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Be Stars as Nonradial Pulsators* (Review Paper)

Published online by Cambridge University Press:  23 September 2016

Dietrich Baade
Dietrich Baade*
Affiliation:
Space Telescope-European Coordinating Facility, European Southern Observatory, Karl-Schwarzschild-Str. 2, D-8046 Garchtng bei München, W. Germany

Abstract

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The observational status of the ubiquitous rapid variability of Be stars is summarized. The most comprehensive interpretation is obtained with a traveling velocity field and associated temperature variations. But neither the available observations nor theoretical predictions presently allow an unambiguous mode determination of these nonradial pulsations. In addition to rapid rotation, an NRP mode of low azimuthal order, m ≈ 2, seems another prerequisite for a B star becoming a Be star. The amplitudes of these modes are variable and have been observed to decrease with some delay after an outburst. For low-order sectorial modes, NRP's therefore have the potential of explaining the three oldest unsolved problems of Be stars: the difference between Be and Bn stars (the latter do not usually have a low-order mode), the episodic component of the mass loss from Be stars, and the equatorial density maximum of their winds. Mechanisms for the transfer of energy to the atmosphere and its transformation into the kinetic energy of an outburst are discussed.

Type
IV. Models
Information
International Astronomical Union Colloquium , Volume 92: Physics of Be Stars , August 1987 , pp. 361 - 383
Copyright
Copyright © Cambridge University Press 1987

Footnotes

*

Based in part on observations collected at the European Southern Observatory, La Silla, Chile

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