a1 Geneva Observatory, Geneva University, CH–1290 Sauverny, Switzerland email: [email protected]
a2 Astrophysics group, Keele University, Lennard-Jones Lab., Keele, ST5 5BG, UK email: [email protected]
a3 IPMU, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
We discuss three effects of axial rotation at low metallicity. The first one is the mixing of the chemical species which is predicted to be more efficient in low metallicity environments. A consequence is the production of important quantities of primary 14N, 13C, 22Ne and a strong impact on the nucleosynthesis of the s-process elements. The second effect is a consequence of the first. Strong mixing makes possible the apparition at the surface of important quantities of CNO elements. This increases the opacity of the outer layers and may trigger important mass loss by line driven winds. The third effect is the fact that, during the main-sequence phase, stars, at very low metallicity, reach more easily than their more metal rich counterparts, the critical velocity. We discuss the respective importance of these three effects as a function of the metallicity. We show the consequences for the early chemical evolution of the galactic halo and for explaining the CEMP stars. We conclude that rotation is probably a key feature which contributes in an important way to shape the evolution of the first stellar generations in the Universe.