Overall Pattern Comparison of the FK5 Proper-Motion System withHipparcos

Abstract

We have performed an overall pattern comparison between the proper motions of the FK5 (Fifth Fundamental Catalogue) systems (FK5, Astrographic Catalog Reference Stars [ACRS], and PPM Catalogue) and those of Hipparcos. The global rotation (time dependent) between the two reference frames is found to be different for different stellar samples, depending on the spectral types. Taking the precessional correction Deltap~-3.00+/-0.20 mas yr^-1 into account, which is given by VLBI and lunar laser ranging observations, we cannot explain the systematic difference in proper motions between the two reference systems. Analyzing the Hipparcos and ACRS proper motions of ~24,000 K-M giants, we have found a remarkably large difference in the Galactic rotation: V_0=249.6+/-7.0 km s^-1 from the Hipparcos proper motions, and V_0=178.3+/-6.6 km s^-1 from the ACRS proper motions. Again it implies an inconsistency of the two proper-motion systems, even if the errors of the precession and the fictitious equinoctial motion have been corrected to the ACRS proper motions.