Ba Isotope Ratio in CEMP-s and CEMP-rs Stars as a Signature of s-Process and i-Process

Abstract

We present a spectroscopic analysis of three carbon-enhanced metal-poor (CEMP) stars of type CEMP-s and CEMP-rs and determine their non-local thermodynamic equilibrium (NLTE) abundances of Ba and the fractions of the odd Ba isotopes (F${}_{\mathrm{odd}}$). We found F${}_{\mathrm{odd}}$ = 0.65${}_{-0.34}^{+0.35}$ in SDSS J1349-0229, which is known in the literature as a CEMP-rs star, while the other two stars, BPS CS 29512-073 and SDSS J1036+1212, exhibit lower F${}_{\mathrm{odd}}$ = 0.23${}_{-0.10}^{+0.19}$ and 0.23${}_{-0.11}^{+0.22}$, respectively, and they are known in the literature as CEMP-s stars. The present result supports our earlier finding about distinct F${}_{\mathrm{odd}}$ in CEMP-s and CEMP-rs stars. For obtaining observational constraints on i-process nucleosynthesis, further NLTE abundance determinations for many chemical elements are required. We provide a tool for generating the lists of Ba II lines for a given F${}_{\mathrm{odd}}$ and it is available on GitHub https://github.com/sitamih/ba_linelist.

Published in a special issue of Galaxies: Neutron Capture Processes in the Universe

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