Picturing the Guide Star Catalog

The information contained in the two CDROMs of the Hubble Space Telescope Guide Star Catalog has been condensed into a series of all-sky images. These images show V-filter flux for all sources, stars, nonstars, and number density for the same three classes of objects. Magnitudes of Guide Stars in the southern hemisphere differ systematically from those in the northern hemisphere due to the different plate emulsion and filter used. Individual object fluxes cannot be calibrated accurately, but by using a large number (16,000 for the first pass, 180,000 for the second) of sources near the equator which were measured on both Palomar and SERC plates, an average calibration can be fit. An intermediate step in the calibration produced a catalog of 180,524 objects in the GSC for which measurements at two colors exist. A catalog binning program, SKYPIC, developed from SKYMAP was used to produce two-dimensional FITS images of Guide Star Catalog fluxes with southern hemisphere plate magnitudes recalibrated to match the northern hemisphere plate V magnitudes. Maps of non-stellar source density, as well as flux, show excesses at the edges of plates, so care should be taken to avoid plate edges when applying characteristics of the Guide Star Catalog to the real universe.