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The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| Initial Results of a Comprehensive Ultrasoft Survey of the Einstein IPC Database: Source List and Confirmation of the Selection Procedure
We have carried out a survey of the entire Einstein IPC database (atotal of 5934 sources) to select objects with strong components ofultrasoft X-ray emission (i.e., emission below 0.5 keV). The selectioncriteria are based on ratios of counts within three broad energy bands(i.e., X-ray ``colors''). A total of 516 objects have been selected,with 202 (39%) having been identified through correlations with otherdatabases. Of the currently identified objects, 45% are active galacticnuclei, 28% are stellar objects, 6% are ``normal'' galaxies and galaxyclusters, and the remaining 21% are ``nonstellar'' Galactic objects suchas cataclysmic variables, pulsars, and white dwarfs. We present adiscussion of the survey selection procedure, the list of selectedsources, and discussions of interesting objects from the aforementionedgroups. We discuss the remarkable success of our rather ``lowresolution'' method of estimating spectral shape and present plans forfollow-up studies of the as yet unidentified sources.
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