Photometric Study of the Old Open Cluster NGC 6791

We present BVI_c photometry of sim 7000 stars from the field of the old open cluster NGC 6791. We also obtained photometry of sim 2000 stars located in the four comparison fields located around the cluster. The radial extent of NGC 6791 is at least 9.'3 and its central radius is r_c approx 124". Contribution of the field stars to the different parts of the cluster color magnitude diagrams (V vs. B-V and V vs. V-I) is studied. NGC 6791 possesses about 47 blue stragglers and about 55 yellow stragglers. We note presence of about 19 "faint" blue stragglers located close to the blue side of the cluster turnoff. NGC 6791 harbors about 174 red giants, 22 of them are horizontal branch stars. Seven candidates for sdB/sdO subdwarfs were discovered in the cluster field. Under assumption of cluster membership they possess 3.6<M_v<4.8 and -0.35<(B-V)_0<-0.14. The color index of the bluest sdB/sdO candidate provides an upper limit on the cluster reddening E(B-V=0) leq 0.195. The observed luminosity function of NGC6791 is more or less constant for 17.5<V<21.0 and then brakes due to increasing incompleteness of the photometry. The conservative lower limit on the cluster total mass is 4070 M_odot.