HSOY is a catalog of 583'001'653 objects with precise astrometry based on
PPMXL and Gaia DR1. Typical formal errors at mean epoch in proper motion are
below 1 mas/yr for objects brighter than 10 mag, and about 5 mas/yr at the
faint end (about 20 mag). South of -30 degrees, astrometry is significantly
worse. HSOY also contains, where available, USNO-B, Gaia, and 2MASS
photometry. HSOY's positions and proper motions are given for epoch J2000.
The catalog becomes severely incomplete faintwards of 16 mag in the G-band.
The mean epochs are typically very close to Gaia's J2015.
HSOY still contains about 0.7% spurious close
"binaries" (non-matched stars) from the original USNO-B (marked with non-NULL
clone). Also, failed matches within Gaia DR1 contribute another 1.5% spurious
pairs (marked with non-NULL comp). In both cases, astrometry presumably is
sub-standard.
More information is available at http://dc.g-vo.org/hsoy.
PPMXL is a catalog of positions, proper motions, 2MASS- and optical
photometry of 900 million stars and galaxies, aiming to be complete
down to about V=20 full-sky. It is the result
of a re-reduction of USNO-B1 together with 2MASS to the ICRS as
represented by PPMX. This service additionally provides improved proper
motions computed according to Vickers et al, 2016
(:bibcode:`2016AJ....151...99V`).
The SPM4 Catalog contains absolute proper motions, celestial
coordinates, and B,V photometry for 103,319,647 stars and galaxies
between the south celestial pole and -20 degrees declination. The
catalog is roughly complete to V=17.5. It is based on photographic and
CCD observations taken with the Yale Southern Observatory's
double-astrograph at Cesco Observatory in El Leoncito, Argentina.