ON THE INTERNATIONAL CELESTIAL REFERENCE SYSTEM (ICRS)
proposed by the IAU Working Group on Reference Frames
The XXIIIrd International Astronomical Union General Assembly Considering
(a) That Recommendation VII of Resolution A4 of the 21st General Assembly specifies the coordinate system for the new celestial reference frame and, in particular, its continuity with the FK5 system at J2000.0;
(b) That Resolution B5 of the 22nd General Assembly specifies a list of extragalactic sources for consideration as candidates for the realization of the new celestial reference frame;
(c) That the IAU Working Group on Reference Frames has in 1995 finalized the positions of these candidate extragalactic sources in a coordinate frame aligned to that of the FK5 to within the tolerance of the errors in the latter (see note 1);
(d) That the Hipparcos Catalogue was finalized in 1996 and that its coordinate frame is aligned to that of the frame of the extragalactic sources in (c) with one sigma uncertainties of +/- 0.6 milliarcseconds (mas) at epoch J1991.25 and +/- 0.25 mas per year in rotation rate;
That all the conditions in the IAU Resolutions have now been met;
(a) That, as from 1 January 1998, the IAU celestial reference system shall be the International Celestial Reference System (ICRS) as specified in the 1991 IAU Resolution on reference frames and as defined by the International Earth Rotation Service (IERS) (see note 2);
(b) That the corresponding fundamental reference frame shall be the International Celestial Reference Frame (ICRF) constructed by the IAU Working Group on Reference Frames;
(c) That the Hipparcos Catalogue shall be the primary realization of the ICRS at optical wavelengths;
(d) That IERS should take appropriate measures, in conjunction with the IAU Working Group on reference frames, to maintain the ICRF and its ties to the reference frames at other wavelengths.
Note 1: IERS 1995 Report, Observatoire de Paris, p.II-19 (1996).
Note 2: "The extragalactic reference system of the International Earth Rotation Service (ICRS)", Arias, E.F. et al. A & A 303, 604 (1995).