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 by recalling the expected main physical properties of the first stellar generations that likely make them 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, provides precious and interesting clues about the early chemical enrichment processes. The talk will end by discussing the exciting cases of nitrogen-rich regions in high redshift galaxies observed by the James Webb Space Telescope.
Antonella Vallenari
