The overlooked role of stellar variability in the extended main sequence of LMC intermediate-age clusters

Abstract

Intermediate-age star clusters in the Large Magellanic Cloud show extended main sequence turn offs (MSTOs), which are not consistent with a canonical single stellar population. These broad turn offs have been interpreted as evidence for extended star formation and/or stellar rotation. Since most of these studies use single frames per filter to do the photometry, the presence of variable stars near the MSTO in these clusters has remained unnoticed and their impact totally ignored. We model the influence of Delta Scuti using synthetic CMDs, adding variable stars following different levels of incidence and amplitude distributions. We show that Delta Scuti observed at a single phase will produce a broadening of the MSTO without affecting other areas of a CMD like the upper MS or the red clump; furthermore, the amount of spread introduced correlates with cluster age as observed. This broadening is constrained to ages ~ 1-3 Gyr when the MSTO area crosses the instability strip, which is also consistent with observations. Variable stars cannot explain bifurcated MSTOs or the extended MSTOs seen in some young clusters, but they can make an important contribution to the extended MSTOs in intermediate-age clusters.

Resubmitted to ApJ Letters after referee's comments

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Cited by in corpus (6)

• NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
• How stellar rotation shapes the colour magnitude diagram of the massive intermediate-age star cluster NGC 1846
• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• Stellar rotation and the extended main sequence turnoff in the open cluster NGC 5822
• WIYN Open Cluster Study LXXIX. M48 (NGC 2548) I. Radial Velocities, Rotational Velocities, and Metallicities of Stars in the Open Cluster M48 (NGC 2548)
• Extended Main Sequences in Star Clusters