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The ages of Galactic globular clusters in the context of self-enrichment

Published online by Cambridge University Press:  01 October 2008

T. Decressin ,
H. Baumgardt ,
P. Kroupa ,
G. Meynet  and
C. Charbonnel
T. Decressin
Affiliation:
Argelander Institute for Astronomy (AIfA), Auf dem Hügel 71, D-53121 Bonn, Germany email: [email protected], [email protected], [email protected]
H. Baumgardt
Affiliation:
Argelander Institute for Astronomy (AIfA), Auf dem Hügel 71, D-53121 Bonn, Germany email: [email protected], [email protected], [email protected]
P. Kroupa
Affiliation:
Argelander Institute for Astronomy (AIfA), Auf dem Hügel 71, D-53121 Bonn, Germany email: [email protected], [email protected], [email protected]
G. Meynet
Affiliation:
Geneva Observatory, University of Geneva, chemin des Maillettes 51, CH-1290 Sauverny, Switzerland email: [email protected], [email protected]
C. Charbonnel
Affiliation:
Geneva Observatory, University of Geneva, chemin des Maillettes 51, CH-1290 Sauverny, Switzerland email: [email protected], [email protected] LATT, CNRS UMR 5572, Université de Toulouse, 14 avenue Edouard Belin, F-31400 Toulouse Cedex 04, France
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Abstract

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A significant fraction of stars in globular clusters (about 70%-85%) exhibit peculiar chemical patterns, with strong abundance variations in light elements along with constant abundances in heavy elements. These abundance anomalies can be created in the H-burning core of a first generation of fast-rotating massive stars, and the corresponding elements are conveyed to the stellar surface thanks to rotational induced mixing. If the rotation of the stars is fast enough, this material is ejected at low velocity through a mechanical wind at the equator. It then pollutes the interstellar medium (ISM) from which a second generation of chemically anomalous stars can be formed. The proportion of anomalous stars to normal stars observed today depends on at least two quantities: (1) the number of polluter stars; (2) the dynamical history of the cluster, which may lose different proportions of first- and second-generation stars during its lifetime. Here we estimate these proportions, based on dynamical models for globular clusters. When internal dynamical evolution and dissolution due to tidal forces are accounted for, starting from an initial fraction of anomalous stars of 10% produces a present-day fraction of about 25%, still too small with respect to the observed 70-85%. In the case of gas expulsion by supernovae, a much higher fraction is expected to be produced. In this paper we also address the question of the evolution of the second-generation stars that are He-rich, and deduce consequences for the age determination of globular clusters.

Keywords

globular clusters: generalstellar dynamicsstellar evolution
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S258: The Ages of Stars , October 2008 , pp. 265 - 274
Copyright
Copyright © International Astronomical Union 2009

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