The self-enrichment scenario in intermediate metallicity globular clusters

INAF – Observatory of Rome, via Frascati 33, 00040 MontePorzio Catone (RM), Italy e-mail: [ventura;dantona]@oa-roma.inaf.it

Received: 25 September 2007
Accepted: 2 November 2007

Abstract

Context.We present stellar yields computed from detailed models of intermediate mass asymptotic giant branch stars of low metallicity. In this work, all the main microphysics inputs have been updated, and in particular α-enhancement is explicitly taken into account in both the opacities and equation of state.

Aims.The target of this work is to provide a basis for testing the reliability of the AGB self-enrichment scenario for globular clusters of intermediate metallicity. These globular clusters exhibit well-defined abundance patterns, which have often been interpreted as the consequence of the pollution of the interstellar medium by the ejecta of massive AGBs.

Methods.We calculated a grid of intermediate-mass models with metallicity ; the evolutionary sequences are followed from the pre-main sequence throughout the whole AGB phase. We focus our attention on those elements widely studied in the spectroscopic investigations of globular clusters stars, i.e. oxygen, sodium, aluminium, magnesium, and fluorine.

Results.The predictions of our models show an encouraging agreement with the demand of the self-enrichment scenario for what concerns the abundances of oxygen, aluminium, fluorine, and magnesium. The question of sodium is more tricky, due to the large uncertainties of the cross-sections of the Ne-Na cycle. The present results show that only a relatively narrow range of initial masses ( ) can be responsible for the self enrichment.