On the early chemical evolution of the Milky Way

Abstract

A few topics concerning the early chemical evolution of the Milky Way are critically discussed. In particular, it is argued that: 1) Observed abundance patterns of extremely metal poor stars (of Pop. II) do not constrain the mass range of the first generation (Pop. III) stars; the latter may well be normal massive stars (10-50 Msun) or very massive ones (140-1000 Msun) or a combination of the two classes. 2) The discrepancy between primordial Li abundance (after WMAP) and the observed ``Spite plateau'' cannot be due to astration by a generation of massive Pop. III stars, as recently suggested, unless if such stars eject negligible amounts of metals. 3) The observed halo metallicity disribution may well be understood in the framework of hierarchical galaxy formation, as shown here with a simple semi-analytical model. 4) Formation of the Milky Way's halo from a myriad of smaller sub-haloes may have important implications for our understanding of the abundance patterns of r-elements, the origin of which remains still unclear.