On the origin of the high helium sequence in ω Centauri

The blue Main Sequence (bMS) of omega Cen implies a ratio of helium to metal enrichment Delta Y/Delta Z approximate to 70, which is a major enigma. We show that rotating models of low met metallicity stars, which account for the anomalous abundance ratios of extremely metal poor stars, are also useful for understanding the very high Delta Y/Delta Z ratio in omega Cen. Models of massive stars with moderate initial rotation velocities produce stellar winds with large He- and N-excesses, but without the large C- (and O-) excesses made by very fast rotation, in agreement with the observed chemical abundance ratios in omega Cen. It is still uncertain whether the abundance peculiarities of omega Cen result from the fact that the high velocity contributions of supernovae escaped the globular cluster, usually considered as a tidally stripped core of a dwarf galaxy. Another possibility is a general dominance of wind ejecta at very low Z, due to the formation of black holes. Some abundance and isotopic ratios like Mg/Al, Na/Mg, Ne/N, C-12/C-13, O-16/O-18 and O-17/O-18 may allow us to further discriminate between these scenarios and between the AGB and massive star contributions.