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Abstract: The rich SMC star cluster NGC419 has recently been found to present both abroad main sequence turn-off and a dual red clump of giants, in the sharpcolour-magnitude diagrams CMD derived from the High Resolution Channel of theAdvanced Camera for Surveys on board the Hubble Space Telescope. In this work,we apply to the NGC419 data the classical method of star formation historySFH recovery via CMD reconstruction, deriving for the first time thisfunction for a star cluster with multiple turn-offs. The values for the clustermetallicity, reddening, distance and binary fraction, were varied within thelimits allowed by present observations. The global best-fitting solution is anexcellent fit to the data, reproducing all the CMD features with strikingaccuracy. The corresponding star formation rate is provided together withestimates of its random and systematic errors. Star formation is found to lastfor at least 700 Myr, and to have a marked peak at the middle of this interval,for an age of 1.5 Gyr. Our findings argue in favour of multiple star formationepisodes or continued star formation being at the origin of the multiple mainsequence turn-offs in Magellanic Cloud clusters with ages around 1 Gyr. Itremains to be tested whether alternative hypotheses, such as a main sequencespread caused by rotation, could produce similarly good fits to the data.

Autor: Stefano Rubele Oss. Dip.Astro. Padova, Leandro Kerber UESC, Ilheus, Leo Girardi Oss.Padova


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