L. Winter

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derived by using over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as yet unpublished remeasures of the AGK2 plates and scans from the NPM and SPM plates.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 First US Naval Observatory CCD Astrograph Catalog

The USNO CCD Astrograph (UCA) started an astrometric survey in 1998 February at Cerro Tololo, Chile. This first, preliminary catalog (UCAC1) includes data taken up to 1999 November with about 80% of the Southern Hemisphere covered. Observing continues, and full sky coverage is expected by mid-2003 after moving the instrument to a Northern Hemisphere site in early 2001. The survey is performed in a single bandpass (579–642 nm), a twofold overlap pattern of fields, and with a long and a short exposure on each field. Stars in the magnitude range 10–14 have positional precisions of ≤20 mas. At the limiting magnitude of R ≈ 16 mag, the positional precision is 70 mas. The UCAC aims at a density (stars per square degree) larger than that of the Guide Star Catalog (GSC) with a positional accuracy similar to Tycho. The UCAC program is a major step toward a high-precision densification of the optical reference frame in the post–Hipparcos era, and the first stage, the UCAC1 contains over 27 million stars. Preliminary proper motions are included, which were derived from Tycho-2, Hipparcos, and ground-based transit circle and photographic surveys for the bright stars (V ≤ 12.5 mag) and the USNO A2.0 for the fainter stars. The accuracy of the proper motions varies widely, from 1 to over 15 mas yr-1. The UCAC1 is available on CD-ROM from the US Naval Observatory.

A Radio-Optical Reference Frame.VIII.CCD Observations from KPNO and CTIO: Internal Calibration and First Results

In this pilot investigation, precise optical positions in the FK5 system are presented for a set of 16 compact extragalactic radio sources, which will be part of the future radio--optical reference frame. The 0.9 m KPNO and CTIO telescopes equipped with 2K CCDs have been used for this project. The astrometric properties of these instruments are investigated in detail. New techniques of using wide field CCD observations for astrometry in general are developed. An internal precision of 5 to 31 mas in position per single exposure is found, depending on the brightness of the object. The tie to the primary optical reference system is established by photographic astrometry using dedicated astrographs on both hemispheres. An accuracy of

Hardware and Software Aspects of CCD Camera-Based Astrometric Plate Measurements

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A Catalog of Faint Reference Stars in 398 Fields of Extragalactic Radio Reference Frame Sources

mas per source is estimated for the multi--step reduction procedure when based on the future Hipparcos catalog, while the FK5--based positions suffer from system errors of 100 to 200 mas as compared to the radio positions. This work provides a contribution to the international effort to link the Hipparcos instrumental coordinate system to the quasi--inertial VLBI radio reference frame. Precise radio and optical astrometry of a large sample of compact extragalactic sources will also contribute to the astrophysics of these objects by comparing the respective centers of emission at the optical and radio wavelengths.

Some Results of CCD-Camera Based Astrometric Plate Measurements

This paper discusses the application of CCD cameras for digitisation of astrometric plate material. Details of the astrometric plate measuring systems and their design principles at Hamburg Observatory are discussed. First results concerning performance and obtainable measurement accuracies are presented.

A New Astrometric Measuring Machine: Design and Astronomical Programmes

Positions of 89,422 stars in 398 fields of extragalactic reference frame sources have been determined using the Hamburg Zone Astrograph (northern hemisphere) and the US Naval Observatory Twin Astrograph, then stationed at the Black Birch Astrometric Observatory, New Zealand (southern hemisphere). Most stars are in the magnitude range 12 ≤ V ≤ 14, and the positions are accurate to ≈50 mas per coordinate at the epoch of observation, which ranges from the beginning of 1976 to the end of 1991. The catalog (ERLcat) is available on-line from USNO.

Astrometric Programs with the New Hamburg Plate Measuring Machine

A measuring accuracy of about 0.3 um per coordinate for well exposed stellar images is achieved over the entire usable measuring area of more than 200 x 200 mm2 with the CCD-camera upgrade of the ‘old’ Mann comparator. The external plate-to-plate comparison shows that the error due to emulsion shifts dominates, which results in an overall accuracy of about 0.8 μm.

The StarScan Plate Measuring Machine: Overview and Calibrations

The design of a new type of astrometric measuring machine, recently installed at Hamburg Observatory is described. The measuring system consists of a very compact high-precision, air-bearing, granite x-y measuring table; the photoplate is digitised in a frame-by-frame mode using the VIDEK-KODAK MEGAPLUS CCD-camera which provides a frame size of 1035 × 1320 square pixels of 6.8 × 6.8 micrometers at unit magnification. The machine design is based on a fully modular concept; machine operation and camera data are handled by independent computer systems. The maximum measuring area is about 270 × 270 mm2, typical astrograph plates (measuring area ≈ 220 × 220 mm2) can be digitised in about 30 minutes. First measuring programs will concentrate on the Hipparcos groundbased extragalactic reference link and various catalogues, in particular remeasurement of AC zones and the AGK2 plates.

The Archive and Digitizer Facility at the ROB

With the new Hamburg astrometric measuring machine, large sets of plates can be digitized very quickly with submicrometer accuracy. In particular about 2000 plates of the AGK2-catalog, mean epoch 1930, can be remeasured now for the first time to their limiting magnitude, about B = 11. The new AGK2-data therefore will cover practically the whole AC-catalog and TYCHO-stars in the northern hemisphere.