Helium enrichment in intermediate-age Magellanic Clouds clusters:
  towards an ubiquity of multiple stellar populations?
  Intermediate-age star clusters in the Magellanic Clouds harbour signatures of
the multiple stellar populations long thought to be restricted to old globular
clusters. We compare synthetic horizontal branch models with Hubble Space
Telescope photometry of clusters in the Magellanic Clouds, with age between ~2
and ~10 Gyr, namely NGC 121, Lindsay 1, NGC 339, NGC 416, Lindsay 38, Lindsay
113, Hodge 6 and NGC 1978. We find a clear signature of initial helium
abundance spreads (delta(Y)) in four out of these eight clusters (NGC 121,
Lindsay 1, NGC 339, NGC 416) and we quantify the value of delta(Y). For two
clusters (Lindsay 38, Lindsay 113) we can only determine an upper limit for
delta(Y), whilst for the two youngest clusters in our sample (Hodge 6 and NGC
1978) no conclusion about the existence of an initial He spread can be reached.
Our delta(Y) estimates are consistent with the correlation between maximum He
abundance spread and mass of the host cluster found in Galactic globular
clusters. This result strengthens the emerging view that the formation of
multiple stellar populations is a standard process in massive star clusters,
not limited to a high redshift environment.
