Fifth Fundamental Catalogue (FK5) - Extension

The positions and proper motions given in the FK5 Extension are in accordance with the IAU (1976) system of astronomical constants; this means that the proper motions are based on the new values for the precessional quantities, the terms of elliptic aberration are eliminated from the mean positions, the correction for the error in the FK4 equinox and its fictitious motion are applied, and the systematic corrections FK5-FK4, as given in the Basic FK5 (page 86), have been taken into account.

More than 200 catalogs providing star positions obtained from throughout the world have been used in the compilation of the FK5 Extension. The source reference should be consulted, along with the FK5 Basic catalog (Fricke et al. 1988) for more detailed information regarding the motivation for construction of the FK5, the determination of its equator and equinox, the expressions for general precession, a discussion of the FK5 system, systematic differences between the FK4 and FK5, the transformation of observational catalogs to the FK5 system and to the reference system J2000.0, and more thorough descriptions of the data contained in the FK5 catalog.

In fact, the source reference should be consulted by all users before utilizing the FK5 data for astrometric applications. The trigonometric parallax and radial velocity fields are blank when data are missing, and because parallax and radial velocity can validly be zero, the fields should be checked for blanks before the data are used. The user should note that the file is ordered by FK5 number, which means that the stars are arranged neither by right ascension nor by declination.