THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 92:125-144, 1994 May

   POST-ASYMPTOTIC GIANT BRANCH EVOLUTION OF LOW- TO INTERMEDIATE-MASS STARS

                                E. VASSILIADIS
 Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies,
     The Australian National Observatory, Private Bag, Weston Creek P.O.,
                            A.C.T. 2611, Australia

                                      AND

                                   P.R. WOOD
 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218
 
                                   ABSTRACT

        In this paper, we present the results for the post-AGB phases of
     stellar evolutionary sequences, complete from the main-sequence phase,
     through the AGB phase, and on into the planetary nebula and white
     dwarf regimes.  Mass loss has been included using an empirical
     formalism derived from observed mass-loss rates of planetary nebula
     nuclei available in the literature and from radiation-pressure-driven
     stellar wind theory.  Models are calculated for initial masses 0.89,
     0.95, 1.0, 1.5, 2.0, 2.5, 3.5, and 5.0 Msun, and metallicities 0.016,
     0.008, 0.004, and 0.001.  These abundance and mass values were chosen
     to allow comparison with Galactic, and Magellanic Cloud planetary
     nebulae and their nuclei.  The post-AGB evolutionary sequences fall
     into two distinct groups depending on when the planetary nebula nuclei
     leave the AGB: one group where helium-shell burning is dominant, and
     the other group where hydrogen-shell burning is dominant.  Of the 27
     computed sequences: 17 are hydrogen-burners, and 10 are helium-
     burners.  In only five cases was any effort made to control the phase
     of departure from the AGB.  Lower mass models are more likely to leave
     the AGB burning helium, as the preceding AGB evolution has a mass-loss
     rate which is greatest immediately prior to a helium-shell flash.  The
     calculations are compared with the large observational database that
     has developed over recent years for the Large Magellanic Cloud.  These
     calculations will be useful for determining the planetary nebula
     luminosity function, and for the study of the ultraviolet excess
     observed in elliptical galaxies.

     Subject headings:  Magellanic Clouds -- planetary nebulae: general --
                        stars: evolution -- stars: interiors