************************************************************************ IERS Message No. 150 August 21, 2009 ************************************************************************ IAU Resolution B3 on the Second Realization of the ICRF Three years of work by the IERS/IVS Working Group for the Second Realization of the International Celestial Reference Frame achieved its goal when the XXVIIth General Assembly of the IAU voted for the adoption of Resolution B3, which establishes the ICRF2 as the fundamental realization of the International Celestial Reference System (ICRS) as of 1 January 2010. This is a significant improvement on the original ICRF, which was adopted as the first extragalactic reference frame twelve years ago, and carries forward the responsibility of the IERS for reference frames in support on science and society. Resolution B3 is attached for your information. Chopo Ma RESOLUTION B3 on the Second Realization of the International Celestial Reference Frame Proposed by: IAU Division I WG on the Second Realization of the International Celestial Reference Frame Supported by: IAU Division I The following persons will be available for consultation and, if necessary to speak on the above resolution at the General Assembly on 13 August 2009: Proposer: Ralph A. Gaume Seconder: Chopo Ma The International Astronomical Union XXVII General Assembly, noting 1. that Resolution B2 of the XXIII General Assembly (1997) resolved “That, as from 1 January 1998, the IAU celestial reference system shall be the International Celestial Reference System (ICRS)”, 2. that Resolution B2 of the XXIII General Assembly (1997) resolved that the “fundamental reference frame shall be the International Celestial Reference Frame (ICRF) constructed by the IAU Working Group on Reference Frames”, 3. that Resolution B2 of the XXIII General Assembly (1997) resolved “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”, 4. that Resolution B7 of the XXIII General Assembly (1997) recommended “that high-precision astronomical observing programs be organized in such a way that astronomical reference systems can be maintained at the highest possible accuracy for both northern and southern hemispheres”, 5. that Resolution B1.1 of the XXIV General Assembly (2000) recognized “the importance of continuing operational observations made with Very Long Baseline Interferometry (VLBI) to maintain the ICRF”, recognizing 1. that since the establishment of the ICRF, continued VLBI observations of ICRF sources have more than tripled the number of source observations, 2. that since the establishment of the ICRF, continued VLBI observations of extragalactic sources have significantly increased the number of sources whose positions are known with a high degree of accuracy, 3. that since the establishment of the ICRF, improved instrumentation, observation strategies, and application of state-of-the-art astrophysical and geophysical models have significantly improved both the data quality and analysis of the entire relevant astrometric and geodetic VLBI data set., 4. that a working group on the ICRF formed by the International Earth Rotation and Reference Systems Service (IERS) and the International VLBI Service for Geodesy and Astrometry (IVS), in conjunction with the IAU Division I Working Group on the Second Realization of the International Celestial Reference Frame has finalized a prospective second realization of the ICRF in a coordinate frame aligned to that of the ICRF to within the tolerance of the errors in the latter (see note 1), 5. that the prospective second realization of the ICRF as presented by the IAU Working Group on the Second Realization of the International Celestial Reference Frame represents a significant improvement in terms of source selection, coordinate accuracy, and total number of sources, and thus represents a significant improvement in the fundamental reference frame realization of the ICRS beyond the ICRF adopted by the XXIII General Assembly (1997), resolves 1. that from 01 January 2010 the fundamental astrometric realization of the International Celestial Reference System (ICRS) shall be the Second Realization of the International Celestial Reference Frame (ICRF2) as constructed by the IERS/IVS working group on the ICRF in conjunction with the IAU Division I Working Group on the Second Realization of the International Celestial Reference Frame (see note 1), 2. that the organizations responsible for astrometric and geodetic VLBI observing programs (e.g. IERS, IVS) take appropriate measures to continue existing and develop improved VLBI observing and analysis programs to both maintain and improve ICRF2, 3. that the IERS, together with other relevant organizations continue efforts to improve and densify high accuracy reference frames defined at other wavelengths and continue to improve ties between these reference frames and ICRF2. Note 1: The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry, Presented on behalf of the IERS / IVS Working Group, Alan Fey and David Gordon (eds.). (IERS Technical Note ; 35) Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie, 2009. See or . ************************************************************************ IERS Messages are edited and distributed by the IERS Central Bureau. To subscribe or unsubscribe, please write to . Archives: http://www.iers.org/iers/publications/messages/ ************************************************************************