New theoretical yields of intermediate mass stars

Abstract

We present theoretical yields of H, 4 He, 12 C, 13 C, 14 N, and 16 O for stars with initial masses between 0.8 and 8 M 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 evo- lution and mass loss up to the end of the AGB including the rst, second, and third dredge-up phases. Most of the relations used are metallicity dependent to make a realis- tic comparison with stars of dierent initial abundances. The eect of Hot Bottom Burning (HBB) is included in an approximate way. The free parameters in our calculations are the mass loss scaling parameter AGB for stars on the AGB (us- ing a Reimers law), the minimum core mass for dredge-up M min c , and the third dredge-up eciency . As derived from previous extensive modeling, AGB =4 , M min c = 0.58 M ,a nd =0 :75 including HBB are in best agree- ment with observations of AGB stars both in the Galactic disk and Magellanic Clouds. The influence of specic 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 nal stages of the AGB with those observed in planetary nebu- lae 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 interme- diate mass stars presented in this paper are well suited for use in galactic chemical evolution models.