Star clusters in M33. I. Detection, morphology, and photometry

In this paper we present the discovery of 60 star clusters in 20 multiband Hubble Space Telescope (HST) WFPC2 fields in M33. The fields sample a varie ty of environments, from outer regions to spiral arms and, central regions, as well as a range of galactocentric distances. The HST spatial resolution allowed us to penetrate the crowded, spiral arm regions of M33 yielding th e first unbiased, representative sample of star clusters for this galaxy. W e discuss the separation of clusters from stellar sources, and from other e xtended sources such as star-forming regions, H II regions, and supernova r emnants. For the clusters we present multiband images and discuss morpholog y, location, and integrated photometry. Measured cluster colors and magnitu des are presented. The cluster density in our sample as a function of galac tocentric distance yields an estimate of 690 total clusters in M33.