Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters

¹ Geneva Observatory, University of Geneva, chemin des Maillettes 51, 1290 Sauverny, Switzerland e-mail: Thibaut.Decressin@obs.unige.ch
² Laboratoire d'Astrophysique de Toulouse et Tarbes – UMR 5572 – Université Paul Sabatier Toulouse 3 – CNRS, 14 Av. E. Belin, 31400 Toulouse, France
³ Institut d'Astrophysique de Paris, CNRS UMR 7095, Univ. P. & M. Curie, 98bis Bd. Arago, 75104 Paris, France

Received: 11 July 2006
Accepted: 27 October 2006

Abstract

Aims.We propose the Wind of Fast Rotating Massive Stars scenario to explain the origin of the abundance anomalies observed in globular clusters.

Methods.We compute and present models of fast rotating stars with initial masses between 20 and 120  for an initial metallicity Z = 0.0005 (). We discuss the nucleosynthesis in the H-burning core of these objects and present the chemical composition of their ejecta. We consider the impact of uncertainties in the relevant nuclear reaction rates.

Results.Fast rotating stars reach critical velocity at the beginning of their evolution and remain near the critical limit during the rest of the main sequence and part of the He-burning phase. As a consequence they lose large amounts of material through a mechanical wind which probably leads to the formation of a slow outflowing disk. The material in this slow wind is enriched in H-burning products and presents abundance patterns similar to the chemical anomalies observed in globular cluster stars. In particular, the C, N, O, Na and Li variations are well reproduced by our model. However the rate of the has to be increased by a factor 1000 around 50  10⁶ K in order to reproduce the amplitude of the observed Mg-Al anticorrelation. We discuss how the long-lived low-mass stars currently observed in globular clusters could have formed out of the slow wind material ejected by massive stars.