International Reference Stars Catalog (Corbin 1991) Documentation for the Computer-Readable Version Thomas E. Corbin U.S. Naval Observatory Wayne H. Warren Jr. National Space Science Data Center April 1991 Doc. No. NSSDC/WDC-A-R&S 91-11 National Space Science Data Center (NSSDC)/ World Data Center A for Rockets and Satellites (WDC-A-R&S) National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, MD 20771 Abstract The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The IRS is an all-sky catalog of positions and proper motions that is based on the AGK3R in the northern hemisphere and on the newly completed SRS in the south. The data for the 36,027 stars of the IRS were compiled on B1950.0 FK4 and then transformed to J2000.0 FK5. The reductions and computations were done at the U. S. Naval Observatory. 1 Introduction 1.1 Description The AGK3R (Corbin 1977, 1978) and the SRS (Smith et al. 1990) are catalogs whose original purpose was to provide reference star positions for the plates of the AGK3 and CPC2 astrographic programs. The stars in these catalogs are primarily in the magnitude range 7.0 to 9.0; when they were selected, first priority was given to those stars with the best observational histories. Thus, the AGK3R and the SRS presented the opportunity to go well beyond their original purpose. This opportunity, to extend the fundamental system to fainter magnitudes, was recognized a number of years ago, and thus the effort to construct the IRS was undertaken. The success of this effort is reflected in the fact that it has provided the positions and proper motions for 68 percent of Part II of the FK5 (Fricke et al. 1988), known as the FK5 Extension (Schwan & Corbin 1991). The IRS was compiled by matching 122 meridian circle catalogs with the AGK3R and SRS to provide the data base. Catalogs whose stars had been observed using screens to minimize magnitude equations and that contained FK4 (Fricke & Kopff 1963) stars were used to form a preliminary system. These catalogs were reduced to the FK4 by direct comparison; the resulting positions and proper motions were then used to reduce all of the other catalogs. Thus, the IRS is a differential catalog compiled from 164,917 positions reduced to the FK4 system. The IRS is divided into two parts. Part 1 contains the stars having better observational histories and, therefore, more reliable positions and proper motions. This part constitutes 81 percent of the catalog; mean errors of the proper motions are +/-0.43 arcsec per century and +/-0.44 arcsec per century in right ascension and declination, respectively. The stars in Part 2 have poor observational histories and consist mostly of objects for which only two catalog positions in one or both coordinates were available for computing the proper motions. Where accuracy is the primary consideration, only the stars in Part 1 should be used, while if the highest possible density is desired, the two parts should be combined, as they are systematically the same. Star numbers with a lead (1) constitute Part 1 and are in the first part of the file while those stars with a lead (2) constitute Part 2 and come at the end of the file. This document describes the machine-readable version of the International Reference Stars Catalog as it is currently being distributed from the international network of astronomical data centers. It is intended to enable users to read and process the data without problems and guesswork. A copy of this document should be transmitted to any recipient of the machine-readable catalog originating directly from the data centers. 1.2 Source Reference Corbin, T. E. 1991, International Reference Stars Catalog (Washington, U. S. Naval Observatory) 2 Structure 2.1 File Summary The machine version of the IRS consists of one file. Table 1 gives the machine-independent file attributes. All logical records are of fixed length, and, if the catalog is received on magnetic tape, it will contain blocks of fixed length, except that the last block of each file may be short. _____________________________________________________ | International Reference Stars Catalog | | (Corbin 1991) | |_____________________________________________________| | | | Record | Record | Number of | | File | Contents | Format | Length | Records | |______|________________|________|________|___________| | 1 | Catalog Part 1 | Fixed | 200 | 29163 | | 1 | Catalog Part 2 | Fixed | 200 | 6864 | |______|________________|________|________|___________| Table 1: Summary Description of Catalog File The information contained in the above table is sufficient for a user to describe the indigenous characteristics of the machine-readable version of the International Reference Stars Catalog to a computer. Information easily varied from installation to installation, such as block size (physical record length), blocking factor (number of logical records per physical record), total number of blocks, density, number of tracks and character coding (ASCII, EBCDIC) for tapes, is not included, but should always accompany secondary copies if any are supplied to other users or installations. 2.2 Catalog As mentioned in the Introduction, the IRS is divided into two parts. Since both parts are identically formatted, the byte-by-byte description given in Table 2 applies to both. The two parts are each ordered by J2000.0 right ascension. Table 2 gives a byte-by-byte description of the contents of the data file. A suggested Fortran format specification for reading each data field is included and can be modified depending upon individual programming and processing requirements (Fortran 77 character string-type formats are used throughout). Only the spectral-type and IAU-recommended IRS identifier fields contain character data, for which the default value (former field only) is the character "-" in the first two bytes of the field (87-88). Note that all numerical data in the catalog are recorded as integers; however, the format specifications given are intended to read the data as real numbers with the correct units as given in the table. Catalog part The part is specifically identified as 1 or 2 so that if the parts are merged, the source remains easily recognizable. IRS number A sequential number beginning with 1 for Part 1 and with 70001 for Part 2. These numbers will not remain ordered as stars migrate from Part 2 to Part 1. Equatorial coordinates Positions are given for equinox and epoch B1950.0 on the system of FK4 (bytes 9-26). They are also given for equinox and epoch J2000.0 on the system of FK5 (bytes 151-159 and 172-180) after transformation of the B1950.0 values. The transformation was done using the coefficients and software package of Schwan (see Schwan 1988) and the algorithm given in the 1991 Astronomical Almanac (page B42) (foreshortening terms set to zero). (See Section 3.1 for additional details.) Proper motions Referred to B1950.0 on FK4 (bytes 33-45) and to J2000.0 on FK5 (bytes 160-165 and 181-186). Mean errors The mean errors of the positions refer to the original epochs given in bytes 54-67. The proper-motion errors were derived in each case from the dispersion of the catalog positions used to determine the proper motion. Original epochs Each refers to the mean epoch of the mean position from the respective proper-motion solution. Number of positions The number of positions used to determine the proper motion and mean position in each coordinate. Weights The sum of the weights of the catalogs used in each coordinate. Magnitude Magnitudes come from the AGK3R or the original SRS observing list. Spectral type Spectral type from the AGK3R and SRS. DM numbers Identifier from one of the Durchmusterung (DM) catalogs, identified as one of the following: BD Bonner Durchmusterung (Argelander 1859- 62, Kuestner 1903, Schoenfeld 1886) CD Cordoba Durchmusterung (Thome 1892-1932) CPD Cape Photographic Durchmusterung (Gill & Kapteyn 1895-1900). ______________________________________________________________________________ | | | Suggested | Default | | | Bytes | Units | Format | Value | Data | |_________|__________|___________|_________|___________________________________| | 1 | --- | I1 | --- | Catalog part | | 2-7 | --- | I6 | --- | IRS number | | 8 | --- | 1X | --- | Zero | | 9-10 | h | I2 | --- | Right ascension, B1950.0 | | 11-12 | min | I2 | --- | RA | | 13-17 | s | F5.3 | --- | RA | | 18-20 | deg | I3 | --- | Declination, B1950.0 | | 21-22 | arcmin | I2 | --- | Dec | | 23-26 | arcsec | F4.2 | --- | Dec | | 27-29 | s | F3.3 | blank | Mean error in RA (at orig. epoch) | | 30-32 | arcsec | F3.2 | blank | Mean error in Dec (orig. epoch) | | 33-38 | s/cy | F6.3 | --- | Centennial proper motion in RA, | | | | | | B1950.0 | | 39-45 | arcsec/cy| F7.2 | --- | Centennial proper motion in Dec, | | | | | | B1950.0 | | 46-49 | s/cy | F4.3 | blank | Mean error in RA PM | | 50-53 | arcsec/cy| F4.2 | blank | Mean error in Dec PM | | 54-60 | years | F7.3 | --- | Original epoch of RA and RA PM | | 61-67 | years | F7.3 | --- | Original epoch of Dec and Dec PM | | 68-70 | --- | I3 | --- | Number of positions in RA | | 71-73 | --- | I3 | --- | Number of positions in Dec | | 74-77 | --- | F4.1 | --- | Weight in RA | | 78-81 | --- | F4.1 | --- | Weight in Dec | | 82-86 | mag | F5.2 | 99.9 | Magnitude | | 87-89 | --- | A3 | --- | Spectral type | | 90-97 | --- | A8 | --- | BD number | | 98-105 | --- | A8 | --- | CD number | | 106-113 | --- | A8 | --- | CPD number | | 114-120 | --- | A7 | --- | AGK3R number | | 121-126 | --- | A6 | --- | SRS number | | 127-150 | --- | A24 | --- | IRS identifier | | 151-152 | h | I2 | --- | Right ascension, J2000.0 | | 153-154 | min | I2 | --- | RA | | 155-159 | s | F5.3 | --- | RA | | 160-165 | s/cy | F6.3 | --- | Centennial proper motion in RA, | | | | | | J2000.0 | | 166-171 | Jcy | F6.5 | --- | Original epoch - J2000.0 in RA | | 172-174 | deg | I3 | --- | Declination, J2000.0 | | 175-176 | arcmin | I2 | --- | Dec | | 177-180 | arcsec | F4.2 | --- | Dec | | 181-186 | arcsec | F6.2 | --- | Centennial proper motion in Dec, | | | | | | J2000.0 | | 187-192 | Jcy | F6.5 | --- | Original epoch - J2000.0 in Dec | |_________|__________|___________|_________|___________________________________| Table 2: Data File Record Format AGK3R number Identifier from the AGK3R catalog (Scott, 1963). SRS number Identifier from the SRS Catalogue (Smith et al, 1990). IRS identifier An identifier for each star based upon the recommended IAU nomenclature (see PASP, 102, 1444, 1990). The field consists of an origin in bytes 127-130 (IRS) and a coordinate specification in bytes 132-150 (byte 132 contains a "J" to indicate that the following coordinates are in the Julian reference system and are for the year 2000.0, the standard equinox designated for Julian system coordinates). Bytes 127 and 131 are blank for this catalog. 3 History 3.1 Remarks The IRS positions and proper motions in the original catalog are given for the equinox and epoch of B1950.0 and are referred to the FK4 system. The reduction of these data to the new reference frame of the FK5 involves the application of transformation coefficients to the FK4 data, followed by another transformation from the equinox and epoch B1950.0 to the equinox and epoch J2000.0. The reduction of the B1950.0 FK4 data to the FK5 system was effected by using the coefficients of H. Schwan (Astronomisches Rechen-Institut, Heidelberg), communicated to us as part of a computer subroutine package (see Schwan 1988). The coefficients represent the systematic differences between the FK4 and FK5 catalog positions and proper motions for the mean equinox and epoch B1950.0; they are given in the system of the FK4 catalog. The arguments needed as input to the computer subroutines are the right ascension, declination, and magnitude. The subroutine returns systematic corrections to the FK4 positions and proper motions. In general, the magnitudes of the IRS catalog stars lie outside the range of magnitudes of the stars in the FK4 catalog and are inappropriate to use as arguments because the magnitude-related error of the FK4 system is not defined outside the magnitude range of the FK4 stars. An average FK4 magnitude was estimated for each IRS position from the average magnitude of all FK4 stars in an area on the celestial sphere bounded by a four-hour interval in right ascension and a 20 degree interval in declination centered on the star. All stars less than 10 degrees from the pole were treated as if they had been at 80 degrees declination for the calculation of the average FK4 magnitude only. After the IRS positions and proper motions had been referred to the FK5 system by using the procedure described above, they were transformed from the equinox B1950.0 basis to J2000.0 using the algorithm given in the 1991 volume of the Astronomical Almanac (page B42). The algorithm was applied with the foreshortening terms set to zero. By the use of that algorithm, elliptic terms in aberration are removed, the IAU 1976 precession is introduced, the FK4 equinox error in the right ascension position and proper-motion system is corrected, and the time scale for the proper motions is shifted from units of tropical centuries to Julian centuries of exactly 36525 days. The completed machine-readable IRS was transferred to the Astronomical Data Center on 16 April 1991. 4 References Argelander, F. W. A. 1859-62, Bonner Sternverzeichniss, erste bis dritte Sek- tion, Astronomischen Beobachtungen auf der Sternwarte der Koeniglichen Rhein., Friedrich-Wilhelms-Universitaet zu Bonn, Baende 3-5 Corbin, T. E. 1974, AJ, 79, 885 Corbin, T. E. 1977, The Proper-Motion System of the AGK3R (Ann Arbor, University Microfilms, Inc.) Corbin, T. E. 1978, in IAU Colloquium 48, Modern Astrometry, ed. F. V. Prochazka & R. H. Tucker (Vienna: University Obs.), p. 505 Corbin, T. E. 1991, International Reference Stars Catalog (Washington, U. S. Naval Observatory) Corbin, T. E., & Urban, S. E. 1990, in IAU Symposium No. 141, Inertial Coordinate System on the Sky, ed. J. H. Lieske & V. K. Abalakin (Dordrecht, Reidel), p. 433 Dieckvoss, W. (in collaboration with H. Kox, A. Guenther, & E. Brosterhus) 1975, AGK3 Star Catalogue of Positions and Proper Motions North of -2.5 Degrees Declination, Hamburg-Bergedorf (printed with financial support from Deutsche Forschungsgemeinschaft, Bonn-Bad Godesburg) Fricke, W., & Kopff, A. 1963, Fourth Fundamental Katalog (FK4), Veroeff. Astron. Rechen-Inst. Heidelberg No. 10. Fricke, W., Schwan, H., & Lederle, T. (in collaboration with Bastian, U., Bien, R., Burkhardt, G., du Mont, B., Hering, R., Jaehrling, R., Jahreiss, H., Roeser, S., Schwerdtfeger, H. M., & Walter, H. G.) 1988, Fifth Fundamental Catalogue (FK5), Part I. The Basic Fundamental Stars, Veroeff. Astron. Rechen-Institut Heidelberg No. 32 Gill, D. & Kapteyn, J. C. 1895-1900, Cape Photographic Durchmusterung, Ann. Cape Obs., 3 (1895, Part I: zones -18 to -37); 4 (1897, Part II: zones -38 to -52); 5 (1900, Part III: zones -53 to -89) Kuestner, F. 1903, Bonner Durchmusterung des Noerdlichen Himmels, zweite berichtigte Auflage, Bonn Universitaets Sternwarte (Bonn, A. Marcus und E. Weber's Verlag) Schoenfeld, E. 1886, Bonner Sternverzeichniss, vierte Sektion, Astronomische Beobachtungen auf der Sternwarte der Koeniglichen Rheinischen Friedrich-Wilhelms-Universitaet zu Bonn, 8, Part IV (Bonn, Adolph Marcus) Schorr, R., & Kohlschuetter, A. 1951-1958, Zweiter Katalog der Astronomischen Gesellschaft fuer das Aquinoktium 1950, 1-10 (Hamburg-Bergedorf), 11-15 (Bonn, Ferd. Duemmlers Verlag) Schwan, H. 1988, A&A, 198, 363 Schwan, H., & Corbin, T. E. 1991, Fifth Fundamental Catalogue (FK5), Part II. The Extension Stars, in preparation Scott, F. P. 1955, Conference d'Astrometrie, Bruxelles, 28-30 mars 1955, in Commun. l'Obs. Roy. Belgique No. 85 Scott, F. P. 1962, AJ, 67, 690 Scott, F. P. 1963, The System of Fundamental Proper Motions, in Basic Astronomical Data, ed. K. Aa. Strand (Chicago, Univ. of Chicago Press), p. 11 Smith, C. A., Corbin, T. E., Hughes, J. A., Jackson, E. S., Krutskaya, E. V., Polozhentsev, A. D., Polozhentsev, D. D., Yagudin, L. I., and Zverev, M. S. 1990, in IAU Symposium No. 141, Inertial Coordinate System on the Sky, ed. J. H. Lieske & V. K. Abalakin (Dordrecht, Reidel), p. 457 Thome, J. M. 1892-1932, Cordoba Durchmusterung, Resultados del Observatorio Nacional Argentino, 16 (1892, Part I: -22 to -32); 17 (1894, Part II: -32 to -42); 18 (1900, Part III: -42 to -52); 21 (Part I) (1914, Part IV, -52 to -62); 21 (Part II) (1932, Part V: -62 to -90)