Where do Be stars stand in the picture of rotational mixing?

AbstractAtmospheric parameters and photospheric abundances have been estimated for 60 Be-type stars located in 4 fields over the Magellanic Clouds. Particular attention has been given to the absolute nitrogen abundances to test theories of rotational mixing, an important factor in the evolutionary status of B-type stars, Hunter et al. (2008). The analysis used the non-LTE atmospheric code TLUSTY and required the implementation of a procedure to compensate for possible contamination due to the presence of a circumstellar disc. Through comparison with evolutionary models of fast rotating B-type stars and projected rotational velocity distributions our results support the theory that Be-type stars are typically faster rotators than B stars, but the measured nitrogen enhancements appear to be significantly less than expected for Be stars rotating with velocities greater than 70% of their critical velocity

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Hipparcos Positions of B/Be Stars on the HR Diagram

International Astronomical Union Colloquium ◽

10.1017/s0252921100055731 ◽

2000 ◽

Vol 175 ◽

pp. 117-128 ◽

Cited By ~ 1

Author(s):

Danielle Briot ◽

Noel Robichon

Keyword(s):

Spectral Type ◽

Rotational Velocity ◽

Absolute Magnitude ◽

Be Stars ◽

Class V ◽

B Stars ◽

Luminosity Class ◽

The Mean ◽

Absolute Magnitudes ◽

Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

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Results from a recent stellar rotation census of B stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311010040 ◽

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.

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Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311010490 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 254-259

Author(s):

Alceste Z. Bonanos ◽

Danny J. Lennon ◽

Derck L. Massa ◽

Marta Sewilo ◽

Fabian Köhlinger ◽

...

Keyword(s):

Magellanic Clouds ◽

Spectral Energy ◽

Be Stars ◽

Energy Distributions ◽

Photometric Variability ◽

B Stars ◽

Ob Stars ◽

Luminous Blue Variables ◽

Red Supergiants ◽

Be Star

AbstractWe present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.

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Non-Radial Pulsation In Be Stars

Highlights of Astronomy ◽

10.1017/s1539299600006535 ◽

1986 ◽

Vol 7 ◽

pp. 265-272

Author(s):

John R. Percy

Keyword(s):

Mass Transfer ◽

Critical Velocity ◽

Main Sequence ◽

Radial Pulsation ◽

Be Stars ◽

Hydrogen Line ◽

Main Sequence Stars ◽

Rapid Rotation ◽

B Stars ◽

Effective Gravity

Be stars are B stars in which emission has been observed in at least one hydrogen line on at least one occasion. Some Be stars are pre-main-sequence stars, mass-transfer binaries, or supergiant stars with extended atmospheres. The majority, however, are classical Be stars: single stars on or near the main sequence. An important characteristic of these stars seems to be their rapid rotation – close to but not at the “critical” velocity at which the effective gravity vanishes at the equator.

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Spectroscopy of Be stars in NGC 330

Symposium - International Astronomical Union ◽

10.1017/s0074180900215039 ◽

1994 ◽

Vol 162 ◽

pp. 269-270 ◽

Cited By ~ 1

Author(s):

Paolo A. Mazzali ◽

F. Pasian ◽

D.J. Lennon ◽

P. Bonifacio ◽

V. Castellani

Keyword(s):

Open Cluster ◽

Model Atmosphere ◽

Evolutionary Status ◽

Be Stars ◽

Atmospheric Parameters ◽

Medium Resolution ◽

Young Open Cluster

Medium resolution (2Å/px) but high s/n spectra of approximately twenty of the brightest blue stars in the young open cluster NGC 330 in the SMC have been obtained with EFOSC1 on the ESO 3.6m telescope, and analyzed in order to determine the atmospheric parameters and the evolutionary status of the stars. LTE and NLTE model atmosphere calculations were used to determine the stellar parameters. The Teff values were derived from fits of the UV continua for all stars where these were available, using Robertson's (1974) B and V photometry to scale the Kurucz model fluxes for metallicity Z = 0.1Z⊙. Luminosities of the sample stars lie in the range 4.0 < log(L*/L⊙) < 5.0 and spectral types between B0 and late-B.

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On the Percentage of Be Stars in Galactic Open Clusters

International Astronomical Union Colloquium ◽

10.1017/s0252921100116689 ◽

1987 ◽

Vol 92 ◽

pp. 503-504

Author(s):

A. Reitermann ◽

J. Krautter ◽

B. Wolf ◽

B. Bashek

Keyword(s):

Spectroscopic Study ◽

Open Clusters ◽

Evolutionary Status ◽

Be Stars ◽

Chemical Abundance ◽

B Stars ◽

Knowing That ◽

Be Star ◽

High Fraction ◽

Young Clusters

Knowing that especially young clusters can contain a considerable high fraction of Be stars (Mermilliod 1982, Feast 1972) we made a spectroscopic study of Hα on the ratio of B/Be stars. The aim was to select normal B stars for chemical abundance analyses.It is well known that a promising way to investigate the evolutionary status of Be stars is to study their frequency and positions in the H-R diagram of open clusters. However, these studies have not yet provided satisfactory results (cf. e.g. Slettebak 1985); observations concerning the B/Be star ratio are badly needed. Therefore we present our observations although they are only a by-product from a different program.

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Stellar parameters of Be stars observed with X-shooter

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731536 ◽

2018 ◽

Vol 609 ◽

pp. A108 ◽

Cited By ~ 6

Author(s):

A. Shokry ◽

Th. Rivinius ◽

A. Mehner ◽

C. Martayan ◽

W. Hummel ◽

...

Keyword(s):

General Trend ◽

Rotational Velocity ◽

Balmer Line ◽

Be Stars ◽

Early Type ◽

Late Type ◽

Standard Star ◽

B Stars ◽

Fundamental Parameters ◽

Profile Fitting

Aims. The X-shooter archive of several thousand telluric standard star spectra was skimmed for Be and Be shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late-type Be stars and the extension of the Be phenomenon into early A stars. Methods. An adapted version of the BCD method is used, using the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but they are only useful for determining the pure emission contribution in a subsample of Be stars owing to uncertainties in determining the photospheric contribution. Results. A total of 78, mostly late-type, Be stars, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. We confirm the general trend that late-type Be stars have more tenuous disks and are less variable than early-type Be stars. The relatively large number (48) of relatively bright (V> 8.5) additional Be stars casts some doubt on the statistics of late-type Be stars; they are more common than currently thought. The Be/B star fraction may not strongly depend on spectral subtype.

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