Helium variation in four Small Magellanic Cloud GCs
  The multiple stellar populations (MPs) of $\sim$11-13 Gyr-old Globular
Clusters (GCs) in our Galaxy are characterized by 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
the MPs in Magellanic Cloud GCs opened up new paths for the investigation of
chemical anomalies in clusters with different age and physical properties. In
this context, we used Hubble Space Telescope photometry to investigate the MPs
and constrain their chemical composition of four $\sim$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 second-population stars of NGC 121, NGC 339, NGC 416 are slightly enhanced
in helium by $\delta$Y = 0.009$\pm$0.006, 0.007$\pm$0.004 and 0.010$\pm$0.003,
respectively, with respect to the first population, while we find no
significant helium variation in Lindsay 1 ($\delta$Y = 0.000$\pm$0.004).
Moreover, 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.
