The mysterious Ba stars
Borbála Cseh
Konkoly Observatory, CSFK, Hungary

Ba (Barium) stars belong to a binary system where the companion star has evolved through the AGB phase and transferred elements heavier than iron produced by the slow neutron-capture process (s process) onto the secondary star, which is now observed. I will present our results based on the comparison of different AGB nucleosynthesis models and the largest set of homogeneous high resolution spectra of Ba stars: the Ba star data show an incontestable increase of the hs-type/ls-type element ratio (for example, [Ce/Y]) with decreasing metallicity. This trend in the Ba star observations is predicted by non-rotating AGB models where 13C is the main neutron source. I will also show the s-process abundance pattern of individual Ba stars and associated AGB models.