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Astron. Astrophys. 333, 977-988 (1998)

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Light elements as probes of weak stellar winds

J.D. , Landstreet 1, 2, N. , Dolez 1, S. and Vauclair 1

1 Observatoire Midi-Pyrénées, 14, ave. Edouard-Bélin, F-31400 Toulouse, France
2 Department of Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7

Received 6 June 1996 / Accepted 8 January 1998

Abstract

The possibility that stars of the upper main sequence possess weak winds (of order [FORMULA] to [FORMULA] [FORMULA] yr-1) that may compete with atomic diffusion has been suggested by several authors, particularly by Babel & Michaud (1991a) and Babel (1992). Such winds may affect the chemical abundances that appear in the atmospheres of these stars. However, obtaining unambiguous evidence for the existence of a weak wind is not easy. We consider the possibility that naturally abundant chemical elements such as C, O and Ne, which are not expected to be made overabundant in a stellar atmosphere by radiative levitation, may accumulate in or near the photosphere of a mass-losing star, thus serving as tracers of mass loss.

We first show that the most abundant elements are not expected to be overabundant in the atmospheres of main sequence stars in the range [FORMULA] K due to radiative acceleration. We next show that hydrogen mass loss from the atmosphere, at a rate in the range of roughly [FORMULA], could lead to accumulation of a few abundant elements in or not far below the stellar photosphere, provided that any turbulence in the wind at the level of the photosphere is not sufficient to prevent diffusion. We find that such mass loss in late B stars should lead to observable overabundance of Ne, while in early A stars, such mass loss causes O to accumulate in the atmosphere. Detection of overabundances of these elements would provide direct evidence of the presence of weak mass loss. The few available Ne abundance determinations do not allow us to decide whether such weak winds are present in any B stars, but numerous measurements of O abundance imply that either winds in this mass loss range do not occur, or else that atmospheric diffusion is prevented by turbulence in early A stars.

Key words: stars: abundances – stars: atmospheres – stars: chemically peculiar – stars: mass loss

Send offprint requests to: J.D. Landstreet (e-mail: jlandstr@phobos.astro.uwo.ca)

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© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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