Compact star clusters in M81. I. Data from Hubble Space Telescope Wide Field Planetary Camera 2 imaging

In this paper, we present the discovery of 114 compact star clusters in the nearby spiral galaxy M81 from B-, V -, and I-band Hubble Space Telescope W ide Field Planetary Camera 2 imaging in eight fields, covering a total area of similar to 40 arcmin(2). The fields sample a variety of environments (b oth spiral and inter-arm regions), as well as a range of projected galactoc entric distances from 2 to 12 kpc. The sample is complete to V similar to 2 2, deeper by similar to1 mag than any previous cluster survey in M81. We pr esent details of the separation of clusters from both stellar sources and b ackground galaxies, which has been based solely on structural parameters an d morphology and not using any color cuts, as is necessary for ground-based surveys. We present magnitudes and colors of detected clusters. Surface br ightness profiles are compared with single-mass King models, giving a range of core radii for the clusters in our sample between 0.2 and 7 pc.