HST OBSERVATIONS OF GLOBULAR-CLUSTERS IN M-31 .1. SURFACE PHOTOMETRY OF 13 OBJECTS

We present the initial results of a study of globular clusters in M 31 , using the Faint Object Camera (FOC) on the Hubble Space Telescope (H ST). The sample of objects consists of 13 clusters spanning a range of properties. Three independent image deconvolution techniques were use d in order to compensate for the optical problems of the HST, leading to mutually fully consistent results. We present detailed tests and co mparisons to determine the reliability and limits of these deconvoluti on methods, and conclude that high-quality surface photometry of M 31 globulars is possible with the HST data. Surface brightness profiles h ave been extracted, and core radii, half-light radii, and central surf ace brightness values have been measured for all of the clusters in di e sample. Their comparison with the values derived from ground-based o bservations indicates the later to be systematically and strongly bias ed by the seeing effects, as it may be expected. A comparison of die s tructural parameters with those of the Galactic globulars shows that t he structural properties of the M 31 globulars are very similar to tho se of their Galactic counterparts. A candidate for a post-core-collaps e cluster, Bo 343 = G 105, has been already identified from these data ; this is the first such detection in die M 31 globular cluster system .