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Astron. Astrophys. 330, 651-658 (1998)
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]](img1.gif)
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
Contents
- 1. Introduction
- 2. The sample and observations
- 3. Calcium abundance
- 4. Discussion
- 5. Conclusion
- Acknowledgements
- References
![[FORMULA]](img5.gif)
© European Southern Observatory (ESO) 1998
Online publication: January 16, 1998
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