S-PROCESS IN INTRINSIC AND EXTRINSIC AGB STARS: THEORY VERSUS OBSERVATIONS

摘要

The Thermal-Pulsing Asymptotic Giant Branch (TP-AGB) phase is the site of the main and strong s-process (Iben & Truran 1978, Iben & Renzini 1983, Travaglio et al. 2001), We use AGB nucleosynthesis models to obtain the theoretical abundances of the elements from carbon to lead. We compare the theoretical predictions to high resolution spectroscopical data of s-enhanced stars, such as AGB, post-AGB, barium and CEMP-s stars.rnAGBs and post-AGBs show in their envelopes the s-elements produced by themselves (intrinsic AGBs). Barium stars and CEMP-s stars have not reached yet the AGB phase, so their s-enhancement is not intrinsic. A mass transfer scenario in a binary system, through stellar winds (Boffin & Jorissen 1988), from an AGB companion, that became later on a white dwarf, (in some cases detectable (Bohm-Vitense 1980, Bohm-Vitense & Johnson 1985, Bohm-Vitense 2000)), was proposed in order to explain their s-enhancement. We have found theoretical solutions for a large sample of s-process rich stars. We present and discuss our results.