Documentation for the machine-readable AGK3-BD and BD-AGK3 cross-index catalogues

The machine-readable cross identification catalogs were prepared by extracting AGK3 and BD numbers from the magnetic tape version of the AGK3 Catalog. After preparation of the AGK3-BD file, which contains all stars in the AGK3 catalog, the file was sorted according to BD number and rearranged so that the BD number occurs at the beginning of each record. During the sorting operation, all AGK3 stars having no BD numbers were omitted. The BD-AGK3 file is especially useful for finding BD stars in the AGK3 catalog, since precession has moved stars across declination boundaries and it often was necessary to examine more than one AGK3 zone to locate a BD star in the catalog. The contents of the cross index files is described so that users can read and process the tape without problems, guesswork, or consulting the parent catalog.