The single star path to Be stars
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TLDR
In this article, the authors identify the main effects which are responsible for single stars to approach critical rotation as functions of initial mass and metallicity, and predict the properties of populations of rotating single stars.Abstract:
Be stars are rapidly rotating B main sequence stars, which show line emission due to an outflowing disc. By studying the evolution of rotating single star models, we can assess their contribution to the observed Be star populations.
We identify the main effects which are responsible for single stars to approach critical rotation as functions of initial mass and metallicity, and predict the properties of populations of rotating single stars.
We perform population synthesis with single star models of initial masses ranging between 3 and 30 solar masses, initial equatorial rotation velocities between 0 and 600 kms$^{-1}$ at compositions representing the Milky Way, Large and Small Magellanic Clouds. These models include efficient core-envelope coupling mediated by internal magnetic fields and correspond to the maximum efficiency of Be star production. We predict Be star fractions and the positions of fast rotating stars in the colour-magnitude diagram.
We identify stellar wind mass-loss and the convective core mass fraction as the key parameters which determine the time dependance of the stellar rotation rates. Using empirical distributions of initial rotational velocities,our single star models can reproduce the trends observed in Be star fractions with mass and metallicity. However,they fail to produce a significant number of stars rotating very close to critical. We also find that rapidly rotating Be stars in the Magellanic Clouds should have significant surface nitrogen enrichments, which may be in conflict with abundance determinations of Be stars.
Single star evolution may explain the high number of Be stars if 70 to 80% of critical rotationwould be sufficient to produce the Be phenomenon. However even in this case, the unexplained presence of many Be stars far below the cluster turn-off indicates the importance of the binary channel for Be star production.read more
Citations
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The VLT-FLAMES Tarantula Survey X: Evidence for a bimodal distribution of rotational velocities for the single early B-type stars
Philip Dufton,Norbert Langer,P. R. Dunstall,Chris Evans,Ines Brott,S. E. de Mink,S. E. de Mink,Ian D. Howarth,Michael B. Kennedy,C. M. McEvoy,A. T. Potter,O.H. Ramírez-Agudelo,Hugues Sana,Sergio Simón-Díaz,Sergio Simón-Díaz,William Taylor,Jorick S. Vink +16 more
TL;DR: In this paper, the Fourier transforms of spectral lines were used to estimate the rotational velocities of stars in the VLT-FLAMES Tarantula survey and the estimates were analyzed to infer the underlying rotational velocity distribution.
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Properties of OB star-black hole systems derived from detailed binary evolution models
Norbert Langer,Norbert Langer,C. Schürmann,C. Schürmann,K. Stoll,Pablo Marchant,Pablo Marchant,D. J. Lennon,D. J. Lennon,Laurent Mahy,S. E. de Mink,S. E. de Mink,M. Quast,W. Riedel,Hugues Sana,Peter Schneider,A. Schootemeijer,Chen Wang,Leonardo A. Almeida,Joachim M. Bestenlehner,J. Bodensteiner,Norberto Castro,Simon Clark,Paul A. Crowther,Philip Dufton,Chris Evans,Luca Fossati,Götz Gräfener,L. Grassitelli,N. J. Grin,Ben Hastings,A. Herrero,A. de Koter,A. de Koter,Athira Menon,Lee Patrick,Joachim Puls,Mathieu Renzo,Mathieu Renzo,Andreas Sander,Fabian Schneider,Fabian Schneider,K. Sen,K. Sen,Tomer Shenar,S. Simón-Días,Thomas M. Tauris,Frank Tramper,Jorick S. Vink,X. T. Xu +49 more
TL;DR: In this article, the authors analyzed 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.
Journal ArticleDOI
Investigating the lack of main-sequence companions to massive Be stars
TL;DR: In this paper, an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars was conducted to investigate whether Be binaries with MS companions are known to exist.
Journal ArticleDOI
Investigating the lack of main-sequence companions to massive Be stars
TL;DR: In this article, an extensive, star-by-star review of the literature of a magnitude-limited sample of early-type Be stars with main-sequence (MS) companions is performed.
Journal ArticleDOI
Stellar mergers as the origin of the blue main-sequence band in young star clusters
Cheng Wang,Norbert Langer,A. Schootemeijer,Antonino Milone,Ben Hastings,Xiao-Tian Xu,J. Bodensteiner,Hugues Sana,Norberto Castro,D. J. Lennon,Pablo Marchant,A. de Koter,S. E. de Mink +12 more
TL;DR: In this paper , the authors derived the masses of the blue MS stars, and found that they follow a nearly flat mass function, which supports their unusual formation path, and shed new light on the origin of the bi-modal mass, spin, and magnetic field distributions of main-sequence stars.
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