Identification of a complete sample of northern ROSAT All-Sky Survey X-ray sources. II. The optical observations

We describe a program for the optical identification of a representative sample of RASS sources contained in six study areas north of delta = -9 deg, with |b^II| >~ 20 deg including one region near the North Galactic pole (NGP) and one near the North Ecliptic pole (NEP) and present some preliminary results. A full identification has been carried out for a count-rate and area-limited complete subsample comprising 674 sources. The ratio of ``extragalactic'' ( e.g. AGN, clusters of galaxies) to ``stellar'' (e.g. coronal emitters, active binaries) counterparts was found to depend on the galactic neutral hydrogen column density, N_H. In the area near the NGP (low N_H) ``extragalactic'' counterparts dominate, while in the area with the highest N_H most X-ray sources are identified with stellar counterparts.