The Single Star Path to Be 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.

arXiv commentin press

References in corpus (42)

• Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets
• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• Dynamo action by differential rotation in a stably stratified stellar interior
• Pre-Supernova Evolution of Massive Single and Binary Stars
• Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones
• Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields
• Evolution of rapidly rotating metal-poor massive stars towards gamma-ray bursts
• Be/X-ray binaries
• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• The rotation rates of massive stars: the role of binary interaction through tides, mass transfer and mergers
• Single star progenitors of long gamma-ray bursts I: Model grids and redshift dependent GRB rate
• Catalogue of high-mass X-ray binaries in the Galaxy ($4^{th}$ edition)
• Be-star rotation: how close to critical?
• Gravity darkening in rotating stars
• A Stellar Rotation Census of B Stars: from ZAMS to TAMS
• The VLT-FLAMES Tarantula Survey XII. Rotational velocities of the single O-type stars
• Evolution towards the critical limit and the origin of Be stars
• The VLT-FLAMES survey of massive stars: atmospheric parameters and rotational velocity distributions for B-type stars in the Magellanic Clouds
• The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters
• White dwarf spins from low mass stellar evolution models
• On the formation of Be stars through binary interaction
• The VLT-FLAMES Tarantula Survey X: Evidence for a bimodal distribution of rotational velocities for the single early B-type stars
• A comparison of evolutionary tracks for single Galactic massive stars
• Multiple stellar populations in Magellanic Cloud clusters. VI. A survey of multiple sequences and Be stars in young clusters
• Be/X-ray binaries and candidates: catalogue
• Populations of rotating stars II. Rapid rotators and their link to Be-type stars
• The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries
• Effects of metallicity, star formation conditions and evolution in B and Be stars. I: Large Magellanic Cloud, field of NGC 2004
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Prevalence of SED turndown among classical Be stars: Are all Be stars close binaries?
• Effects of close binary evolution on the main-sequence morphology of young star clusters
• Clues about the scarcity of stripped-envelope stars from the evolutionary state of the sdO+Be binary system phi Persei
• The VLT-FLAMES Tarantula Survey: The fastest rotating O-type star and shortest period LMC pulsar - remnants of a supernova disrupted binary?
• The young massive SMC cluster NGC 330 seen by MUSE. I. Observations and stellar content
• Rotation of Early B-type Stars in the Large Magellanic Cloud - The role of evolution and metallicity
• A slitless spectroscopic survey for Halpha emission-line objects in SMC clusters
• Effects of Metallicity on the Rotation Rates of Massive Stars
• The VLT-FLAMES survey of massive stars: Nitrogen abundances for Be-type stars in the Magellanic Clouds
• A study of Be stars in the Magellanic Clouds
• Classical Oe Stars in the Field of the Small Magellanic Cloud
• A Be star with a low nitrogen abundance in the SMC cluster NGC330
• New Oe stars in LAMOST DR5

Cited by in corpus (34)

• Properties of OB star-black hole systems derived from detailed binary evolution models
• Investigating the lack of main-sequence companions to massive Be stars
• Stellar mergers as the origin of the blue main-sequence band in young star clusters
• Hubble Space Telescope survey of Magellanic Cloud star clusters. Photometry and astrometry of 113 clusters and early results
• The young massive SMC cluster NGC 330 seen by MUSE II. Multiplicity properties of the massive-star population
• Population Synthesis of Galactic Be-star Binaries with A Helium-star Companion
• The effects of stellar rotation along the main sequence of the 100 Myr old massive cluster NGC 1850
• Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)
• A dearth of young and bright massive stars in the Small Magellanic Cloud
• The B-type Binaries Characterisation Programme II. VFTS 291: A stripped star from a recent mass transfer phase
• The initial spin distribution of B-type stars revealed by the split main sequences of young star clusters
• A census of OBe stars in nearby metal-poor dwarf galaxies reveals a high fraction of extreme rotators
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• The young massive SMC cluster NGC 330 seen by MUSE III. Stellar parameters and rotational velocities
• Centrifugally Driven Mass Loss and Outbursts of Massive Stars
• Binarity at Low Metallicity (BLOeM) -- Multiplicity properties of Oe and Be stars
• Properties of the Be-type stars in 30 Doradus
• Boron depletion in Galactic early B-type stars reveals two different main sequence star populations
• The spins of stripped B stars support magnetic internal angular momentum transport
• Populations of evolved massive binary stars in the Small Magellanic Cloud I: Predictions from detailed evolution models
• Populations of evolved massive binary stars in the Small Magellanic Cloud II: Predictions from rapid binary evolution
• A model of anisotropic winds from rotating stars for evolutionary calculations
• A study of the F-giant star $\theta$ Scorpii A: a post-merger rapid rotator?
• A Be Star + He Star Binary as an Indicator of a Binary Mass Transfer Phase
• Spindown of massive main sequence stars in the Milky Way
• Thermal-timescale accretion does not always yield critical rotation in mass gainers
• NGC 663 as a laboratory for massive star evolution
• A stringent upper limit on Be star fractions produced by binary interaction
• The Blue supergiant problem and the main-sequence width
• Classical Be Stars and Classical Be Star Binaries from LAMOST DR12
• Investigation of projected rotational velocities of Be-type stars in LAMOST DR7
• Angular momentum relaxation in models of rotating early-type stars
• Viscous and centrifugal instabilities of massive stars
• The effect of near-core mixing on rejuvenation and the asteroseismic properties of massive accretors