Characterizing and correcting the proper motion bias of the bright <i>Gaia</i> EDR3 sources

In this paper, we characterize magnitude-dependent systematics in the proper motions of Gaia EDR3 catalog and provide a prescription for their removal. The reference frame bright stars ( G ? 13) is known to rotate with respect extragalactic objects, but rotation has proven difficult correct. We employ sample binary open cluster members motion bias as spin frame. show that varies magnitude, reaching up 80 ?as yr ?1 sources range = 11–13, several times formal uncertainties. also evidence an additional dependence on color source, magnitude ~10 . However, correction proportional effective wavenumber unsatisfactory very red or blue stars, do not recommend its use. recipe align brighter than 13 International Celestial Reference Frame.