The Search for Multiple Populations in Magellanic Cloud Clusters II: The
  Detection of Multiple Populations in Three Intermediate-Age SMC Clusters
  This is the second paper in our series about the search for multiple
populations in Magellanic Cloud star clusters using the Hubble Space Telescope.
Here we report the detection of multiple stellar populations in the
colour-magnitude diagrams of the intermediate-age clusters Lindsay 1, NGC 416
and NGC 339. With ages between 6.0 and 7.5 Gyr, these clusters are the youngest
ones in which chemical abundance spreads have been detected so far. This
confirms that the appearance of multiple populations is not restricted to only
ancient globular clusters, but may also be a common feature in clusters as
young as 6 Gyr. Our results are in agreement with a recent spectroscopic study
of Lindsay 1. We found that the fraction of enriched stars in NGC 416 is ~45%
whereas it is ~25% in NGC 339 and ~36% in Lindsay 1. Similar to NGC 121, these
fractions are lower than the average value for globular clusters in the Milky
Way.
