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Barium Stars: Theoretical Interpretation

Published online by Cambridge University Press:  05 March 2013

Laura Husti ,
Roberto Gallino ,
Sara Bisterzo ,
Oscar Straniero  and
Sergio Cristallo
Laura Husti*
Affiliation:
Dipartimento di Fisica Generale, Università degli Studi di Torino, via P. Giuria 1, 10125 Torino, Italia Research Centre for Atomic Physics and Astrophysics, University of Bucharest, P.O. Box MG-6, RO-077125 Bucharest-Magurele, Romania
Roberto Gallino
Affiliation:
Dipartimento di Fisica Generale, Università degli Studi di Torino, via P. Giuria 1, 10125 Torino, Italia
Sara Bisterzo
Affiliation:
Dipartimento di Fisica Generale, Università degli Studi di Torino, via P. Giuria 1, 10125 Torino, Italia
Oscar Straniero
Affiliation:
INAF Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy
Sergio Cristallo
Affiliation:
INAF Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy
*
DCorresponding author. Email: [email protected]
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Abstract

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Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.

Keywords

stars: abundancesstars: AGB and post-AGB(stars:) binaries: generalstars: chemically peculiarstars: mass loss
Type
Theory, Evolution and Models
Information
Publications of the Astronomical Society of Australia , Volume 26 , Issue 3 , 2009 , pp. 176 - 183
Copyright
Copyright © Astronomical Society of Australia 2009

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