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

Barium is a neutron-capture element that, in open clusters, is frequently overabundant with respect to iron. A clear explanation for this is still missing. Additionally, its gradient across the Galactic disc 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 non-local thermodynamic equilibrium approximation. We confirm that barium is indeed overabundant 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 overabundance are then discussed.