% Documentation for International Reference Stars Catalog (Corbin 1991)
%
% Document Number: NSSDC/WDC-A-R&S 91-11
%
% Written: April 1991 by Corbin and Warren
% TeX Ver: June 1991 by Lee E. Brotzman
%
\documentstyle [adc,11pt]{article}
%
\newcommand{\dmv}{Documentation for the Machine-Readable Version of the}
\newcommand{\cat}{International Reference Stars Catalog}
\newcommand{\abbr}{1172}
\newcommand{\prefp}{Corbin 1991}
\newcommand{\adc}{Astronomical Data Center}
\newcommand{\docnum}{NSSDC/WDC-A-R\&S 91-11}
%
\begin{document}
%
\setcounter{page}{0}
\thispagestyle{empty}
\null \vfil \vskip 1in
\begin{center}
\begin{tabular}{c}
      {\LARGE \cat} \\
      \\
      {\Large (\prefp)} \\
      \\
      Documentation for the Computer-Readable Version \\
      \\
      {\small Thomas E. Corbin} \\
      {\small U.S. Naval Observatory} \\
      \\
      {\small Wayne H. Warren Jr.} \\
      {\small National Space Science Data Center} \\
      \\
      {\small April 1991} \\
      \\
      {\small Doc. No. \docnum} \\
      \\
      \\
      {\small National Space Science Data Center (NSSDC)/} \\
      {\small World Data Center A for Rockets and Satellites (WDC-A-R\&S)} \\
      {\small National Aeronautics and Space Administration} \\
      {\small Goddard Space Flight Center} \\
      {\small Greenbelt, MD 20771}
\end{tabular}
\end{center}
\vfil \null
\pagebreak

\begin{abstract}

The machine-readable version of the catalog, as it is currently being
distributed from the \adc , 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.

\end{abstract}

\section{Introduction}

\subsection{Description}

The AGK3R (Corbin 1977, 1978) and the SRS (Smith {\em 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 {\em et al.} 1988), known as the {\em 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 $\pm0\secdot43$ per century and $\pm0\secdot44$ 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.

This document describes the machine-readable version of the {\em \cat} 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. {\bf A copy of this document should be transmitted to
any recipient of the machine-readable catalog originating directly from the data
centers.}

\subsection{Source Reference}

\begin{references}
\item Corbin, T. E. 1991, \cat\ (Washington, U.~S. Naval Observatory)
\end{references}

\section{Structure}

\subsection{File Summary}
\label{s:FS}

The machine version of the IRS consists of two files. Table \ref{t:sumtab} 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.

\begin{table}[htbp]
\centering
\begin{tabular}{|c|l|c|c|r|}
\hline
\multicolumn{5}{|c|}{\cat}     \\
\multicolumn{5}{|c|}{(\prefp)} \\
\hline
     &                               & Record & Record &
                                     \multicolumn{1}{c|}{Number of} \\
File & \multicolumn{1}{c|}{Contents} & Format & Length &
                                     \multicolumn{1}{c|}{Records}   \\
\hline
 1   & Catalog Part 1 & Fixed & 192 & 29163 \\
 2   & Catalog Part 2 & Fixed & 192 &  6864 \\
\hline
\end{tabular}
\caption{Summary Description of Catalog File}
\label{t:sumtab}
\end{table}

The information contained in the above table is sufficient for a user to
describe the indigenous characteristics of the machine-readable version of the
{\em \cat} 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.

\subsection{Catalog (Files 1 and 2 of 2)}
\label{s:cathdc}

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 data files are ordered by J2000.0 right ascension.

Table \ref{t:cattab} gives a byte-by-byte description of the contents of the
data files. 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.

\begin{table}[htbp]
\centering
\begin{tabular}{|c|c|c|c|l|}
\hline
        &           & Suggested & Default &                            \\
 Bytes  &   Units   &   Format  &  Value  & \multicolumn{1}{c|}{Data}  \\
\hline
  1     & ---       & I1   & ---   & Catalog part                       \\
  2-7   & ---       & I6   & ---   & IRS number                         \\
  8     & ---       & 1X   & ---   & Zero                               \\
  9-10  & h         & I2   & ---   & Right ascension, $\alpha$, B1950.0 \\
 11-12  & min       & I2   & ---   & $\alpha$                           \\
 13-17  & s         & F5.3 & ---   & $\alpha$                           \\
 18-20  & deg       & I3   & ---   & Declination, $\delta$, B1950.0     \\
 21-22  & arcmin    & I2   & ---   & $\delta$                           \\
 23-26  & arcsec    & F4.2 & ---   & $\delta$                           \\
 27-29  & s         & F3.3 & blank & Mean error in $\alpha$ (at original
                                     epoch)                             \\
 30-32  & arcsec    & F3.2 & blank & Mean error in $\delta$ (at original
                                     epoch)                             \\
 33-38  & s         & F6.3 & ---   & Centennial proper motion, $\mu_{\alpha}$,
                                     B1950.0                            \\
 39-45  & arcsec    & F7.2 & ---   & Centennial proper motion, $\mu_{\delta}$,
                                     B1950.0                            \\
 46-49  & s/cy      & F4.3 & blank & Mean error in $\mu_{\alpha}$       \\
 51-53  & arcsec/cy & F4.2 & blank & Mean error in $\mu_{\delta}$       \\
 54-60  & years     & F7.3 & ---   & Original epoch of $\alpha$ and
                                     $\mu_{\alpha}$                     \\
 61-67  & years     & F7.3 & ---   & Original epoch of $\delta$ and
                                     $\mu_{\delta}$                     \\
 68-70  & ---       & I3   & ---   & Number of positions in $\alpha$    \\
 71-73  & ---       & I3   & ---   & Number of positions in $\delta$    \\
 74-77  & ---       & F4.1 & ---   & Weight in $\alpha$                 \\
 78-81  & ---       & F4.1 & ---   & Weight in $\delta$                 \\
 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   & ---   & AGK3 number                        \\
121-126 & ---       & A6   & ---   & CPC2 number                        \\
127-150 & ---       & A24  & ---   & IRS identifier                     \\
151-152 & hours     & I2   & ---   & Right ascension, $\alpha$, J2000.0 \\
153-154 & m         & I2   & ---   & $\alpha$                           \\
155-159 & s         & F5.3 & ---   & $\alpha$                           \\
160-165 & s         & F6.3 & ---   & Centennial proper motion, $\mu_{\alpha}$,
                                     J2000.0                            \\
166-171 & Jcy       & F6.5 & ---   & Original epoch - J2000.0 in $\alpha$ \\
172-174 & deg       & I3   & ---   & Declination, $\delta$, J2000.0     \\
175-176 & arcmin    & I2   & ---   & $\delta$                           \\
177-180 & arcsec    & F4.2 & ---   & $\delta$                           \\
181-186 & arcsec    & F6.2 & ---   & Centennial proper motion, $\mu_{\delta}$,
                                     J2000.0                            \\
187-192 & Jcy       & F6.5 & ---   & Original epoch - J2000.0 in $\delta$ \\
\hline
\end{tabular}
\caption{Data File Record Format}
\label{t:cattab}
\end{table}

\begin{definition}{24ex}

\item[Catalog part] The part is specifically identified as 1 or 2 so that if the
parts are merged, the source remains easily recognizable.

\item[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.

\item[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
{\em Astronomical Almanac} (page B42) (foreshortening terms set to zero). (See
Section 3.1 for additional details.)

\item[Proper motions] Referred to B1950.0 on FK4 (bytes 33-45) and to J2000.0 on
FK5 (bytes 160-165 and 181-186).

\item[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.

\item[Original epochs] Each refers to the mean epoch of the mean position from
the respective proper-motion solution.

\item[Number of positions] The number of positions used to determine the proper
motion and mean position in each coordinate.

\item[Weights] The sum of the weights of the catalogs used in each coordinate.

\item[Magnitude] Magnitudes are photographic and come from the AGK3 in the north
and the CPC2 in the south.

\item[Spectral type] Spectral type from the AGK3 (north only). No spectral types
are given for the southern stars.

\item[DM numbers] Identifier from one of the Durchmusterung (DM) catalogs,
identified as one of the following:

\begin{definition}{5ex}

\item[BD] {\em Bonner Durchmusterung} (Argelander 1859-62, K\"{u}stner 1903,
Sch\"{o}nfeld 1886)

\item[CD] {\em C\'{o}rdoba Durchmusterung} (Thome 1892-1932)

\item[CPD] {\em Cape Photographic Durchmusterung} (Gill \& Kapteyn 1895-1900).

\end{definition}

\item[AGK3 number] Identifier from the AGK3 catalog (Dieckvoss 1975).

\item[CPC2 number] Identifier from the {\em Second Cape Photographic Catalogue}
(de Vegt {\em et al.} 1989).

\item[IRS identifier] An identifier for each star based upon the recommended IAU
nomenclature (see PASP, 102, 1444, 1990). The field consists of an {\em 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.

\end{definition}

\section{History}
\label{s:history}

\subsection{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 $20^{\circ}$ interval in declination centered on the star. All
stars less than $10^{\circ}$ from the pole were treated as if they had been at
$80^{\circ}$ 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
{\em 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 \adc\ on 16 April
1991.

\section{References}

\begin{references}

\item Argelander, F. W. A. 1859-62, Bonner Sternverzeichniss, erste bis dritte
Sektion, Astronomischen Beobachtungen auf der Sternwarte der K\"{o}niglichen
Rhein., Friedrich-Wilhelms-Universit\"{a}t zu Bonn, B\"{a}nde 3-5

\item Corbin, T. E. 1974, AJ, 79, 885

\item Corbin, T. E. 1977, The Proper-Motion System of the AGK3R (Ann Arbor,
University Microfilms, Inc.)

\item Corbin, T. E. 1978, in IAU Colloquium 48, Modern Astrometry, ed. F. V.
Prochazka \& R. H. Tucker (Vienna: University Obs.), p. 505

\item Corbin, T. E. 1991, \cat\ (Washington, U. S. Naval Observatory)

\item 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

\item Dieckvoss, W. (in collaboration with H. Kox, A. G\"{u}nther, \& 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)

\item Fricke, W., \& Kopff, A. 1963, Fourth Fundamental Katalog (FK4),
Ver\"{o}ff. Astron. Rechen-Inst. Heidelberg No. 10.

\item Fricke, W., Schwan, H., \& Lederle, T. (in collaboration with Bastian, U.,
Bien, R., Burkhardt, G., du Mont, B., Hering, R., J\"{a}hrling, R., Jahreiss,
H., R\"{o}ser, S., Schwerdtfeger, H. M., \& Walter, H. G.) 1988, Fifth
Fundamental Catalogue (FK5), Part I. The Basic Fundamental Stars, Ver\"{o}ff.
Astron. Rechen-Institut Heidelberg No. 32

\item Gill, D. \& Kapteyn, J. C. 1895-1900, Cape Photographic Durchmusterung,
Ann. Cape Obs., 3 (1895, Part I: zones $-18^{\circ}$ to $-37^{\circ}$); 4 (1897,
Part II: zones $-38^{\circ}$ to $-52^{\circ}$); 5 (1900, Part III: zones
$-53^{\circ}$ to $-89^{\circ}$)

\item K\"{u}stner, F. 1903, Bonner Durchmusterung des N\"{o}rdlichen Himmels,
zweite berichtigte Auflage, Bonn Universit\"{a}ts Sternwarte (Bonn, A. Marcus
und E. Weber's Verlag)

\item Sch\"{o}nfeld, E. 1886, Bonner Sternverzeichniss, vierte Sektion,
Astronomische Beobachtungen auf der Sternwarte der K\"{o}niglichen Rheinischen
Friedrich-Wilhelms-Universit\"{a}t zu Bonn, 8, Part IV (Bonn, Adolph Marcus)

\item Schorr, R., \& Kohlsch\"{u}tter, A. 1951-1958, Zweiter Katalog der
Astronomischen Gesellschaft f\"{u}r das \"{A}quinoktium 1950, 1-10
(Hamburg-Bergedorf), 11-15 (Bonn, Ferd. D\"{u}mmlers Verlag)

\item Schwan, H. 1988, A\&A, 198, 363

\item Schwan, H., \& Corbin, T. E. 1991, Fifth Fundamental Catalogue (FK5), Part
II. The Extension Stars, in preparation

\item Scott, F. P. 1955, Conference d'Astrometrie, Bruxelles, 28-30 mars 1955,
in Commun. l'Obs. Roy. Belgique No. 85

\item Scott, F. P. 1962, AJ, 67, 690

\item 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

\item 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

\item Thome, J. M. 1892-1932, C\'{o}rdoba Durchmusterung, Resultados del
Observatorio Nacional Argentino, 16 (1892, Part I: $-22^{\circ}$ to
$-32^{\circ}$); 17 (1894, Part II: $-32^{\circ}$ to $-42^{\circ}$); 18 (1900,
Part III: $-42^{\circ}$ to $-52^{\circ}$); 21 (Part I) (1914, Part IV,
$-52^{\circ}$ to $-62^{\circ}$); 21 (Part II) (1932, Part V: $-62^{\circ}$ to
$-90^{\circ}$)
\end{references}
\end{document}
