SCYON Abstract

Received on June 02 2011

The oxygen vs. sodium (anti)correlation(s) in omega Centauri
AuthorsF. D'Antona (1), A. D'Ercole (2), A.F. Marino (3), A.P. Milone (4), P. Ventura (1), E. Vesperini (5)
Affiliation(1) INAF, Osservatorio Astronomico di Roma, Monteporzio Catone (Roma), Italy
(2) INAF - Osservatorio di Bologna, via Ranzani, 1, I-40127 Bologna. Italy
(3) Max-Planck-Institut für Astrophysik, Garching, Germany
(4) IAC-Instituto de Astrofisica de Canarias, & Department of Astrophysics, University of La Laguna, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Canary Islands, Spain
(5) Department of Physics, Drexel University, Philadelphia, PA 19104, USA
Accepted byThe Astrophysical Journal
Contactdantona@oa-roma.inaf.it
URLhttp://arxiv.org/abs/1105.0366
Links

Abstract

Recent exam of large samples of omega Centauri giants shows that it shares with mono-metallic globular clusters the presence of the sodium versus oxygen anticorrelation, within each subset of stars with iron content in the range -1.9~<[Fe/H]~<-1.3. These findings suggest that, while the second generation formation history in omega Centauri is more complex than that of mono-metallic clusters, it shares some key steps with those simpler cluster. In addition, the giants in the range -1.3<[Fe/H]~<-0.7 show a direct O-Na correlation, at moderately low O, but Na up to 20 times solar. These peculiar Na abundances are not shared by stars in other environments often assumed to undergo a similar chemical evolution, such as in the field of the Sagittarius dwarf galaxy. These O and Na abundances match well the yields of the massive asymptotic giant branch stars (AGB) in the same range of metallicity, suggesting that the stars at [Fe/H]>-1.3 in omega Centauri are likely to have formed directly from the pure ejecta of massive AGBs of the same metallicities. This is possible if the massive AGBs of [Fe/H];gt;-1.3 in the progenitor system evolve when all the pristine gas surrounding the cluster has been exhausted by the previous star formation events, or the proto-cluster interaction with the Galaxy caused the loss of a significant fraction of its mass, or of its dark matter halo, and the supernova ejecta have been able to clear the gas out of the system. The absence of dilution in the metal richer populations lends further support to a scenario of the formation of second generation stars in cooling flows from massive AGB progenitors. We suggest that the entire formation of omega Centauri took place in a few 108yr, and discuss the problem of a prompt formation of s-process elements.