Comparisons of the Tycho-2 catalogue proper motions with Hipparcos and ACT

The recently released Tycho-a Catalogue is expected to supersede the curren tly used catalogs based on the Tycho data, specifically, the ACT Reference Catalog and the Tycho Reference Catalogue. Here the proper motions of the n ewly released Tycho-2 Catalogue are compared with those of the Hipparcos Ca talogue and the ACT Reference Catalog. Tycho-2 is found to be consistent wi th Hipparcos at a level below 0.5 mas yr(-1). Comparisons with the ACT reve al differences in systematic errors between the two, most likely due to the 1997 reduction of the Astrographic Catalogue. This comparison shows that t he ACT follows the Hipparcos system at a level better than 1.0 mas yr(-1), but Tycho-2 is an improvement. Some of the largest deviations of individual stars between Tycho-2 and the other two catalogs are also investigated.