Contents, Test Results, and Data Availability for GSC 1.2

Abstract

A collaboration between STScI and ARI has produced a new astrometric reduction of the Guide Star Catalog (GSC, Lasker et al. 1990). This new version, GSC 1.2, has dramatically reduced the systematic errors present in GSC 1.1. The positions in GSC 1.1 are affected by plate-based systematic distortions which are largest at the plate edges (1.0″, north; 1.2″, south) (Taff et al. 1990a). These positions also suffer from systematic errors which are a function of magnitude and radial distance from the plate center (Morrison et al. 1996). This effect is small for radii under 2.7° from the plate center, then rapidly increases producing an average offset of the faint stars (15m) versus the reference stars (10m) of 0.9″ at the plate edges.