Stellar Evolution, Mass Loss and Nucleosynthesis on the Asymptotic Giant Branch

In this review, I will be concentrating on problems related to the evolution of stars on the asymptotic giant branch (AGB). AGB stars are defined as stars which have completed core helium burning and have subsequently developed degenerate carbon/oxygen cores surrounded by hydrogen and helium burning shells; such stars have main sequence masses M≤9 M⊙ (Paczynski 1971; Becker and Iben 1980). In the HR diagram most AGB stars sit on the red giant branch. An exception to this rule occurs in Population II systems, where the AGB stars evolve asymptotically to the red giant branch from the blue side as the luminosity increases after completion of core helium burning on the horizontal branch.