Stellar Evolution in the Early Universe

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this paper, we describe the strong impact of rotation induced mixing and mass loss at very low metallicity (Z). The strong mixing leads to a significant production of primary 14N, 13C and 22Ne. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z = 0 for stars more massive than 60 M. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and 12C/13C. We calculated the weak s-process production induced by the primary 22Ne and obtain overproduction factors (relative to the initial composition, Z = 10−6) between 100-1000 in the mass range 60-90