Representation of the International Celestial Reference System (ICRS) by different sets of selected radio sources

To contribute to the maintenance and extension of the ICRF, we have studied representations of the ICRS by different sets of selected radio sources. The axes of the ICRS are realized by the coordinates of 212 sources in the ICRF qualified as the “defining” objects of the frame. They have been selected by the WGRF of the IAU by applying quality criteria to VLBI observations from 1975-1995. A different selection of sources has been proposed by Feissel-Vernier based on an analysis of time series of radio source coordinates over the period 1989-2002. We compare the quality of the realization of the ICRS by the two sets of selected sources.