Nucleosynthesis of Elements in Low to Intermediate Mass Stars through the Agb Phase I Introduction Ii Basic Stellar Evolution

We present a review of the main phases of stellar evolution with particular emphasis on the nucleosynthesis and mixing mechanisms in low-and intermediate-mass stars. In addition to explicit studies of the eeects of the rst, second and third dredge-up, we also discuss cool bottom processing and hot bottom burning. In recent years a wealth of new abundance data has been obtained, both from stellar abundance observations and from precise laboratory measurements of isotope ratios in stellar grains from meteorites. This places strong constraints on nucleosynthesis and mixing in low and intermediate mass stars. A quantitative understanding relies on our knowledge of both the stellar evolution and the nucleosynthesis occurring in the stars. There are speciic phases of a star's life where mixing brings to the surface the products of interior nucleosynthesis. These are referred to as \dredge-up" events, and there are basically three, although the details are mass-dependent. There are also observations which require mixing beyond what is found in the standard theory. This paper aims to review these events, both qualitatively, for non-experts, and quantitatively, for those more familiar with the area. In this section we give a qualitative overview of the evolution of stars of masses 1 and 5 M , with emphasis on the mechanisms and phenomenology of the structural and evolutionary changes. We consider in detail the evolution up to the beginning of thermal pulses on the AGB (the \TP-AGB"), with a brief discussion of further evolution (which is discussed in detail in section IV).