UCAC5 Catalog Definitions


The US Naval Observatory (USNO) has a long history of providing accurate astrometric data for millions of stars from their own observations plus other data. The USNO CCD Astrograph Catalog (UCAC) project utiized the "redlens" 20 cm aperture astrograph in an all-sky observing program between 1997 and 2004 (CTIO in the south, NOFS in the north) with a limiting magnitude of about R = 16.5. The previous release, UCAC4, became available in 2012.

The 1st Gaia data release provides proper motions for only about 2 million stars (TGAS subset of the Tycho-2 stars) in the mainly 6 to 11.5 magnitude range. Gaia DR2 which will contain proper motions of about a billion stars is scheduled for release in April 2018. In the meantime the astronomical community would benefit from proper motions of millions of stars fainter than the Tycho-2 limit, if a substantial improvement in precision and accuraccy could be made beyond what was available in the pre-Gaia era.

Re-reduction of UCAC + combine with Gaia DR1 provides proper motions for over 107 million stars on the 1 to 5 mas/yr level, strongly depending on magnitude. UCAC observations (mean epoch 2001) provide positions with 10 to 70 mas precision, and about 14 years of epoch difference to Gaia DR1.
Please see also the paper, Zacharias, Finch, & Frouard (2017), which contains several usful figures and validation results for the UCAC5 data. Full UCAC5 documentation is available here.

Name Intype Units Description
srcid long Gaia source ID
ra double deg Gaia RA at epoch 2015.0
dec double deg Gaia Dec at epoch 2015.0
erg float mas Gaia DR1 position error RA at epoch 2015.0
edg float mas Gaia DR1 position error Dec at epoch 2015.0
flg int flag: 1 = TGAS, 2 = other UCAC-Gaia star, 3 = other NOMAD
nu int number of images used for UCAC mean position
epu double year mean UCAC epoch
ira double deg mean UCAC RA at epu epoch on Gaia reference frame
idc double deg mean UCAC Dec at epu epoch on Gaia reference frame
pmur float mas/yr proper motion RA*cosDec (UCAC-Gaia)
pmer float mas/yr formal error of UCAC-Gaia proper motion RA*cosDec
pmud float mas/yr proper motion Dec (UCAC-Gaia)
pmed float mas/yr formal error of UCAC-Gaia proper motion Dec
gmag float mag Gaia DR1 G magnitude
umag float mag mean UCAC model magnitude
rmag float mag NOMAD photographic R magnitude
jmag float mag 2MASS J magnitude
hmag float mag 2MASS H magnitude
kmag float mag 2MASS K magnitude