Newly Identified Star Clusters in M33. II. Radial Hubble Space Telescope/Advanced Camera for Surveys Fields

We present integrated photometry and color-magnitude diagrams (CMDs) for 161 star clusters in M33, of which 115 were previously uncataloged, using the Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope. The integrated V-band magnitudes of these clusters range from M_V ~-9 to as faint as M_V ~-4, extending the depth of the existing M33 cluster catalogs by ~1 mag. Comparisons of theoretical isochrones to the CMDs using the Padova models yield ages for 148 of these star clusters. The ages range from log(t) ~ 7.0 to log(t) ~ 9.0. Our CMDs are not sensitive to clusters older than ~1 Gyr. We find that the variation of the clusters' integrated colors and absolute magnitudes with age is consistent with the predictions of simple stellar population models. These same models suggest that the masses of the clusters in our sample range from 5 × 10³ to 5 × 10⁴ M _sun.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.