2007ApJ...657.1037C

The s-enhanced and very metal-poor star CS 30322-023 shows a puzzling abundance pattern of the neutron-capture elements. In particular, several neutron-capture elements, such as Ba and Pb, show enhancement, but other neutron-capture elements, such as Sr and Eu, exhibit deficiencies with respect to iron. The study of this sample star could provide a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model, we find that the abundance pattern of neutron-capture elements could be best explained by a star that was polluted by an asymptotic giant branch (AGB) star, and if the CS 30322-023 binary system formed in a molecular cloud that had never been polluted by r-process material. The lack of r-process material also indicates that the AGB companion cannot have undergone a Type 1.5 supernova, and thus must have had an initial mass below 4.0 M_☉, while the strong N overabundance and the absence of a strong C overabundance indicate that the companion's initial mass was larger than 2.0 M_☉. The smaller s-process-component coefficient of this star illustrates that there is less material accreted onto this star from the AGB companion and that the sample star should have formed in a binary system with a larger initial orbital separation, where the accretion-induced collapse (AIC) mechanism cannot work.