2019ApJ...871..140L

The multiple stellar populations (MPs) of the ∼11-13 Gyr old globular clusters (GCs) in our Galaxy are characterized by the different content of several light elements. These elements describe well-defined patterns like the C-N and the Na-O anticorrelations and the He-N and Na-N correlations. The discovery of MPs in Magellanic Cloud GCs opened up new paths for the investigation of chemical anomalies in clusters with different ages and physical properties. In this context, we used Hubble Space Telescope photometry to investigate the MPs and constrain their chemical composition of four ∼6-11 Gyr extragalactic GCs, namely NGC 121, NGC 339, NGC 416, and Lindsay 1 in the Small Magellanic Cloud. The comparison of the stellar colors with synthetic spectra suggests that the second-population stars of NGC 121, NGC 339, and NGC 416 are slightly enhanced in helium by δY=0.009±0.006,0.007±0.004 and 0.010 ± 0.003, respectively, with respect to the first population, while we find no significant helium variation in Lindsay 1 (δY=0.000±0.004). Moreover, the second-population stars of all the clusters are, on average, enhanced in nitrogen and depleted in carbon and oxygen, in close analogy with what we observe in Galactic GCs.