Extended Main Sequence Turn-Offs in Low Mass Intermediate Age Clusters

TL;DR

This study investigates the presence of extended main sequence turn-offs in low mass intermediate age clusters in the LMC, challenging previous assumptions about cluster mass and eMSTO occurrence, and supports stellar rotation as a key factor.

Contribution

It demonstrates that low mass clusters can host eMSTOs, indicating mass is not the sole factor, and provides observational support for the stellar rotation scenario.

Findings

eMSTOs found in clusters less massive than previously studied

Lower mass stars in older clusters show narrower eMSTOs

Large core radius is not necessary for eMSTO presence

Abstract

We present an imaging analysis of four low mass stellar clusters (< 5000 Mo) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1-2 Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters - > 5 times less massive than the eMSTO clusters previously studied - suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older (~ 2 Gyr) clusters is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their CMDs should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO.