—Zacharias et al. 2015.
URAT (USNO Robotic Astrometric Telescope) is a follow-up project to the successful UCAC project using the same astrograph but with a much larger focal plane array and a bandpass shifted further to the red. Longer integration times and more sensitive, backside CCDs allowed for a substantial increase in limiting magnitude, resulting in about 4-fold increase in the average number of stars per square degree as compared to UCAC. Additional observations with an objective grating largely extend the dynamic range to include observations of stars as bright as about 3rd magnitude. Multiple sky overlaps per year result in a significant improvement in positional precision as compared to UCAC.
URAT-1 is an observational catalogue at a mean epoch between 2012.3 and 2014.6; it covers the magnitude range 3 to 18.5 in R-band, with a positional precision of 5 to 40 mas. It covers most of the northern hemisphere and some areas down to –24.8 degrees in declination.
According to the definition used in this work, URAT-1 is a dense survey, in the cross-match algorithm Gaia is the leading catalogue, this means that Gaia objects matches are searched for in URAT-1.
For this catalogue special treatment was done for a) the sources which are resolved in Gaia, b) the possible underestimation of astrometric errors in URAT-1, and c) small issues in Gaia astrometry, especially for bright stars.