CCD photometric and spectroscopic observations of the young open cluster NGC 433

This paper presents the first CMD diagram and spectral types of stars in the field of NGC 433. The cluster is rather poor, containing 12 stars down to V = 16 in a radius of 106 arcsec around R.A. 1h 15m 07s, Dec. + 60 deg 11 arcmin 11.7 arcsec (2000.0). The averaged reddening is (E(B - V)) = 0.8. The brightest stars are B5, corresponding to an age less than 110 Myr. The derived cluster distance of 2.1 Kpc is compatible with a physical association with an H I cloud detected in the cluster direction, while the CO clouds observed in the same direction are very likely in the foreground. Within the limits of the photometry, the cluster consists of a clump of B stars and is lacking of fainter stars. This work supports the idea that the population of disk stellar clusters cannot be sharply divided into 'true' bound open clusters and unbound stellar groups.