The Chemical Composition of Red Giant Stars in Four Intermediate-Age Clusters of the Large Magellanic Cloud

This paper presents the chemical abundance analysis of a sample of 27 red giant stars located in four populous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978, and 2173. This analysis is based on high-resolution (R~ 47,000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, α, iron-peak, and neutron-capture elements. All the analyzed abundance patterns behave similarly in the four clusters and also show negligible star-to-star scatter within each cluster. We find [Fe/H] = 0.30 ± 0.03, 0.35 ± 0.02, 0.38 ± 0.02, and 0.51 ± 0.03 dex for NGC 1651, 1783, 1978, and 2173, respectively. The measurement of light odd-Z nuclei gives slightly subsolar [Na/Fe] and a more significant [Al/Fe] depletion (~ 0.50 dex). The [α/Fe] abundance ratios are nearly solar, while the iron-peak elements well trace those of the iron. S-process elements behave in a peculiar way: light s-elements give subsolar [Y/Fe] and [Zr/Fe] abundance ratios, while heavy s-elements give enhanced [Ba/Fe], [La/Fe], and [Nd/Fe] with respect to the solar values. Also, the [Eu/Fe] abundance ratio turns out to be enhanced (~0.4 dex).