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Up: The Hamburg/RASS


4. Availability of the catalogue

Until November 1996 10800 X-ray sources from RASSI have gone through the identification process on the HQS Schmidt plates. The HRC was compiled with these data and a correlation with the RASS-BSC. The HRC contains for each X-ray source the X-ray position and the error circle, the positions of the optical candidates and their offsets from the X-ray position. For each optical candidate its optical brightness and a classification is given, if possible. The most likely optical counterpart is marked, if possible, and an identification code is given. The current version of the HRC with 3847 entries is available via anonymous ftp ( in the subdirectory pub/outgoing/rass-id. A README file explains the structure of the catalogue.

Finding charts were prepared from the digitized direct plates and are available as compressed Postscript-files on the ftp-server as well. For the work with the HRC they are considered to be superior to finding charts obtained from the digitized POSSI, because of differences in colour and of the epoch of observation. Since only the red plates of the POSS are currently digitally available, the wavelength overlap with the KODAK IIIa-J emulsion is small. In addition the epochs of the POSS and the HQS plates are 30 - 40 years apart from each other, making proper motions of nearby stars a significant problem for the assignment of catalogue entries to images on the POSS plates. Nevertheless, we recommend to use POSSI plates as well, because they are in general more sensitive and provide additional colour information.

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