Early Nucleosynthesis and Chemical Abundances of Stars in Globular Clusters

Summary

This cycle of lectures presents a self consistent sketch of current understanding about chemical composition of globular clusters and its aftermaths. The first two lectures give basic about nucleosynthesis, chemical models, and abundance determinations. Main results for globular clusters are presented in the next two lectures. In the final lecture I review various indices used to derive abundances from photometry and low dispersion spectroscopy.

Early Nucleosynthesis and models of galactic chemical evolution

In this first lecture I will briefly present the fundamentals of nucleosynthesis and chemical evolution. Owing to lack of time, only few sketches can be given.

The basic observation that we live in an environment rather rich in heavy elements (hereinafter metals) that could not be produced by Big Bang leads us to try to describe the mechanisms of formation of these elements. There is a close interaction between chemical and dynamical evolution of stellar systems; chemical abundances provide then a basic diagnostic for models of galactic evolution.

Figure 1 sketches the most important features to be introduced in this picture. Stars form from condensation of the most dense clouds within the interstellar medium (ISM). Metals are produced by nucleosynthesis processes within the stellar interiors. Stars lose part of their metal-enriched material either through more or less quiescent stellar winds, or through explosive events (SNe) at the end of their lives: the amount of each element produced within stars and returned to the ISM depends on the stellar masses and in some case on the presence of close companions.