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Astron. Astrophys. 345, 156-162 (1999)

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Microscopic diffusion and subdwarfs

P. Morel 1 and A. Baglin 2

1 Département Cassini, UMR CNRS 6529, Observatoire de la Côte d'Azur, BP 4229, F-06304 Nice Cedex 4, France
2 DESPA, URA CNRS 264, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France

Received 16 November 1998 / Accepted 4 February 1999

Abstract

The recent distance determinations by HIPPARCOS have allowed to locate very precisely a reasonable set of subdwarfs in the HR diagram. A detailed comparison with evolutionary models is now possible and it has been recently claimed that the observed lower part of the main-sequence is cooler than the computed one. In this paper we show that microscopic diffusion could be the physical explanation of such a systematic shift. We emphazise the fact that, as diffusion alters surface abundances, the initial metal content of the stellar material is higher than the present one. A "calibration" procedure is necessary when comparing observed and theoretical HR diagram, to take into account this effect.

Key words: diffusion – stars: Hertzsprung – Russel (HR) and C-M diagrams – stars: late-type

Send offprint requests to: P. Morel

Correspondence to: Pierre.Morel@obs-nice.fr

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999
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