Barium and Yttrium abundance in intermediate-age and old open clusters

TL;DR

This study measures yttrium and barium abundances in eight open clusters using high-resolution spectra, confirming barium over-abundance especially in young clusters, and explores their distribution across the Galaxy.

Contribution

It provides new measurements of yttrium and barium in multiple open clusters and analyzes their abundance trends with respect to age and galactic position.

Findings

Barium is over-abundant in most clusters, especially young ones.

Confirmed barium over-abundance using NLTE approximation.

Explored the abundance gradient of yttrium and barium across the Galaxy.

Abstract

Barium is a neutron capture element, that, in open clusters, is frequently over-abundant with respect to the Iron. A clear explanation for this is still missing. Additionally, its gradient across the Galactic disk is poorly constrained. We measure the abundance of yttrium and barium using the synthetic spectrum method from UVES high-resolution spectra of eight distant open clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75, NGC 6192, NGC 6404, and NGC 6583. The barium abundance was estimated using NLTE approximation. We confirm that Barium is indeed over-abundant in most clusters, especially young clusters. Finally, we investigated the trend of yttrium and barium abundances as a function of distance in the Galaxy and ages. Several scenarios for the barium over-abundance are then discussed.