Marion I. Zacharias

The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)

The second US Naval Observatory (USNO) CCD Astrograph Catalog, UCAC2 was released in 2003 July. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with Two Micron All Sky Survey photometry for 99.5% of the sources. The catalog covers the sky area from -90° to +40° declination, going up to +52° in some areas; this completely supersedes the UCAC1 released in 2001. Current epoch positions are obtained from observations with the USNO 8 inch (0.2 m) Twin Astrograph equipped with a 4K CCD camera. The precision of the positions are 15–70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by using over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as yet unpublished remeasures of the AGK2 plates and scans from the NPM and SPM plates. Proper-motion errors are about 1–3 mas yr-1 for stars to 12th magnitude, and about 4–7 mas yr-1 for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.

The Twin Astrographic Catalog (TAC) Version 1.0

A first version of the Twin Astrographic Catalog (TAC) of positions for 705,679 stars within

CTIO 0.9m observations of ICRF optical counterparts

-18^{\circ} \le \delta \le 90^{\circ}

The UCAC as Input Catalog for FAME

has been produced. The sky coverage of the TAC is complete to over 90\% in that area. The limiting magnitude is about B=11.5. Positions are based on

RADIO-OPTICAL REFERENCE FRAME LINK USING THE U.S. NAVAL OBSERVATORY ASTROGRAPH AND DEEP CCD IMAGING

4912

The UCAC Astrometric Survey

plates taken with the U.S. Naval Observatory Twin Astrograph (blue, yellow lens) at epochs 1977--1986. The TAC is supplemented by proper motions which are obtained from a combination with a re--reduced Astrographic Catalog (AC). Some AC zones are available now and a complete northern hemisphere is expected by fall 1996. Proper motions of almost all TAC stars will be generated as the AC work progresses. The average precision of a catalog position is 90 mas per coordinate at epoch of observation. A large fraction of that error is introduced by the currently available reference stars. The inherent precision of the TAC data is considerably better. The precision of the proper motions is currently 2.5 to 4 mas/yr. Magnitude--dependent systematic errors have been found and preliminarily corrected. The final reduction of this plate material will be performed with the Hipparcos catalog in 1997. The TAC is about 3 times more precise than the PPM or ACRS in the northern hemisphere at current epochs and contains about 3 times more stars. The TAC has a higher star density than the Tycho catalog and provides independent, high precision positions for a large fraction of the Tycho stars at an epoch about 10 years earlier than the Tycho mean epoch. The TAC version 1.0 data are released as the AC zones become available. For latest information, look at the US Naval Observatory World Wide Web page this http URL

A new astrometric survey of the southern hemisphere.

Abstract : We present astrometric results from 7 observing runs at the Cerro Tololo Interamerican Observatory (CTIO) 0.9m telescope of 197 extragalactic reference frame sources, selected from the original International Celestial Reference Frame (ICRF) catalog. This is part of the U.S. Naval Observatory (USNO) reference frame link program. Contemporaneous to the CTIO deep imaging, wide-field CCD data were taken with the USNO Twin Astrogragh to provide accurate secondary reference stars in the 13 to 16 mag range. The optical positions are on the Hipparcos system (via Tycho-2 stars). The unweighted, mean RMS position difference optical-radio for a single source is 28 and 25 mas for RA and Dec, respectively.

UCAC3 Is Coming

Abstract : A new highly accurate, astrometric star catalog is available from the U.S. Naval Observatory, covering approximately equal 80% of the Southern Hemisphere to R approximately 16 m. The observing program is ongoing and full-sky coverage is expected by 2003. The final catalog will be used as the input catalog for the FAME space mission.