Interpretation of CEMP(s) and CEMP(s + r) Stars with AGB Models

Abstract

Asymptotic Giant Branch (AGB) stars play a fundamental role in the s-process nucleosynthesis during their thermal pulsing phase. The theoretical predictions obtained by AGB models at different masses, s-process efficiencies, dilution factors and initial r-enrichment, are compared with spectroscopic observations of Carbon-Enhanced Metal-Poor stars enriched in s-process elements, CEMP(s), collected from the literature. We discuss here five stars as example, CS 22880-074, CS 22942-019, CS 29526-110, HE 0202-2204, and LP 625-44. All these objects lie on the main-sequence or on the giant phase, clearly before the TP-AGB stage: the hypothesis of mass transfer from an AGB companion, would explain the observed s-process enhancement. CS 29526-110 and LP 625-44 are CEMP(s+r) objects, and are interpreted assuming that the molecular cloud, from which the binary system formed, was already enriched in r-process elements by SNII pollution. In several cases, the observed s-process distribution may be accounted for AGB models of different initial masses with proper 13C-pocket efficiency and dilution factor. Na (and Mg), produced via the neutron capture chain starting from 22Ne, may provide an indicator of the initial AGB mass.

8 pages, 6 figures, 2 tables

References in corpus (3)

• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
• Carbon Abundances of Three Carbon-Enhanced Metal-Poor Stars from High-Resolution Gemini-S/bHROS Spectra of the 8727A [C I] Line

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