scholarly journals Wolf Rayet stars in galaxies and the role of binaries and hydrodynamics

1995 ◽  
Vol 163 ◽  
pp. 280-290
Author(s):  
André Maeder
Keyword(s):  
Mass Transfer ◽  
Massive Star ◽  
Main Sequence ◽  
Stellar Winds ◽  
Star Evolution ◽  
Model Independent ◽  
Domain Of Parameters ◽  
Massive Star Evolution ◽  
Good Agreement

WR stars obey M-L-·-Teff-R-chemistry relations, which are in general model independent (with the exception of chemistry). The processes of WR formation (stellar winds, hydrodynamical mixing, binary mass transfer etc.) influence, however, the domain of parameters occupied by WR stars. We specifically examine the distribution of luminosities and H-contents of WN stars, which both support heavy mass loss rates, or possibly mixing, in the main sequence and WNL phases. Detailed studies of the number ratios WR/O, WC/WN, WC/WR, etc. are made for galaxies at various metallicities Z which exhibit extremely different WR populations. Good agreement of models and observations is found. It is also shown that the data are better explained if a certain fraction Φ (less than 10%) of the O-stars become WR stars, preferentially of type WNE as a result of Roche lobe overflow (RLOF) in binaries. This result necessarily implies that the fraction of WR stars, owing their existence to RLOF, is variable with Z, being nearly 100% at low Z and much smaller at high Z. We also identify several hydrodynamical developments physically required in stellar models. Among them, we collect the available observational and theoretical arguments supporting an important role of mixing in massive star evolution.

scholarly journals The Point on the Theoretical Changes of Surface Chemistry During Massive Star Evolution

1988 ◽  
Vol 108 ◽  
pp. 79-85
Author(s):  
André Maeder
Keyword(s):  
Surface Chemistry ◽  
Cross Sections ◽  
Massive Star ◽  
Main Sequence ◽  
Tidal Mixing ◽  
Main Sequence Stars ◽  
Star Evolution ◽  
Cno Abundances ◽  
Massive Star Evolution ◽  
Nuclear Processing

For main sequence stars, the central nuclear processing generally has no effect on surface abundances. Later in the evolution, the newly synthetized elements may be revealed at the stellar surface by processes such as mass loss, convective dredge-up, overshooting, diffusion, rotational and tidal mixing, etc. The changes of CNO abundances are the most conspicuous and the easiest to observe spectroscopically; some abundance ratios like C/N, O/N may undergo changes by more than 102. On the whole, surface chemistry is a most powerful diagnostics of stellar evolution, model assumptions and nuclear cross sections.

scholarly journals Massive star evolution revealed in the Mass-Luminosity plane

2018 ◽  
Vol 14 (S346) ◽  
pp. 480-485
Author(s):  
Erin R. Higgins ◽  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Main Sequence ◽  
Theoretical Models ◽  
Physical Processes ◽  
Single Star ◽  
Star Evolution ◽  
Novel Method ◽  
Massive Star Evolution

AbstractMassive star evolution is dominated by key physical processes such as mass loss, convection and rotation, yet these effects are poorly constrained, even on the main sequence. We utilise a detached, eclipsing binary HD166734 as a testbed for single star evolution to calibrate new MESA stellar evolution grids. We introduce a novel method of comparing theoretical models with observations in the ‘Mass-Luminosity Plane’, as an equivalent to the HRD (see Higgins & Vink 2018). We reproduce stellar parameters and abundances of HD166734 with enhanced overshooting (αov=0.5), mass loss and rotational mixing. When comparing the constraints of our testbed to the systematic grid of models we find that a higher value of αov=0.5 (rather than αov=0.1) results in a solution which is more likely to evolve to a neutron star than a black hole, due to a lower value of the compactness parameter.

scholarly journals Massive star evolution: rotation, winds, and overshooting vectors in the mass-luminosity plane

2019 ◽  
Vol 622 ◽  
pp. A50 ◽  
Author(s):  
Erin R. Higgins ◽  
Jorick S. Vink
Keyword(s):  
Binary System ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Main Sequence ◽  
Test Bed ◽  
Star Evolution ◽  
Red Supergiants ◽  
Nitrogen Abundance ◽  
Massive Star Evolution

Context. Massive star evolution is dominated by various physical effects, including mass loss, overshooting, and rotation, but the prescriptions of their effects are poorly constrained and even affect our understanding of the main sequence. Aims. We aim to constrain massive star evolution models using the unique test-bed eclipsing binary HD 166734 with new grids of MESA stellar evolution models, adopting calibrated prescriptions of overshooting, mass loss, and rotation. Methods. We introduce a novel tool, called the mass-luminosity plane or M−L plane, as an equivalent to the traditional HR diagram, utilising it to reproduce the test-bed binary HD 166734 with newly calibrated MESA stellar evolution models for single stars. Results. We can only reproduce the Galactic binary system with an enhanced amount of core overshooting (αov = 0.5), mass loss, and rotational mixing. We can utilise the gradient in the M−L plane to constrain the amount of mass loss to 0.5–1.5 times the standard prescription test-bed, and we can exclude extreme reduction or multiplication factors. The extent of the vectors in the M−L plane leads us to conclude that the amount of core overshooting is larger than is normally adopted in contemporary massive star evolution models. We furthermore conclude that rotational mixing is mandatory to obtain the correct nitrogen abundance ratios between the primary and secondary components (3:1) in our test-bed binary system. Conclusions. Our calibrated grid of models, alongside our new M−L plane approach, present the possibility of a widened main sequence due to an increased demand for core overshooting. The increased amount of core overshooting is not only needed to explain the extended main sequence, but the enhanced overshooting is also needed to explain the location of the upper-luminosity limit of the red supergiants. Finally, the increased amount of core overshooting has – via the compactness parameter – implications for supernova explodability.

scholarly journals How common is LBV S Doradus variability at low metallicity?

2018 ◽  
Vol 618 ◽  
pp. A17 ◽  
Author(s):  
V. M. Kalari ◽  
J. S. Vink ◽  
P. L. Dufton ◽  
M. Fraser
Keyword(s):  
Mass Loss ◽  
Effective Temperature ◽  
Massive Star ◽  
Stellar Winds ◽  
First Stars ◽  
Star Evolution ◽  
Low Metallicity ◽  
Bona Fide ◽  
Massive Star Evolution ◽  
Luminous Blue Variable

It remains unclear whether massive star evolution is facilitated by mass loss through stellar winds only or whether episodic mass loss during an eruptive luminous blue variable (LBV) phase is also significant. LBVs exhibit unique photometric and spectroscopic variability (termed S Doradus variables). This may have tremendous implications for our understanding of the first stars, gravitational wave events, and supernovae. A key question here is whether all evolved massive stars passing through the blue supergiant phase are dormant S Doradus variables transforming during a brief period or whether LBVs are truly unique objects. By investigating the OGLE light curves of 64 B supergiants (Bsgs) in the Small Magellanic Cloud (SMC) on a timescale of three years with a cadence of one night, the incidence of S Doradus variables amongst the Bsgs population is investigated. From our sample, we find just one Bsg, AzV 261, that displays the photometric behaviour characteristic of S Doradus variables. We obtain and study a new VLT X-shooter spectrum of AzV 261 in order to investigate whether the object has changed its effective temperature over the last decade. We do not find any effective temperature variations indicating that the object is unlikely to be a LBV S Doradus variable. As there is only one previous bona fide S Doradus variable known to be present in the SMC (R 40), we find the maximum duration of the LBV phase in the SMC to be at most a few 103 yr or more likely that canonical Bsgs, and S Doradus LBVs are intrinsically different objects. We discuss the implications for massive star evolution in low-metallicity environments, characteristic of the early Universe.

scholarly journals Massive star evolution in the Small Magellanic Cloud

2003 ◽  
Vol 212 ◽  
pp. 308-315 ◽  
Author(s):  
Daniel J. Lennon
Keyword(s):  
Stellar Evolution ◽  
Massive Star ◽  
Main Sequence ◽  
Single Star ◽  
Promising Alternative ◽  
Star Models ◽  
Abundance Patterns ◽  
Star Evolution ◽  
Type Giant ◽  
Massive Star Evolution

We discuss abundances for eight early B-type giant/supergiant stars in the SMC cluster NGC 330. All are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field. Given the number of B-type stars with low rotational projected velocities in NGC 330 (all our targets have v sin i < 50 kms–1), we suggest that it is unlikely that the stars in our sample are seen almost pole-on, but rather that they are intrinsically slow rotators. Comparing these results with the predictions of stellar evolution models including the effects of rotationally induced mixing, we conclude that while the abundance patterns may indeed be reproduced, those models with initially large rotational velocities do not reproduce the observed range of effective temperatures of our sample, nor the currently observed rotational velocities. Binary models may be able to produce stars in the observed temperature range and provide a promising alternative to single star models for explaining the observations. We also discuss the clear need for stellar evolution calculations employing the correct chemical mix of carbon, nitrogen and oxygen for the SMC.

scholarly journals Evolution of High Mass Stars

1986 ◽  
Vol 7 ◽  
pp. 475-479
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Massive Stars ◽  
High Mass ◽  
Stellar Winds ◽  
Star Evolution ◽  
Interstellar Material ◽  
Massive Star Evolution

Several properties of massive star evolution are of great interest for the understanding of young populations in galaxies: -the genetic connections predicted by the models for the various types of massive stars allow us to understand their filiation; -in order to study the differences of the relative star frequencies in galaxies, we have to know which properties affect the lifetimes in the various evolutionary stages; -the composition of stellar winds is interesting to discuss the wind injections into the interstellar material, particularly the injections by Wolf-Rayet stars, and to discuss the influence of mass loss on nucleosynthesis and chemical yields. Here we shall briefly summarize some recent results on these various problems. For more details the reader may refer to general reviews (cf. Humphreys, 1984; Maeder, 1984a,b; Chiosi and Maeder, 1986).

scholarly journals Properties of OB star−black hole systems derived from detailed binary evolution models

2020 ◽  
Vol 638 ◽  
pp. A39 ◽  
Author(s):  
N. Langer ◽  
C. Schürmann ◽  
K. Stoll ◽  
P. Marchant ◽  
D. J. Lennon ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Radial Velocity ◽  
Massive Star ◽  
Main Sequence ◽  
X Ray ◽  
Black Hole Binaries ◽  
Star Evolution ◽  
Binary Evolution ◽  
Massive Star Evolution

Context. The recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. It is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes. Aims. A promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples, such as the population in 30 Doradus in the Large Magellanic Cloud (LMC). Methods. With this purpose in mind, we analysed a large grid of detailed binary evolution models at LMC metallicity with initial primary masses between 10 and 40 M⊙, and identified the model systems that potentially evolve into a binary consisting of a black hole and a massive main-sequence star. We then derived the observable properties of such systems, as well as peculiarities of the OB star component. Results. We find that ∼3% of the LMC late-O and early-B stars in binaries are expected to possess a black hole companion when stars with a final helium core mass above 6.6 M⊙ are assumed to form black holes. While the vast majority of them may be X-ray quiet, our models suggest that these black holes may be identified in spectroscopic binaries, either by large amplitude radial velocity variations (≳50 km s−1) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity (≳10 km s−1) and simultaneous rapid rotation of the OB star. The predicted mass ratios are such that main-sequence companions can be excluded in most cases. A comparison to the observed OB+WR binaries in the LMC, Be and X-ray binaries, and known massive black hole binaries supports our conclusion. Conclusions. We expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general and for the formation of double black hole mergers in particular.

scholarly journals The dynamics of red supergiant winds

2002 ◽  
Vol 206 ◽  
pp. 306-309
Author(s):  
Anita M. S. Richards ◽  
Raymond J. Cohen ◽  
Malcolm D. Gray ◽  
Koji Murakawa ◽  
Jeremy A. Yates ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Supernova Remnant ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Stellar Winds ◽  
Maser Emission ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Loss Rates

During the red supergiant (RSG) stage of massive star evolution, emission from dust and molecules allows the copious stellar winds to be studied in great detail. This help us understand not only the evolutionary stages of the star (which are highly dependent on mass loss rates), but also the morphology of the eventual supernova remnant. Maser emission from OH and H2O has been mapped with milli-arcsec resolution (using MERLIN and the EVN/global VLBI) around RSG including VY CMa, S Per and VX Sgr. The H2O masers originate in clouds accelerating away from the star and OH mainlines masers interleave the outer parts of the H2O maser shell. Zeeman splitting of OH maser lines reveals the orientation and strength of stellar-centred magnetic fields.

scholarly journals Massive Star Evolution: Mass Loss and Mixing

1986 ◽  
Vol 116 ◽  
pp. 287-300
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Main Sequence ◽  
Relative Mass ◽  
Physical Processes ◽  
Mixing Processes ◽  
Physical Reason ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Evolutionary Consequences

At first it may be surprising that mass loss, overshooting and mixing, which are indeed very different physical processes, have similar consequences on stellar evolution. These various processes may increase the Main-Sequence (MS) lifetime, extend the width of the MS, bring CNO-processed materials to stellar surfaces and, in extreme cases, lead to quasi-homogeneous evolution. The physical reason of this similarity is that these processes increase the relative mass fraction of the stellar cores. Thus we understand that, on the basis of their evolutionary consequences, it may not be easy to disentangle the contributions of mass loss, overshooting and mixing processes. The present status of our knowledge on these effects, which appear to have major consequences on the evolution of massive stars, is now examined in detail.

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