The Heavy-nuclide Abundances of the Intrinsic and Extrinsic Asymptotic Giant Branch Stars

In this paper we present the nucleosynthesis calculations for the AGB stars during the He-shell flash phase. The main neutron source at the origin of s-process nucleosynthesis is assumed to be the reaction ¹³C(T, n)¹⁶O; a minor cont ribution derives also from the marginal activation of the reaction²²Ne(T, n)²⁵Mg at the end of each flash. We adopt a unbranched s-process network, and use standard models for the recurrent thermal pulses: core mass increasing with pulse number, overlap factor and stellar winds varying with core mass. After asymptotic abundances have been achieved, the distributions of s-nuclei can be simply characteri zed by τ₀. The distributions of heavy-nuclide abundances in the He-shell and envelope of the AGB star are given. Taking account of Wr≠0, through the equation of conservation of orbital ang ualar momentum, orbital parameter equations on the mass change are re-deduced. Combined with wind accretion equations, calculations of nucleosynthesis for intrnsic AGB stars first used to calculate s-elements enrichment of the extrinsic AGB stars. The distributions of heavy-nuclide abundances in the env elope of the extrinsic AGB star are also given.