USNO-A V2.0: Catalog Help
USNO: A Catalog of Astrometric Standards
David Monet1 Alan Bird1, Blaise Canzian1, Conard Dahn1, Harry Guetter1, Hugh Harris1, Arne Henden2, Stephen Levine1, Chris Luginbuhl1, Alice K. B. Monet1, Albert Rhodes1, Betty Riepe1, Steve Sell1, Ron Stone1, Fred Vrba1, Richard Walker1
1) U.S. Naval Observatory Flagstaff Station (USNOFS)
2) Universities Space Research Association (USRA) stationed at USNOFS.
Note: for more detailed information on the USNO-A2.0 catalog,
please consult the documentation provided by Dave Monet at USNOFS.
USNO-A2.0 is a catalog of 526,280,881 stars, and is based on a re-reduction of the Precision Measuring Machine (PMM) photographic plate scans that were the basis for the USNO-A1.0 catalog. For field centres of declination -30 degrees and above, the survey plates are taken from the Palomar Observatory Sky Survey I (POSS-I) O and E plates. For field centres of declination -35 degrees and below, the survey plates are taken from the UK Science Research Council SRC-J and European Southern Observatory ESO-R survey plates.
The major difference between A2.0 and A1.0 is that A1.0 used the Guide Star Catalog (Lasker et al. 1986) as its reference frame, whereas A2.0 uses the International Celestial Reference Frame (ICRF), with the ACT catalog (Urban et al. 1997) for its astrometric reference catalog.
USNO-A2.0 (as with A1.0) does not assign arbitrary names to each object, so the co-ordinates and source catalogue should be quoted.
USNO-A2.0 provides calculated B and V magnitudes for its stars, calibrated from the input O+E+J+F photographic magnitudes. The brightest stars on each plate were calibrated from the Tycho experiment on the Hipparcos satellite, while the fainter photometric calibration came from the USNO CCD parallax fields in the North, and the Yale Southern Proper Motion CCD calibration fields (van Altena et al. 1998) for fields near the South Galactic Pole. Typical photometric errors are ~0.25 mag.
USNO-A2.0 presents a right ascension and declination for each star computed from the mean of the 'red' (E or F) and 'blue' (O or J) plate exposures (J2000 co-ordinates, at the epoch of the mean of the 'red' and 'blue' observations). The catalog provides useful positions for stars fainter than about 11th magnitude. Because brighter stars have saturated images (and hence less accurate positions), the positions of bright stars were found by cross-correlation with the Tycho and ACT catalogs. The USNO-A2.0 co-ordinates of ACT and Tycho stars should not be used where astrometric accuracy is critical. Typical astrometric errors are ~0.25 arcsec.
Notes and Acknowledgments:
The PMM program has been supported through internal funding by USNO, and by funding provided by the U.S. Air Force through the Space Surveillance Network Improvement Program.
This work is based partly on photographic plates obtained at the Palomar Observatory 48-inch Oschin Telescope for the First and Second Palomar Observatory Sky Surveys which was funded by the Eastman Kodak Company, the Alfred Sloan Foundation, the National Science Foundation grants AST84-08225, AST87-19465, AST90-23115 and AST93-18984, and the National Aeronautics and Space Administration grants NGL 05002140 and NAGW 1710.
This catalog is based, in part, upon original material from the UK Schmidt telescope. copyright in which is owned by the UK Particle Physics and Astronomy Research Council. No charge beyond recovery of costs has been made by USNO or PPARC for the provision of these data. These data are provided to its recipient for its purpose without restriction, except on the condition that the data should not be replicated, in whole or in part, and passed on for profit. The plates for the SRC-J survey were taken with the UK Schmidt Telescope (UKST).
The European Southern Observatory holds the copyright to the ESO-R Survey
plate material, and USNO scanned these plates under an agreement with ESO.
This agreement states, in part, that the data derived from these scans
shall be available to the public without restriction and without charge
beyond recovery of the cost of distribution.