: A continuation of this WG was voted for at the IAU GA 2006 in Prague. The International Celestial Reference Frame (ICRF) is defined by the positions of 212 distant quasars at radio wavelengths. The primary, optical reference frame is the Hipparcos Celestial Reference Frame (HCRF), which is the Hipparcos Catalog without astrometric problem stars (in: H. Rickman (ed.) 2001, Proceedings IAU XXIV General Assembly, Transactions IAU XXIVB (San Francisco: ASP), Resolution B1.2). The Tycho-2 catalog with its 2.5 million brightest stars forms the first step in the densification of the optical reference frame. However, the limiting magnitude of about V=12 of the Tycho-2 catalog is not sufficient for most applications in astronomy and the goal of this IAU Working Group is to further extend the grid of highly accurate positions and motions toward more and fainter stars.

The results of 3056 speckle interferometric observations of double stars, made with the 26 inch (66 cm) refractor of the US Naval Observatory, are presented. Each speckle interferometric observation of a system represents a combination of over a thousand short-exposure images. These observations are averaged into 1675 mean relative positions and range in separation from 0."19 to 45."21, with a median separation of 2."99. This is the ninth in a series of papers presenting measures obtained with this system and covers the period 2002 January 1 through 2002 December 29. Included in these data are 28 older measures whose positions were previously deemed possibly aberrant but are no longer classified this way following a confirming observation. Nine of these systems have new orbital elements, which are presented here as well.

AbstractThe current optical realization of the International Celestial Reference System is the Hipparcos main catalog in its entirety. This paper demonstrates that a subset of the main catalog stars — specifically those marked as double (“C” stars), acceleration solution (“G”), variability induced movers (“V”), and stochastic solution stars (“X”) — is of much lower quality than the majority of the catalog. Stars marked as suspected doubles (“S”) were investigated and found to show few problems. The authors have put forth a resolution (Resolution 2, this conference) to remove the C, G, V, and X stars, in addition to the Hipparcos orbit stars (“O stars”), from the optical realization of the reference frame.

The US Naval Observatory has completed the compilation of the ACT Reference Catalog, containing 988,758 stars covering the entire sky. The motivation behind the ACT was to provide accurate proper motions for the majority of the stars in the Tycho Catalogue. To do this, positions from new reductions of the Astrographic Catalogue (AC 2000) were combined with those of the Tycho Catalogue. The large epoch span between the two catalogs yields proper motions about an order of magnitude more accurate than those found in the Tycho Catalogue. The astrometric data contained in the ACT Reference Catalog include positions and proper motions and their corresponding errors. These are on the Hipparcos system (ICRS) for epoch J2000.0. Photometric and variability data from Tycho are included. In addition, crossreferences to the Tycho, AC 2000, Bonner Durchmusterung (BD), Cordoba Durchmusterung (CD), Cape Durchmusterung (CPD), Henry Draper (HD), and Hipparcos catalogs are given. The ACT is now available at the international data centers and by contacting the authors via electronic mail.

The Version 1.0 of the U.S. Naval Observatory Twin Astrographic Catalog (TAC) contains positions of 705,679 stars (Zacharias et al. 1996). The TAC 1.0 covers over 90% of the sky from +90° to −18° declination; 260 out of 5180 plates are not yet measured. Plates were taken in both the yellow (508-578 nm) and in the blue (410-486 nm) bandpass between 1978 and 1986 at the U.S. Naval Observatory (USNO) in Washington, DC.

The AC 2000 is a positional catalog of 4,621,836 stars covering the entire sky. The average epoch of position is 1907. The data are from the images measured and published as part of the Astrographic Catalogue (AC). The positions are on the system defined by the Hipparcos Catalogue, having originally been reduced plate-by-plate using the Astrographic Catalog Reference Stars. In addition to the astrometric data, magnitudes (on the Tycho B system) and cross-referencing information are included. These positions are valuable for the computation of proper motions, and were combined with the positions from the recently released Tycho Catalogue to improve proper motions of almost 1 million stars. The resulting catalog is known as the ACT Reference Catalog (the name ACT is from AC 2000 and Tycho). Both the AC 2000 and ACT are now available on CD-ROM and can be obtained by contacting the first author above. A World Wide Web site describing various aspects of the reductions is also maintained by the Astrometry Department, US Naval Observatory.

Selected fields around radio-optical reference frame sources have been observed with the U.S. Naval Observatory CCD astrograph (UCA). This telescope is equipped with a red-corrected 206mm 5-element lens and a 4k by 4k CCD camera which provides a 1 square degree field of view. Positions with internal precisions of 20 mas for stars in the 7 to 12 magnitude range have been obtained with 30 second exposures. A comparison is made with the Tycho Catalogue, which is accurate to about 5 to 50 mas at mean epoch of J1991.25, depending on the magnitude of the star. Preliminary proper motions are obtained using the Astrographic Catalogue (AC) to update the Tycho positions to the epoch of the UCA observations, which adds an error contribution of about 15 to 20 mas. Individual CCD frames have been reduced with an average of 30 Tycho reference stars per frame. A linear plate model gives an average adjustment standard error of 46 mas, consistent with the internal errors. The UCA is capable of significantly improving the positions of Tycho stars fainter than about visual magnitude 9.5.

The U. S. Naval Observatory is in the process of making new reductions of the Astrographic Catalogue using a modern reference star system, the ACRS, created specifically for that purpose. The application of that system to the plates of the Cape Zone is discussed as well as the software that has been developed to make the reductions. An analysis of scale, rotation, tilt, coma, magnitude equation, radial distortion and distortions introduced by the use of reseaux in the Carte du Ciel program is made for each plate. The result is a catalog of 544 629 stars from plates taken at the Cape Observatory between 1897 and 1911 on the system of FK5 J2000. The average standard deviations of an individual plate image after reduction are 0 ''.31 in right ascension and 0 ''.28 in declination. Thus the positions of the Cape Zone, and of the other zones subsequently to be reduced, can be combined with modern astrometric catalogs to give accurate proper motions for large numbers of stars.