Chemical Composition of the Old Globular Clusters NGC 1786, NGC 2210, and NGC 2257 in the Large Magellanic Cloud

This paper presents the chemical abundance analysis of a sample of 18 giant stars in three old globular clusters in the Large Magellanic Cloud (LMC), NGC 1786, NGC 2210, and NGC 2257. The derived iron content is [Fe/H] = -1.75 ± 0.01 dex (σ = 0.02 dex), -1.65 ± 0.02 dex (σ = 0.04 dex), and -1.95 ± 0.02 dex (σ = 0.04 dex) for NGC 1786, NGC 2210, and NGC 2257, respectively. All the clusters exhibit similar abundance ratios, with enhanced values (~+0.30 dex) of [α/Fe], consistent with the Galactic halo stars, thus indicating that these clusters have formed from a gas enriched by Type II supernovae. We also found evidence that r-process is the main channel of production of the measured neutron capture elements (Y, Ba, La, Nd, Ce, and Eu). In particular, the quite large enhancement of [Eu/Fe] (~+0.70 dex) found in these old clusters clearly indicates a relevant efficiency of the r-process mechanism in the LMC environment.