A Young Cluster With an Extended Main Sequence Turnoff: Confirmation of a Prediction of the Stellar Rotation Scenario

TL;DR

This study uses Hubble data to confirm that the extended main sequence turnoff in NGC1850 is consistent with stellar rotation effects, challenging the idea of multiple star formation episodes.

Contribution

It provides observational evidence supporting stellar rotation as the cause of eMSTO, aligning with theoretical predictions and ruling out multiple star formation events.

Findings

eMSTO in NGC1850 matches rotation scenario predictions

No evidence for multiple star formation episodes

Age spread correlates with cluster age

Abstract

We present Hubble Space Telescope photometry of NGC1850, a ~100 Myr, ~10^5 Msun cluster in the Large Magellanic Cloud. The colour magnitude diagram clearly shows the presence of an extended main sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ~40 Myr. This is in good agreement with the age range expected when the effects of rotation in MSTO stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star-formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.