This catalog combines Gaia DR1, Pan-STARRS 1, SDSS and 2MASS astrometry
to compute proper motions for 350 million sources across three-fourths of
the sky down to a magnitude of mr≈20. Positions of galaxies from Pan-STARRS 1
are used to build a reference frame for PS1, SDSS, and 2MASS data.
Gaia DR1 is adapted to that reference frame by exploiting that locally,
proper motions are linear.
GPS1 has a characteristic systematic error of less than 0.3 mas/yr, and
a typical precision of 1.5−2.0 mas/yr. The proper motions have been
validated using galaxies, open clusters, distant giant stars and QSOs. In
comparison with other published faint proper motion catalogs, GPS1's
systematic error (2.0 mas/yr). Similarly, its precision (~1.5 mas/yr) is
an improvement by ∼ 4 times relative to PPMXL and UCAC4 (∼6.0 mas/yr).
For QSOs, the precision of GPS1 is found to be worse (∼2.0−3.0 mas/yr),
possibly due to their particular differential chromatic refraction (DCR).
