Evolution of the First Stars: the major role of rotation for mixing and mass loss

Abstract

We show that rotation plays a major role for very low metallicity stars, even if the distribution of angular velocities Ω with respect to critical values is the same as at solar Z.T he internal gradients of Ω are much larger at lower metallicity Z, which enhance internal mixing and give rise to N-enrichments. Low Z stars easily reach break-up during MS evolution and lose mass. They also lose mass as red giants or supergiants due to their surface enrichments in heavy elements. The winds of low Z stars make peculiar contributions to the chemical yields. We suggest that the helium rich blue Main Sequence (bMS) of ω Centauri bears the signature of such enrichments by the stellar winds of rotating stars in the first stellar generations.