The overlooked role of stellar variability in LMC intermediate-age clusters

TL;DR

This paper suggests stellar variability, particularly Delta Scuti stars, may significantly contribute to the observed extended main sequence turnoffs in intermediate-age LMC clusters, challenging previous explanations based solely on star formation history or stellar rotation.

Contribution

It introduces the idea that stellar variability could explain the extended turnoffs, supported by initial findings from a variability survey in NGC 1846.

Findings

Detected a notable number of Delta Scuti variables in NGC 1846

Variability alone is unlikely to fully account for the extended turnoff

Further HST observations are needed to determine true variable content

Abstract

Broad, extended main sequence turnoffs seen in the majority of the intermediate-age (1-3 Gyr) LMC star clusters, have been interpreted as the result of an extended star formation history and/or the effect of extreme stellar rotation. A more fundamental explanation may be given by stellar variability. For clusters in these age range, the instability strip crosses the upper main sequence producing a number of variable stars (known as Delta Scuti) which, if nor properly taken into account, could appear as an extended turnoff. First results of a variability program in the LMC cluster NGC 1846 reveals a sizeable number of this type of variables, although still too low to produce a meaningful broadening, with the caveat that the true variable content of the center of this and other clusters in the LMC will only be revealed with a dedicated HST program.