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  1. Brian McLean

    GSC 1.0

    The original version of this catalog was created to support the identification and use of Guide Stars for the pointing of the HST. It is based on the Palomar Quick-V survey in the northern hemisphere and the SERC-J survey in the south. This catalog contains objects in the magnitude range 7-16 and the classification was biased to prevent the use of a non-stellar object as a guide star. The photometry is based on a photoelectric sequence (9-15th mag) near the center of each Schmidt plate. Only stellar photometry was performed so magnitudes of galaxies in this catalog are systematically in error. Astrometry was determined using the AGK3, SAOC or CPC stars depending on plate declination. Although the relative astrometry (required for HST) is about 0.3 arcsec, there are known systematic errors near the plate edges of about 1-2 arcsec.

  2. Brian McLean

    GSC 1.1

    A revised version of the GSC was created with the cooperation of the HIPPARCOS/TYCHO consortia. As part of the preparation for this mission, an input catalog containing the best available data for all stars to at least 11th magnitude was created. By merging these data with the GSC, we were able to add the missing bright star data to provide a complete all-sky catalogue down to the GSC limiting magnitude. In addition, many of the false objects due to artifacts around the halos and diffraction spikes of the bright stars were identified and corrected as well as a number of reported errors. A number of astrographic plates centered on southern hemisphere bright stars (m<3) were also processed and added to the catalog.
    This is the version used by HST operations prior to cycle 15 and is published to the community.

  3. Brian McLean

    GSC 1.2

    In collaboration with the Astronomisches Rechen-Institut in Heidelberg, a new astrometric reduction of the GSC has been completed. This new version, GSC 1.2 has dramatically reduced the plate-based position-dependant and magnitude-dependant systematics present in GSC 1.1
    The PPM and AC reference catalogues were used and absolute position errors have been reduced to about 0.3-0.4 arcsec.