Origin and Evolution of Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 377-381
Author(s):  
A. Tutukov ◽  
L. Yungelson
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Close Binary ◽  
Initial Mass ◽  
Convective Stability ◽  
Helium Burning ◽  
Origin And Evolution ◽  
The Core

The larger part of close binary components with initial mass exceeding ∼20 Mo becomes WR stars in the core helium burning stage. Some of the most massive WR stars may be products of evolution of single massive stars with initial masses exceeding ∼50 M0 if the mass loss in the infrared supergiant stage is effective enough. The Ledoux criterion of convective stability seems more promising to explain the observed properties of WR stars.

scholarly journals Stellar evolution with SMC chemical abundances

1981 ◽  
Vol 59 ◽  
pp. 279-282
Author(s):  
P. Hellings ◽  
D. Vanbeveren
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Binary Systems ◽  
Massive Stars ◽  
Close Binary ◽  
Evolutionary Computations ◽  
Chemical Abundances ◽  
Hydrogen Burning ◽  
The Core ◽  
Early Case

Evolutionary computations are presented for massive stars between 20 Mo and 100 Mo with chemical abundances holding for the Small Magellanic Cloud, i.e. X = .76 and Z = .003. Mass loss by stellar wind is taken into account during core hydrogen burning. After core hydrogen burning some models are considered as members of close binary systems and are followed during their Roche lobe overflow stage according an early case B of mass transfer. During the core helium burning stage of the RL0F remnants mass loss rates comparable to WR stars are included in order to study the formation and the evolution of WR stars. Comparison with similar galactic computations (Vanbeveren, Packet, 1978) is made.

scholarly journals Low-metallicity massive single stars with rotation

2019 ◽  
Vol 623 ◽  
pp. A8 ◽  
Author(s):  
B. Kubátová ◽  
D. Szécsi ◽  
A. A. C. Sander ◽  
J. Kubát ◽  
F. Tramper ◽  
...  
Keyword(s):  
Mass Loss ◽  
Gamma Ray ◽  
Massive Stars ◽  
Compact Object ◽  
Stellar Atmospheres ◽  
Emission Lines ◽  
Helium Burning ◽  
The Core ◽  
Low Metallicity ◽  
The Universe

Context. Metal-poor massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and compact object mergers that might contribute to the early epochs of the Universe with their strong ionizing radiation. However, this assumption remains mainly theoretical because individual spectroscopic observations of such objects have rarely been carried out below the metallicity of the Small Magellanic Cloud. Aims. Here we explore the predictions of the state-of-the-art theories of stellar evolution combined with those of stellar atmospheres about a certain type of metal-poor (0.02 Z⊙) hot massive stars, the chemically homogeneously evolving stars that we call Transparent Wind Ultraviolet INtense (TWUIN) stars. Methods. We computed synthetic spectra corresponding to a broad range in masses (20−130 M⊙) and covering several evolutionary phases from the zero-age main-sequence up to the core helium-burning stage. We investigated the influence of mass loss and wind clumping on spectral appearance and classified the spectra according to the Morgan-Keenan (MK) system. Results. We find that TWUIN stars show almost no emission lines during most of their core hydrogen-burning lifetimes. Most metal lines are completely absent, including nitrogen. During their core helium-burning stage, lines switch to emission, and even some metal lines (oxygen and carbon, but still almost no nitrogen) are detected. Mass loss and clumping play a significant role in line formation in later evolutionary phases, particularly during core helium-burning. Most of our spectra are classified as an early-O type giant or supergiant, and we find Wolf–Rayet stars of type WO in the core helium-burning phase. Conclusions. An extremely hot, early-O type star observed in a low-metallicity galaxy could be the result of chemically homogeneous evolution and might therefore be the progenitor of a long-duration gamma-ray burst or a type Ic supernova. TWUIN stars may play an important role in reionizing the Universe because they are hot without showing prominent emission lines during most of their lifetime.

scholarly journals Convective zones in the envelope of massive stars

1994 ◽  
Vol 162 ◽  
pp. 67-68
Author(s):  
Frank M. Alberts
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Convective Zone ◽  
Helium Burning ◽  
The Core ◽  
Negligible Amount ◽  
Stellar Models

In the calculation of stellar models with the Cox–Stewart opacities no convective zones in the outer layers of massive stars appear. The new OPAL opacities (Rogers & Iglesias, 1992) show a significant bump in the opacity near temperatures of log T = 5.2. This opacity effect results in a small convective zone in the envelope of stars with mass ranging from 15 M⊙ to 150 M⊙, apart from possible convective zones caused by ionization. This was also briefly mentioned by Glatzel & Kiriakidis (1993). For stars on the main sequence this zone is small, about 1% of its radius on the zero age main sequence up to 7% at the onset of the core helium burning and contains a negligible amount of mass. For helium burning stars, however, this convective zone moves inward, keeping the same size but containing more and more mass.

scholarly journals On the significance of mass loss for the evolution of massive stars

1981 ◽  
Vol 59 ◽  
pp. 265-270
Author(s):  
L.R. Yungelson ◽  
A.G. Massevitch ◽  
A.V. Tutukov
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Hydrogen Burning ◽  
B Stars ◽  
The Core ◽  
Input Parameters ◽  
Satisfactory Theory

It is shown that mass loss by stellar wind with rates observed in O, B-stars cannot change qualitatively their evolution in the core hydrogen-burning stage. The effects, that are usually attributed to the mass loss, can be explained by other causes: e.g., duplicity or enlarged chemically homogeneous stellar cores.The significance of mass loss by stellar wind for the evolution of massive stars was studied extensively by numerous authors (see e.g. Chiosi et al. (1979) and references therein). However, the problem is unclear as yet. There does not exist any satisfactory theory of mass loss by stars. Therefore one is usually forced to assume that mass loss rate depends on some input parameters.

scholarly journals Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies

1981 ◽  
Vol 59 ◽  
pp. 283-287
Author(s):  
A. Maeder
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Short Note ◽  
Evolutionary Models ◽  
Helium Burning ◽  
Red Supergiants ◽  
Low Mass ◽  
Age Sequence ◽  
Carbon Burning ◽  
Loss Rates

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).

scholarly journals New Results in Evolution in the Upper HRD

1991 ◽  
Vol 143 ◽  
pp. 552-552
Author(s):  
E.I. Staritsin
Keyword(s):  
Mass Loss ◽  
Hydrogen Content ◽  
Stellar Wind ◽  
Convection Zone ◽  
Life Time ◽  
Convective Zone ◽  
Theoretical Interpretation ◽  
Helium Burning ◽  
The Core ◽  
Full Life

A theoretical interpretation of the observed upper luminosity limit is suggested here. Staritsin (1989) considered the core hydrogen and helium burning stages in a 64 M⊙ star. Mixing in a semi-convection zone in a diffusion approximation (Staritsin, 1987) and mass loss by stellar wind (de Jager et al., 1988) were taken into account. During MS evolution the star looses half of its initial envelope. After MS evolution an intermediate convective zone appears. The hydrogen content in the shell source increases. As a result, the star burns helium in its blue supergiant stage. After the hydrogen content in the envelope has decreased to 10% of its mass, the star looses mass with Wolf-Rayet mass loss rates according to de Jager et al. (1988). The star has a WR character during 5% of its full life time.

scholarly journals The Structure and Evolution of Massive Stars

1978 ◽  
Vol 80 ◽  
pp. 357-368 ◽  
Author(s):  
C. Chiosi
Keyword(s):  
Mass Loss ◽  
Lower Limit ◽  
Main Sequence ◽  
Massive Stars ◽  
The Core ◽  
Upper Limit ◽  
Non Linear ◽  
Vibrational Instability

This review is restricted to the most recent studies of the structure of stars in the approximate range from 10 to 100 M⊙, during the core H- and He-burning phases. Other recent major reviews on this subject are by Dallaporta (1971), Massevich and Tutukov (1974) and Iben (1974). The lower limit was chosen to be just above the transition from degeneracy to non-degeneracy in the core at carbon ignition (Schwarzschild and Härm 1958). The upper limit is very uncertain. The canonical value of about 60 M⊙for Pop I composition was set by Schwarzschild and Harm (1959), using linear pulsation theory. More recent non-linear dynamical calculations lift the limit above 100 M⊙, and also show that mass loss by vibrational instability occurs at such a rate that stars in the range from 100 to 200 M⊙can survive for a time comparable to the total main sequence lifetime (Appenzeller 1970a, b, Ziebarth 1970, Talbot 1971a,b and Papaloizou and Taylor 1974).

scholarly journals Common envelope binaries and mass loss

1979 ◽  
Vol 83 ◽  
pp. 415-420
Author(s):  
A. Delgado
Keyword(s):  
Neutron Star ◽  
Binary System ◽  
Mass Loss ◽  
Free Parameter ◽  
Mass Ratio ◽  
Initial State ◽  
Helium Burning ◽  
Common Envelope ◽  
The Core ◽  
Before And After

In this work we calculate the evolution of a binary system with a common envelope, which consists of a blue supergiant and a neutron star. We consider as a free parameter the effectivity with which the energy liberated at the orbit produces mass loss from the system.The evolutionary calculations were made, using various values of this parameter, for a system with mass ratio 25:1. As initial state we choose a model in the phase of Hydrogen-shell burning, before and after the begin of Helium-burning in the core.We found that, under certain conditions, it is possible for the radius of the orbit and the period of the system to increase; the time scale for the “spiral-in” would be of the order of 104-105 years. Mass loss rates are between 10−3 M⊙/y and 10−4 M⊙/y.

scholarly journals From LBV Binary to WR+OB Binary

1991 ◽  
Vol 143 ◽  
pp. 556-556
Author(s):  
D. Vanbeveren
Keyword(s):  
Mass Loss ◽  
Thermal Equilibrium ◽  
General Theorem ◽  
Equipotential Surface ◽  
Roche Lobe ◽  
Close Binary ◽  
Initial Mass ◽  
Close Binaries ◽  
Evolutionary Models ◽  
Massive Close Binary

The LBV phase is generally identified with the hydrogen shell burning phase of a star with initial mass larger than 40-50 M⊙ (see also Humphreys, this volume) and therefore in binaries with ZAMS component masses larger than 40-50 M⊙ and periods larger than 4-7 days the primary may experience a LBV mass loss phase before it reaches its critical equipotential surface (the Roche lobe). I then define the ‘LBV scenario’ of massive close binaries as follows:when a binary component (initial mass larger than 40-50 M⊙) reaches the LBV phase prior to its Roche lobe overflow phase (RLOF), a stellar wind mass loss phase sets in at rates comparable to the rates encounterd during a RLOF process and which are large enough in order to prohibit the occurence of a RLOF.Evolutionary models are computed for close binaries with initial primary masses larger than 50 M⊙ and mass ratios ranging between 0.2 and 1. Special attention is given at the predicted spectral type of the secondary component. In order to determine the mass of the primary at the end of its LBV phase, I have used the following general theorem holding for the most massive stars, i.e.a hydrogen shell burning mass loser with mass larger than 50 M⊙ in a massive close binary restores thermal equilibrium (and becomes a WR star) when helium starts burning in its core and when its atmospherical hydrogen abundance has dropped to Xatm = 0.2-0.3 (by weight).

scholarly journals Effects of a stochastic initial mass function on the upper main sequence band

1981 ◽  
Vol 59 ◽  
pp. 293-296
Author(s):  
C. Chiosi ◽  
L. Greggio
Keyword(s):  
Mass Loss ◽  
Effective Temperature ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Sequence Band ◽  
High Mass Loss

The theoretical (Mb versus Log Te) HR diagram for the brightest galactic OB stars shows an upper boundary for the luminosity, which is characterized by a decreasing luminosity with decreasing effective temperature (Humphreys and Davidson, 1979). The existence of this limit was interpreted by Chiosi et al. (1978) as due to the effect of mass loss by stellar wind on the evolution of most massive stars in core H-burning phase. In fact, evolutionary models calculated at constant mass cover a wider and wider range in effective temperature as the initial mass increases during the main sequence phase. On the contrary, sufficiently high mass-loss rates make the evolutionary sequences of most massive stars (M 60⩾Mʘ) shrink toward the zero age main sequence whenever, due to mass loss, CNO processed material is brought to the surface (Chiosi et al., 1978; de Loore et al., 1978; Maeder, 1980).

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