Enhanced production of barium in low-mass stars: evidence from open clusters

TL;DR

This study reveals that low-mass stars produce more barium than previously thought, with open cluster data supporting a model where extra-mixing processes enhance neutron capture in these stars, affecting galactic chemical evolution.

Contribution

It demonstrates that higher Ba yields from low-mass stars are necessary to explain observed abundance trends, proposing a new scenario involving mass-dependent extra-mixing efficiency.

Findings

Barium abundance increases with decreasing cluster age.

Galactic chemical evolution models require higher Ba yields from low-mass stars.

Extra-mixing processes are more efficient in lower-mass stars.

Abstract

We report the discovery of a trend of increasing barium abundance with decreasing age for a large sample of Galactic open clusters. The observed pattern of [Ba/Fe] vs. age can be reproduced with a Galactic chemical evolution model only assuming a higher Ba yield from the $s$-process in low-mass stars than the average one suggested by parametrized models of neutron-capture nucleosynthesis. We show that this is possible in a scenario where the efficiency of the extra-mixing processes producing the neutron source $^{13}$C is anti-correlated with the initial mass, with a larger efficiency for lower masses. This is similar to the known trend of extended mixing episodes acting in H-rich layers and might suggest a common physical mechanism.