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Astron. Astrophys. 330, 651-658 (1998)

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Behaviour of calcium abundance in Am-Fm stars with evolution *

M. Künzli and P. North

Institut d'Astronomie de l'Université de Lausanne, CH-1290 Chavannes-des-Bois, Switzerland

Received 7 July 1997 / Accepted 29 September 1997

Abstract

Calcium abundance in the atmosphere of Am stars is examined as a function of their evolutionary state within the main sequence. New spectroscopic abundances as well as abundances obtained photometrically by Guthrie (1987) are used, since they are mutually quite consistent.

The main result of this work is that, contrary to earlier suggestions, calcium abundance does not tend to be larger in evolved Am stars than in unevolved ones, for objects distributed along a given evolutionary track in the HR diagram. The trend appears to be the reverse, if it is present at all.

For our whole sample of Am stars, there is a significant correlation between calcium abundance and effective temperature, in the sense that the cooler objects are the most Ca-deficient, hance have the most pronounced Am peculiarity. This implies an apparent correlation between calcium deficiency and age, although the lack of Am stars younger than [FORMULA] seems real. Our results are fully consistent with the low rate of Am stars observed in young clusters and with theoretical predictions of time-dependent radiative diffusion (Alecian 1996).

Key words: stars: chemically peculiar – stars: abundances – stars: evolution – stars: fundamental parameters

* Based on observations collected at Observatoire de Haute Provence (CNRS), France, and on data from the ESA HIPPARCOS astrometry satellite.

Send offprint requests to: P. North

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© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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