The Morphology of the Sub-Giant Branch and Red Clump Reveal No Sign of Age Spreads in Intermediate Age Clusters

Abstract

A recent surprise in stellar cluster research, made possible through the precision of Hubble Space Telescope photometry, was that some intermediate age (1-2 Gyr) clusters in the Large and Small Magellanic Clouds have main sequence turn-off (MSTO) widths that are significantly broader than would be expected for a simple stellar population (SSP). One interpretation of these extended MSTOs (eMSTOs) is that age spreads of the order of ~500 Myr exist within the clusters, radically redefining our view of stellar clusters, which are traditionally thought of as single age, single metallicity stellar populations. Here we test this interpretation by studying other regions of the CMD that should also be affected by such large age spreads, namely the width of the sub-giant branch (SGB) and the red clump (RC). We study two massive clusters in the LMC that display the eMSTO phenomenon (NGC 1806 & NGC 1846) and show that both have SGB and RC morphologies that are in conflict with expectations if large age spreads exist within the clusters. We conclude that the SGB and RC widths are inconsistent with extended star-formation histories within these clusters, hence age spreads are not likely to be the cause of the eMSTO phenomenon. Our results are in agreement with recent studies that also have cast doubt on whether large age spreads can exist in massive clusters; namely the failure to find age spreads in young massive clusters, a lack of gas/dust detected within massive clusters, and homogeneous abundances within clusters that exhibit the eMSTO phenomenon.

12 pages, 19 figures, accepted MNRAS

References in corpus (16)

• The Dartmouth Stellar Evolution Database
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• A double main sequence turn-off in the rich star cluster NGC 1846 in the Large Magellanic Cloud
• Multiple stellar populations in three rich Large Magellanic Cloud star clusters
• Multiple stellar populations in Magellanic Clouds clusters. I. An ordinary feature for intermediate age globulars in the LMC?
• The chemical composition of red giant stars in four intermediate-age clusters of the Large Magellanic Cloud
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Discovery of two distinct red clumps in NGC419: a rare snapshot of a cluster at the onset of degeneracy
• An alternative method to study star cluster disruption
• No Evidence for Significant Age Spreads in Young Massive LMC Clusters
• Constraining globular cluster formation through studies of young massive clusters - II. A Single Stellar Population Young Massive Cluster in NGC 34
• No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the LMC
• The exclusion of a significant range of ages in a massive star cluster
• Constraining globular cluster formation through studies of young massive clusters - III. A lack of gas and dust in massive stellar clusters in the LMC and SMC
• New Clues to the Cause of Extended Main Sequence Turn-Offs in Intermediate-Age Star Clusters in the Magellanic Clouds
• A HST/WFPC2 survey of bright young clusters in M31. I. VdB0, a massive star cluster seen at ~= 25 Myr

Cited by in corpus (15)

• Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
• Rotating Stellar Models Can Account for the Extended Main Sequence Turnoffs in Intermediate Age Clusters
• The SLUGGS Survey: Measuring globular cluster ages using both photometry and spectroscopy
• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
• The radial distributions of the two main-sequence components in the young massive star cluster NGC 1856
• The effects of the overshooting of the convective core on main-sequence turnoffs of young- and intermediate-age star clusters
• The role of binarity and stellar rotation in the split main sequence of NGC 2422
• First Observational Signature of Rotational Deceleration in a Massive, Intermediate-age Star Cluster in the Magellanic Clouds
• The overlooked role of stellar variability in the extended main sequence of LMC intermediate-age clusters
• Stellar populations in star clusters
• On the origin of the split main sequences of the young massive cluster NGC 1856
• Rotational Variation Allows for Narrow Age Spread in the Extended Main Sequence Turnoff of Massive Cluster NGC 1846
• Extended Main Sequences in Star Clusters
• Not-so-simple stellar populations in nearby, resolved massive star clusters