Hints for multiple populations in intermediate-age clusters of the Small Magellanic Cloud

TL;DR

This study investigates the metallicity spreads in several intermediate-age SMC clusters using precise photometry, finding minimal Fe-abundance variations that challenge theories of multiple populations in star clusters.

Contribution

It provides new observational constraints on Fe-abundance spreads in intermediate-age clusters, using accurate photometry and a maximum likelihood approach.

Findings

NGC 339 and NGC 361 have marginal Fe spreads (~0.05 dex)

Lindsay 1 and Lindsay 113 show negligible Fe spreads (~0.00 dex)

Results challenge existing theories on multiple populations in clusters

Abstract

We report on the magnitude of the intrinsic [Fe/H] spread in the Small Magellanic Cloud (SMC) intermediate-age massive clusters NGC 339, 361, Lindsay 1 and 113, respectively. In order to measure the cluster metallicity dispersions, we used accurate Stromgren photometry of carefully selected cluster red giant branch (RGB) stars. We determined the Fe-abundance spreads by employing a maximum likelihood approach. The spreads obtained using the more accurate photometry of the brighter RGB stars resulted to be marginal (~ 0.05+-0.03 dex) for NGC 339 and NGC 361, while for Lindsay 1 and Lindsay 113 we obtained metallicity spreads of 0.00+-0.04 dex. From these results, we speculated with the possibility that NGC 361 is added to the group of four SMC clusters with observational evidence of multiple populations (MPs). Furthermore, in the context of the present debate about the existence of Fe-abundance inhomogeneities among old clusters with MPs, these outcomes put new constrains to recent theoretical speculations for making this phenomenon visible.