EDP Sciences
Free access
Volume 433, Number 1, April I 2005
Page(s) 285 - 295
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20040507

A&A 433, 285-295 (2005)
DOI: 10.1051/0004-6361:20040507

Abundance correlations in mildly metal-poor stars

II. Light elements (C to Ca)
H. Decauwer1, E. Jehin2, G. Parmentier3 and P. Magain1

1  Institute of Astrophysics and Geophysics, University of Liège, 17 Allée du 6 Août, 4000 Liège, Belgium
    e-mail: decauwer@astro.ulg.ac.be
2  European Southern Observatory, Casilla 19001, Alonso de Cordova 3107, Vitacura, Santiago, Chile
3  Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

(Received 23 March 2004 / Accepted 16 November 2004)

Accurate relative abundances have been obtained for carbon, oxygen, sodium, aluminium, silicon, and calcium in a sample of mildly metal-poor stars. This analysis complements a previous study carried out by Jehin et al. (1999, A&A, 341, 241), which provided the basis for the EASE scenario. This scenario postulates that field metal-poor stars were born in self-enriched proto-globular cluster clouds. By further investigating the correlations between the different $\alpha$-element abundances, we propose a modified scenario for the formation of intermediate metallicity stars, in which the stars exhibiting lower than average $\alpha$/Fe abundance ratios would form in low mass clouds, unable to sustain the formation of very massive stars ( $M \ga 30~M_\odot$).

Moreover, the carbon-to-iron ratio is found to decrease as one climbs the so-called Population IIb branch, i.e. when the s-element abundance increases. In the framework of the EASE scenario, we interpret this anticorrelation between the carbon and the s-element abundances as a signature of a hot bottom burning process in the metal-poor AGB stars which expelled the matter subsequently accreted by our Population IIb stars.

Key words: stars: abundances -- stars: Population II -- stars: atmospheres -- nuclear reactions, nucleosynthesis, abundances -- Galaxy: evolution

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© ESO 2005