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GSC: Help

GSC - HST Guide Star Catalog, Version 1.2


Overview

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 STScI Website provides more complete details of the various GSC versions: http://www-gsss.stsci.edu/Catalogs/Catalogs.htm

The Guide Star Catalog Version, Version 1.2 contains an astrometric recalibration and other refinements compared to the previous version (1.1). The overall rms error of the GSC 1.2 is estimated to be better than 0.3 arcseconds. 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. Additional information on the reduction is available at http://www-gsss.stsci.edu/Catalogs/GSC/GSC1/gsc12/DESCRIPTION.HTM

Notice that the HEASARC has made no attempt to combine objects with multiple listings in the GSC 1.2 Catalog (due to their being present on more than the plate) into a single entry in this database, as the HEASARC had done for its database version of the GSC 1.1 Catalog.

The HEASARC recommends that Browse cone searches not exceed a radius of 30 arcminutes, since, as one will quickly discover, a radius of 30 arcminutes usually contains hundreds if not thousands of stars. To search a larger area, we recommend that users construct a mosaic of the results of a sequence of 30-arcminute searches using offset coordinates. Notice that the default cone search radius is 1 arcminute.

Finally, notice that the STScI states that GSC 1.2 should NOT be used for HST phase 2 coordinates, as GSC 1.2 has not been installed in the HST ground system.


References

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

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)

Provenance

This database table was created by the HEASARC in May 2001 based on a CD-ROM version of the GSC 1.2 supplied by the STScI. This version of GSC is out of date, and it is no longer available in HEASARC Browse as a result. This documentation is maintained for historical reference only. The HEASARC recommends accessing the latest version of GSC either from VizieR or directly from the STScI web site. Note that HEASARC's Browse web application can query any VizieR table.

Parameters

Name
The GSC identification of the object; this is made up of the GSC prefix, a plate number (5 digits) and a star number on the plate (5 digits), with the latter two fields separated by a dash, as recommended by the Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the object in the selected equinox. In the original STScI Catalog, this was given in equinox J2000 and at the epoch of the plate in decimal degrees, to a precision of 0.00001 degrees. The overall rms error of positions in the the GSC 1.2 is estimated to be better than 0.3 arcsec.

Dec
The Declination of the object in the selected equinox. In the original STScI Catalog, this was given in equinox J2000 and at the epoch of the plate in decimal degrees, to a precision of 0.00001 degrees. The overall rms error of positions in the the GSC 1.2 is estimated to be better than 0.3 arcsec.

Error_Radius
The esimated mean error in the position, in arseconds (").

Pmag
The (usually photographic) magnitude for the object, in the band specified by the pmag_band parameter.

Pmag_Error
The mean error in the magnitude.

Pmag_Band
The band code for the magnitude designating the following combination of emulsion and filter:

         pmag_band 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
  

GSC_Class
A stellar/non-stellar classification flag for the object, using the following definitions:

         Code     Meaning
         ----     -------
           0      Star
           1      Galaxy
           2      Blend
           3      Non-Star
           4      Unclassified
           5      Artifact
  

Plate_ID
An alphanumeric designation for the plate on which the object was found. This is referred to as the GSSS No. in the GSC documentation (cf. Lasker et al. 1990, AJ, 99, 2019, Table III), and is described as an "internal designation generated by the GSSS software system to provide a unique and operationally consistent plate name for catalog generation and storage."

Multiple_Flag
A flag that is set to "T" if there are multiple entries at the same position in the GSC 1.2, and set to "F" otherwise.


Contact Person

Questions regarding the GSC database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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