Search for (globular) clusters in M31. I. Candidates in a70'square field centered on M31.

B and V plates for 19 fields covering a 4° × 4° area centered on M31 have been obtained with the Loiano 152 cm F/8 Ritchey-Chrétien telescope (17"/mm scale). A search is in progress for (globular) clusters in M31. This search, made by visual inspection, has yielded, in the central field (70' × 70'), three classes of candidates with different degrees of confidence. A cross check against available lists of H II regions, planetary nebulae, miscellaneous objects has been made to limit contamination of the sample. The two best classes obtained (A, B in table III) include 240 objects, representing an increment of the number of candidates, in the same field, of about 20 % with respect to previous lists. A comparison with the Sargent et al. (1977) catalogue shows that 13 of the 208 candidates they found in the same area have to be discarded. The third class (C in table III) lists 48 objects, mostly faint, whose degree of confidence as globular cluster candidates is lower. limiting magnitude down to which this survey is estimated to be complete is V ≃ 18.

Two tests to check the self-consistency of the criteria used in the selection have been made: the first one by inspecting a deep red plate, the second one by applying a modified spatial gray tone co-occurrence method to the data obtained by scanning a considerable sample of images of candidates and stars on the V plate with a PDS microphotometer.

The flattening of the projected density profile of clusters found in the inner region by Harris and Racine (1979) with respect to the r^1/4 law is still evident although reduced.