Stellar evolution and feedback connections to stellar dynamics

Abstract

Until a few years ago, the common paradigm for the formation of Globular Clusters (GCs) was that they constitute a ‘simple stellar population’ in which all the stars were formed from a chemically homogeneous cluster medium within a relatively short interval of time, at the beginning of the galactic life. In recent years, the spectroscopic information on the low luminosity (turnoff) cluster stars have extended to the unevolved stars the recognition that chemical anomalies are a common feature of GCs and not an exception. This has provoked a revolution in the simple view of GC formation, and requires an adequate dynamical modelling including gas dynamics. It is by now well accepted that at least two different stellar components are common in most GCs. These are almost unequivocally identified with (i) a first stellar generation, which gave origin to stars of all masses; and (ii)) a second generation, born from the ejecta of the most massive asymptotic giant branch stars of the first generation, in the first 100–200 Myr from the first burst of star formation. A ‘third’ population is present only in some GCs, and is more difficult to be understood. It is characterized by stars having a huge helium content (Y ≃ 0.4, if stellar modelling is reasonable) and extreme chemical anomalies in the proton capture elements (Na, O, Al). The status of understanding of the GC properties, based on our most recent models of stellar evolution, is discussed.