The odd-isotope fractions of Barium in CEMP-r/s star HE 0338-3945 and r-II star CS 31082-001

TL;DR

This study measures the odd-isotope fractions of barium in two extremely metal-poor stars, revealing their dominant nucleosynthesis processes as either r-process or mixed s- and r-process contributions, providing insights into stellar element formation.

Contribution

First measurement of barium odd-isotope fractions in two metal-poor stars, linking isotope ratios to nucleosynthesis pathways and stellar evolution.

Findings

Star CS 31082-001 shows 91.4% r-process contribution to barium.

Star HE 0338-3945 exhibits a mixed s- and r-process signature.

Results align with AGB model predictions for element synthesis.

Abstract

We report the first measurement of the odd-isotope fractions for barium, \fodd\, in two extremely metal-poor stars: a CEMP-r/s star \he\ (\feh\,$=-2.42\pm0.11$) and an r-II star \cs\ (\feh\,$=-2.90\pm0.13$). The measured \fodd\ values are $0.23\pm0.12$ corresponding to $34.3\pm34.3$\% of the r-process contributions for \he\ and $0.43\pm0.09$ corresponding to $91.4\pm25.7$\% of the r-process contribution to Ba production for \cs. The high r-process signature of barium in \cs\ ($91.4\pm25.7\%$) suggests that the majority of the heavy elements in this star were synthesised via an r-process path, while the lower r-process value ($34.3\pm34.3\%$) found in \he\ indicates that the heavy elements in this star formed through a mix of s-process and r-process synthesis. These conclusions are consistent with studies based on AGB model calculations to fit their abundance distributions.