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First Stars. II. Evolution with mass loss  [PDF]
David Bahena,Petr Hadrava
Physics , 2011, DOI: 10.1007/s10509-011-0898-0
Abstract: The first stars are assumed to be predominantly massive. Although, due to the low initial abundances of heavy elements the line-driven stellar winds are supposed to be inefficient in the first stars, these stars may loose a significant amount of their initial mass by other mechanisms. In this work, we study the evolution with a prescribed mass loss rate of very massive, galactic and pregalactic, Population III stars, with initial metallicities $Z=10^{-6}$ and $Z=10^{-9}$, respectively, and initial masses 100, 120, 150, 200, and 250$\,M_{\odot}$ during the hydrogen and helium burning phases. The evolution of these stars depends on their initial mass, metallicity and the mass loss rate. Low metallicity stars are hotter, compact and luminous, and they are shifted to the blue upper part in the Hertzprung-Russell diagram. With mass loss these stars provide an efficient mixing of nucleosynthetic products, and depending on the He-core mass their final fate could be either pair-instability supernovae or energetic hypernovae. These stars contributed to the reionization of the universe and its enrichment with heavy elements, which influences the subsequent star formation properties.
The final fate of very massive first stars
Klapp, J;Bahena, D;
Revista mexicana de física , 2008,
Abstract: a generation of stars which formed from primordial nearly pure h/he gas, the so-called first stars or population iii stars, must have existed since heavy elements can only be synthesized in the interior of the stars. these stars were responsible for the initial heavy elements enrichment of the intergalactic medium. in this work we analyze the possible outcome of the evolution of very massive population iii stars and whether their final fate can avoid the pair instability supernovae explosion. we have recently calculated the evolution and nucleosynthesis of mass losing very massive population iii stars during the hydrogen and helium burning phases, and proposed a new scenario for the first stars in the universe. according to this scenario, the first stars were born very massive, but evolve with mass loss, and its possible endpoint is a hypernovae stage. at low metallicity the effects on the presupernova structure depends on the initial mass and the mass loss rate during the main sequence evolution. presupernova stars of lower metallicity have different characteristics depending if they are galactic or pregalactic, and if they evolve without or with mass loss. when these stars evolve with mass loss, their convective core size increase and their helium- or carbon-oxygen core mass decreases. then, the stars could explode like hypernovae or supernovae.
Evolution and Nucleosynthesis of Very Massive Stars  [PDF]
Raphael Hirschi
Physics , 2014, DOI: 10.1007/978-3-319-09596-7_6
Abstract: In this chapter, after a brief introduction and overview of stellar evolution, we discuss the evolution and nucleosynthesis of very massive stars (VMS: M>100 solar masses) in the context of recent stellar evolution model calculations. This chapter covers the following aspects: general properties, evolution of surface properties, late central evolution, and nucleosynthesis including their dependence on metallicity, mass loss and rotation. Since very massive stars have very large convective cores during the main-sequence phase, their evolution is not so much affected by rotational mixing, but more by mass loss through stellar winds. Their evolution is never far from a homogeneous evolution even without rotational mixing. All VMS at metallicities close to solar end their life as WC(-WO) type Wolf-Rayet stars. Due to very important mass loss through stellar winds, these stars may have luminosities during the advanced phases of their evolution similar to stars with initial masses between 60 and 120 solar masses. A distinctive feature which may be used to disentangle Wolf-Rayet stars originating from VMS from those originating from lower initial masses is the enhanced abundances of neon and magnesium at the surface of WC stars. At solar metallicity, mass loss is so strong that even if a star is born with several hundred solar masses, it will end its life with less than 50 solar masses (using current mass loss prescriptions). At the metallicity of the LMC and lower, on the other hand, mass loss is weaker and might enable star to undergo pair-instability supernovae.
Evolution and fate of very massive stars  [PDF]
Norhasliza Yusof,Raphael Hirschi,Georges Meynet,Paul A. Crowther,Sylvia Ekstrom,Urs Frischknecht,Cyril Georgy,Hasan Abu Kassim,Olivier Schnurr
Physics , 2013, DOI: 10.1093/mnras/stt794
Abstract: There is observational evidence that supports the existence of Very Massive Stars in the local universe. First, very massive stars (Mini<=320 M) have been observed in the Large Magellanic Cloud . Second, there are observed SNe that bear the characteristics of Pair Creation Supernovae which have very massive stars as progenitors. The most promising candidate to date is SN2007bi. In order to investigate the evolution and fate of nearby very massive stars, we calculated a new grid of models for such objects, for solar, LMC and SMC metallicities, which covers the initial mass range from 120 to 500M. Both rotating and non-rotating models were calculated using the Geneva stellar evolution code and evolved until at least the end of helium burning and for most models until oxygen burning. Since very massive stars have very large convective cores during the Main-Sequence phase, their evolution is not so much affected by rotational mixing, but more by mass loss through stellar winds. Their evolution is never far from a homogeneous evolution even without rotational mixing. All the VMS, at all the metallicities studied here, end their life as WC(WO) type stars. At solar metallicity, none of our models is expected to explode as a PCSN. At the metallicity of the LMC, only stars more massive than 300 M are expected to explode as PCSNe. At the SMC metallicity, the mass range for the PCSN progenitors is much larger and comprises stars with initial masses between about 100 and 290 M . All VMS stars in the metallicity range studied here produce either a type Ib or a type Ic SN. We estimate that the progenitor of SN2007bi, assuming a SMC metallicity, had an initial mass between 160 and 175 M . None of models presented in this grid produce GRBs or magnetars. They lose too much angular momentum by mass loss or avoid the formation of a BH by producing a completely disruptive PCSN.
Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars  [PDF]
Nathan Smith
Physics , 2014, DOI: 10.1146/annurev-astro-081913-040025
Abstract: Our understanding of massive star evolution is in flux, due to recent upheavals in our view of mass loss, and observations of a high binary fraction among O-type stars. Mass-loss rates for standard metallicity-dependent winds of hot stars are now thought to be lower by a factor of 2-3 compared to rates adopted in modern stellar evolution models, due to the influence of clumping. Weaker line-driven winds shift the burden of H-envelope removal elsewhere, so that the dominant modes of mass loss are the winds, pulsations, and eruptions of evolved supergiants, as well as binary mass transfer. Studies of stripped-envelope supernovae, in particular, require binary mass transfer. Dramatic examples of eruptive mass loss are seen in Type IIn supernovae, which have massive shells ejected just a few years before core collapse. The shifting emphasis from steady winds to episodic mass loss is a major change for low-metallicity regions, since eruptions and binary mass transfer are less sensitive to metallicity. We encounter the predicament that the most important modes of mass loss are also the most uncertain, undermining the predictive power of single-star evolution models beyond core H burning. Moreover, the influence of winds and rotation in models has been evaluated by testing single-star models against observed statistics that, as it turns out, are heavily influenced by binary evolution. This alters our view about the most basic outcomes of massive-star mass loss --- are WR stars and SNe Ibc the products of single-star winds, or are they mostly the result of binary evolution and eruptive mass loss? This paradigm shift has far-reaching impact on a number of other areas of astronomy. (abridged)
The Deaths of Very Massive Stars  [PDF]
S. E. Woosley,Alexander Heger
Physics , 2014, DOI: 10.1007/978-3-319-09596-7_7
Abstract: The theory underlying the evolution and death of stars heavier than 10 Msun on the main sequence is reviewed with an emphasis upon stars much heavier than 30 Msun. These are stars that, in the absence of substantial mass loss, are expected to either produce black holes when they die, or, for helium cores heavier than about 35 Msun, encounter the pair instability. A wide variety of outcomes is possible depending upon the initial composition of the star, its rotation rate, and the physics used to model its evolution. These heavier stars can produce some of the brightest supernovae in the universe, but also some of the faintest. They can make gamma-ray bursts or collapse without a whimper. Their nucleosynthesis can range from just CNO to a broad range of elements up to the iron group. Though rare nowadays, they probably played a disproportionate role in shaping the evolution of the universe following the formation of its first stars.
AmFm and lithium gap stars: Stellar evolution models with mass loss  [PDF]
Mathieu Vick,Georges Michaud,Jacques Richer,Olivier Richard
Physics , 2010, DOI: 10.1051/0004-6361/201014307
Abstract: A thorough study of the effects of mass loss on internal and surface abundances of A and F stars is carried out in order to constrain mass loss rates for these stars, as well as further elucidate some of the processes which compete with atomic diffusion. Self-consistent stellar evolution models of 1.3 to 2.5 M_sun stars including atomic diffusion and radiative accelerations for all species within the OPAL opacity database were computed with mass loss and compared to observations as well as previous calculations with turbulent mixing. Models with unseparated mass loss rates between 5 x 10^-14 and 10^-13 M_sun/yr reproduce observations for many cluster AmFm stars as well as Sirius A and o Leonis. These models also explain cool Fm stars, but not the Hyades lithium gap. Like turbulent mixing, these mass loss rates reduce surface abundance anomalies; however, their effects are very different with respect to internal abundances. For most of the main sequence lifetime of an A or F star, surface abundances in the presence of such mass loss depend on separation which takes place between log(Delta M/M_star)= -6 and -5. The current observational constraints do not allow us to conclude that mass loss is to be preferred over turbulent mixing (induced by rotation or otherwise) in order to explain the AmFm phenomenon. Internal concentration variations which could be detectable through asteroseismic tests should provide further information. If atomic diffusion coupled with mass loss are to explain the Hyades Li gap, the wind would need to be separated.
Infrared photometry and evolution of mass-losing AGB stars. III. Mass loss rates of MS and S stars  [PDF]
R. Guandalini
Physics , 2010, DOI: 10.1051/0004-6361/200911764
Abstract: Context. The asymptotic giant branch (AGB) phase marks the end of the evolution for low- and intermediate-mass stars, which are fundamental contributors to the mass return to the interstellar medium and to the chemical evolution of galaxies. The detailed understanding of mass loss processes is hampered by the poor knowledge of the luminosities and distances of AGB stars. Aims. In a series of papers we are trying to establish criteria permitting a more quantitative determination of luminosities for the various types of AGB stars, using the infrared (IR) fluxes as a basis. An updated compilation of the mass loss rates is also required, as it is crucial in our studies of the evolutionary properties of these stars. In this paper we concentrate our analysis on the study of the mass loss rates for a sample of galactic S stars. Methods. We reanalyze the properties of the stellar winds for a sample of galactic MS, S, SC stars with reliable estimates of the distance on the basis of criteria previously determined. We then compare the resulting mass loss rates with those previously obtained for a sample of C-rich AGB stars. Results. Stellar winds in S stars are on average less efficient than those of C-rich AGB stars of the same luminosity. Near-to-mid infrared colors appear to be crucial in our analysis. They show a good correlation with mass loss rates in particular for the Mira stars. We suggest that the relations between the rates of the stellar winds and both the near-to-mid infrared colors and the periods of variability improve the understanding of the late evolutionary stages of low mass stars and could be the origin of the relation between the rates of the stellar winds and the bolometric magnitudes.
Analysis of Stars Common to the IRAS and HIPPARCOS Surveys  [PDF]
T. G. Knauer,Z. Ivezic,G. R. Knapp
Physics , 2001, DOI: 10.1086/320584
Abstract: For about 11,000 stars observed in the HIPPARCOS Survey and detected by IRAS we calculate bolometric luminosities by integrating their spectral energy distributions from the B band to far-IR wavelengths. We present an analysis of the dependence of dust emission on spectral type and correlations between the luminosity and dust emission for about 1000 sources with the best data (parallax error less than 30%, error in luminosity of about 50% or better). This subsample includes stars of all spectral types and is dominated by K and M giants. We use the IRAS [25]-[12] color to select stars with emission from circumstellar dust and show that they are found throughout the Hertzsprung-Russell diagram, including on the main sequence. Clear evidence is found that M giants with dust emission have luminosities about 3 times larger (about 3000 Lsun) than their counterparts without dust, and that mass loss on the asymptotic giant branch for both M and C stars requires a minimum luminosity of order 2000 Lsun. Above this threshold the mass-loss rate seems to be independent of, or only weakly dependent on, luminosity. We also show that the mass-loss rate for these stars is larger than the core mass growth rate, indicating that their evolution is dominated by mass loss.
Local Radiation-Driven Instabilities in Post-Main Sequence Massive Stars  [PDF]
Andrés Suárez-Madrigal,Mark Krumholz,Enrico Ramirez-Ruiz
Physics , 2013,
Abstract: Late in their evolution, massive stars may undergo periods of violent instability and mass loss, but the mechanism responsible for these episodes has not been identified. We study one potential contributor: the development of local radiation-driven instabilities in the outer layers of main sequence (MS) and post-MS massive stars. We construct a sequence of massive stellar evolution models and investigate where they are subject to local radiative instabilities, both in the presence of magnetic fields and without them,and at a range of metallicities. We find that these types of instabilities do not occur in solar-metallicity MS stars up to 100\,M$_\odot$, but they set in immediately post-MS for stars heavier than $\sim 25$\,M$_\odot$. Once an instability appears, it involves a significant amount of mass in the star's upper layers (up to $\sim 1$ per cent of the initial stellar mass), suggesting that radiation-driven instabilities are a potentially viable mechanism for dynamic mass loss. We find that the presence of magnetic fields at strengths low enough not to disturb the hydrostatic balance of the star does not alter these results. Stars with sub-Solar metallicity also show instability, but their instabilities involve less mass and appear later in the star's evolution.
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