NOAO >   Observing Info >   Approved Programs >   2001A-0058

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Proposal Information for 2001A-0058


PI: Norbert Zacharias, U.S. Naval Observatory, nz@pisces.usno.navy.mil
Address: 3450 Mass.~Ave.~N.W., Washington, DC 20392, USA

CoI: Theodore J. Rafferty, USNO
CoI: Marion I. Zacharias, Univ. Space Research Ass. (USRA) / USNO

Title: Extragalactic reference frame link of the UCAC project

Abstract: In January 1998 the US Naval Observatory CCD Astrograph (UCAC) project, a high accuracy, high density, astrometric survey was started at CTIO. Observations of the southern hemisphere were completed in August 2000 and the instrument is scheduled to be re--located to Flagstaff, AZ, in April 2001. Full sky coverage is expected by mid 2003. The 2--fold overlap pattern and block adjustment techniques will allow for a strong link to extragalactic reference frame sources utilizing deep CCD frames obtained with the CTIO 0.9m, and proposed KPNO 2.1m observations, to cover the northern hemisphere. Assuming a small epoch difference between the 2.1m and the astrograph observations for each of the about 300 fields to be observed over 2 years, an unprecedented accuracy of the optical--radio reference frame link can be achieved. The rotation of the Hipparcos system with respect to the International Celestial Reference System (ICRS) will be determined by a factor of 2 more precisely than is currently known. Absolute position differences in the radio--optical centers of emission for individual sources on the 10 mas level will be derived. Outliers will indicate astrophysically interesting sources. The maintenance of a high accuracy radio--optical reference frame link is important for current and future high resolution imaging in all wavelengths, providing absolute positions (in an inertial frame) on the 10 mas level at any location in the sky. To our knowledge, this is the only major project in its area of research.


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