Low mass asymptotic giant branch evolution. I.

Studies of carbon stars and M stars in several external star complexes have demonstrated conclusively that low-mass asymptotic giant branch (AGB) stars of intermediate and low metallicity transform from M stars into C stars. This transformation occurs at a bolometric luminosity brighter than -4. One of the objectives of the present study is to examine theoretical light curves in the small core mass, small M case in more detail than appears in most earlier studies in order to investigate the core mass dependence of the magnitude and duration of the extended luminosity dip which follows a thermal pulse. It is shown that convective dredge-up of carbon to the surface does not occur in standard AGB models of small mass until the core mass approaches a value of approximately 0.7 solar mass. Attention is given to the time dependence of observables for 0.6 solar mass and 0.7 solar mass models, the fine-structure time dependence for the models, and the properties of convective regions.