Ages of M33 Star Clusters Based on the HST/WFPC2 Photometry

Abstract

We present a result of age estimation for star clusters in M33. We obtain color-magnitude diagrams (CMDs) of resolved stars in 242 star clusters from the HST/WFPC2 images. We estimate ages of 100 star clusters among these, by fitting the Padova theoretical isochrones to the observational CMDs. Age distribution of the star clusters shows a dominant peak at log(t) ~ 7.8. Majority of star clusters are younger than log(t) = 9.0, while ten star clusters are older than log(t) ~ 9.0. There are few clusters younger than log(t) = 7 in this study, which is in contrast with the results based on the integrated photometry of star clusters in the previous studies. Radial distribution of the cluster ages shows that young to intermediate-age clusters are found from the center to the outer region, while old clusters are distributed farther from M33 center. We discuss briefly the implication of the results with regard to the formation of M33 cluster system.

arXiv comment28 pages including 9 figures and 1 table. Accepted for publication in ApJ

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• Young massive star clusters
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• Star clusters in M33: updated UBVRI photometry, ages, metallicities, and masses
• The Stellar Archeology of the M33 Disk: Recent Star-Forming History and Constraints on the Timing of an Interaction with M31
• New $ubvri$ photometry of 234 M33 star clusters
• Structural Parameters for 10 Halo Globular Clusters in M33