Chemical composition of the old globular clusters NGC 1786, NGC 2210 and NGC 2257 in the Large Magellanic Cloud

TL;DR

This study analyzes the chemical compositions of 18 giant stars across three old globular clusters in the Large Magellanic Cloud, revealing their metallicities, alpha-element enhancements, and r-process element production, which shed light on their formation history.

Contribution

It provides detailed chemical abundance measurements for stars in LMC globular clusters, highlighting similarities with Galactic Halo stars and emphasizing the role of r-process nucleosynthesis.

Findings

Clusters have similar [alpha/Fe] ratios (+0.30 dex).

Iron abundances range from --1.65 to --1.95 dex.

High [Eu/Fe] (+0.70 dex) indicates efficient r-process enrichment.

Abstract

This paper presents the chemical abundance analysis of a sample of 18 giant stars in 3 old globular clusters in the Large Magellanic Cloud, namely NGC 1786, NGC 2210 and NGC 2257. The derived iron content is [Fe/H]= --1.75+-0.01 dex (sigma= 0.02 dex), --1.65+-0.02 dex (sigma= 0.04 dex) and --1.95+-0.02 dex (sigma= 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 [alpha/Fe], consistent with the Galactic Halo stars, thus indicating that these clusters have formed from a gas enriched by Type II SNe. We also found evidence that r-process are 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.