K_s-band images of UCDs from our input catalogs that are in a CPM binary or triple system. The images are centered on the eROSITA X-ray source position, and a 15″ radius around this position is shown as magenta dashed circle. The Gaia DR2 source from our input UCD catalogs is represented by a red square, its CPM companion by an orange triangle and further Gaia DR2 sources in the field by cyan diamonds. The arrows indicate the PM, and their length and orientation are scaled to the Gaia DR2 values. Note, that for the actual identification of our UCDs with the eRASS1 catalog the Gaia DR2 coordinates had been propagated with their proper motions to the mean eRASS1 observing data (see Sect. 3), while here they have been projected backwards to the 2MASS epoch.