A&A Supplement series, Vol. 123, June I 1997, 305-328
Received July 29; accepted September 25, 1996
L.B. van den Hoek and M.A.T. Groenewegen
Send offprint request: L.B. van den Hoek(firstname.lastname@example.org)
Astronomical Institute ``Anton Pannekoek'', Kruislaan 403, NL 1098 SJ Amsterdam, The Netherlands
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, D-85748 Garching, Germany
We present theoretical yields of H, He, C, C, N, and O for stars with initial masses between 0.8 and 8 and initial metallicities Z = 0.001, 0.004, 0.008, 0.02, and 0.04. We use the evolutionary tracks of the Geneva group up to the early asymptotic giant branch (AGB) in combination with a synthetic thermal-pulsing AGB evolution model to follow in detail the chemical evolution and mass loss up to the end of the AGB including the first, second, and third dredge-up phases. Most of the relations used are metallicity dependent to make a realistic comparison with stars of different initial abundances. The effect of Hot Bottom Burning (HBB) is included in an approximate way.
The free parameters in our calculations are the mass loss scaling parameter for stars on the AGB (using a Reimers law), the minimum core mass for dredge-up , and the third dredge-up efficiency . As derived from previous extensive modeling, = 4, = 0.58 , and including HBB are in best agreement with observations of AGB stars both in the Galactic disk and Magellanic Clouds.
The influence of specific model assumptions and adopted parameter values on the resulting AGB yields is examined and compared with earlier theoretical work. We compare the abundances predicted during the final stages of the AGB with those observed in planetary nebulae in the Galactic disk and show that the model with the aforementioned parameters is in good agreement with the observations. The metallicity dependent yields of intermediate mass stars presented in this paper are well suited for use in galactic chemical evolution models.
keywords: stars: abundances, evolution, AGB -- ISM: abundances -- galaxies: abundances