A DEEP UBVRI CCD PHOTOMETRIC-STUDY OF THE MODERATELY YOUNG SOUTHERN OPEN STAR CLUSTER NGC-4755=KAPPA-CRUCIS

CCD observations in U, B, V, R and I passbands have been used to gener ate (U-B), (B-V) colour-colour and deep V, (B - V); V, (U - B) and V, (V - I) colour-magnitude diagrams for the young open cluster NGC 4755. The sample consists of 813 stars reaching down to V similar to 20 mag . There appears to be non-uniform extinction over the face of the clus ter with a mean value of E (B - V) = 0.41 mag and a range of about 0.0 5 mag. The true distance modulus to the cluster has been estimated as 11.6+/-0.2 mag. An age of similar to 10 Myr has been assigned to the p ost-main sequence (MS) cluster members. Ages of the post-MS and pre-MS stars indicate that massive (M > 10 M.) and low mass (M < 2 M.) stars in the cluster are formed nearly at the same time from a molecular cl oud which might have existed for a minimum period of about 6 - 7 Myr.