Looking outside the Galaxy: the discovery of chemical anomalies in 3 old Large Magellanic Cloud clusters

TL;DR

This study reveals chemical abundance anomalies, including Na, Al, O, and Mg variations, in three old Large Magellanic Cloud clusters, indicating that such features are common in old stellar systems regardless of galaxy environment.

Contribution

First detection of extreme chemical abundance anomalies in an extragalactic stellar cluster, expanding understanding of chemical inhomogeneities beyond the Milky Way.

Findings

Detected significant inhomogeneities in Na, Al, O, Mg ratios.

Observed anticorrelations between O and Na, Mg and Al.

First firm evidence of extreme chemical anomalies outside the Milky Way.

Abstract

By using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have obtained high-resolution spectra for 18 giant stars, belonging to 3 old globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210 and 2257). While stars in each cluster showed quite homogeneous iron content, within a few cents of dex (the mean values being Fe/H]= -1.75+-0.01 dex, -1.65+-0.02 dex and -1.95+-0.02 dex for NGC 1786, 2210 and 2257, respectively), we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe] and [Mg/Fe] abundance ratios, with evidence of [O/Fe] vs [Na/Fe] and [Mg/Fe] vs [Al/Fe] anticorrelations. The trends detected nicely agree with those observed in Galactic Globular Clusters, suggesting that such abundance anomalies are ubiquitous features of old stellar systems and they do not depend on the parent galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich stars. This is the first time that a firm signature of extreme chemical abundance anomalies has been found in an extragalactic stellar cluster.