Astrometric reference stars: from UCAC to URAT

Abstract

Abstract Currently available astrometric catalogs will be reviewed, and instrumentation and observational issues discussed, particularly systematic errors and their control. The U.S. Naval Observatory (USNO) CCD Astrograph Catalog (UCAC) is an all‐sky astrometric survey to 16th magnitude. It was observed with a semi‐automated telescope on a low budget. The second data release (July 2003) contains positions, proper motions, and photometry for over 48 million stars; the final release is expected in 2006. Design studies have been performed for a new 0.9‐meter aperture USNO Robotic Astrometric Telescope (URAT) with a single chip (≥100 Mpixel), 3 degree FOV and circular symmetric pupil. Its operation is envisioned to be fully automatic, generating stellar positions on the 5 to 10 mas level to at least 18th magnitude with a limiting magnitude of about 20 to 21. These reference stars, being on an inertial system (linked to quasars), will be very beneficial for LSST, PanSTARRS and other projects. With a few years of observing, absolute trigonometric parallaxes (5‐20 mas, depending on magnitude) could be obtained for all stars accessible by URAT from an initially southern hemisphere location. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)