Identification of a complete sample of northern ROSAT All-Sky Survey X-ray sources

We describe a program for the optical identi fication of a re presen tative sample of RASS sources contained in six study areas north of , with including one region near the North Galactic pole (NGP) and one near the North Ecliptic pole (NEP) and present some pre liminary results. A full identi fication has been carried out for a count-rate and area-limited complete sub sample 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, NH. In the area near the NGP (low NH) "extra galactic” counter parts dominate, while in the area with the highest NH most X-ray sources are identi fied with stellar counter parts.