Version 1.0 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. This was the version used by HST operations prior to cycle 15.
Version 1.2 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. ==Catalog format==