SIMPLE = T / Standard FITS format BITPIX = 8 / Character information NAXIS = 0 / No image data array present EXTEND = T / There may be standard extensions BLOCKED = T / The file may be blocked ORIGIN = 'ADC ' / This file written at the ADC, NASA/GSFC DATE = '23/09/91' / Date file written (dd/mm/yy) COMMENT International Reference Stars Catalog COMMENT COMMENT The AGK3R (Corbin 1977, 1978) and the SRS (Smith et al. 1990) are COMMENT catalogs whose original purpose was to provide reference star positions COMMENT for the plates of the AGK3 and CPC2 astrographic programs. The stars in COMMENT these catalogs are primarily in the magnitude range 7.0 to 9.0; when COMMENT they were selected, first priority was given to those stars with the COMMENT best observational histories. Thus, the AGK3R and the SRS presented the COMMENT opportunity to go well beyond their original purpose. This opportunity, COMMENT to extend the fundamental system to fainter magnitudes, was recognized a COMMENT number of years ago, and thus the effort to construct the IRS was COMMENT undertaken. The success of this effort is reflected in the fact that it COMMENT has provided the positions and proper motions for 68 percent of Part II COMMENT of the FK5 (Fricke et al. 1988), known as the FK5 Extension (Schwan & COMMENT Corbin 1991). COMMENT COMMENT The IRS was compiled by matching 122 meridian circle catalogs with the COMMENT AGK3R and SRS to provide the data base. Catalogs whose stars had been COMMENT observed using screens to minimize magnitude equations and that COMMENT contained FK4 (Fricke & Kopff 1963) stars were used to form a COMMENT preliminary system. These catalogs were reduced to the FK4 by direct COMMENT comparison; the resulting positions and proper motions were then used to COMMENT reduce all of the other catalogs. Thus, the IRS is a differential COMMENT catalog compiled from 164,917 positions reduced to the FK4 system. COMMENT COMMENT The IRS is divided into two parts. Part 1 contains the stars having COMMENT better observational histories and, therefore, more reliable positions COMMENT and proper motions. This part constitutes 81 percent of the catalog; COMMENT mean errors of the proper motions are +/-0.43 arcsec per century and COMMENT +/-0.44 arcsec per century in right ascension and declination, COMMENT respectively. The stars in Part 2 have poor observational histories and COMMENT consist mostly of objects for which only two catalog positions in one or COMMENT both coordinates were available for computing the proper motions. Where COMMENT accuracy is the primary consideration, only the stars in Part 1 should COMMENT be used, while if the highest possible density is desired, the two parts COMMENT should be combined, as they are systematically the same. COMMENT COMMENT Source Catalog Reference: Corbin, T.E. 1991 (Washington, U.S. Naval COMMENT Observatory) COMMENT COMMENT Documentation Reference: Warren Jr. W.H., NSSDC/WDC-A-R&S 91-11 COMMENT COMMENT A copy of the documentation should accompany any computer-readable COMMENT version of the catalog. The FITS Table header(s) in this file only give COMMENT the basic format of the catalog. Please refer to the documentation or COMMENT source reference for a more detailed discussion of the data. END