New astrometric reductions of the US Naval Observatory CCD Astrograph
Catalog (UCAC) all-sky observations were performed from first
principles using the TGAS stars in the 8 to 11 magnitude range as
reference star catalog. Significant improvements in the astrometric
solutions were obtained and the UCAC5 catalog of mean positions at a
mean epoch near 2001 was generated. By combining UCAC5 with Gaia DR1
data new proper motions on the Gaia coordinate system for over 107
million stars were obtained with typical accuracies of 1 to 2 mas/yr
(R = 11 to 15 mag), and about 5 mas/yr at 16th mag. Proper motions of
most TGAS stars are improved over their Gaia data and the precision
level of TGAS proper motions is extended to many millions more,
fainter stars.
The database table uses actual NULLs for missing photometry, and all
angular coordinates have been homogenised to degrees.
