Abstract

The first stellar generations in the Universe were sources of ionizing radiation and of newly synthesized elements. They played a key role in the reionization process as well as initiating the chemical evolution of the Universe. The talk will begin recalling the expected main physical properties of the first stellar generations that likely make them to evolve significantly differently from stars in the present-day Universe. We will then focus on aspects dealing with the chemical enrichments by the first stellar generations. Comparisons between predictions of models with the observed surface composition of halo stars will be presented. The special case of the Carbon-Enhanced Metal poor stars (CEMP), especially the most iron-poor ones, provide very precious and interesting clues about the very early chemical enrichment processes. The talk will end by discussing the extremely interesting cases of nitrogen-rich regions in high redshift galaxies.