A Hubble Space Telescope Survey of the Disk Cluster Population of M31. I. WFPC2 Pointings11Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555.

Abstract

ABSTRACTAs a follow‐up to the automated cluster search carried out by Williams & Hodge, we have examined 39 Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) pointings to locate and study a comprehensive collection of disk clusters. The Williams technique was effective in finding young clusters, but not intermediate‐age or old clusters. Our searches have shown that M31 has large numbers of these intermediate and older open clusters, most of them undetected by both the Williams survey and other ground‐based searches. We present a catalog of 343 clusters detected on the WFPC2 images. Extrapolation from our data indicates that the entire disk of M31 contains approximately 80,000 star clusters. We have carried out integrated multicolor photometry of these clusters to ascertain their properties and to compare their properties with cluster systems of other galaxies. We show the cluster luminosity function, the color‐magnitude diagram, the formation function, and the size distribution. Cluster densities and colors show trends with disk position. An age distribution is derived and, although the ages are very uncertain for the fainter clusters, there is evidence for cluster dynamical destruction at about the same rate as in our Galaxy.