UBV photometry of the southern galactic cluster NGC 4755 = KHI Crucis.

UBV photoelectric magnitudes and colors are presented for 86 stars together with photographic magnitudes and colors for 553 stars in the vicinity of the southern young open cluster NGC 4755. A true distance modulus of 11.82 m is derived corresponding to a linear distance of 2.3 kpc. The evolutionary age is determined to be between 8 and 11.5 x 10 to the 6th years, depending on the assumed chemical composition of the cluster stars. The mean interstellar reddening E(B-V) across the cluster increases with galactic latitude and angular distance from the Coalsack from about 0.40 m to 0.48 m with an average value of 0.44 m. The total number of probable cluster members detected in the field down to a limiting visual magnitude of V = 16.0 m is 203. The linear gravitational radius of the cluster obtained from star strip counts down to visual magnitude 14.5 m is found to be 3.4 pc. The luminosity function derived for NGC 4755 is in good agreement with the initial luminosity function as given by Sandage (1957). The cluster contains six supergiants and three variable Be stars.