Evolution of low- and intermediate-mass stars to the end of the asymptotic giant branch with mass loss

The results of stellar evolution calculations from the main sequence through to the end of the asymptotic giant branch (AGB) phase with mass loss are presented. It is shown that typical low mass AGB stars naturally suffer one or more superwind phases of mass loss toward the end of the AGB. These superwinds occur during the latter parts of the quiescent phases of helium shell flash cycles. The mass loss rates produced by the superwinds are similar to those required for PN production, and the occurrence of multiple superwind phases can account for the existence of AGB stars with hollow shells and multiple shell PNs. Each superwind phase leads to the loss of a few tenths of a solar mass. The mass loss rate used are based on empirical determinations for AGB stars; comparisons of model predictions with observations suggest that these rates can be used to model AGB evolution realistically.

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