Membership, binarity, reddening and metallicity of red giant candidates in three southern open clusters

37 potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268 were observed in the UBV system, while 22 of them were also observed in the DDO system. The observations were made at La Silla and Cerro Tololo Inter-American observatories (Chile), using pulse-counting photoelectric photometers. Coravel radial velocities (RVs) were obtained at La Silla for 24 red giant candidates in the three clusters. Five stars of NGC 6192 have RVs in the narrow range -8.8 km/s < VR < -6.4 km/s, including two new spectroscopic binaries (SBs). Three stars of NGC 6208 - including a new SB - and three stars of NGC 6268 show similar RVs so that their physical membership to NGC 6208 and NGC 6268, respectively, is highly probable. Mean radial velocities are: -7.7 ± 0.38 km/s (NGC 6192), -32.21 ± 0.28 km/s (NGC 6208) and -15.11 ± 0.08 km/s (NGC 6268). We have also derived the following mean E(B-V) values from Janes (1977) iterative method: 0.63 ± 0.02 (NGC 6192), 0.31 ± 0.02 (NGC 6208) and 0.43 ± 0.02 (NGC 6268).