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

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.

5 pages, 2 figures, accepted for publication in ApJL

References in corpus (4)

• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261, and Melotte 66
• Abundances of four open clusters from solar stars
• The Alpha Centauri Binary System: Atmospheric Parameters and Element Abundances