I/252            The USNO-A2.0 Catalogue                     (Monet+ 1998)
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USNO-A V2.0, A Catalog of Astrometric Standards
     Monet D.
     Bird A., Canzian B., Dahn C., Guetter H., Harris H., Henden A.,
     Levine S., Luginbuhl C., Monet A.K.B., Rhodes A., Riepe B.,
     Sell S., Stone R., Vrba F., Walker R.
    
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ADC_Keywords: Surveys ; Positional data

Description:

    USNO-A2.0 is a catalog  of  526,280,881  stars,  and  is  based  on  a
    re-reduction  of the Precision Measuring Machine (PMM) scans that were
    the basis for the USNO-A1.0 catalog. The major difference between A2.0
    and A1.0 is that A1.0 used the Guide Star Catalog (Lasker et al. 1986,
    see Cat. ) as its reference frame whereas A2.0 uses the ICRF as
    realized by the  USNO  ACT  catalog  (Urban  et  al.  1997,  see  Cat.
    ).

    A2.0 presents  right ascension  and declination  (J2000, epoch  of the
    mean of  the blue and  red plate) and  the blue and  red magnitude for
    each star.  Usage  of  the  ACT  catalog  as  well  as  usage  of  new
    astrometric   and  photometric  reduction  algorithms  should  provide
    improved astrometry (mostly in the reduction of systematic errors) and
    improved  photometry (because the brightest stars  on each plate had B
    and V magnitudes  measured by  the Tycho  experiment on  the Hipparcos
    satellite). The basic format of the catalog and its compilation is the
    same as  for A1.0, and  most users should  be able to  migrate to this
    newer version with minimal effort.


File Summary:
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 FileName    Lrecl  Records    Explanations
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ReadMe          80        .    This file
out.sam         55      100   *Sample output (out of 526,280,881 stars)
read.me         79      353    Author's Original Catalogue Description
usnoa/*          .        .    Compact version of Catalogue (3.6Gbytes)
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Note on out.sam: this file is actually the result of the execution
     of the query on the compacted version of USNO-A2.0 at CDS
     (in subdirectory usnoa, not yet accessible)
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See also:
    ftp://ftp.nofs.navy.mil/usnoa : The Flagstaff FTP site with
         the original catalogue
    http://www.usno.navy.mil/pmm/ : The Precision Measuring Machine
         home page at Flagstaff Station, U.S. Naval Observatory

Byte-by-byte Description of file: out.sam
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   Bytes Format Units   Label     Explanations
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   1- 13  A13   ---   USNO-A2.0 *Original designation in USNO-A2.0 catalogue
  15- 24  F10.6 deg    RAdeg     Right ascension (ICRS) mean of blue/red plates
  25- 34  F10.6 deg    DEdeg     Declination (ICRS) mean of blue/red plates
      35  A1    ---    ACTflag   [A] 'A' when star belongs to ACT (Cat. )
      36  A1    ---    Mflag     [*] '*' magnitudes are probably wrong
  38- 41  F4.1  mag    Bmag      Magnitude from blue plate
  43- 46  F4.1  mag    Rmag      Magnitude from red plate
  48- 55  F8.3  yr     Epoch    *?=0.0 Mean epoch of position
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Note on USNO-A2.0:
    This number allows to retrieve the exact original record: it is made
    of a zone number (4 digits from 0000 to 1725 representing the distance
    in 0.1deg to the South Pole, stepped by 75 = 7.5degrees), and a number
    in the area (8 digits, order by IRCS (J2000) RA);
    ****Note that this number differs from the USNO-A1.0 one.
Note on Epoch:
    Epoch is the averaged date of observation between the blue and
    the red plates.
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Author's Address:
   Dave Monet
   US Naval Observatory Flagstaff Station
   PO Box 1149  (US Mail Only)
   West Highway 66  (FedEx, UPS, etc.)
   Flagstaff AZ 86001 USA

   Voice: 520-779-5132
   FAX:   520-774-3626
   e-mail:  dgm@nofs.navy.mil
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(End)                                     Francois Ochsenbein [CDS]  27-Oct-1998