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SC 1.4 - Interaction of Celestial and Terrestrial Reference Frames

WG 1.4.3: Realization of Celestial Reference Frames

Chair: Chopo Ma (U.S.A.)

To achieve further progress regarding the realization of celestial reference frames it is essential to review the current status, to identify deficiencies and to make proposals for improvements. This task is closely related to various components of the IERS and the techniques analysis coordinators (in particular of the IVS), and requires a close cooperation between the different groups. The activities include the survey of the current status of CRF realization, a review regarding the implementation of IERS Conventions and IAG Fundamental Parameters and different space techniques for CRF realization.

The International Celestial Reference Frame (ICRF2) realized by VLBI is currently defined by the radio positions of 295 extragalactic objects (IERS TN 35, Fey, Gordon and Jacobs, eds., 2009). The ICRF2 was endorsed by the IAU in 2009 and by the IUGG in 2011. The noise floor is ~40 ľas and the uncertainty of the axes is ~10 ľas. Precise positions of 3414 extragalactic radio sources are included in the ICRF2 catalogue.

The GAIA (Global Astrometry Interferometer for Astrophysics) mission scheduled for launch in 2013 is expected to achieve an optical realization of the CRF with precision similar to or better than the ICRF2 and with at least an order of magnitude more objects. However, as the set of extragalactic objects suitable for both optical and radio observation is limited, one goal of the Working Group is to identify such objects, oversee the relevant observations, and analyze the data to permit the best possible connection between the radio and optical CRF realizations.

For geodetic use the CRF realization must be accessible from the ground. For the foreseeable future this connection will be through VLBI observations. In cooperation with the IVS and IERS, this Working Group will oversee the maintenance and improvement of the ICRF2, in particular the set of sources used for geodetic observations and the ICRF2 defining sources.

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