Source classification for OM SUSS 5.0

Since the launch of the XMM in 1999 OM images in the six filters have been obtained which are used to construct the SUSS catalogue and the Epoch of observation in the catalogue spans therefore close to 24 years by now. With a positional accuracy of 0.5" some nearby stars show proper motion and it is useful to compute the Epoch 2000 positions for those. The positions are otherwise reported on the (J2000) ICRS system.
The SUSS catalogue has two parts. The first table, called SUMMARY contains the information for each observation. For each observation this table contains the start and end date of the observation, the pointing direction, the exposure time for each of the OM filters and some other parameters. The second table lists all the SOURCES found in all of the images, the magnitudes in different filters, magnitude errors, significance, source extent, quality flags, and a link to the information in the SUMMARY. The epoch of observation can be derived from the start and end time of the observation in the SUMMARY table. Each row in the SOURCES table can be matched to the observation in the SUMMARY and thus be given the epoch of observation. Once the epoch for an observation is known, the observation can be matched to the Gaia DR3 list of high proper
motion objects transformed to the time of the SUSS observation. In order to do this, the following procedure was used: (1) the sources with proper motions larger than 25 mas/yr and absolute PM/error larger than 10 were extracted from the Gaia DR3 catalogue. (2) for each SUSS observation the Gaia DR3 sources within 15 arcminutes of the center of that field were selected. (3) the selected Gaia DR3 were transformed to the epoch of the SUSS observation. (4) the SUSS sources were then matched using XArches[2] to those equal-epoch sources from Gaia-DR3. XArches also provides a probability that of a good match between a SUSS and Gaia DR3 source. Only sources with a probability of good match greater than 0.5 were retained. (5) the Epoch 2000 positions were computed for the matches. (6) after all SUSS observations were processed, the positions of sources which had not been identified as having a high PM were added to the Epoch 2000 positions, so that for all SUSS sources Epoch 2000 position were defined. For clarification, all SUSS positions were J2000, even if at the observed Epoch.