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Session 16 - Astrometry.
Display session, Wednesday, January 07
Exhibit Hall,
The United States Naval Observatory has completed new reductions of the Astrographic Catalogue data. This catalog, called AC 2000, contains 4.6 million stars distributed globally. Since the density of Hipparcos stars is inadequate to reduce the AC data on a plate-by-plate basis, the measures have been initially reduced using the Astrographic Catalog Reference Stars (ACRS). All positions have been converted to the Hipparcos system using systematic differences computed for those stars in common between Hipparcos and the AC. Since each participating observatory used different instruments in photographing and measuring the plates, data from each were reduced as if they comprised an independent catalog. Measured images from each plate have been analyzed for scale, rotation, non-perpendicularity of measuring axes, differences in scale between measuring axes and plate tilt. Presence of radial and non-radial optical distortions, coma and magnitude equation were investigated and corrected, where applicable. Every attempt has been made to apply all published errata to the data, and a detailed search for previously unknown typographical errors was performed. All data have been combined and the final catalog contains positions, magnitudes, epochs, error estimates, and cross reference information. All positions are on the Hipparcos system for equinox J2000.0. A CD-ROM containing the catalog and the reduction details is available. For additional information visit WWW site http://aries.usno.navy.mil/ad/ac.html.
