New Observations Testing the Adopted HIPPARCOS Link to the International Celestial Reference Frame

Abstract

This paper tests the Hipparcos link to the extragalactic reference frame by using new data obtained after the release of the catalog, thereby providing an external check on the accuracy of the established link process. The new data consist of 689 positions of Hipparcos stars determined in the International Celestial Reference Frame (ICRF) from CCD observations taken with the Flagstaff Astrometric Scanning Transit Telescope (FASTT). A comparison of the FASTT and Hipparcos catalog star positions observed in common finds that the axial rotations between the Hipparcos and ICRF reference frames are, respectively, (ɛ_x, ɛ_y, ɛ_z) = (-2.2+/-3.3, -2.2+/-3.3, 3.3+/-2.9) (s.e.) mas at epoch 1996.5. All of these rotations are small and insignificant with respect to their errors (ɛ_x and ɛ_y are less than 1 σ detections whereas ɛ_z is only a 1.1 σ detection). Hence, this paper finds that the Hipparcos link to the ICRF was well determined and is not seriously degrading with time.