New Reductions of the Astrographic Catalogue: High Accuracy, Early Epoch Positions for Proper Motion Studies

Abstract

AbstractThe Astrographic Catalogue (AC) measures are being reduced at the U.S. Naval Observatory to provide early epoch positions for approximately 5 million stars. The data, when combined with recent observations, provide a baseline of about 100 years with which to compute proper motions. Due to the inhomogeneity of telescopes and measuring techniques used in the AC program, each of the 22 zones is being reduced independently with the Astrographic Catalog Reference Stars (ACRS). The data are analyzed and corrected for radial distortions, tilt, magnitude-dependent terms, coma, and distortions based on reseaux and measuring apparatus. To date, eleven zones have been reduced and are available on the WWW (http://aries.usno.navy.mil/ad/ac.html) or the international data centers. Mean errors of the positional data vary from zone to zone, but are generally in the 190-320 mas range per each image.The newly reduced AC data are being combined with the USNO’s Twin Astrograph Catalog (TAC) in support of the Sloan Digital Sky Survey. This catalog should be available by the end of 1996. When the Tycho data are released, the AC positions will be used to improve the proper motions of the Tycho stars. In order to aid this work, the AC zones released by USNO have Tycho identifications, where applicable.