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

¹ Department of Physics, Hebei Normal University, No. 20 South 2nd Ring Road East, 050024 Shijiazhuang, PR China
e-mail: wycui@bao.ac.cn; wenyuancui@126.com
² School of Space Science and Physics, Shandong University at Weihai, 264209 Weihai, PR China
³ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, 100012 Beijing, PR China

Received: 7 September 2015
Accepted: 20 June 2016

Abstract

We report the first measurement of the odd-isotope fractions for barium, f_odd,Ba  in two extremely metal-poor stars: a CEMP-r/s star HE 0338-3945 ([Fe/H] =−2.42 ± 0.11) and an r-II star CS 31082-001 ([Fe/H] =−2.90 ± 0.13). The measured f_odd,Ba values are 0.23 ± 0.12 corresponding to 34.3 ± 34.3% of the r-process contributions for HE 0338-3945 and 0.43 ± 0.09 corresponding to 91.4 ± 25.7% of the r-process contribution to Ba production for CS 31082-001. The high r-process signature of barium in CS 31082-001 (91.4 ± 25.7%) 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 ± 34.3%) found in HE 0338-3945 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 asymptotic giant branch star model calculations to fit their abundance distributions.