The Hipparcos, Tycho, TRC, and ACT catalogues --- A whole sky comparison of the proper motions

Abstract

We present a whole sky comparison of the proper motions contained in the Hipparcos Catalogue, the Tycho Catalogue, the Tycho Reference Catalogue (TRC), and the Astrographic Catalogue plus Tycho Reference Catalogue (ACT). The catalogues are compared in the 20 declination zones defined by the original Carte du Ciel project. We find that (1) the proper-motion errors in the ACT Catalogue are underestimated in all zones, sometimes by as much as 30%. (2) There are systematic differences, as large as 1.2 mas yr^-1, between the proper motions in the TRC and ACT depending on the zone. We confirm the known underestimation of the proper-motion error (by as much as 40%) of the faint stars (B_T > 10 mag) in the Tycho Catalogue.