The tight subgiant branch of the intermediate-age star cluster NGC 411 implies a single-aged stellar population

Abstract

The presence of extended main-sequence turn-off (eMSTO) regions in intermediate-age star clusters in the Large and Small Magellanic Clouds is often interpreted as resulting from extended star-formation histories (SFHs), lasting $\ge$ 300 Myr. This strongly conflicts with the traditional view of the dominant star-formation mode in stellar clusters, which are thought of as single-aged stellar populations. Here we present a test of this interpretation by exploring the morphology of the subgiant branch (SGB) of NGC 411, which hosts possibly the most extended eMSTO among all known intermediate-age star clusters. We show that the width of the NGC 411 SGB favours the single-aged stellar population interpretation and rules out an extended SFH. In addition, when considering the red clump (RC) morphology and adopting the unproven premise that the widths of all features in the colour--magnitude diagram are determined by an underlying range in ages, we find that the SFH implied is still very close to that resulting from a single-aged stellar population, with a minor fraction of stars scattering to younger ages compared with the bulk of the population. The SFHs derived from the SGB and RC are both inconsistent with the SFH derived from the eMSTO region. NGC 411 has a very low escape velocity and it has unlikely undergone significant mass loss at an early stage, thus indicating that it may lack the capacity to capture most of its initial, expelled gas from stellar evolutionary processes, a condition often required for extended SFHs to take root.

11 pages, 11 figures, MNRAS accepted

References in corpus (21)

• Pre-Supernova Evolution of Massive Single and Binary Stars
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Scaled solar tracks and isochrones in a large region of the Z-Y plane I. From the ZAMS to the TP-AGB end for 0.15 - 2.5 Mo stars
• Age Determination of Six Intermediate-age SMC Star Clusters with HST/ACS
• 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?
• Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity
• Populations of rotating stars III. SYCLIST, the new Geneva Population Synthesis code
• 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
• 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
• The exclusion of a significant range of ages in a massive star cluster
• Controversial Age Spreads from the Main Sequence Turn-Off and Red Clump in Intermediate-Age Clusters in the LMC
• The Morphology of the Sub-Giant Branch and Red Clump Reveal No Sign of Age Spreads in Intermediate Age Clusters
• Is the Escape Velocity in Star Clusters Linked to Extended Star Formation Histories? Using NGC 7252: W3 as a Test Case
• Formation of new stellar populations from gas accreted by massive young star clusters
• On the Interpretation of Sub-Giant Branch Morphologies of Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
• Extended Main Sequence Turn-Offs in Low Mass Intermediate Age Clusters
• No evidence for younger stellar generations within the intermediate age massive clusters NGC 1783, NGC 1696 and NGC 411

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• Multiple Stellar Populations in Globular Clusters
• Discovery of Extended Main Sequence Turn-offs in Four Young Massive Clusters in the Magellanic Clouds
• Testing the Limits of Precise Subgiant Characterization with APOGEE and Gaia: Opening a Window to Unprecedented Astrophysical Studies
• 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
• When does the onset of multiple stellar populations in star clusters occur? Detection of enriched stellar populations in NGC 2121
• Stellar populations in star clusters
• On the origin of the split main sequences of the young massive cluster NGC 1856
• New insights into the formation of the blue main sequence in NGC 1850
• The spatial distributions of blue main-sequence stars in Magellanic Cloud star clusters
• Blue straggler stars beyond the Milky Way. III. Detection of evolved blue straggler candidates in Large Magellanic Cloud clusters
• Extended Main Sequences in Star Clusters
• Searching for chemical abundance variations in young star clusters in the Magellanic Clouds: NGC 411, NGC 1718 and NGC 2213
• Not-so-simple stellar populations in nearby, resolved massive star clusters