Journal Article

The star-formation history of the Small Magellanic Cloud star cluster NGC 419

Stefano Rubele, Leandro Kerber and Léo Girardi

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 3, pages 1156-1164
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI:
The star-formation history of the Small Magellanic Cloud star cluster NGC 419

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The rich Small Magellanic Cloud (SMC) star cluster NGC 419 has recently been found to present both a broad main-sequence turn-off and a dual red clump of giants in the sharp colour–magnitude diagrams (CMDs) derived from the High-Resolution Channel of the Advanced Camera for Surveys onboard the Hubble Space Telescope. In this work, we apply to the NGC 419 data the classical method of star-formation-history (SFH) recovery through CMD reconstruction, deriving for the first time this function for a star cluster with multiple turn-offs. The values for the cluster metallicity, reddening, distance and binary fraction were varied within the limits allowed by present observations. The global best-fitting solution is an excellent fit to the data, reproducing all the CMD features with striking accuracy. The corresponding star-formation rate is provided together with estimates of its random and systematic errors. Star formation is found to last for at least 700 Myr, and to have a marked peak in the middle of this interval, for an age of 1.5 Gyr. Our findings argue in favour of multiple star-formation episodes (or continuous star formation) being at the origin of the multiple main-sequence turn-offs in Magellanic Cloud clusters with ages of about 1 Gyr. It remains to be tested whether alternative hypotheses, such as a main-sequence spread caused by rotation, could produce similarly good fits to the data.

Keywords: stars: evolution; Hertzsprung–Russell (HR) diagram

Journal Article.  5847 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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