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Description
UCAC3 is a compiled, all-sky star catalog covering mainly the 8 to 16
magnitude range in a single bandpass between V and R. Positional
errors are about 15 to 20 mas for stars in the 10 to 14 mag range.
It is supplemented by proper motions and SuperCosmos and 2MASS
photometric data, as well as various flags.
The proper motions of bright stars are based on about 140 catalogs,
including Hipparcos and Tycho, as well as all catalogs used for the
Tycho-2 proper motion construction. Proper motions of faint stars are
based on a re-reduction of early epoch SPM data (-90 to -10 deg Dec)
plus Schmidt plate data from the SuperCosmos project (down weighted
due to systematic errors of order 100 mas). The proper motions of
faint stars (R <= 13.5) therefore should be used with caution. The
unpublished plate measure data from the AGK2, the Hamburg Zone
Astrograph, the USNO Black Birch Astrograph, and the Lick Astrograph
have considerably contributed to improve proper motions for stars
mainly in the 10 to 14 mag range (down to the UCAC3 limit for Lick
data); however, these data do not cover all sky.
UCAC3 features a number of major differences with respect to UCAC2:
- complete sky coverage
- re-reduction of the pixel data with better modeling
- double stars are resolved to the limit of the data
- significantly improved photometry from CCD data
- slightly deeper limiting magnitude with larger number of stars/area
- reduced systematic errors of CCD observations
- the addition of several new catalogs for improved proper motions
- photometry in the B, R, and I bands from the SuperCosmos project
- minor planet observations have been sorted out
- identification of more high proper motion stars
- match with 2MASS extended sources and LEDA galaxies
Additional details will be published in the upcoming release paper
(Zacharias et al. 2009) and in several technical papers describing
details of the reduction procedures and results. For the latest
updates see http://www.usno.navy.mil/usno/astrometry .
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