Element Yields of Intermediate-Mass Stars

Abstract

Intermediate mass stars occupy the mass range between 0.8-8 solar masses. In this review, evolutionary models of these stars from numerous sources are compared in terms of their input physics and predicted yields. In particular, the results of Renzini & Voli, van den Hoek & Groenewegen, and Marigo are discussed. Generally speaking, it is shown that yields of He-4, C-12, and N-14 decrease with increasing metallicity, reduced mass loss rate, and increased rotation rate. Integrated yields and recently published chemical evolution model studies are used to assess the relative importance of intermediate mass and massive stars in terms of their contributions to universal element buildup. Intermediate mass stars appear to play a major role in the chemical evolution of N-14, a modest role in the case of C-12, and a small role for He-4. Furthermore, the time delay in their release of nuclear products appears to play an important part in explaining the apparent bimodality in the distribution of damped Lyman alpha systems in the N/alpha--alpha/H plane.