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I/254               The HST Guide Star Catalog, Version 1.2   (Lasker+ 1996)
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The Guide Star Catalog Version 1.2: an astrometric recalibration and
other refinements.
     Morrison J.E., Roeser S., McLean B., Bucciarelli B., Lasker B.
    <Astron. J., 121, 1752 (2001)>
    =2001AJ....121.1752M
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ADC_Keywords: Surveys ; Positional data

Description:
    The Guide Star Catalog (GSC), which has been constructed to support
    the operational need of the Hubble Space Telescope contains nearly 19
    million objects brighter than sixteenth magnitude, of which more than
    15 million are classified as stars. This catalog provides positions
    and magnitudes for these stars.

    The original version of this catalog, GSC 1.0, is described in a
    series of papers: Lasker et al. (1990AJ.....99.2019L);
    Russell et al. (1990AJ.....99.2059R); and
    Jenkner et al. (1990AJ.....99.2082J)

    The reference material for the GSC 1.2 reduction is the "Positions and
    Proper Motions Catalogue":
    PPM-North, Roeser S. and Bastian U., 1988, Cat. <I/146>
    PPM-South, Bastian U. and Roeser S., 1993, Cat. <I/193>
    PPM-Suppl, Roeser S., Bastian U. and Kuzmin A., 1994, Cat. <I/208>
    and the Astrographic Catalogue (AC) which was used to remove the mean
    systematics common to all the plates.

    The overall rms error of the GSC 1.2 is estimated better than 0.3arcsec

    The STScI provides the details of the GSC versions
    ("See also" section below)
    A binary version of the GSC1.2, with C code for querying, is available
    in the subdirectory GSC.

File Summary:
--------------------------------------------------------------------------------
 FileName    Lrecl    Records    Explanations
--------------------------------------------------------------------------------
ReadMe         80         .    This file
out.sam        68       100    Sample output (out of 25,258,765 positions)
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See also:
    http://www-gsss.stsci.edu/gsc/gsc.html : GSC pages at STScI
    http://www-gsss.stsci.edu/gsc/gsc12/description.html : GSC 1.2 page
    http://www-gsss.stsci.edu/gsc/gsc12/gsc12_form.html :  GSC 1.2 access
    I/220 : The HST Guide Star Catalog, Version 1.1 (Lasker+ 1992)

Byte-by-byte Description of file: out.sam
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   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1- 10  I10   ---     GSC      *GSC designation
  12- 20  F9.5  deg     RAdeg     Right ascension in J2000, epoch of plate
  22- 30  F9.5  deg     DEdeg     Declination in J2000, epoch of plate
  33- 36  F4.1  arcsec  PosErr    Mean error on position
  38- 42  F5.2  mag     Pmag      photographic magnitude (see n_Pmag)
  44- 47  F4.2  mag   e_Pmag      Mean error on photographic magnitude
  49- 50  I2    ---   n_Pmag     *[0,18] Coded passband for magnitude
      52  I1    ---     Class     [0,3] Class of object (0=star; 3=non-stellar)
  54- 57  A4    ---     Plate    *Plate designation
  59- 66  F8.3  yr      Epoch    *? Epoch of plate
      68  A1    ---     Mult      [TF] True if multiple object / False otherwise
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Note on GSC: the GSC Identification is made of a plate number
     (5 digits) and star number on the plate (5 digits); note that,
     in the literature, a dash separates generally the two parts.

Note on n_Pmag: the number designates the following combination
     of emulsion and filter:
           magband emulsion filter    Notes
           ------- -------- --------  -----------------------
                 0 IIIaJ    GG395     SERC-J/EJ
                 1 IIaD     W12       Pal Quick-V
                 3 ---      B         Johnson
                 4 ---      V         Johnson
                 5 IIIaF    RG630     Red
                 6 IIaD     GG495     Pal QV/AAO XV
                 7 103aO    ---       POSS-I Blue
                 8 103aE    red plex  POSS-I Red
                10 IIaD     GG495     GPO Astrograph
                11 103aO    GG400     Black Birch Astrograph
                16 IIIaJ    GG495     QV
                18 IIIaJ    GG385     POSS-II Blue
           ------- -------- --------  -----------------------

Note on Plate, Epoch: two plates (+056 and +017) represent data from
    catalogues (mainly Hipparcos Input Catalogue, Cat. <I/196>).
    They have no associated epoch.
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(End)               Brian McLean [STScI], Francois Ochsenbein [CDS]  08-May-1999