Populations of rotating stars II. Rapid rotators and their link to Be-type stars

Abstract

Even though it is broadly accepted that single Be stars are rapidly rotating stars surrounded by a flat rotating circumstellar disk, there is still a debate about how fast these stars rotate and also about the mechanisms involved in the angular-momentum and mass input in the disk. We study the properties of stars that rotate near their critical-rotation rate and investigate the properties of the disks formed by equatorial mass ejections. We used the most recent Geneva stellar evolutionary tracks for rapidly rotating stars that reach the critical limit and used a simple model for the disk structure. We obtain that for a 9 Msun star at solar metallicity, the minimum average velocity during the Main Sequence phase to reach the critical velocity is around 330 km/s, whereas it would be 390 km/s at the metallicity of the Small Magellanic Cloud (SMC). Red giants or supergiants originating from very rapid rotators rotate six times faster and show N/C ratios three times higher than those originating from slowly rotating stars. This difference becomes stronger at lower metallicity. It might therefore be very interesting to study the red giants in clusters that show a large number of Be stars on the MS band. On the basis of our single-star models, we show that the observed Be-star fraction with cluster age is compatible with the existence of a temperature-dependent lower limit in the velocity rate required for a star to become a Be star. The mass, extension, and diffusion time of the disks produced when the star is losing mass at the critical velocity, obtained from simple parametrized expressions, are not too far from those estimated for disks around Be-type stars. At a given metallicity, the mass and the extension of the disk increase with the initial mass and with age on the MS phase. Denser disks are expected in low-metallicity regions.

Accepted for publication in A&A, language edited

References in corpus (3)

• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• Populations of rotating stars. - I. Models from 1.7 to 15 Msun at Z = 0.014, 0.006, and 0.002 with Ω/Ωcrit between 0 and 1
• A Pulsational Mechanism for Producing Keplerian Disks around Be Stars

Cited by in corpus (54)

• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• Investigating the lack of main-sequence companions to massive Be stars
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Spectral and spatial imaging of the Be+sdO binary phi Persei
• The life cycles of Be viscous decretion discs: time-dependent modelling of infrared continuum observations
• A high fraction of Be stars in young massive clusters: evidence for a large population of near-critically rotating stars
• Prevalence of SED turndown among classical Be stars: Are all Be stars close binaries?
• The life cycles of Be viscous decretion discs: The case of ω CMa
• The Single Star Path to Be Stars
• The pseudo-photosphere model for the continuum emission of gaseous discs
• gamma Cas stars: Normal Be stars with disks impacted by the wind of a helium-star companion?
• Multiple stellar populations and their evolution in globular clusters: A nucleosynthesis perspective
• NGC 6067: a young and massive open cluster with high metallicity
• The effects of stellar rotation along the main sequence of the 100 Myr old massive cluster NGC 1850
• Stellar wind models of subluminous hot stars
• The orbital and physical properties of five southern Be+sdO binary systems
• On the formation and evolution of the first Be star in a black hole binary MWC 656
• Evidence for Different Disk Mass Distributions Between Early and Late-Type Be Stars in the BeSOS Survey
• Critical angular velocity and anisotropic mass loss of rotating stars with radiation-driven winds
• Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)
• Angular momentum transport by stochastically excited oscillations in rapidly rotating massive stars
• Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters
• Time-dependent modeling of extended thin decretion disks of critically rotating stars
• Rotational Mixing in Be Stars: Nitrogen Abundances for a Sample of Be Stars from the MiMeS Survey
• Stellar parameters of Be stars observed with X-shooter
• Evidence of the Evolved Nature of the B[e] Star MWC 137
• Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of $\nu$ Puppis (B7-8 IIIe)
• Short-term variability and mass loss in Be stars V. Space photometry and ground-based spectroscopy of $\gamma$ Cas
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• The evolution of single B-type stars with a large angular momentum content
• Centrifugally Driven Mass Loss and Outbursts of Massive Stars
• Modeling of interactions between supernovae ejecta and aspherical circumstellar environments
• Two-dimensional modeling of density and thermal structure of dense circumstellar outflowing disks
• Viscous decretion discs around rapidly rotating stars
• On the role of dust and mass loss in the extended main sequence turnoff of star clusters: the case of NGC 1783
• Stellar Inclination Angles from Be Star H$\alpha$ Emission-Line Profiles
• Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks
• Quiescent and active phases in Be stars: A WISE snapshot of young galactic open clusters
• PARSEC V2.0: Rotating tracks and isochrones for seven addtional metallicities in the range Z=0.0001-0.03
• Newborn Be star systems observed shortly after mass transfer
• A model of anisotropic winds from rotating stars for evolutionary calculations
• HD 60431, the CP2 star with the shortest rotational period -- Physical parameters and period analysis
• A Be Star + He Star Binary as an Indicator of a Binary Mass Transfer Phase
• Pulsation-driven mean zonal and meridional flows in rotating massive stars
• The ultraviolet study of B[e] stars: evidence for pulsations, LBV-type variations, and processes in envelope
• NGC 663 as a laboratory for massive star evolution
• The Puzzling Spectrum of HD 94509
• Angular Momentum Loss Rates in Be Stars Determined by the Viscous Decretion Disc Model
• The rotational shear in pre-collapse cores of massive stars
• The B and Be States of the Star EM Cepheus
• 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