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

AbstractThe standard theory of radiation driven winds has provided a useful framework to understand stellar winds arising from massive stars (O stars, Wolf-Rayet stars, and luminous blue variables). However, with new diagnostics, and advances in spectral modeling, deficiencies in our understanding of stellar winds have been thrust to the forefront of our research efforts. Spectroscopic observations and analyses have shown the importance of inhomogeneities in stellar winds, and revealed that there are fundamental discrepancies between predicted and theoretical mass-loss rates. For late O stars, spectroscopic analyses derive mass-loss rates significantly lower than predicted. For all O stars, observed X-ray fluxes are difficult to reproduce using standard shock theory, while observed X-ray profiles indicate lower mass-loss rates, the potential importance of porosity effects, and an origin surprisingly close to the stellar photosphere. In O stars with weak winds, X-rays play a crucial role in determining the ionization balance, and must be taken into account.

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Clumps in stellar winds

ASTRA Proceedings ◽

10.5194/ap-1-39-2014 ◽

2014 ◽

Vol 1 ◽

pp. 39-41 ◽

Cited By ~ 1

Author(s):

J. S. Vink

Keyword(s):

Mass Loss ◽

Massive Stars ◽

Stellar Winds ◽

Present Evidence ◽

Close Proximity ◽

Stellar Photosphere ◽

Loss Rates

Abstract. We discuss the origin and quantification of wind clumping and mass–loss rates (Ṁ), particularly in close proximity to the Eddington (Γ) limit, relevant for very massive stars (VMS). We present evidence that clumping may not be the result of the line-deshadowing instability (LDI), but that clumps are already present in the stellar photosphere.

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Stellar Winds and Mass-Loss Rates from Be Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900038055 ◽

1982 ◽

Vol 98 ◽

pp. 377-385 ◽

Cited By ~ 1

Author(s):

Theodore P. Snow

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Stellar Winds ◽

Be Stars ◽

Line Profiles ◽

Sample Group ◽

Show Evidence ◽

Acceleration Zone ◽

Low Levels ◽

Loss Rates

Resonance-line profiles of SiIII and SiIV lines in 22 B and Be stars have been analyzed in the derivation of mass-loss rates. Of the 19 known Be or shell stars in the sample group, all but one show evidence of winds. It is argued that for stars of spectral type B1.5 and later, SiIII and SiIV are the dominant stages of ionization, and this conclusion, together with theoretical fits to the line profiles, leads to mass-loss rates between 10-11 and 3 × 10-9 for the stars. The rate of mass loss does not correlate simply with stellar parameters, and probably is variable with time. The narrow FeIII shell lines often seen in the ultraviolet spectra of Be stars may arise at low levels in the wind, below the strong acceleration zone. The mass-loss rates from Be stars are apparently insufficient to affect stellar evolution.

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Massive stars: stellar models and stellar yields, impact on Galactic Archaeology

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317010808 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 170-177

Author(s):

Georges Meynet ◽

Arthur Choplin ◽

Sylvia Ekström ◽

Cyril Georgy

Keyword(s):

Magnetic Fields ◽

Mass Loss ◽

Massive Stars ◽

Stellar Winds ◽

Stellar Models ◽

The Impact

AbstractThe physics of massive stars depends (at least) on convection, mass loss by stellar winds, rotation, magnetic fields and multiplicity. We briefly discuss the impact of the first three processes on the stellar yields trying to identify some guidelines for future works.

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Spectroscopy of complete populations of Wolf-Rayet binaries in the Magellanic Clouds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001303 ◽

2018 ◽

Vol 14 (S346) ◽

pp. 307-315

Author(s):

Tomer Shenar ◽

R. Hainich ◽

W.-R. Hamann ◽

A. F. J. Moffat ◽

H. Todt ◽

...

Keyword(s):

Spectral Analysis ◽

Mass Loss ◽

Massive Stars ◽

Large Population ◽

Magellanic Clouds ◽

Binary Interaction ◽

Stellar Winds ◽

Single Star ◽

Mass Removal ◽

Star Evolution

AbstractClassical Wolf-Rayet stars are evolved, hydrogen depleted massive stars that exhibit strong mass-loss. In theory, these stars can form either by intrinsic mass loss (stellar winds or eruptions), or via mass-removal in binaries. The Wolf-Rayet stars in the Magellanic Clouds are often thought to have originated through binary interaction due to the low ambient metallicity and, correspondingly, reduced wind mass-loss. We performed a complete spectral analysis of all known WR binaries of the nitrogen sequence in the Small and Large Magellanic Clouds, as well as additional orbital analyses, and constrained the evolutionary histories of these stars. We find that the bulk of Wolf-Rayet stars are luminous enough to be explained by single-star evolution. In contrast to prediction, we do not find clear evidence for a large population of low-luminosity Wolf-Rayet stars that could only form via binary interaction, suggesting a discrepancy between predictions and observations.

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The Brightest Stars in the Magellanic Clouds and Other Late-Type Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900040134 ◽

1984 ◽

Vol 108 ◽

pp. 145-156

Author(s):

Roberta M. Humphreys

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Stellar Population ◽

Massive Stars ◽

Magellanic Clouds ◽

Stellar Winds ◽

Stellar Content ◽

Late Type ◽

Observational Astronomy ◽

Distant Galaxies

The brightest stars always receive considerable attention in observational astronomy, but why are we so interested in these most luminous, and therefore most massive stars? These stars are our first probes for exploring the stellar content of distant galaxies. Admittedly, they are only the tip of the iceberg for the whole stellar population and very interesting processes are occurring among the less massive, older stars, but the most massive stars are our first indicators for studies of stellar evolution in other galaxies. They provide the first hint that stellar evolution may have been different in a particular galaxy because they evolve so quickly. The most luminous stars also highly influence their environments via their strong stellar winds and mass loss and eventually as supernovae.

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New models of massive and Wolf-Rayet stars with mass loss and rotation

Symposium - International Astronomical Union ◽

10.1017/s0074180900205287 ◽

1999 ◽

Vol 193 ◽

pp. 177-186 ◽

Cited By ~ 1

Author(s):

André Maeder

Keyword(s):

Mass Loss ◽

Massive Stars ◽

Life Time ◽

Structural Equations ◽

Be Stars ◽

Rotating Stars ◽

Physical Treatment ◽

B Stars ◽

History Of ◽

New Treatments

We give results of models of massive stars which have a detailed physical treatment of rotation, including structural equations for shellular rotation, new treatments of shears in differentially rotating stars and of meridional circulation, together with mass loss rates depending on rotation. For a 20 M⊙ star, He- and N-enrichments at the stellar surface already occur during the MS phase for moderately low rotational velocities, thus most supergiants are enriched in helium and nitrogen. A long B- and A-supergiant phase results from rotational mixing, with some primary nitrogen formed at this stage. For the most massive stars, rotation makes the star to enter the WR stage during the MS phase thus avoiding the LBV and red supergiant stage.The WR life-times are considerably increased by rotation and the minimum mass for forming WR stars is lowered. Interestingly enough, the increase of the WN life-time is larger than for WC stars, so that rotation leads to a decrease of the WC/WN number ratio. Also, the fraction of transition WN/WC stars is much larger at higher rotation.Finally, on the basis of clusters in the SMC, in the LMC and towards the galactic interior and exterior, we show that for clusters with ages between about 1 and 3 x 107 yr the fraction of Be stars with respect to normal B stars is larger at lower metallicities. This may suggest a higher rotation at lower metallicities for massive stars, due to a different history of star formation.

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Mass-Loss From Spinning Stars

Highlights of Astronomy ◽

10.1017/s1539299600004494 ◽

1980 ◽

Vol 5 ◽

pp. 601-613

Author(s):

S. R. Sreenivasan

Keyword(s):

Angular Momentum ◽

Mass Loss ◽

Massive Stars ◽

Stellar Winds ◽

Late Type ◽

Momentum Loss ◽

Adequate Understanding ◽

Angular Momentum Loss ◽

Evolutionary Consequences ◽

Acceptable Theory

AbstractThe effects of mass-loss and angular momentum loss on the evolution of massive stars are discussed bringing out the main results as well as the limitations of recent studies. It is pointed out that an acceptable theory of stellar winds in early as well as late type stars is needed as well as a satisfactory assessment of a number of instabilities in these contexts for an adequate understanding of the evolutionary consequences for a wide variety of population I and polulation II stars, which are affected by mass-loss.

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