A Joint Collaboration Between USNO and Brazil on the Astrometry of ICRF Sources.

Details A Joint Collaboration Between USNO and Brazil on the Astrometry of ICRF Sources. A Joint Collaboration Between USNO and Brazil on the Astrometry of ICRF Sources.

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003ala..conf..137a&link_type=abstract

Astronomy in Latin America, Second Meeting on Astrometry in Latin America and Third Brazilian Meeting on Fundamental Astronomy,

Astronomy and Astrophysics

Astronomy

Scientific paper

In the context of a joint collaboration involving the United States Naval Observatory (USNO) and 3 Brazilian research institutions: the Valongo Observatory (OV/UFRJ), the National Observatory (ON) and the National Laboratory for Astrophysics (LNA), we report new optical positions on the 30 mas precision level for 172 extragalactic, International Celestial Reference Frame (ICRF) sources mainly between -30< = d = >+25. Results are from a pilot investigation including four CTIO 0.9-meter runs (1999-2001). Reference stars in the R ~ 10 to 16.5 magnitude range from a preliminary USNO CCD Astrograph Catalog (UCAC) are used. Systematic errors have been investigated and a field distortion pattern based on the residuals has been removed. The errors of the fainter stars in the CTIO data were assessed by evaluating an auxiliary set of CCD observations of common ICRF sources, taken at the 1.60m Cassegrain telescope of the (LNA). A significant improvement in the optical positions was achieved over a previous determination of source positions (Zacharias et al. 1999). The mean optical positions are compared with the ICRF radio positions. The overall optical minus radio offsets are -6 mas and -15 mas for RA and Dec, respectively. The formal, internal error of these mean offsets is ~ 2.3 mas. This indicates a possible systematic error in the UCAC declinations of ~ 10 to 15 mas. Both the optical counterpart observations and the optical reference stars are observed about 9 years after the Hipparcos mean epoch and our result set an upper limit for a possible Hipparcos system rotation w.r.t. the ICRS for the z-axis of about 0.7 mas/year.

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