Guide Star Catalog

The first version of this catalog was published in 1989. The first catalog was created by digitizing photographic plates produced by the Palomar Schmidt Quick-V survey for the northern hemisphere and the UK Schmidt SERC-J survey for the southern hemisphere. 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. Stellar photometry was performed in a manner that would systematically reject galaxies. Astrometry was determined using the AGK3, SAOC or CPC catalog stars depending on plate declination. Although the relative astrometry (required for HST) is about 0.3 arc seconds, there are known systematic errors near the plate edges of 1 to 2 arc seconds.[1]

The first revision of the catalog was published in 1992. The Tycho Input Catalog was created by the Hipparcos/Tycho international consortia in preparation for the Hipparcos satellite mission. They produced a catalog containing the best available data for all stars to magnitude 11. Adding the bright star data from this catalog to the GSC produced a complete all-sky catalog 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 (of magnitude less than 3) were also processed and added to the catalog.[2] This was the version used by HST operations prior to cycle 15.

Version 1.2 was published in 2001. It was produced in collaboration with the Astronomisches Rechen-Institut in Heidelberg. This version reduces the plate-based position-dependent and magnitude-dependent systematic errors. The PPM and AC reference catalogs were used and absolute position errors have been reduced to between 0.3 and 0.4 arc seconds.[3]