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 $\Omega$ with respect to critical values is the same as at solar $Z$. The internal gradients of $\Omega$ 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 $\omega$ Centauri bears the signature of such enrichments by the stellar winds of rotating stars in the first stellar generations.