WFPC2 Observations of Massive and Compact Young Star Clusters in M31

Abstract

We present color-magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values range from EB-V = 0.20 ± 0.10 to 0.31 ± 0.11. We statistically remove field stars on the basis of completeness, magnitude, and color. Isochrone fits to the field-subtracted, reddening-corrected diagrams yield age estimates ranging from 63 ± 15 to 160 ± 60 Myr. Implications for the recent evolution of the disk near NGC 206 are discussed.