Abstract. We present the Hamburg/RASS Catalogue of optical identifications (HRC). The catalogue contains optical information about objects inside the error circles of ROSAT All-Sky Survey (RASS) sources. The information was gathered from objective prism and direct plates taken by the Hamburg Quasar Survey (HQS). The plates enable an effective selection of several X-ray emitting classes of objects, as there are galaxies, AGN, QSOs, galaxy clusters and several types of galactic stars, in particular M dwarfs, hot white dwarfs and cataclysmic variables. In the current state (November 1996) the HRC contains information about 3847 X-ray positions and covers about 8480 deg 2 of the high galactic latitude (|b| > 20• ) northern sky. For 81.2% of the X-ray sources a plausible optical counterpart is given. The counterparts of the remaining sources are probably faint (B > 18.5) AGN and galaxy clusters. The HRC is available electronically together with finding charts taken from the digitized direct HQS plates.

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Abstract. We present the X-ray source catalogue obtained from a ROSAT survey in the HQS field HS 47.5/22. The survey consists of 48 overlapping PSPC pointings which were first analysed individually, and then merged to increase the sensitivity. Both modes bring forth sources missed in the other, showing that both are necessary to detect all X-ray sources in the field. The final catalogue contains 574 X-ray sources. The identifications are mainly based on the HQS objective prism plate which allows object classification down to a magnitude m b < ∼ 18.m 5, and a rough distinction between red and blue objects more than a magnitude deeper. Follow-up observations were performed for a number of objects, mainly faint quasar candidates.

The field studied is part of the Hamburg Quasar Survey (Engels et al. 1988, PASPC 2, 143). It contains a spatially and magnitude (down to ∼ 18.m5) complete AGN sample. Several follow-up observations were made: a deep radio continuum survey at 21 cm and 74 cm, a HI survey and a ROSAT survey consisting of 48 overlapping PSPC pointings with .

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