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

摘要

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.