Self-enrichment in omega Centauri

The origin of abundance spreads observed in omega Centauri is studied in th e context of the self-enrichment scenario. Five chemical evolution models a re constructed and are compared with empirical metallicity distribution of omega Cen. After a series of simulations, it is found that neither of close d-box, outflow, nor infall models can reproduce the empirical metallicity d istribution of omega Cen, while a modified outflow model with a bimodal ini tial mass function (IMF) gives a metallicity distribution that fits closely to the empirical ones. In the modified outflow model, long-lived stars are assumed to form after the first explosion of type II supernovae (SNII) in a proto-cloud. The modified outflow model involves gas infall at the very f irst chemical evolution. Thus we conclude that self-enrichment causes the a bundance dispersion in omega Cen. A success of the outflow model with the b imodal IMF implies that low mass stars in a globular cluster (GC) should ha ve formed in the gas already enriched by the first generation of SNII. This scenario, originally proposed by Cayrel (1986), can explain a lack of globular clusters with [Fe/H]less than or similar to -2.2 in the Milky Way Galaxy.