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Maintenance of the link to Hipparcos

Zacharias, N.

The optical wavelength astrometric reference frame is currently based on observations made by the Hipparcos astrometric satellite. Unfortunately, since the Hipparcos Celestial Reference Frame (HCRF) is comprised of bright stars which are sparsely distributed on the sky, the frame often is inappropriate for astronomical and astrometric programs req…

The IERS extragalactic Celestial Reference Frame and its tie with HIPPARCOS.

Lestrade, J. -F.; Arias, E. F.; Feissel, M.

This Technical Note gives a presentation of analyses of VLBI extragalactic reference frames performed in the framework of IERS, in the course of the maintenance of its conventional celestial frame. In section 1 the definition of the IERS celestial reference system and its relationship with the 1991 IAU Resolution A4 on Reference Systems are descri…