and extreme population declines may further elucidate the role of echinoderms in temperate seas, and provide insight into the resilience of marine ecosystems to biological disturbances.

  16. HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

    Energy Technology Data Exchange (ETDEWEB)

    Miles, Brittany E. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu [School of Earth and Space Exploration, Arizona State University, 781 S Terrace Road, Tempe, AZ 85281 (United States)

    2017-08-01

    The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope . These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer ( GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771–2831 Å) and far-ultraviolet (FUV; 1344–1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.

  17. The cooling, mass and radius of the neutron star in EXO 0748-676 in quiescence with XMM-Newton

    NARCIS (Netherlands)

    Cheng, Zheng; Méndez, Mariano; Díaz-Trigo, María; Costantini, Elisa

    2017-01-01

    We analyse four XMM-Newton observations of the neutron-star low-mass X-ray binary EXO 0748-676 in quiescence. We fit the spectra with an absorbed neutron-star atmosphere model, without the need for a high-energy (power-law) component; with a 95 per cent confidence the power law contributes less than

  18. Dark-matter halo mergers as a fertile environment for low-mass Population III star formation

    DEFF Research Database (Denmark)

    Bovino, S.; Latif, M. A.; Grassi, Tommaso

    2014-01-01

    While Population III (Pop III) stars are typically thought to be massive, pathways towards lower mass Pop III stars may exist when the cooling of the gas is particularly enhanced. A possible route is enhanced HD cooling during the merging of dark-matter haloes. The mergers can lead to a high ioni...

  19. General Relativistic Simulations of Low-Mass Magnetized Binary Neutron Star Mergers

    Science.gov (United States)

    Giacomazzo, Bruno

    2017-01-01

    We will present general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) systems that produce long-lived neutron stars (NSs) after merger. While the standard scenario for short gamma-ray bursts (SGRBs) requires the formation after merger of a spinning black hole surrounded by an accretion disk, other theoretical models, such as the time-reversal scenario, predict the formation of a long-lived magnetar. The formation of a long-lived magnetar could in particular explain the X-ray plateaus that have been observed in some SGRBs. Moreover, observations of NSs with masses of 2 solar masses indicate that the equation of state of NS matter should support masses larger than that. Therefore a significant fraction of BNS mergers will produce long-lived NSs. This has important consequences both on the emission of gravitational wave signals and on their electromagnetic counterparts. We will discuss GRMHD simulations of ``low-mass'' magnetized BNS systems with different equations of state and mass ratios. We will describe the properties of their post-merger remnants and of their gravitational and electromagnetic emission.

  20. Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles - I. Theoretical model - Mass-loss history unravelled in VYCMa

    NARCIS (Netherlands)

    Decin, L.; Hony, S.; de Koter, A.; Justtanont, K.; Tielens, A. G. G. M.; Waters, L. B. F. M.

    Context. Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of

  1. THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    De Mink, S. E. [Space Telescope Science Institute, Baltimore, MD (United States); Langer, N.; Izzard, R. G. [Argelander-Institut fuer Astronomie der Universitaet Bonn, D-53121 Bonn (Germany); Sana, H.; De Koter, A. [Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam (Netherlands)

    2013-02-20

    Rotation is thought to be a major factor in the evolution of massive stars-especially at low metallicity-with consequences for their chemical yields, ionizing flux, and final fate. Deriving the birth spin distribution is of high priority given its importance as a constraint on theories of massive star formation and as input for models of stellar populations in the local universe and at high redshift. Recently, it has become clear that the majority of massive stars interact with a binary companion before they die. We investigate how this affects the distribution of rotation rates, through stellar winds, expansion, tides, mass transfer, and mergers. For this purpose, we simulate a massive binary-star population typical for our Galaxy assuming continuous star formation. We find that, because of binary interaction, 20{sup +5} {sub -10}% of all massive main-sequence stars have projected rotational velocities in excess of 200 km s{sup -1}. We evaluate the effect of uncertain input distributions and physical processes and conclude that the main uncertainties are the mass transfer efficiency and the possible effect of magnetic braking, especially if magnetic fields are generated or amplified during mass accretion and stellar mergers. The fraction of rapid rotators we derive is similar to that observed. If indeed mass transfer and mergers are the main cause for rapid rotation in massive stars, little room remains for rapidly rotating stars that are born single. This implies that spin-down during star formation is even more efficient than previously thought. In addition, this raises questions about the interpretation of the surface abundances of rapidly rotating stars as evidence for rotational mixing. Furthermore, our results allow for the possibility that all early-type Be stars result from binary interactions and suggest that evidence for rotation in explosions, such as long gamma-ray bursts, points to a binary origin.

  2. Method of LSD profile asymmetry for estimating the center of mass velocities of pulsating stars

    Science.gov (United States)

    Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Cacciari, C.; Clementini, C.

    2016-05-01

    We present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. High-resolution spectra were observed with either TNG/SARG or VLT/UVES over varying phases. To estimate the center of mass (barycentric) velocities of the program stars, we utilized two independent methods. First, the 'classic' method was employed, which is based on RR Lyrae radial velocity curve templates. Second, we provide the new method that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This new method is based on a least squares deconvolution (LSD) of the line profiles in order to an- alyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements (+- 2 kms^-1) of the pulsation component of the radial velocity. This results in determination of the barycentric velocity to within 5 kms^-1 even with a low number of high- resolution spectra. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars.

  3. A Search for Host Stars of Free-Floating Planetary Mass Objects

    Science.gov (United States)

    Tristan, Isaiah; Bowler, Brendan P.

    2017-01-01

    Over the past decade, the number of free-floating planetary-mass objects (FFPMOs) and imaged planets in widely-bound orbits (from hundreds to thousand of AU) have increased steadily, but the origin of these objects and the relationship between them is unclear. To test if known free-floating objects could actually be distant companions to stars, we searched for wide co-moving companions around a sample of 77 young brown dwarfs and FFPMOs using the PPMXL proper motion catalog. Contamination rates (the probability of field stars co-moving by chance) were then calculated using nearby but unrelated fields, and host star candidates were further vetted using their positions in color magnitude diagrams. Using this method, we recovered all previously known widely-bound host stars within our sample and identified several promising widely separated systems, with separations ranging from 10^4-10^5 AU. Follow up radial velocities are currently being obtained to validate the shared space motion of the most promising candidates; if confirmed, these will be the widest planetary systems known.

  4. Identifying the Young Low-mass Stars within 25 pc. II. Distances, Kinematics, and Group Membership

    Science.gov (United States)

    Shkolnik, Evgenya L.; Anglada-Escudé, Guillem; Liu, Michael C.; Bowler, Brendan P.; Weinberger, Alycia J.; Boss, Alan P.; Reid, I. Neill; Tamura, Motohide

    2012-10-01

    We have conducted a kinematic study of 165 young M dwarfs with ages of lsim300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of lsim25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (lsim3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and β Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages lsim150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope, the du Pont Telescope at Las Campanas Observatory, and the Subaru Telescope. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial

  5. 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.

  6. Subsonic islands within a high-mass star-forming infrared dark cloud

    Science.gov (United States)

    Sokolov, Vlas; Wang, Ke; Pineda, Jaime E.; Caselli, Paola; Henshaw, Jonathan D.; Barnes, Ashley T.; Tan, Jonathan C.; Fontani, Francesco; Jiménez-Serra, Izaskun; Zhang, Qizhou

    2018-03-01

    High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combined Very Large Array and Green Bank Telescope (VLA+GBT) observations of NH3 (1,1) and (2,2) in the infrared dark cloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast to previous, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermal motions (mean line width of 0.71 km s-1), and sonic Mach number distribution peaks around ℳ = 1. As possible observational and instrumental biases would only broaden the line profiles, our results provide strong upper limits to the actual value of ℳ, further strengthening our findings of narrow line widths. This finding calls for a re-evaluation of the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findings in G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH3 studies may have inhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamically important magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Our results offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-mass star and cluster formation.

  7. Atmospheric mass-loss of extrasolar planets orbiting magnetically active host stars

    Science.gov (United States)

    Lalitha, Sairam; Schmitt, J. H. M. M.; Dash, Spandan

    2018-06-01

    Magnetic stellar activity of exoplanet hosts can lead to the production of large amounts of high-energy emission, which irradiates extrasolar planets, located in the immediate vicinity of such stars. This radiation is absorbed in the planets' upper atmospheres, which consequently heat up and evaporate, possibly leading to an irradiation-induced mass-loss. We present a study of the high-energy emission in the four magnetically active planet-bearing host stars, Kepler-63, Kepler-210, WASP-19, and HAT-P-11, based on new XMM-Newton observations. We find that the X-ray luminosities of these stars are rather high with orders of magnitude above the level of the active Sun. The total XUV irradiation of these planets is expected to be stronger than that of well-studied hot Jupiters. Using the estimated XUV luminosities as the energy input to the planetary atmospheres, we obtain upper limits for the total mass- loss in these hot Jupiters.

  8. Electromagnetic pulse from supernovae. [model for old low-mass stars

    Science.gov (United States)

    Colgate, S. A.

    1975-01-01

    Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

  9. Big Fish in Small Ponds: massive stars in the low-mass clusters of M83

    Energy Technology Data Exchange (ETDEWEB)

    Andrews, J. E.; Calzetti, D.; McElwee, Sean [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Chandar, R. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Elmegreen, B. G. [IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Kim, Hwihyun [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Krumholz, Mark R. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Lee, J. C.; Whitmore, B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); O' Connell, R. W., E-mail: jandrews@astro.umass.edu, E-mail: callzetti@astro.umass.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

    2014-09-20

    We have used multi-wavelength Hubble Space Telescope WFC3 data of the starbursting spiral galaxy M83 in order to measure variations in the upper end of the stellar initial mass function (uIMF) using the production rate of ionizing photons in unresolved clusters with ages ≤ 8 Myr. As in earlier papers on M51 and NGC 4214, the uIMF in M83 is consistent with a universal IMF, and stochastic sampling of the stellar populations in the ∼<10{sup 3} M {sub ☉} clusters are responsible for any deviations in this universality. The ensemble cluster population, as well as individual clusters, also imply that the most massive star in a cluster does not depend on the cluster mass. In fact, we have found that these small clusters seem to have an over-abundance of ionizing photons when compared to an expected universal or truncated IMF. This also suggests that the presence of massive stars in these clusters does not affect the star formation in a destructive way.

  10. BINARY STARS WITH COMPONENTS OF SOLAR TYPE: 25 ORBITS AND SYSTEM MASSES

    International Nuclear Information System (INIS)

    Docobo, J. A.; Ling, J. F.

    2009-01-01

    Revised orbits and system masses are presented for the following 25 visual double stars: WDS 00593-0040 (A 1902), WDS 00596-0111 (A 1903 AB), WDS 01023+0552 (A 2003), WDS 01049+3649 (A 1515), WDS 01234+5809 (STF 115 AB), WDS 02399+0009 (A 1928), WDS 03310+2937 (A 983), WDS 06573-3530 (I 65), WDS 07043-0303 (A 519), WDS 08267+2432 (A 1746 BC), WDS 10585+1711 (A 2375), WDS 11308+4117 (STT 234), WDS 15370+6426 (HU 1168), WDS 16044-1122 (STF 1998 AB), WDS 16283-1613 (RST 3950), WDS 17324+2848 (A 352), WDS 18466+3821 (HU 1191), WDS 19039+2642 (A 2992), WDS 19055+3352(HU 940), WDS 19282-1209 (SCJ 22), WDS 19487+1504 (A 1658), WDS 22400+0113 (A 2099), WDS 23506-5142 (SLR 14), WDS 23518-0637 (A 2700), and WDS 23529-0309 (FIN 359). In all of these systems, at least one component is of solar type. Total system masses were calculated in each case from the orbital period and semiaxis major together with the Hipparcos parallax, except in the cases for which there are no Hipparcos data or when these values are not precise. Other orbital and physical properties of these stars are also discussed. This paper is the second of three collating the revised double star orbits we have calculated in the past 15 yr.

  11. Search for gravitational wave ringdowns from perturbed intermediate mass black holes in LIGO-Virgo data from 2005-2010

    OpenAIRE

    Aasi, J.; Abbott, B.; Abbott, R.; Abbott, T.; Abernathy, M.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R.; Affeldt, C.; Agathos, M.; Aggarwal, N.; Aguiar, O.

    2014-01-01

    We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency $50\\le f_{0}/\\mathrm{Hz} \\le 2000$ and decay timescale $0.0001\\lesssim \\tau/\\mathrm{s} \\lesssim 0.1$ characteristic of those produced in mergers of IMBH pairs. No significant ...

  12. Trajectories of bright stars at the Galactic Center as a tool to evaluate a graviton mass

    Directory of Open Access Journals (Sweden)

    Zakharov Alexander

    2016-01-01

    Full Text Available Scientists worked in Saint-Petersburg (Petrograd, Leningrad played the extremely important role in creation of scientific school and development of general relativity in Russia. Very recently LIGO collaboration discovered gravitational waves [1] predicted 100 years ago by A. Einstein. In the papers reporting about this discovery, the joint LIGO & VIRGO team presented an upper limit on graviton mass such as mg < 1.2 × 10−22eV [1, 2]. The authors concluded that their observational data do not show violations of classical general relativity because the graviton mass limit is very small. We show that an analysis of bright star trajectories could bound graviton mass with a comparable accuracy with accuracies reached with gravitational wave interferometers and expected with forthcoming pulsar timing observations for gravitational wave detection. This analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a tool for an evaluation specific parameters of the black hole and also to obtain constraints on the fundamental gravity law such as a modifications of Newton gravity law in a weak field approximation. In that way, based on a potential reconstruction at the Galactic Center we give a bounds on a graviton mass.

  13. Evolution models of helium white dwarf--main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    OpenAIRE

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2017-01-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with ...

  14. Variable stars in the VVV globular clusters. I. 2MASS-GC 02 and Terzan 10

    Energy Technology Data Exchange (ETDEWEB)

    Alonso-García, Javier; Dékány, István; Catelan, Márcio; Ramos, Rodrigo Contreras; Gran, Felipe; Leyton, Paul; Minniti, Dante [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Amigo, Pía, E-mail: jalonso@astro.puc.cl, E-mail: idekany@astro.puc.cl, E-mail: mcatelan@astro.puc.cl, E-mail: rcontrer@astro.puc.cl, E-mail: fgran@astro.puc.cl, E-mail: pia.amigo@uv.cl, E-mail: pleyton@astro.puc.cl, E-mail: dante@astrofisica.cl [Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2015-03-01

    The VISTA Variables in the Vía Láctea (VVV) ESO Public Survey is opening a new window to study inner Galactic globular clusters (GCs) using their variable stars. These GCs have been neglected in the past due to the difficulties caused by the presence of elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RR Lyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the questions raised by the intriguing Oosterhoff dichotomy in the Galactic GC system. In a series of papers we plan to explore variable stars in the GCs falling inside the field of the VVV survey. In this first paper, we search for and study the variables present in two highly reddened, moderately metal-poor, faint, inner Galactic GCs: 2MASS-GC 02 and Terzan 10. We report the discovery of sizable populations of RR Lyrae stars in both GCs. We use near-infrared period–luminosity relations to determine the color excess of each RR Lyrae star, from which we obtain both accurate distances to the GCs and the ratios of the selective-to-total extinction in their directions. We find the extinction toward both clusters to be elevated, non-standard, and highly differential. We also find both clusters to be closer to the Galactic center than previously thought, with Terzan 10 being on the far side of the Galactic bulge. Finally, we discuss their Oosterhoff properties, and conclude that both clusters stand out from the dichotomy followed by most Galactic GCs.

  15. Determination of the upper mass limit for stars producing white-dwarf remnants

    International Nuclear Information System (INIS)

    Romanishin, W.; Angel, J.R.P.

    1980-01-01

    We have searched ultraviolet and red plates of four open clusters (NGC 2168, 2287, 2422, and 6633) for faint blue objects which might be white dwarf members of the clusters. The most massive stars in these clusters range from 3 to 6 M/sub sun/. We find a definite concentration of faint blue objects in the clusters. This fact, plus initial photoelectric photometry, provides strong support for the identification of many of these objects as cluster white dwarfs. By modeling the expected number of possible white dwarfs in each cluster, we are able to put some limits on m/sub w/, the upper stellar mass limit for formation of white dwarfs. Our data require that some stars of at least 5 M/sub sun/ have evolved into white dwarfs and give a most probable value of 7 M/sub sun/ for m/sub w/

  16. Excitation of Neutron Star f-mode in Low Mass X-ray Binaries

    International Nuclear Information System (INIS)

    Araujo, J C N de; Miranda, O D; Aguiar, O D

    2006-01-01

    Neutron Stars (NSs) present a host of pulsation modes. Only a few of them, however, is of relevance from the gravitational wave (GW) point of view. Among the various possible modes the pulsation energy is mostly stored in the f-mode in which the fluid parameters undergo the largest changes. An important question is how the pulsation modes are excited in NSs. Here we consider the excitation of the f-mode in the accreting NSs belonging to Low Mass X-ray Binaries (LMXBs), which may well be a recurrent source of GWs, since the NSs are continuously receiving matter from their companion stars. We also discuss the detectability of the GWs for the scenario considered here

  17. Complex organic molecules toward low-mass and high-mass star forming regions

    Science.gov (United States)

    Favre, C.; Ceccarelli, C.; Lefloch, B.; Bergin, E.; Carvajal, M.; Brouillet, N.; Despois, D.; Jørgensen, J.; Kleiner, I.

    2016-12-01

    One of the most important questions in molecular astrophysics is how, when, and where complex organic molecules, COMs (≥ 6 atoms) are formed. In the Interstellar-Earth connection context, could this have a bearing on the origin of life on Earth? Formation mechanisms of COMs, which include potentially prebiotic molecules, are still debated and may include grain-mantle and/or gas-phase chemistry. Understanding the mechanisms that lead to the interstellar molecular complexification, along with the involved physicochemical processes, is mandatory to answer the above questions. In that context, active researches are ongoing in theory, laboratory experiment, chemical modeling and observations. Thanks to recent progress in radioastronomy instrumentation for both single-dish and millimeter array (e.g. Herschel, NOEMA, ALMA), new results have been obtained. I will review some notable results on the detection of COMs, including prebiotic molecules, towards star forming regions.

  18. THE EATING HABITS OF MILKY WAY-MASS HALOS: DESTROYED DWARF SATELLITES AND THE METALLICITY DISTRIBUTION OF ACCRETED STARS

    International Nuclear Information System (INIS)

    Deason, Alis J.; Mao, Yao-Yuan; Wechsler, Risa H.

    2016-01-01

    We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M vir  ∼ 10 12.1 M ⊙ ) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M star  ∼ 10 8 –10 10 M ⊙ . Halos with more quiescent accretion histories tend to have lower mass progenitors (10 8 –10 9 M ⊙ ), and lower overall accreted stellar masses. Ultra-faint mass (M star  < 10 5 M ⊙ ) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10 5  < M star /M ⊙  < 10 8 provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M star  > 10 8 M ⊙ can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

  20. Empirical Accurate Masses and Radii of Single Stars with TESS and Gaia

    Science.gov (United States)

    Stassun, Keivan G.; Corsaro, Enrico; Pepper, Joshua A.; Gaudi, B. Scott

    2018-01-01

    We present a methodology for the determination of empirical masses of single stars through the combination of three direct observables with Gaia and Transiting Exoplanet Survey Satellite (TESS): (i) the surface gravity via granulation-driven variations in the TESS light curve, (ii) the bolometric flux at Earth via the broadband spectral energy distribution, and (iii) the distance via the Gaia parallax. We demonstrate the method using 525 Kepler stars for which these measures are available in the literature, and show that the stellar masses can be measured with this method to a precision of ∼25%, limited by the surface-gravity precision of the granulation “flicker” method (∼0.1 dex) and by the parallax uncertainties (∼10% for the Kepler sample). We explore the impact of expected improvements in the surface gravity determinations—through the application of granulation background fitting and the use of recently published granulation-metallicity relations—and improvements in the parallaxes with the arrival of the Gaia second data release. We show that the application of this methodology to stars that will be observed by TESS should yield radii good to a few percent and masses good to ≈10%. Importantly, the method does not require the presence of an orbiting, eclipsing, or transiting body, nor does it require spatial resolution of the stellar surface. Thus, we can anticipate the determination of fundamental, accurate stellar radii and masses for hundreds of thousands of bright single stars—across the entire sky and spanning the Hertzsprung–Russell diagram—including those that will ultimately be found to host planets.

  1. Deriving temperature, mass, and age of evolved stars from high-resolution spectra. Application to field stars and the open cluster IC 4651

    Science.gov (United States)

    Biazzo, K.; Pasquini, L.; Girardi, L.; Frasca, A.; da Silva, L.; Setiawan, J.; Marilli, E.; Hatzes, A. P.; Catalano, S.

    2007-12-01

    Aims:We test our capability of deriving stellar physical parameters of giant stars by analysing a sample of field stars and the well studied open cluster IC 4651 with different spectroscopic methods. Methods: The use of a technique based on line-depth ratios (LDRs) allows us to determine with high precision the effective temperature of the stars and to compare the results with those obtained with a classical LTE abundance analysis. Results: (i) For the field stars we find that the temperatures derived by means of the LDR method are in excellent agreement with those found by the spectral synthesis. This result is extremely encouraging because it shows that spectra can be used to firmly derive population characteristics (e.g., mass and age) of the observed stars. (ii) For the IC 4651 stars we use the determined effective temperature to derive the following results. a) The reddening E(B-V) of the cluster is 0.12±0.02, largely independent of the color-temperature calibration used. b) The age of the cluster is 1.2±0.2 Gyr. c) The typical mass of the analysed giant stars is 2.0±0.2~M⊙. Moreover, we find a systematic difference of about 0.2 dex in log g between spectroscopic and evolutionary values. Conclusions: We conclude that, in spite of known limitations, a classical spectroscopic analysis of giant stars may indeed result in very reliable stellar parameters. We caution that the quality of the agreement, on the other hand, depends on the details of the adopted spectroscopic analysis. Based on observations collected at the ESO telescopes at the Paranal and La Silla Observatories, Chile.

  2. Theoretical study of intermediate-mass fragments in proton-nucleus reactions at 200 MeV

    Energy Technology Data Exchange (ETDEWEB)

    Sabra, Mohammad S. [NASA Marshall Space Flight Center, USRA Space Science Department, Huntsville, AL (United States)

    2017-03-15

    We have analyzed energy spectra, angular distributions, and mass and charge distributions of intermediate-mass fragments (IMFs) from the interaction of {sup 27}Al, {sup 59}Co, and {sup 197}Au with 200 MeV protons. Calculations within the modified statistical model with final-state interaction were performed using SAPTON code. Within the experimental uncertainty and constraint, SAPTON shows good agreement with the data, and suggests that the IMFs are produced after the intra-nuclear cascade stage, and during the surface coalescence, as well as the evaporation/fission stages. (orig.)

  3. Water in star-forming regions with Herschel (WISH) : IV. A survey of low-J H2O line profiles toward high-mass protostars

    NARCIS (Netherlands)

    van der Tak, F. F. S.; Chavarria, L.; Herpin, F.; Wyrowski, F.; Walmsley, C. M.; van Dishoeck, E. F.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Hogerheijde, M. R.; Johnstone, D.; Kristensen, L. E.; Liseau, R.; Nisini, B.; Tafalla, M.

    Context. Water is a key constituent of star-forming matter, but the origin of its line emission and absorption during high-mass star formation is not well understood. Aims. We study the velocity profiles of low-excitation H2O lines toward 19 high-mass star-forming regions and search for trends with

  4. 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.

  5. Electron capture on 20Ne and the ultimate fate of stars in the mass range 8-10 M⊙

    International Nuclear Information System (INIS)

    Kirsebom, Oliver S.; Cederkall, Joakim; Jenkins, David G.; Joshi, Pankaj; Julin, Rauno; Kankainen, Anu; Trzaska, Wladyslaw H.; Kibedi, Tibor; Tengblad, Olof

    2016-01-01

    Knowledge of the electron-capture rate on 20 Ne is of critical importance to understand the final evolution of stars in the mass range 8-10M⊙. A recent study has highlighted the importance of the second-forbidden transition between the ground states of 20 Ne and 20 F, which is believed to dominate the capture rate in an important temperature-density range. The strength of this transition is, however, not well constrained, neither experimentally nor theoretically, making an experimental determination highly desirable. The transition strength can be determined from the branching ratio of the inverse transition in the decay of 20 F, for which the experimental upper limit is 10 -5 , while the most recent theoretical prediction is 1.3 x 10 -6 . To facilitate an experimental determination of the branching ratio we are refurbishing an intermediate-image magnetic spectrometer capable of focusing 7 MeV electrons, and designing a scintillator detector surrounded by an active cosmic-ray veto shield, which will serve as an energy- dispersive device at the focal plane. In this contribution, GEANT4 simulations of the expected performance of the setup will be presented and the astrophysical motivation for the experiment will be discussed. (author)

  6. DISCOVERY OF A LOW-MASS COMPANION TO THE SOLAR-TYPE STAR TYC 2534-698-1

    International Nuclear Information System (INIS)

    Kane, Stephen R.; Mahadevan, Suvrath; Sivarani, Thirupathi; Cochran, William D.; Street, Rachel A.; Henry, Gregory W.; Williamson, Michael H.

    2009-01-01

    Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M sun and an orbital period of ∼103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ∼6 millimags. The semimajor axis of the orbit places the companion in the 'brown dwarf desert' and we discuss potential follow-up observations that could constrain the mass of the companion.

  7. Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. V. Asteroseismology of ELMV white dwarf stars

    Science.gov (United States)

    Calcaferro, Leila M.; Córsico, Alejandro H.; Althaus, Leandro G.

    2017-11-01

    Context. Many pulsating low-mass white dwarf stars have been detected in the past years in the field of our Galaxy. Some of them exhibit multiperiodic brightness variation, therefore it is possible to probe their interiors through asteroseismology. Aims: We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete set of fully evolutionary models that are representative of low-mass He-core white dwarf stars. Methods: We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses ranging from 0.1554 to 0.4352 M⊙ that were derived by simulating the nonconservative evolution of a binary system consisting of an initially 1 M⊙ zero-age main-sequence (ZAMS) star and a 1.4 M⊙ neutron star companion. We estimated the mean period spacing for the stars under study (where this was possible), and then we constrained the stellar mass by comparing the observed period spacing with the average of the computed period spacings for our grid of models. We also employed the individual observed periods of every known pulsating low-mass white dwarf star to search for a representative seismological model. Results: We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it is possible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopy for most of the cases. Unfortunately, we were not able to constrain the stellar masses by employing the observed period spacing because, in general, only few periods are exhibited by these stars. In the two cases where we were able to extract the period spacing from the set of observed periods, this method led to stellar mass values that were substantially higher than expected for this type of stars. Conclusions: The results presented in this work show the need for further photometric searches, on the one hand

  8. Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

    Science.gov (United States)

    Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

    2018-02-01

    It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

  9. 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.

  10. Graviton mass bounds from an analysis of bright star trajectories at the Galactic Center

    Directory of Open Access Journals (Sweden)

    Zakharov Alexander

    2017-01-01

    Full Text Available In February 2016 the LIGO & VIRGO collaboration reported the discovery of gravitational waves in merging black holes, therefore, the team confirmed GR predictions about an existence of black holes and gravitational waves in the strong gravitational field limit. Moreover, in their papers the joint LIGO & VIRGO team presented an upper limit on graviton mass such as mg < 1.2 × 10−22 eV (Abbott et al. 2016. So, the authors concluded that their observational data do not show any violation of classical general relativity. We show that an analysis of bright star trajectories could constrain graviton mass with a comparable accuracy with accuracies reached with gravitational wave interferometers and the estimate is consistent with the one obtained by the LIGO & VIRGO collaboration. This analysis gives an opportunity to treat observations of bright stars near the Galactic Center as a useful tool to obtain constraints on the fundamental gravity law such as modifications of the Newton gravity law in a weak field approximation. In that way, based on a potential reconstruction at the Galactic Center we obtain bounds on a graviton mass.

  11. Understanding of variability properties in very low mass stars and brown dwarfs

    Science.gov (United States)

    Mondal, Soumen; Ghosh, Samrat; Khata, Dhrimadri; Joshi, Santosh; Das, Ramkrishna

    2018-04-01

    We report on photometric variability studies of a L3.5 brown dwarf 2MASS J00361617+1821104 (2M0036+18) in the field and of four young brown dwarfs in the star-forming region IC 348. From muti-epoch observations, we found significant periodic variability in 2M0036+18 with a period of 2.66 ± 0.55 hours on one occasion while it seemed to be non-variable on three other occasions. An evolving dust cloud might cause such a scenario. Among four young brown dwarfs of IC 348 in the spectral range M7.25 - M8, one brown dwarf 2MASS J03443921+3208138 shows significant variability. The K-band spectra (2.0-2.4 μm) of nine very low mass stars (M1 - M9 V) are used to characterize the water band index (H20-K2). We found that it is strongly correlated with the surface temperature of M dwarfs.

  12. Discovery of a wide planetary-mass companion to the young M3 star GU PSC

    Energy Technology Data Exchange (ETDEWEB)

    Naud, Marie-Eve; Artigau, Étienne; Malo, Lison; Albert, Loïc; Doyon, René; Lafrenière, David; Gagné, Jonathan; Boucher, Anne [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal H3C 3J7 (Canada); Saumon, Didier [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Morley, Caroline V. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Allard, France; Homeier, Derek [Centre de Recherche Astrophysique de Lyon, UMR 5574 CNRS, Université de Lyon, École Normale Supérieure de Lyon, 46 Allée d' Italie, F-69364 Lyon Cedex 07 (France); Beichman, Charles A.; Gelino, Christopher R., E-mail: naud@astro.umontreal.ca [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)

    2014-05-20

    We present the discovery of a comoving planetary-mass companion ∼42'' (∼2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T {sub eff} = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M {sub Jup} for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE 9.

  13. Search for Gravitational Wave Ringdowns from Perturbed Intermediate Mass Black Holes in LIGO-Virgo Data from 2005-2010

    Science.gov (United States)

    Aasi, J.; Abbott, B. P.; Abbott, R.; Abbott, T.; Abernathy, M. R.; Acernese, F.; Blackburn, Lindy L.; Camp, J. B.; Gehrels, N.; Graff, P. B.

    2014-01-01

    We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency 50 less than or equal to italic f0/Hz less than or equal to 2000 and decay timescale 0.0001 approximately less than t/s approximately less than 0.1 characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass 50 less than or equal to M/solar mass less than or equal to 450 and component mass ratios of either 1:1 or 4:1. For systems with total mass 100 less than or equal to M/solar mass 150, we report a 90%-confidence upper limit on the rate of binary IMBH mergers with non-spinning and equal mass components of 6:9 x 10(exp 8) Mpc(exp -3)yr(exp -1). We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, l=m=2, oscillation mode, that is nearly three orders of magnitude more stringent than previous results.

  14. Searching for intermediate-mass black holes in galaxies with low-luminosity AGN: a multiple-method approach

    Science.gov (United States)

    Koliopanos, F.; Ciambur, B.; Graham, A.; Webb, N.; Coriat, M.; Mutlu-Pakdil, B.; Davis, B.; Godet, O.; Barret, D.; Seigar, M.

    2017-10-01

    Intermediate Mass Black Holes (IMBHs) are predicted by a variety of models and are the likely seeds for super massive BHs (SMBHs). However, we have yet to establish their existence. One method, by which we can discover IMBHs, is by measuring the mass of an accreting BH, using X-ray and radio observations and drawing on the correlation between radio luminosity, X-ray luminosity and the BH mass, known as the fundamental plane of BH activity (FP-BH). Furthermore, the mass of BHs in the centers of galaxies, can be estimated using scaling relations between BH mass and galactic properties. We are initiating a campaign to search for IMBH candidates in dwarf galaxies with low-luminosity AGN, using - for the first time - three different scaling relations and the FP-BH, simultaneously. In this first stage of our campaign, we measure the mass of seven LLAGN, that have been previously suggested to host central IMBHs, investigate the consistency between the predictions of the BH scaling relations and the FP-BH, in the low mass regime and demonstrate that this multiple method approach provides a robust average mass prediction. In my talk, I will discuss our methodology, results and next steps of this campaign.

  15. 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.

  16. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    International Nuclear Information System (INIS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M ⊕ and 5 M ⊕ . Assuming H 2 O-(inner HZ) and CO 2 -(outer HZ) dominated atmospheres, and scaling the background N 2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H 2 O column depth. For larger planets, the H 2 O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs

  17. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    Science.gov (United States)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  18. Long-term captures of low-mass intruders by binary stars

    International Nuclear Information System (INIS)

    Hills, J.G.

    1983-01-01

    Intensive computer simulations were made of three families of encounters between a binary star and a low-mass intruder which previous work indicated have a high probability of producing long-lived triple-star systems. For comparison, a fourth family which produces few long-lived trinaries was also studied. In the first two families, the binary components are equally massive and the closest approach of the intruder to the center of mass of the binary is about two times its semimajor axis, a 0 . In Family 1, the orbit of the original binary is circular, e = 0, while in Family 2, e 0 = 0.95. In Family 3 one binary component is 100 times as massive as the other, the orbit is circular, and the low-mass intruder enters the binary at nearly zero impact parameter. The probability that the intruder is trapped for at least one revolution around the binary is 0.24, 0.46, and 0.51, respectively, for these three families of encounters. The fraction of the intruders surviving successive revolutions drops rapidly. However, one encounter in Family 1 and two in Family 3 resulted in the intruder making more than 300 revolutions around the inner binary before escaping. Some intruders remained bound for more than 20 000 revolutions of the inner binary. The longest duration captures occur when the intruder is thrown into an orbit with a very large semimajor axis. About 20% of the encounters in the three families result in the intruder being thrown into an orbit with a semimajor axis a>100 a 0 , while about 2% result in the intruder going into an orbit with a>1000 a 0 . Intruders thrown into these large semimajor axis orbits have the best chance of having their orbits stabilized by passing stars

  19. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    Energy Technology Data Exchange (ETDEWEB)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F. [Department of Geosciences, Penn State University, 443 Deike Building, University Park, PA 16802 (United States); SchottelKotte, James [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Domagal-Goldman, Shawn [NASA Astrobiology Institute' s Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195 (United States); Eymet, Vincent, E-mail: ruk15@psu.edu [Laboratoire d' Astrophysique de Bordeaux, Universite de Bordeaux 1, UMR 5804, F-33270 Floirac (France)

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  20. Planck intermediate results: III. the relation between galaxy cluster mass and Sunyaev-Zeldovich signal

    DEFF Research Database (Denmark)

    Bartlett, J.G.; Bucher, M.; Cardoso, J.-F.

    2013-01-01

    We examine the relation between the galaxy cluster mass M and Sunyaev-Zeldovich (SZ) effect signal DA2 Y500 for a sample of 19 objects for which weak lensing (WL) mass measurements obtained from Subaru Telescope data are available in the literature. Hydrostatic X-ray masses are derived from XMM-N...

  1. 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 ...

  2. Modelling the evolution of solar-mass stars with a range of metallicities using MESA

    Directory of Open Access Journals (Sweden)

    Jones E.F.

    2015-01-01

    Full Text Available The nuclides 1,2H, 3,4He, 7Li, 7Be, 8B, 12,13C, 13-15N, 14-18O, 17-19F, 18-22Ne, 22Mg, and 24Mg were used in the code package MESA (Modules for Experiments in Stellar Astrophysics[Paxton] to model a one-solar-mass star with a range of metallicities, z, from 0 to 0.1. On HR diagrams of each star model’s luminosity and effective temperature from before zero-age main sequence (pre-ZAMS to white dwarf, oscillations were noted in the horizontal branch at intervals from z = 0 to 0.0070. At z, = 0, the calculated stellar lifetime is 6.09x109 years. The calculated lifetime of the model stars increases to a maximum of 1.25x1010 years at z = 0.022 and then decreases to 2.59x109 years at z = 0.1. A piecewise fit of the model lifetimes vs. metallicity was obtained.

  3. 2D dynamics of the radiative core of low mass stars

    Directory of Open Access Journals (Sweden)

    Hypolite Delphine

    2017-01-01

    Full Text Available Understanding the internal rotation of low mass stars all along their evolution is of primary interest when studying their rotational dynamics, internal mixing and magnetic field generation. In this context, helio- and asteroseismology probe angular velocity gradients deep within solar type stars at different evolutionary stages. Still the rotation close to the center of such stars on the main sequence is hardly detectable and the dynamical interaction of the radiative core with the surface convective envelope is not well understood. For instance, the influence of the differential rotation profile sustained by convection and applied as a boundary condition to the radiation zone is very important in the formation of tachoclines. In this work, we study a 2D hydrodynamical model of a radiative core when an imposed, solar or anti-solar, differential rotation is applied at the upper boundary. This model uses the Boussinesq approximation and we find that the shear induces a cylindrical differential rotation associated with a unique cell of meridional circulation in each hemisphere (counterclockwise when the shear is solar-like and clockwise when it is anti-solar. The results are discussed in the framework of seismic observables (internal rotation rate, core-to-surface rotation ratio while perspectives to improve our modeling by including magnetic field or transport by internal gravity waves will be discussed.

  4. The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst

    Science.gov (United States)

    Motte, F.; Nony, T.; Louvet, F.; Marsh, K. A.; Bontemps, S.; Whitworth, A. P.; Men'shchikov, A.; Nguyáën Luong, Q.; Csengeri, T.; Maury, A. J.; Gusdorf, A.; Chapillon, E.; Könyves, V.; Schilke, P.; Duarte-Cabral, A.; Didelon, P.; Gaudel, M.

    2018-04-01

    Understanding the processes that determine the stellar initial mass function (IMF) is a critical unsolved problem, with profound implications for many areas of astrophysics1. In molecular clouds, stars are formed in cores—gas condensations sufficiently dense that gravitational collapse converts a large fraction of their mass into a star or small clutch of stars. In nearby star-formation regions, the core mass function (CMF) is strikingly similar to the IMF, suggesting that the shape of the IMF may simply be inherited from the CMF2-5. Here, we present 1.3 mm observations, obtained with the Atacama Large Millimeter/submillimeter Array telescope, of the active star-formation region W43-MM1, which may be more representative of the Galactic-arm regions where most stars form6,7. The unprecedented resolution of these observations reveals a statistically robust CMF at high masses, with a slope that is markedly shallower than the IMF. This seriously challenges our understanding of the origin of the IMF.

  5. The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst

    Science.gov (United States)

    Motte, F.; Nony, T.; Louvet, F.; Marsh, K. A.; Bontemps, S.; Whitworth, A. P.; Men'shchikov, A.; Nguyen Luong, Q.; Csengeri, T.; Maury, A. J.; Gusdorf, A.; Chapillon, E.; Könyves, V.; Schilke, P.; Duarte-Cabral, A.; Didelon, P.; Gaudel, M.

    2018-06-01

    Understanding the processes that determine the stellar initial mass function (IMF) is a critical unsolved problem, with profound implications for many areas of astrophysics1. In molecular clouds, stars are formed in cores—gas condensations sufficiently dense that gravitational collapse converts a large fraction of their mass into a star or small clutch of stars. In nearby star-formation regions, the core mass function (CMF) is strikingly similar to the IMF, suggesting that the shape of the IMF may simply be inherited from the CMF2-5. Here, we present 1.3 mm observations, obtained with the Atacama Large Millimeter/submillimeter Array telescope, of the active star-formation region W43-MM1, which may be more representative of the Galactic-arm regions where most stars form6,7. The unprecedented resolution of these observations reveals a statistically robust CMF at high masses, with a slope that is markedly shallower than the IMF. This seriously challenges our understanding of the origin of the IMF.

  6. SPITZER OBSERVATIONS OF THE λ ORIONIS CLUSTER. II. DISKS AROUND SOLAR-TYPE AND LOW-MASS STARS

    International Nuclear Information System (INIS)

    Hernandez, Jesus; Morales-Calderon, Maria; Calvet, Nuria; Hartmann, L.; Muzerolle, J.; Gutermuth, R.; Luhman, K. L.; Stauffer, J.

    2010-01-01

    We present IRAC/MIPS Spitzer Space Telescope observations of the solar-type and the low-mass stellar population of the young (∼5 Myr) λ Orionis cluster. Combining optical and Two Micron All Sky Survey photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 M sun to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with 'evolved disks' (with smaller excesses than optically thick disk systems), and 'transitional disk' candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from ∼6% for K-type stars (R C - J C - J>4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the λ Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as ∼5 Myr.

  7. THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yun; Kouwenhoven, M. B. N. [Department of Astronomy, School of Physics, Peking University, Yiheyuan Lu 5, Haidian Qu, Beijing 100871 (China); Stamatellos, D. [Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Goodwin, S. P., E-mail: yunli@pku.edu.cn [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2015-06-01

    Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low-mass

  8. PERIODIC VARIABILITY OF LOW-MASS STARS IN SLOAN DIGITAL SKY SURVEY STRIPE 82

    International Nuclear Information System (INIS)

    Becker, A. C.; Hawley, S. L.; Ivezic, Z.; Kowalski, A. F.; Sesar, B.; Bochanski, J. J.; West, A. A.

    2011-01-01

    We present a catalog of periodic stellar variability in the 'Stripe 82' region of the Sloan Digital Sky Survey. After aggregating and re-calibrating catalog-level data from the survey, we ran a period-finding algorithm (Supersmoother) on all point-source light curves. We used color selection to identify systems that are likely to contain low-mass stars, in particular M dwarfs and white dwarfs. In total, we found 207 candidates, the vast majority of which appear to be in eclipsing binary systems. The catalog described in this paper includes 42 candidate M dwarf/white dwarf pairs, four white dwarf pairs, 59 systems whose colors indicate they are composed of two M dwarfs and whose light-curve shapes suggest they are in detached eclipsing binaries, and 28 M dwarf systems whose light-curve shapes suggest they are in contact binaries. We find no detached systems with periods longer than 3 days, thus the majority of our sources are likely to have experienced orbital spin-up and enhanced magnetic activity. Indeed, 26 of 27 M dwarf systems that we have spectra for show signs of chromospheric magnetic activity, far higher than the 24% seen in field stars of the same spectral type. We also find binaries composed of stars that bracket the expected boundary between partially and fully convective interiors, which will allow the measurement of the stellar mass-radius relationship across this transition. The majority of our contact systems have short orbital periods, with small variance (0.02 days) in the sample near the observed cutoff of 0.22 days. The accumulation of these stars at short orbital period suggests that the process of angular momentum loss, leading to period evolution, becomes less efficient at short periods. These short-period systems are in a novel regime for studying the effects of orbital spin-up and enhanced magnetic activity, which are thought to be the source of discrepancies between mass-radius predictions and measurements of these properties in eclipsing

  9. TIME-SERIES PHOTOMETRY OF STARS IN AND AROUND THE LAGOON NEBULA. I. ROTATION PERIODS OF 290 LOW-MASS PRE-MAIN-SEQUENCE STARS IN NGC 6530

    International Nuclear Information System (INIS)

    Henderson, Calen B.; Stassun, Keivan G.

    2012-01-01

    We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ∼50,000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5 days X /L bol ≈ –3.3). However, we find a significant positive correlation between L X /L bol and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.

  10. CHEMICAL EVOLUTION IN HIGH-MASS STAR-FORMING REGIONS: RESULTS FROM THE MALT90 SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Hoq, Sadia; Jackson, James M.; Foster, Jonathan B.; Sanhueza, Patricio; Claysmith, Christopher [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States); Guzmán, Andrés [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Whitaker, J. Scott [Physics Department, Boston University, Boston, MA 02215 (United States); Rathborne, Jill M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Epping, NSW (Australia); Vasyunina, Tatiana; Vasyunin, Anton, E-mail: shoq@bu.edu, E-mail: jackson@bu.edu, E-mail: patricio@bu.edu, E-mail: claysmit@bu.edu, E-mail: jonathan.b.foster@yale.edu, E-mail: aguzmanf@cfa.harvard.edu, E-mail: scott@bu.edu, E-mail: rathborne@csiro.au, E-mail: tv3h@virginia.edu, E-mail: aiv3f@virginia.edu [Department of Chemistry, University of Virginia, Charlottesville, VA 22904 (United States)

    2013-11-10

    The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H{sub 2} column densities for each clump from Herschel/Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N{sub 2}H{sup +}, HCO{sup +}, HCN and HNC (1-0) lines, and derive the column densities and abundances of N{sub 2}H{sup +} and HCO{sup +}. The Herschel dust temperatures increase as a function of the IR-based Spitzer evolutionary classification scheme, with the youngest clumps being the coldest, which gives confidence that this classification method provides a reliable way to assign evolutionary stages to clumps. Both N{sub 2}H{sup +} and HCO{sup +} abundances increase as a function of evolutionary stage, whereas the N{sub 2}H{sup +} (1-0) to HCO{sup +} (1-0) integrated intensity ratios show no discernable trend. The HCN (1-0) to HNC(1-0) integrated intensity ratios show marginal evidence of an increase as the clumps evolve.

  11. ON THE NEED FOR DEEP-MIXING IN ASYMPTOTIC GIANT BRANCH STARS OF LOW MASS

    International Nuclear Information System (INIS)

    Busso, M.; Palmerini, S.; Maiorca, E.; Cristallo, S.; Abia, C.; Straniero, O.; Gallino, R.; Cognata, M. La

    2010-01-01

    The photospheres of low-mass red giants show CNO isotopic abundances that are not satisfactorily accounted for by canonical stellar models. The same is true for the measurements of these isotopes and of the 26 Al/ 27 Al ratio in presolar grains of circumstellar origin. Non-convective mixing, occurring during both red giant branch (RGB) and asymptotic giant branch (AGB) stages, is the explanation commonly invoked to account for the above evidence. Recently, the need for such mixing phenomena on the AGB was questioned, and chemical anomalies usually attributed to them were suggested to be formed in earlier phases. We have therefore re-calculated extra-mixing effects in low-mass stars for both the RGB and AGB stages, in order to verify the above claims. Our results contradict them; we actually confirm that slow transport below the convective envelope occurs also on the AGB. This is required primarily by the oxygen isotopic mix and the 26 Al content of presolar oxide grains. Other pieces of evidence exist, in particular from the isotopic ratios of carbon stars of type N, or C(N), in the Galaxy and in the LMC, as well as of SiC grains of AGB origin. We further show that, when extra-mixing occurs in the RGB phases of Population I stars above about 1.2 M sun , this consumes 3 He in the envelope, probably preventing the occurrence of thermohaline diffusion on the AGB. Therefore, we argue that other extra-mixing mechanisms should be active in those final evolutionary phases.

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

    Science.gov (United States)

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

    2017-12-01

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

  13. High-mass twins & resolution of the reconfinement, masquerade and hyperon puzzles of compact star interiors

    International Nuclear Information System (INIS)

    Blaschke, David; Alvarez-Castillo, David E.

    2016-01-01

    We aim at contributing to the resolution of three of the fundamental puzzles related to the still unsolved problem of the structure of the dense core of compact stars (CS): (i) the hyperon puzzle: how to reconcile pulsar masses of 2 M ⊙ with the hyperon softening of the equation of state (EoS); (ii) the masquerade problem: modern EoS for cold, high density hadronic and quark matter are almost identical; and (iii) the reconfinement puzzle: what to do when after a deconfinement transition the hadronic EoS becomes favorable again? We show that taking into account the compositeness of baryons (by excluded volume and/or quark Pauli blocking) on the hadronic side and confining and stiffening effects on the quark matter side results in an early phase transition to quark matter with sufficient stiffening at high densities which removes all three present-day puzzles of CS interiors. Moreover, in this new class of EoS for hybrid CS falls the interesting case of a strong first order phase transition which results in the observable high mass twin star phenomenon, an astrophysical observation of a critical endpoint in the QCD phase diagram

  14. Accurate evolutions of inspiralling and magnetized neutron stars: Equal-mass binaries

    International Nuclear Information System (INIS)

    Giacomazzo, Bruno; Rezzolla, Luciano; Baiotti, Luca

    2011-01-01

    By performing new, long and numerically accurate general-relativistic simulations of magnetized, equal-mass neutron-star binaries, we investigate the role that realistic magnetic fields may have in the evolution of these systems. In particular, we study the evolution of the magnetic fields and show that they can influence the survival of the hypermassive neutron star produced at the merger by accelerating its collapse to a black hole. We also provide evidence that, even if purely poloidal initially, the magnetic fields produced in the tori surrounding the black hole have toroidal and poloidal components of equivalent strength. When estimating the possibility that magnetic fields could have an impact on the gravitational-wave signals emitted by these systems either during the inspiral or after the merger, we conclude that for realistic magnetic-field strengths B 12 G such effects could be detected, but only marginally, by detectors such as advanced LIGO or advanced Virgo. However, magnetically induced modifications could become detectable in the case of small-mass binaries and with the development of gravitational-wave detectors, such as the Einstein Telescope, with much higher sensitivities at frequencies larger than ≅2 kHz.

  15. THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

    International Nuclear Information System (INIS)

    Riebel, D.; Meixner, M.; Srinivasan, S.; Sargent, B.

    2012-01-01

    We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ∼30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10 –5 M ☉ yr –1 , equivalent to a total mass injection rate (including the gas) into the ISM of ∼6 × 10 –3 M ☉ yr –1 . Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K s band as a function of J – K s color, BC K s = -0.40(J-K s ) 2 + 1.83(J-K s ) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot d ) from C-rich AGB stars, such as log M-dot d = (-18.90/((K s -[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

  16. HOBYS and W43-HERO: Two more steps toward a Galaxy-wide understanding of high-mass star formation

    Science.gov (United States)

    Motte, Frédérique; Bontemps, Sylvain; Tigé, Jérémy

    The Herschel/HOBYS key program allows to statistically study the formation of 10-20 M ⊙ stars. The IRAM/W43-HERO large program is itself dedicated to the much more extreme W43 molecular complex, which forms stars up to 50 M ⊙. Both reveal high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. Given their activity, these so-called mini-starburst cloud ridges could be seen as ``miniature and instant models'' of starburst galaxies. Both surveys also strongly suggest that high-mass prestellar cores do not exist, in agreement with the dynamical formation of cloud ridges. The HOBYS and W43 surveys are necessary steps towards Galaxy-wide studies of high-mass star formation.

  17. Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-radiation Hydrodynamics Study

    Science.gov (United States)

    Fujibayashi, Sho; Kiuchi, Kenta; Nishimura, Nobuya; Sekiguchi, Yuichiro; Shibata, Masaru

    2018-06-01

    We perform long-term general relativistic neutrino radiation hydrodynamics simulations (in axisymmetry) for a massive neutron star (MNS) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. We take into account the effects of viscosity, which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. The viscous effect plays key roles for the mass ejection from the remnant in two phases of the evolution. In the first t ≲ 10 ms, a differential rotation state of the MNS is changed to a rigidly rotating state. A shock wave caused by the variation of its quasi-equilibrium state induces significant mass ejection of mass ∼(0.5–2.0) × {10}-2 {M}ȯ for the α-viscosity parameter of 0.01–0.04. For the longer-term evolution with ∼0.1–10 s, a significant fraction of the torus material is ejected. We find that the total mass of the viscosity-driven ejecta (≳ {10}-2 {M}ȯ ) could dominate over that of the dynamical ejecta (≲ {10}-2 {M}ȯ ). The electron fraction, Y e , of the ejecta is always high enough (Y e ≳ 0.25) that this post-merger ejecta is lanthanide-poor; hence, the opacity of the ejecta is likely to be ∼10–100 times lower than that of the dynamical ejecta. This indicates that the electromagnetic signal from the ejecta would be rapidly evolving, bright, and blue if it is observed from a small viewing angle (≲45°) for which the effect of the dynamical ejecta is minor.

  18. The atomic and molecular content of disks around very low-mass stars and brown dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Pascucci, I. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Herczeg, G. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Carr, J. S. [Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States); Bruderer, S., E-mail: pascucci@lpl.arizona.edu [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany)

    2013-12-20

    There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne{sup +}, H{sub 2}, CO{sub 2}, and tentative detections of H{sub 2}O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (≥5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H{sub 2} S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C{sub 2}H{sub 2}/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H{sub 2}O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H{sub 2}O lines trace warm ≥600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs.

  19. Sequential star formation in RCW 34: A spectroscopic census of the stellar content of high-mass star-forming regions

    NARCIS (Netherlands)

    Bik, A.; Puga, E.; Waters, L.B.F.M.; Horrobin, M.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Kaper, L.; Van Den Ancker, M.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; de Koter, A.; Thi, W. F.; Comerón, F.; Waelkens, Ch

    2010-01-01

    In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is

  20. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Chaboyer, Brian, E-mail: gregory.a.feiden@gmail.com, E-mail: brian.chaboyer@dartmouth.edu [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  1. The extraordinary mass-loss bubble G2.4 + 1.4 and its central star

    International Nuclear Information System (INIS)

    Dopita, M.A.; Mcgregor, P.J.; Rawlings, S.J.; Lozinskaia, T.A.

    1990-01-01

    Data are presented on the WR 102 star and the surrounding nebula (G2.4 + 1.4). It is shown that WR 102 and the nebula are associated, the nebula being a mass-loss bubble powered by the central star. From a photoionization analysis of the surrounding nebula, the star was determined to have the following parameters: log T(ion) = 5.20 + or - 0.05; log (R/solar R) = about 0.05; and log (L/solar L) = 5.85 + or - 0.20. 42 refs

  2. 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

  3. An intermediate-mass black hole in the darf galaxy Pox 52

    Science.gov (United States)

    Barth, Aaron

    2005-01-01

    Do dwarf elliptical and dwarf spiral galaxies contain central black holes with masses below 106 solar masses? Beyond the Local Group dynamical searches for black holes in this mass range are very difficult but the detection of accretion-powered nuclear activity could be used to infer the presence of a black hole. The nearby dwarf spiral galaxy NGC 4395 hosts a faint Seyfert 1 nucleus with a likely black hole mass in the range 104-105 solar masses and for more than a decade it has been the only known example of a Seyfert 1 nucleus in a dwarf galaxy. I will present new Keck spectra of the dwarf galaxy POX 52 which demonstrate that it has a Seyfert 1 spectrum nearly identical to that of NGC 4395. Its velocity dispersion is 37 km/s suggesting a possible black hole mass of order 105 solar masses. I will discuss the prospects for systematic searches for nuclear activity in dwarf galaxies and the implications for black hole demographics.

  4. An Intermediate-Mass Black Hole in the Dwarf Galaxy Pox 52

    Science.gov (United States)

    Barth, Aaron

    Do dwarf elliptical and dwarf spiral galaxies contain central black holes with masses below 106 solar masses? Beyond the Local Group dynamical searches for black holes in this mass range are very difficult but the detection of accretion-powered nuclear activity could be used to infer the presence of a black hole. The nearby dwarf spiral galaxy NGC 4395 hosts a faint Seyfert 1 nucleus with a likely black hole mass in the range 104-105 solar masses and for more than a decade it has been the only known example of a Seyfert 1 nucleus in a dwarf galaxy. I will present new Keck spectra of the dwarf galaxy POX 52 which demonstrate that it has a Seyfert 1 spectrum nearly identical to that of NGC 4395. Its velocity dispersion is 37 km/s suggesting a possible black hole mass of order 105 solar masses. I will discuss the prospects for systematic searches for nuclear activity in dwarf galaxies and the implications for black hole demographics.

  5. Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds

    Science.gov (United States)

    Zakharov, A. F.; Jovanović, P.; Borka, D.; Borka Jovanović, V.

    2018-04-01

    Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as mg advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity [5] and graviton mass [6] from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around 5 × 10‑23 eV or slightly better than current estimates obtained with LIGO observations.

  6. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Rossi, Silvia [Departamento de Astronomia-Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Sao Paulo, SP 05508-900 (Brazil); Frebel, Anna [Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Karakas, Amanda I.; Kennedy, Catherine R. [Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut fuer Astronomie der Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  7. Correlation between the helium abundances in the atmospheres of early B stars and their ages and masses

    International Nuclear Information System (INIS)

    Lyubimkov, L.S.

    1989-01-01

    The masses M and ages t are found for early main sequence B stars for which fairly accurate estimates of the helium abundance var-epsilon He are available. It is shown that if the stars are grouped according to M and then var-epsilon He is compared with t a correlation between var-epsilon He and t is found in each such group. Moreover, the rate of enrichment of the atmospheres of B stars with helium, var-epsilon He , is higher the larger the mass M. In the interval M/M circle-dot = 6-14 the value of var-epsilon He depends linearly on M. For stars with such masses the helium abundance in the atmosphere is increased during the time of hydrogen burning in the core by 0.03-0.05, whereas for stars with M ≤ 5M circle-dot the addition to var-epsilon He does not exceed 0.01. The dependence of var-epsilon He on M and t, together with the analogous dependence found for nitrogen [10], may have an evolutionary nature and indicate that already in the main sequence stage there exists a mechanism which carries products of the CNO cycle from the interior of the stars to the surface

  8. The photometric evolution of star clusters and the preferential loss of low-mass bodies – with an application to globular clusters

    NARCIS (Netherlands)

    Kruijssen, J.M.D.; Lamers, H.J.G.L.M.

    2008-01-01

    Context. To obtain an accurate description of broad-band photometric star cluster evolution, certain effects should be accounted for. Energy equipartition leads to mass segregation and the preferential loss of low-mass stars, while stellar remnants severely influence cluster mass-to-light ratios.

  9. A Multiwavelength Study of POX 52, a Dwarf Seyfert Galaxy with an Intermediate Mass Black Hole

    Science.gov (United States)

    Barth, Aaron

    2004-09-01

    POX 52 is a Seyfert 1 galaxy with unprecedented properties: its host galaxy is a dwarf elliptical, and its stellar velocity dispersion is only 36 km/s. The stellar velocity dispersion and the broad emission-line widths both suggest a black hole mass of order 10^5 solar masses. We request HST ACS/HRC imaging to perform a definitive measurement of the host galaxy structure; STIS UV and optical spectroscopy to study the nonstellar continuum and the structure of the broad-line region; and Chandra ACIS imaging to investigate the spectral and variability properties of the X-ray emission. The results of this program will give a detailed understanding of the host galaxy and accretion properties of one of the very few known black holes in the mass range around 10^5 solar masses.

  10. Photometric Determination of the Mass Accretion Rates of Pre-main-sequence Stars. V. Recent Star Formation in the 30 Dor Nebula

    Science.gov (United States)

    De Marchi, Guido; Panagia, Nino; Beccari, Giacomo

    2017-09-01

    We report on the properties of the low-mass stars that recently formed in the central ˜ 2\\buildrel{ \\prime}\\over{.} 7× 2\\buildrel{ \\prime}\\over{.} 7 of 30 Dor, including the R136 cluster. Using the photometric catalog of De Marchi et al., based on observations with the Hubble Space Telescope, and the most recent extinction law for this field, we identify 1035 bona fide pre-main-sequence (PMS) stars showing {{H}}α excess emission at the 4σ level with an {{H}}α equivalent width of 20 Å or more. We find a wide spread in age spanning the range ˜ 0.1{--}50 {Myr}. We also find that the older PMS objects are placed in front of the R136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. We derive physical parameters for all PMS stars, including masses m, ages t, and mass accretion rates {\\dot{M}}{acc}. To identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type {log}{\\dot{M}}{acc}=a× {log}t+b× {log}m+c. The values of a and b for 30 Dor are compatible with those found in NGC 346 and NGC 602. We extend the fit to a uniform sample of 1307 PMS stars with 0.5contract NAS5-26555.

  11. White-dwarf rotational equilibria in magnetic cataclysmic variable stars

    Energy Technology Data Exchange (ETDEWEB)

    Warner, B. (Cape Town Univ. (South Africa). Dept. of Astronomy Australian National Univ., Canberra (Australia). Dept. of Mathematics); Wickramasinghe, D.T. (Australian National Univ., Canberra (Australia). Dept. of Mathematics)

    1991-02-01

    The magnetic cataclysmic variable stars (polars, intermediate polars and DQ Her stars) are grouped about three lines in the orbital period-spin period diagram. This segregation is shown to be the consequence of competition between braking and accretion torques when combined with the effects of cyclical variations in rate of mass transfer. (author).

  12. THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Vink, Jorick S.; Graefener, Goetz, E-mail: jsv@arm.ac.uk [Armagh Observatory, College Hill, BT61 9DG Armagh (United Kingdom)

    2012-06-01

    A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of {approx_equal}2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate M-dot{sub trans} between O and Wolf-Rayet stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modeling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the {approx}50 M{sub Sun} mass range. Our results do not confirm the specific need for eruptive mass loss as luminous blue variables, and current stellar evolution modeling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.

  13. THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION