Abstract:
The colour-magnitude diagram for NGC 1851 is presented to a limit of V = 21.0 mag, approximately 2 mag below the main-sequence turn-off point, on the basis of UBV photoelectric photometry and electronographic BV photometry. The main-sequence turn-off parameters are (B-V)t = 0.40±0.03 mag; Vt = 19.45±0.1 mag. From the location of the horizontal branch stars, the apparent distance modulus to the cluster has been estimated as 15.45±0.2 mag. An age of 15±3 Gyr has been assigned to the cluster from the fitting of VandenBerg & Bell theoreticalisochrones
