Exploring giant barium stars: ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}$ ratio and elemental abundances of carbon, nitrogen, and oxygen

Abstract

Barium (Ba) stars belong to binary systems that underwent mass transfer events. As a consequence, their envelopes were enriched with material synthesized in the interiors of their evolved companions via \textit{slow} neutron-capture nucleosynthesis, the $s$-process. As post-interacting binaries, Ba stars figure as powerful tracers of the $s$-process. In this study, we conduct a classical local thermodynamic equilibrium analysis for a sample of 180 Ba giant stars to find complementary insights for the $s$-process, in form of elemental abundances of carbon, nitrogen, and oxygen, as well as the ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}$ ratio. We found carbon abundances systematically larger than those observed in normal giants, with [C/Fe] ratios ranging within from $-0.30$ to $+0.60$~dex. As expected, the [C/Fe] ratios increase for lower metallicity regimes and are strongly correlated with the average $s$-process abundances. Nitrogen abundances have a flat behavior around $[N/Fe]\sim +0.50$~dex and are moderately correlated with sodium abundances. Except for HD~107541, the entire sample shows $C/O<1$. We found ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}<20$ for $\sim 80\%$ of the sampled stars and ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}>60$ for three objects.

17 pages, 7 figures, and 4 tables; accepted for publication in The Astronomical Journal

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