Abstract
Little is known about the first stars, but hints on this stellar population can be derived from the peculiar chemical composition of the most metal-poor objects in the Milky Way and in resolved stellar populations of nearby galaxies. In this paper, we review the evolution and nucleosynthesis of metal-poor and extremely metal-poor (EMP) stars with low and intermediate masses. In particular, new models of 6 M⊙ with three different levels of metallicity, namely Z=10−4, 10−6 and 10−10, are presented. In addition, we illustrate the results obtained for a 2 M⊙, Z=10−5 model. All these models have been computed by means of the latest version of the FuNS code. We adopted a fully coupled scheme of solutions for the complete set of differential equations describing the evolution of the physical structure and the chemical abundances, as modified by nuclear processes and convective mixing. The scarcity of CNO in the material from which these stars formed significantly affects their evolution, their final fate and their contribution to the chemical pollution of the ISM in primordial galaxies. We show the potential of these models for the interpretation of the composition of EMP stars, with particular emphasis on CEMP stars.
Highlights
The oldest stellar component of the Milky Way, i.e., the stars belonging to the galactic halo, covers a rather large range of under-solar metallicities
Little is known about the first stars, but hints on this stellar population can be derived from the peculiar chemical composition of the most metal-poor objects in the Milky Way and in resolved stellar populations of nearby galaxies
We have reviewed the evolution and the nucleosynthesis of metal-poor and extremely metal-poor (EMP) stars (Z ≤ 10−4 ) with a mass low enough to skip the activation of central-C
Summary
The oldest stellar component of the Milky Way, i.e., the stars belonging to the galactic halo, covers a rather large range of under-solar metallicities. This is a necessary condition to properly account for the reciprocal feedback occurring in all the cases in which a convective zone extends into a region of variable composition, so fresh nuclear fuel is moved to a higher temperature where nuclear reactions proceed at a faster rate These episodes are expected to be quite common in pop III and EMP stars. Several theoretical studies on EMP stars have been previously conducted [11,16,17,18,19,20], this is the first time that metal-deficient intermediate-mass models have been computed with a fully coupled scheme Since this computational scheme is time-consuming, we have selected a nuclear network limited to the processes that produce a major contribution to the nuclear energy release.
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