English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

We present color-magnitude diagram analysis of deep Hubble Space Telescopeimaging of a mass-limited sample of 18 intermediate-age (1 - 2 Gyr old) starclusters in the Magellanic Clouds, including 8 clusters for which new data wasobtained. We find that ${\it all}$ star clusters in our sample feature extendedmain sequence turnoff (eMSTO) regions that are wider than can be accounted forby a simple stellar population (including unresolved binary stars). FWHM widthsof the MSTOs indicate age spreads of 200-550 Myr. We evaluate dynamicalevolution of clusters with and without initial mass segregation. Our mainresults are: (1) the fraction of red clump (RC) stars in secondary RCs in eMSTOclusters scales with the fraction of MSTO stars having pseudo-ages $\leq 1.35$Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters iscorrelated with their central escape velocity $v_{\rm esc}$, both currently andat an age of 10 Myr. We find that these two results are unlikely to bereproduced by the effects of interactive binary stars or a range of stellarrotation velocities. We therefore argue that the eMSTO phenomenon is mainlycaused by extended star formation within the clusters; (3) we find that $v_{\rmesc} \geq 15$ km/s out to ages of at least 100 Myr for ${\it all}$ clustersfeaturing eMSTOs, while $v_{\rm esc} \leq 12$ km/s at all ages for twolower-mass clusters in the same age range that do ${\it not}$ show eMSTOs. Weargue that eMSTOs only occur for clusters whose early escape velocities arehigher than the wind velocities of stars that provide material from whichsecond-generation stars can form. The threshold of 12-15 km/s is consistentwith wind velocities of intermediate-mass AGB stars in the literature.

Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity