ADC/CDS Standard Document for Catalog:
/catalogs/1/1247/

IMPORTANT NOTICE:

Superseded          The AC2000 Catalogue             (Urban+ 1997)
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The AC2000: the Astrographic Catalogue on the Hipparcos System
    Urban S.E., Corbin T.E., Wycoff G.L., Martin J.C., Jackson E.S.,
    Zacharias M.I., Hall D.M.
    <Astron. J. 115, 1212 (1998)>
    =1998AJ....115.1212U
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ADC_Keywords: Positional data ; Astrographic zones ; Surveys

Description:

    The Astrographic Catalogue (AC) was an international effort designed
    to photograph and measure the positions of all stars brighter than
    magnitude 11.0. In total, some 4.6 million stars were observed, many
    as faint as 13th magnitude. Users should realize that a few thousand
    of the brightest stars are not included; their images on the source
    plates were grossly over-exposed and therefore measurements were often
    not made. This project was started over 100 years ago, and the
    positions that have been derived from the AC data are being used, in
    combination with modern epoch positions, to determine accurate proper
    motions.

    The United States Naval Observatory has completed the reductions of
    the Astrographic Catalogue data (AC) to a consistent system. The
    resulting catalog, called AC 2000, contains 4,621,836 stars covering
    the entire sky, at an average epoch of 1907. The positions are on the
    Hipparcos reference frame (J2000.0) at the epochs of observation.

    Each of the 22 zones making up the Astrographic Catalogue was reduced
    independently using the Astrographic Catalog Reference Stars (ACRS).
    Each was analyzed for tilt, radial and tangential distortions, coma,
    magnitude equation and non-symmetric field distortions. Following
    these reductions, the data were placed on the Hipparcos system and the
    magnitudes were converted to be close to that of the Tycho B data. The
    resulting data were then combined into the final catalog. Detailed
    information on the reduction methodology and input data can be found
    in the file "intro.tex", or in the postscript documents provided
    provided in the "ps" subdirectory.

    The data contain the positions (eq. J2000.0) at mean epochs of
    observation, magnitude estimates and accuracy estimates for each star.
    Cross identifications with the Hipparcos Catalogue, Tycho Catalogue
    and the Astrographic Catalog Reference Stars are provided to
    facilitate future work with these stars. Interested parties are
    encouraged to visit the AC web site at
    http://ad.usno.navy.mil/proj/AC/ac.html

See also:
    Superseded by catalog 1275:

    1275 : The AC 2000.2 Catalogue             (Urban+ 2001) 
    at URL ftp://adc.astro.umd.edu/pub/adc/archives/catalogs/1/1275/


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