2004A&A...417..945P

We present a BVI photometric and astrometric catalogue of the open cluster NGC 3960, down to limiting magnitude V∼22, obtained from observations taken with the Wide Field Imager camera at the MPG/ESO 2.2m Telescope at La Silla. The photometry of all the stars detected in our field of view has been used to estimate a map of the strong differential reddening affecting this area. Our results indicate that, within the region where the cluster dominates, the E(V-I) values range from 0.21 up to 0.78, with E(V-I)=0.36 (E(B-V)=0.29) at the nominal cluster centroid position; color excesses E(V-I) up to 1 mag have been measured in the external regions of the field of view where field stars dominate. The reddening-corrected color-magnitude diagram (CMD) allows us to conclude that the cluster has an age between 0.9 and 1.4Gyr and a distance modulus of (V-M_V)₀=11.35. In order to minimize field star contamination, their number has been statistically subtracted based on the surface density map. The empirical cluster main sequence has been recovered in the V vs. V-I and in the J vs. J-K_S planes, using optical and infrared data, respectively. From these empirical cluster main sequences, two samples of candidate cluster members were derived in order to obtain the luminosity distributions as functions of the V and J magnitudes. The Luminosity Functions have been transformed into the corresponding Mass Functions; for M>1M_☉, the two distributions have been fitted with a power law of index α_V=2.95±0.53 and α_J=2.81±0.84 in V and in J, respectively, while the Salpeter Mass Function in this notation has index α=2.35.