SYNTHETIC POSTASYMPTOTIC GIANT BRANCH EVOLUTION f BASIC MODELS AND APPLICATIONS TO DISK POPULATIONS

摘要

We explore the realm of post--asymptotic giant branch (post-AGB) stars from a theoretical viewpoint, by constructing a synthetic population of transition objects, proto--planetary nebulae, planetary nebula nuclei (PNNs), and post--planetary nebula objects. We use the Monte Carlo procedure to filter out the populations according to a given set of assumptions. We explore the parameter space by studying the effects of the initial mass function (IMF), the initial mass--final mass relation (IMFMR), the transition time (t_tr,.), the envelope mass at the end of the envelope ejection (M~R_e), the planetary nebula (PN) lifetime tPN' and the hydrogen- and helium-burning phases of the central stars. The results are discussed on the basis of the H-R diagram distributions, the Mv -t plane, and mass histograms. We found that (1) the dependence of the synthetic populations on the assumed IMF and IMFMR is generally mild, (2) the Mf indetermination produces very high indeterminations in the t,. and thus in the resulting post-AGB popu- lations; and (3) the synthetic models give a test check for the ratio of He- to H-burning PNNs. In this paper, disk post-AGB populations are considered. Future applications will include Magellanic Cloud PNs and populations of bulges and elliptical galaxies.