scholarly journals Helium-star Mass Loss and Its Implications for Black Hole Formation and Supernova Progenitors

2002 ◽  
Vol 19 (2) ◽  
pp. 233-237 ◽  
Author(s):  
Onno R. Pols ◽  
Jasinta D. M. Dewi
Keyword(s):  
Black Hole ◽  
Mass Loss ◽  
High Mass ◽  
Binary Interaction ◽  
Compact Binary ◽  
Helium Stars ◽  
High Mass Loss ◽  
Helium Star ◽  
Black Hole Masses ◽  
Loss Rates

AbstractRecently the observationally derived stellar-wind mass-loss rates for Wolf-Rayet stars, or massive naked helium stars, have been revised downwards by a substantial amount. We present evolutionary calculations of helium stars incorporating such revised mass-loss rates, as well as mass transfer to a close compact binary companion. Our models reach final masses well in excess of 10 M⊙, consistent with the observed masses of black holes in X-ray binaries. This resolves the discrepancy found with previously assumed high mass-loss rates between the final masses of stars which spend most of their helium-burning lifetime as Wolf-Rayet stars (˜3 M⊙) and the minimum observed black hole masses (6 M⊙). Our calculations also suggest that there are two distinct classes of progenitors for Type Ic supernovae: one with very large initial masses (35 M⊙), which are still massive when they explode and leave black hole remnants, and one with moderate initial masses (˜12–20 M⊙) undergoing binary interaction, which end up with small pre-explosion masses and leave neutron star remnants.

scholarly journals ISOCAM and DENIS Survey of 0.5 square degrees in the Bar of the LMC. Detection of the whole TP-AGB Star Population

1999 ◽  
Vol 191 ◽  
pp. 561-566
Author(s):  
C. Loup ◽  
E. Josselin ◽  
M.-R. Cioni ◽  
H.J. Habing ◽  
J.A.D.L. Blommaert ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Complete Sample ◽  
High Mass Loss ◽  
Low Mass ◽  
The One ◽  
Good Agreement ◽  
Loss Rates

We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

scholarly journals Observational connections between LBV’s and other stars, with emphasis on Wolf-Rayet stars

1989 ◽  
Vol 113 ◽  
pp. 229-240
Author(s):  
A. F. J. Moffat ◽  
L. Drissen ◽  
C. Robert
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Underlying Mechanism ◽  
High Mass ◽  
Strong Line ◽  
Essential Step ◽  
High Mass Loss ◽  
Loss Rates ◽  
R Domain

Abstract.We suggest that the LBV mechanism is an essential step to “force” massive stars (M(ZAMS) ≥ 40M⊙) to finally enter the Wolf-Rayet (W-R) domain in the Hertzsprung-Russel diagram (HRD). Just as massive supergiants showincreasingvariability as theyapproachthe Humphreys-Davidson (H-D)instability limit (horizontally in the HRD diagram), so the W-R stars showdecreasingvariability as theyrecede fromthe H-D limit (at first horizontally into the WNL domain, then, with their high mass loss rates, plunging irreversably downwards as ever hotter, smaller and fainter, strong-line W-R stars). Among the W-R stars, the luminous WNL subtypes (especially WN8) are the most variable, probably as a consequence of blob ejection in the wind. The underlying mechanism which triggers this ejection is possibly related to wind instabilities and may thus be quite different from the source of variability in luminous supergiants or LBV’s in quiescence, where photospheric effects dominate.

scholarly journals Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate

1995 ◽  
Vol 163 ◽  
pp. 318-319
Author(s):  
G. Meynet
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
High Mass ◽  
New Models ◽  
Theoretical Predictions ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

scholarly journals Wolf-Rayet stars in I Zw 18

1999 ◽  
Vol 193 ◽  
pp. 606-607
Author(s):  
Francoid Legrand ◽  
Daniel Kunth ◽  
Jean-René Roy ◽  
J. Miguel Mas-Hesse ◽  
Jeremy R. Walsh
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Mass ◽  
Starburst Galaxy ◽  
Individual Stars ◽  
Binary Channel ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates ◽  
Integrated Luminosity

Wolf-Rayet stars have been detected in the NW region of the metal–poor starburst galaxy I Zw 18. The integrated luminosity and FWHM of the bumps at 4650 Å and 5808 Å are consistent with the presence of a few individual stars of WC4 or WC5 type. The unexpected presence of WC stars in such a low-metallicity galaxy could, however, be explained by high mass loss rates, or alternatively favor a binary channel for WR formation. WC stars could also account for the strong and narrow He II 4686Å emission line which peaks co-spatially with the WR bump emission (see Schaerer 1996).

scholarly journals Helium stars: Towards an understanding of Wolf–Rayet evolution

2016 ◽  
Vol 12 (S329) ◽  
pp. 255-259
Author(s):  
Liam A. S. McClelland ◽  
J. J. Eldridge
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Convection Zone ◽  
Star Models ◽  
Surface Temperatures ◽  
Helium Stars ◽  
Pure Helium ◽  
Helium Star ◽  
Large Grid ◽  
Loss Rates

AbstractRecent observational modelling of the atmospheres of hydrogen-free Wolf–Rayet stars have indicated that their stellar surfaces are cooler than those predicted by the latest stellar evolution models. We have created a large grid of pure helium star models to investigate the dependence of the surface temperatures on factors such as the rate of mass loss and the amount of clumping in the outer convection zone. Upon comparing our results with Galactic and LMC WR observations, we find that the outer convection zones should be clumped and that the mass-loss rates need to be slightly reduced. We discuss the implications of these findings in terms of the detectability of Type Ibc supernovae progenitors, and in terms of refining the Conti scenario.

scholarly journals Masses of Magellanic Wolf-Rayet stars: mass loss and evidence for a WR subclass vs. mass relation

1981 ◽  
Vol 59 ◽  
pp. 301-305
Author(s):  
A.F.J. Moffat
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Published Data ◽  
Mass Relation ◽  
Mass Ratio ◽  
Spectroscopic Observations ◽  
High Mass Loss ◽  
Loss Rates

AbstractNew spectroscopic observations in the LMC/SMC combined with published data on Galactic WR stars lead to a correlation between mass ratio, MWR/MO, and WR subclass. As a consequence of this and their high mass loss rates, WR stars probably evolve from cool to hot ionization class in a way which depends on the metallicity.

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