The open cluster NGC 7142: interstellar extinction, distance and age

The results of medium-band photometry of 1037 stars in the area of the old open cluster NGC 7142 down to V = 20.1 mag in the Vilnius seven-colour system are presented. Photometric results are used to classify in spectral and luminosity classes about 80 per cent of stars down to V = 18.5 mag, to identify cluster members, to determine the main cluster parameters and to investigate the interstellar extinction in this direction. The average extinction A V of the cluster is about 1.1 mag [E(B − V) = 0.35], and its distance is 2.3 kpc (the distance modulus 11.8 mag). The age of the cluster, 3.0 Gyr, is estimated from the intrinsic colour-magnitude diagram with individual dereddening of each star and the Padova isochrones. The surface distribution of the extinction is shown. The reddening of the eclipsing variable V375 Cep is found to be close to the average reddening of the cluster. Probably, the cluster contains five red clump giants, two asymptotic branch stars and four blue stragglers.