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First Stars III
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Poster
Title: Envelope enrichment predictions for Barium stars confronted with high-resolution spectroscopic observations: a link with CEMPs stars Author(s): L. Husti, R. Gallino Abstract: Barium stars (the classical Ba, and dwarf Ba) are formed in binarysystems. When the primary star is on the Asymptotic Giant Branch, masstransfer by efficient stellar winds from the carbon and s-element rich primary onto the secondary star, which is observed on the main sequence or on the subgiant/redgiant phase. The envelope of the secondary star becomes thus enriched in barium and s-elements. Dilution of the elements with in the envelope may occur mixing processes.We have made a comparison between theoretical predictions of AGB stellar models and high-resolution spectroscopic observations of a large sample of barium stars (Allen \& Barbuy 2006; Smiljanic \& al 2007). Good agreement between predicted and observed enhancements of s-elementsare found for most stars, including Pb. Values of [Pb/Fe] $>$ 1 dexhave indeed been observed for the first time in Barium stars by Allen \& Barbuy (2006), and can easily be explained by adopting a high efficiency of the main $^{13}$C neutron source in AGB models, making a direct link with the class of very-metal poor C-rich and s-process richstars (CEMPs). The physical mechanism, mass transfer of C-rich and s-processrich material for the primary companion while on the AGB in a binary systemis the same. The much higher [Pb/Fe] values that can be achieved in CEMPsstars is explained by the primary nature of the $^{13}$C neutron sourceand by the decreasing of Fe seeds with metallicity.
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