The Search for Multiple Populations in Magellanic Cloud Clusters II: The Detection of Multiple Populations in Three Intermediate-Age SMC Clusters

TL;DR

This study detects multiple stellar populations in three intermediate-age Magellanic Cloud clusters, showing that such features are present in clusters as young as 6 Gyr, challenging previous notions that they only occur in ancient globular clusters.

Contribution

First detection of multiple populations in intermediate-age clusters in the Magellanic Clouds, expanding understanding of cluster evolution and chemical diversity.

Findings

Multiple populations detected in three clusters aged 6-7.5 Gyr.

Enriched star fractions range from 25% to 45%.

Results align with recent spectroscopic studies.

Abstract

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.