The Evolution of Rapidly Rotating B/Be Stars

1982 ◽  
Vol 98 ◽  
pp. 299-302 ◽  
Author(s):  
A. S. Endal
Keyword(s):  
Rotation Rate ◽  
Main Sequence ◽  
Critical Value ◽  
Moment Of Inertia ◽  
Maxwellian Distribution ◽  
Be Stars ◽  
Rotating Stars ◽  
Hydrogen Burning ◽  
Critical Rotation ◽  
The Moment

Rotation can significantly change the moment-of-inertia of a main sequence star. As a result, the ZAMS rotation rate need only be within ~30% of the critical value in order to reach critical rotation during the hydrogen burning stage. Calculations of the evolution of rotating stars show that the Be stars result from a normal (Maxwellian) distribution of B-star rotation velocities.

scholarly journals A Study of Be Stars in Clusters

1976 ◽  
Vol 70 ◽  
pp. 31-32
Author(s):  
R. Schild ◽  
W. Romanishin
Keyword(s):  
Main Sequence ◽  
Sequence Evolution ◽  
Be Stars ◽  
Rotating Stars ◽  
Time Duration ◽  
Hydrogen Burning ◽  
Fourfold Increase ◽  
Cluster Membership ◽  
Galactic Clusters ◽  
Short Time

Calibrated spectrograms at Hα of 566 stars in 29 young galactic clusters led to the detection of 41 Be stars in clusters. Using cluster membership we have inferred ages and intrinsic (B – V) colors of Be stars to permit a discussion of their evolutionary states.Rotating stars can become Be stars in their early hydrogen burning evolution away from the main sequence. Both the fraction of stars showing hydrogen emission and the strength of emission appear to vary little during the first 80% of post main sequence evolution. However, at the onset of gravitational core contraction, both the fraction of stars showing emission and their mean emission strength undergo a fourfold increase. Many stars in the core contraction phase develop an intrinsic (B – V) excess of 0.15 mag. due to the H− free-bound continuum radiation. Because of the great strength of Hα emission and the short time duration of the effect, the extreme Be stars would be excellent probes for studies of spiral structure and would also serve as probes for studies of ages and distances of extragalactic systems.Analysis of the corrected colors of the Be stars in clusters suggests that the Lucy and Solomon (1970) mechanism for reduction of effective surface gravity by ultraviolet resonance line scattering is probably important for the hotter Be stars. However, a discrepancy exists for the cooler stars between the predicted and observed colors.

scholarly journals Applegate mechanism in post-common-envelope binaries: Investigating the role of rotation

2018 ◽  
Vol 615 ◽  
pp. A81 ◽  
Author(s):  
F. H. Navarrete ◽  
D. R. G. Schleicher ◽  
J. Zamponi Fuentealba ◽  
M. Völschow
Keyword(s):  
Orbital Period ◽  
Rotation Rate ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Main Sequence Star ◽  
Common Envelope ◽  
Rotation Rates ◽  
Critical Rotation ◽  
Period Variations ◽  
Time Variations

Context. Eclipsing time variations are observed in many close binary systems. In particular, for several post-common-envelope binaries (PCEBs) that consist of a white dwarf and a main sequence star, the observed-minus-calculated (O–C) diagram suggests that real or apparent orbital period variations are driven by Jupiter-mass planets or as a result of magnetic activity, the so-called Applegate mechanism. The latter explains orbital period variations as a result of changes in the stellar quadrupole moment due to magnetic activity. Aims. In this work we explore the feasibility of driving eclipsing time variations via the Applegate mechanism for a sample of PCEB systems, including a range of different rotation rates. Methods. We used the MESA code to evolve 12 stars with different masses and rotation rates. We applied simple dynamo models to their radial profiles to investigate the scale at which the predicted activity cycle matches the observed modulation period, and quantifiy the uncertainty. We further calculated the required energies to drive the Applegate mechanism. Results. We show that the Applegate mechanism is energetically feasible in 5 PCEB systems. In RX J2130.6+4710, it may be feasible as well considering the uncertainties. We note that these are the systems with the highest rotation rate compared to the critical rotation rate of the main-sequence star. Conclusions. The results suggest that the ratio of physical to critical rotation rate in the main sequence star is an important indicator for the feasibility of Applegate’s mechanism, but exploring larger samples will be necessary to probe this hypothesis.

scholarly journals The Evolution of Rapidly Rotating B Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 486-499
Author(s):  
Robert Connon Smith
Keyword(s):  
Main Sequence ◽  
Review Paper ◽  
Rotation Axis ◽  
Evolutionary Stage ◽  
Radial Pulsation ◽  
Be Stars ◽  
Rotating Stars ◽  
B Stars ◽  
Sequence Band ◽  
Main Effects

AbstractBe stars are located in or near the main-sequence band for non-rotating stars. Although this stage of evolution is relatively well understood, there are two main effects that make it impossible to say whether all Be stars are in the same stage of evolution and, if so, what that stage is. One effect is the spread in observed magnitude and colour as a result of rotation. Correction for rotation is not possible because of the unknown inclination of any particular star's rotation axis to the line of sight and because it is not clear what the internal angular momentum distribution is or how it changes as a result of evolution. The other effect is that there are uncertainties in the theoretical evolutionary tracks because the amount of convective overshooting is unclear. Other mixing mechanisms that might in principle also confuse the tracks seem to be small near the main sequence. If Be stars are related to the β Cephei and 53 Persei stars in the same part of the HR diagram, then the non-radial pulsation properties of Be stars may give a clue to their evolutionary state. The existence of a circumstellar disc or ring, however, tells us very little about the evolutionary stage of the underlying star. A useful way forward may be to try to understand individual stars in as much detail as possible.

scholarly journals Evolution of the rotational properties and nitrogen surface abundances of B-Type stellar populations

2014 ◽  
Vol 9 (S307) ◽  
pp. 102-103
Author(s):  
A. Granada ◽  
G. Meynet ◽  
S. Ekström ◽  
C. Georgy ◽  
L. Haemmerlé
Keyword(s):  
Main Sequence ◽  
Chemical Species ◽  
Stellar Populations ◽  
Be Stars ◽  
Population Synthesis ◽  
Rotating Stars ◽  
Surface Enrichment ◽  
Stellar Rotation ◽  
Abundance Anomalies ◽  
Synthetic Intermediate

AbstractStellar evolution models predict that rotation induces the mixing of chemical species, with the subsequent surface abundance anomalies relative to single non-rotating models, even during the main sequence (MS) evolution. The lack of measurable nitrogen surface enrichment in MS rotating stars, such as Be stars, has been interpreted as being in conflict with evolutionary models (e.g. Lennon et al. 2005; Hunter et al. 2008). In order to have an insight on the kind of ambient we do or we do not expect to find enriched rotating stars, we use our new population synthesis code, to produce synthetic intermediate-mass stellar populations fully accounting for stellar rotation effects, and study their evolution in time.

scholarly journals Results from a recent stellar rotation census of B stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 89-90
Author(s):  
Wenjin Huang ◽  
Douglas R. Gies ◽  
M. Virginia McSwain
Keyword(s):  
Effective Temperature ◽  
Rotation Rate ◽  
Rotation Speed ◽  
Rotational Velocity ◽  
Rotation Velocity ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Critical Rotation ◽  
Critical Rotation Speed

AbstractIn an analysis of the rotational properties of more than 1100 B stars (~660 cluster and ~500 field B stars), we determine the projected rotational velocity (V sin i), effective temperature, gravity, mass, and critical rotation speed for each star. The new data provide us a solid observational base to explore many hot topics in this area: Why do field B stars rotate slower than cluster B stars? How fast do B stars rotate when they are just born? How fast can B stars rotate before they become Be stars? How does the rotation rate of B stars change with time? Does the evolutionary change in rotation velocity lead to the Be phenomenon? Here we report the results of our efforts in searching for answers to these questions based on the latest B star census.

scholarly journals Hydrodynamics of Decretion Disks of Rapidly Rotating Stars

2011 ◽  
Vol 7 (S282) ◽  
pp. 257-258
Author(s):  
Petr Kurfürst
Keyword(s):  
Angular Momentum ◽  
Rotational Velocity ◽  
Critical Value ◽  
Rotating Stars ◽  
Hot Stars ◽  
Radial Temperature ◽  
Critical Rotation ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Rapidly Rotating Stars

AbstractDuring the evolution of hot stars, the equatorial rotational velocity can approach its critical value. Further increase in rotation rate is not allowed, consequently mass and angular momentum loss is needed to keep the star near and below its critical rotation. The matter ejected from the equatorial surface forms the outflowing viscous decretion disk. Models of outflowing disks of hot stars have not yet been elaborated in detail, although it is clear that such disks can significantly influence the evolution of rapidly rotating stars. One of the most important features is the disk radial temperature variation because the results will help us to specify the mass and angular momentum loss of rotating stars via decretion disks.

scholarly journals Two-dimensional models of early-type fast rotating stars: the ESTER project

2015 ◽  
Vol 11 (A29B) ◽  
pp. 147-148
Author(s):  
Michel Rieutord
Keyword(s):  
Main Sequence ◽  
Mass Star ◽  
Two Dimensional ◽  
Be Stars ◽  
Rotating Stars ◽  
Intermediate Mass ◽  
Fundamental Parameters ◽  
Intermediate Mass Stars ◽  
Intermediate Mass Star ◽  
Fast Rotating

AbstractIn this talk I present the latest results of the ESTER project that has taken up the challenge of building two dimensional (axisymmetric) models of stars rotating at any rotation rate. In particular, I focus on main sequence massive and intermediate mass stars. I show what should be expected in such stars as far as the differential rotation and the associated meridional circulation are concerned, notably the emergence of a Stewartson layer along the tangent cylinder of the core. I also indicate what may be inferred about the evolution of an intermediate-mass star at constant angular momentum and how Be stars may form. I finally give some comparisons between models and observations of the gravity darkening on some nearby fast rotators as it has been derived from interferometric observations. In passing, I also discuss how 2D models can help to recover the fundamental parameters of a star.

scholarly journals Mass and angular momentum loss of fast rotating stars via decretion disks

2010 ◽  
Vol 6 (S272) ◽  
pp. 91-92 ◽  
Author(s):  
Jiří Krtička ◽  
Stan P. Owocki ◽  
Georges Meynet
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Outer Radius ◽  
Moment Of Inertia ◽  
Rotating Stars ◽  
Critical Rotation ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Fast Rotating

AbstractThe spinup of massive stars induced by evolution of the stellar interior can bring the star to near-critical rotation. In critically rotating stars the decrease of the stellar moment of inertia must be balanced by a net loss of angular momentum through an equatorial decretion disk. We examine the nature and role of mass loss via such disks. In contrast to the usual stellar wind mass loss set by exterior driving from the stellar luminosity, such decretion-disk mass loss stems from the angular momentum loss needed to keep the star near and below critical rotation, given the interior evolution and decline in the star's moment of inertia. Because the specific angular momentum in a Keplerian disk increases with the square root of the radius, the decretion mass loss associated with a required level of angular momentum loss critically depends on the outer radius for viscous coupling of the disk, and can be significantly less than the spherical, wind-like mass loss commonly assumed in evolutionary calculations.

scholarly journals Be and Bn stars: Balmer discontinuity and stellar-class relationship

2020 ◽  
Vol 634 ◽  
pp. A18
Author(s):  
Y. R. Cochetti ◽  
J. Zorec ◽  
L. S. Cidale ◽  
M. L. Arias ◽  
Y. Aidelman ◽  
...  
Keyword(s):  
High Resolution ◽  
Main Sequence ◽  
Rotational Velocity ◽  
Evolutionary Stage ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Rotating Stars ◽  
Circumstellar Material ◽  
Low Mass ◽  
Rapidly Rotating Stars

Context. A significant number of Be stars show a second Balmer discontinuity (sBD) attributed to an extended circumstellar envelope (CE). The fast rotational velocity of Be stars undoubtedly plays a significant role in the formation of the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not all present clear evidence of being surrounded by circumstellar material. Aims. We aim to characterize the populations of Be and Bn stars, and discuss the appearance of the sBD as a function of the stellar parameters. We expect to find new indices characterizing the properties of CEs in Be stars and properties relating Be and Bn stars. Methods. We obtained low- and high-resolution spectra of a sample of Be and Bn stars, derived stellar parameters, characterized the sBD, and measured the emission in the Hα line. Results. Correlations of the aspect and intensity of the sBD and the emission in the Hα line with the stellar parameters and the V sin i are presented. Some Bn stars exhibit the sBD in absorption, which may indicate the presence of rather dense CEs. Six Bn stars show emission in the Hα line, so they are reclassified as Be stars. The sBD in emission appears in Be stars with V sin i ≲ 250 km s−1, and in absorption in both Be and Bn stars with V sin i ≳ 50 km s−1. Low-mass Be and Bn stars share the same region in the Hertzsprung-Russell diagram. The distributions of rotational to critical velocity ratios of Be and Bn stars corresponding to the current stellar evolutionary stage are similar, while distributions inferred for the zero-age main sequence have different skewness. Conclusions. We found emission in the Hα line and signs of a CE in some Bn stars, which motivated us to think that Bn and Be stars probably belong to the same population. It should be noted that some of the most massive Bn stars could display the Be phenomenon at any time. The similarities found among Be and Bn stars deserve to be more deeply pursued.

scholarly journals The single star path to Be stars

2020 ◽  
Vol 633 ◽  
pp. A165
Author(s):  
Ben Hastings ◽  
Chen Wang ◽  
Norbert Langer
Keyword(s):  
Line Emission ◽  
Magellanic Clouds ◽  
Maximum Efficiency ◽  
Be Stars ◽  
Rotating Stars ◽  
Single Star ◽  
Critical Rotation ◽  
Star Models ◽  
Star Production ◽  
Be Star

Context. Be stars are rapidly rotating B main sequence stars that 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. Aims. We identify the main effects that cause single stars to approach critical rotation as functions of initial mass and metallicity, and predict the properties of populations of rotating single stars. Methods. We perform population synthesis with single-star models of initial masses ranging between 3 and 30 M⊙ and initial equatorial rotation velocities between 0 and 600 km s−1 at compositions representing the Milky Way and the 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. Results. We identify stellar wind mass-loss and the convective core mass fraction as the key parameters determining 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 the critical velocity. We also find that rapidly rotating Be stars in the Magellanic Clouds should have significant surface nitrogen enrichment, which may be in conflict with abundance determinations of Be stars. Conclusions. Single-star evolution might explain the high number of Be stars if 70 to 80% of critical rotation would 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.

Sign in / Sign up

Export Citation Format

Share Document