Rotation and Properties of Be Stars

Zorec, J.

doi:10.1017/s0074180900195269

Symp. - Int. Astron. Union

2004

DOI: 10.1017/s0074180900195269

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Rotation and Properties of Be Stars

J. Zorec¹

Abstract: Abstract. The actual characteristic average surface angular velocity ratio of the Be phenomenon may be higher than nine = 0.8 ± 0.1 derived from vsini values not corrected from gravity darkening effects. Late Be stars need not only higher values of nine, but also larger main sequence age ratios TITMs than early Be stars to display the Be phenomenon. Galactic field Be stars appear at any MS phase, but their frequency is higher for T / TMS ;(j 0.5. Be stars are probably neat differential rotators, i.e. they rota… Show more

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Cited by 5 publications

References 62 publications

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Continuum Energy Distribution of Bright Be Stars

Goraya

2006

Astrophys Space Sci

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This paper presents the spectrophotometric observations of five Be stars belonging to spectral type from B2.5 to B5 and luminosity class from III to V. The continuum energy distribution data of these stars are extracted from the spectrophotometric measurements over the wavelength range of λλ 3200-8000Å. The observed data of continuum energy distribution are compared with the theoretical energy distribution curves to derive the value of effective temperatures of these stars. We have also examined the effect of circumstellar envelopes of Be stars on their continuum energy distribution. It has been found that the extended circumstellar envelope of Be stars affect the underlying continua in the near-ultraviolet and near-infrared regions. Three Be stars are found to exhibit near-ultraviolet and near-infrared flux deficiency in their continua. For one of the Be, namely star HR 1289, we report the first continuum energy distribution measurements. Another normal B star HR 1363, which was observed as comparison star, was found to exhibit near-ultraviolet and near-infrared excess emission, which are signatures of a Be star, thus putting this star in the category of Be stars.

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Continuum Energy Distribution of Bright Be Stars

Goraya

2006

Astrophys Space Sci

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Differential rotation in rapidly rotating early-type stars

Zorec

Frémat

Souza

et al. 2010

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Context. Since the external regions of the envelopes of rapidly rotating early-type stars are unstable to convection, a coupling may exist between the convection and the internal rotation. Aims. We explore what can be learned from spectroscopic and interferometric observations about the properties of the rotation law in the external layers of these objects. Methods. Using simple relations between the entropy and specific rotational quantities, some of which are found to be efficient at accounting for the solar differential rotation in the convective region, we derived analytical solutions that represent possible differential rotations in the envelope of early-type stars. A surface latitudinal differential rotation may not only be an external imprint of the inner rotation, but induces changes in the stellar geometry, the gravitational darkening, the aspect of spectral line profiles, and the emitted spectral energy distribution. Results. By studying the equation of the surface of stars with non-conservative rotation laws, we conclude that objects undergo geometrical deformations that are a function of the latitudinal differential rotation able to be scrutinized both spectroscopically and by interferometry. The combination of Fourier analysis of spectral lines with model atmospheres provides independent estimates of the surface latitudinal differential rotation and the inclination angle. Models of stars at different evolutionary stages rotating with internal conservative rotation laws were calculated to show that the Roche approximation can be safely used to account for the gravitational potential. The surface temperature gradient in rapid rotators induce an acceleration to the surface angular velocity. Although a nonzero differential rotation parameter may indicate that the rotation is neither rigid nor shellular underneath the stellar surface, still further information, perhaps non-radial pulsations, is needed to determine its characteristics as a function of depth.

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A study of the B and Be star population in the field of the LMC open cluster NGC 2004 with VLT-FLAMES

Martayan¹,

Hubert²,

Floquet³

et al. 2006

A&A

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Observations of hot stars belonging to the young cluster LMC-NGC 2004 and its surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA mode. 25 Be stars were discovered; the proportion of Be stars compared to B-type stars is found to be of the same order in the LMC and in the Galaxy fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5 of these are found to be eclipsing systems from the MACHO database, with periods of a few days. About 75% of the spectra in our sample are polluted by hydrogen

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Rotation and Properties of Be Stars

Cited by 5 publications

References 62 publications

Continuum Energy Distribution of Bright Be Stars

Continuum Energy Distribution of Bright Be Stars

Differential rotation in rapidly rotating early-type stars

A study of the B and Be star population in the field of the LMC open cluster NGC 2004 with VLT-FLAMES

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