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Stellar variability and individuality: observations and implications (invited paper)

Published online by Cambridge University Press:  12 April 2016

R. Costero ,
V. Doazan ,
R. Stalio  and
R.N. Thomas
R. Costero
Affiliation:
Institute de Astronomia, UNAM, Mexico
V. Doazan
Affiliation:
Observatoire de Paris, France
R. Stalio
Affiliation:
Osservatorio Astronomico, Trieste, Italy
R.N. Thomas
Affiliation:
Institut d'Astrophysique, Paris, France.

Abstract

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Customarily, one assumes that the internal structure of the star is not changed by a mass-flux from the atmosphere; thus one changes evolutionary calculations with mass-loss from those without it only by homologously decreasing the mass at each static evolutionary step. Furthermore, it is customary to assume that the mass-flux can be expressed in terms of only the thermal parameters (luminosity, Tepp) or (g, Teff). Sometimes rotation is introduced, but only as a modification of equatorial gravity, not of internal nonthermal structure. The phenomena of large-amplitude variability in times short compared with evolutionary ones, and of individuality (two stars of the same taxonomic class having different atmospheric distributions of Te and density) invalidate such static evolutionary calculations. We summarize the evidence for such large-amplitude variability in Be and la supergiant B stars. We also summarize the evidence for individuality as exhibited by observations: of OVI in OB stars; of x-ray luminosity across the HR diagram; of far-UV spectra of O stars; and of visual and far-UV spectra of Be stars. These observational results require nonthermal fluxes of mass and nonradiative energy to be imposed from below by the subatmosphere; which implies a nonthermal structure of subatmosphere and at least some part of the interior. Such nonthermal structure must then be included in evolutionary calculations. Thus current observations of nonthermal mass-flux from essentially all stars require including a nonthermal internal structure, not simply a mass-loss, in evolutionary calculations.

Type
Session III - Winds From Early Type Stars: Theory
Information
International Astronomical Union Colloquium , Volume 59: Effects of Mass Loss on Stellar Evolution , 1981 , pp. 131 - 153
Copyright
Copyright © Reidel 1981

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