% Documentation for the SAO/J000/HD/DM/GC Cross Index (Roman, Warren, &
%     Schofield 1991)
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% Document Number: NSSDC/WDC-A-R&S 91-20
%
% Written: June 19, 1991 by N. G. Roman
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\documentstyle [titlepage,adc,11pt]{article}
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\newcommand{\dmv}{Documentation for the Computer-Readable Version}
\newcommand{\cat}{SAO/J2000/HD/DM/GC Cross Index}
\newcommand{\abbr}{Cross Index}
\newcommand{\catref}{Roman {\em etal} (1991)}
\newcommand{\pcatref}{Roman, N. G., Warren, W. H. and Schofield, N. J.}
\newcommand{\docnum}{NSSDC/WDC-A-R\&S 91-20}
%
\begin{document}
%
\title{ \cat}
\author{{\LARGE (\pcatref)}  \\
\\
Documentation for the Computer-Readable Version \\
\\
{\small Nancy G. Roman} \\
{\small June 1991}      \\
\\
{\small Doc. No. \docnum} \\
\\[2in]
{\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}}
\date{}
\maketitle

\begin{abstract}
The machine-readable version of the {\em Smithsonian Astrophysical Observatory
Star Catalog} which is being distributed currently by the astronomical data
centers contains data not included in the printed version of the catalog. The
additional data include the numbers in the HD, and GC catalogs and the J2000
positions. The latter, which are on the FK5 system, have been supplied by the US
Naval Observatory. This catalog extracts the additional data and the DM numbers
to provide a cross index among the J2000 position and the number assigned to
each star in the SAO, DM, HD, and GC catalogs.
\end{abstract}

\tableofcontents
\listoftables
\pagebreak

\section{Introduction}

This cross index lists for each entry in the {\em Smithsonian Astrophysical
Observatory Star Catalog} the J2000 position, the SAO number, the HD number, the
DM number, and the GC number. As in the machine-readable catalog from which it
is extracted, multiple entries with the same DM number have been discriminated
by capital letters indicating the components, and small letters have been added
for the supplemental stars in the northern zones of the BD. A code has been
included following the HD number to indicate to which component the HD number
refers or that the number refers to a composite spectrum. We thank the U.S.
Naval Observatory for computing the J2000 positions and proper motions on the
FK5 system. Although the J2000 positions in the complete catalog are given to
the same precision as the B1950 positions in the printed catalog, in this cross
index, the positions have been rounded to one second of time in right ascension
and 0.1 minute of arc in declination. This accuracy should be adequate for
identifying a star.

This document describes the current version of the machine-readable {\em
SAO/J2000/HD/DM/GC Cross Index}. It outlines the procedures used to correct and
extend the previous versions and is intended to enable users to read and process
the data without problems and guesswork. {\bf A copy of this document should
accompany any machine-readable version of the SAO/J2000/DM/HD/GC Cross Index
Catalog originating from any one of the international network of astronomical
data centers}.

\section{Structure}

\subsection{File Summary}

The {\em SAO/J2000/DM/HD/GC Cross Index} consists of three files. Table
\ref{t:files} gives the machine-independent attributes of these files. All
records are of fixed length, except that the last block may be short.

\begin{table}[ht]
\begin{center}
\begin{tabular}{|c|l|c|c|}                        \hline
\multicolumn{4}{|c|}{\em SAO/J2000/DM/HD/GC Cross Index} \\ \hline
File & Contents   &  Record Length & Number of Records  \\ \hline
  1  & SAO Sort   &       44       & 258944 \\
  2  & J2000 Sort &       44       & 258944 \\
  3  & DM Sort    &       44       & 258218 \\   \hline
\end{tabular}
\end{center}
\caption{Summary Description of Catalog Files}
\label{t:files}
\end{table}

The information contained in the above table is sufficient for a user to
describe the indigenous chracteristics of the machine-readable version of the
{\em SAO/J2000/DM/HD/GC} cross index to a computer. Stars marked ``delete'' in
the full catalog have not been included in this cross index. Hence the number of
records is less than that in the printed SAO. Similarly, file 3 does not
contains stars with no DM number. 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{File Formats}

Tables \ref{t:sao}, \ref{t:j2000}, and \ref{t:DM} give the formats for the three
files. A suggested Fortran format specification is given for each field. If a
datum is missing for any field, that field is blank. When an {\bf F} or an {\bf
I} format is indicated, the blank fields may be read as zeros. This should cause
no problem since no missing datum could have a sensible value of zero.

The following gives the meaning of the HD code:

\begin{description}
\item [0] Single star or primary with a companion $> 0.3$ mag (visual) fainter.
\item [1] Brighter component with a companion $\leq 0.3$ mag fainter.
\item [2] Fainter component with a companion $\leq 0.3$ mag brighter.
\item [9] The {\em SAO Catalog} entry refers to two consecutive HD numbers, the
lower of which is given.

\end{description}

\clearpage
\begin{table}[ht]
\begin{center}
\begin{tabular}{|c|c|c|l|}            \hline
       &       & Suggested &          \\
 Bytes & Units &   Format  &  Data    \\ \hline
  1-6  &  ---  &   I6      &  SAO number                      \\
  7-8  & hours &   I2      &  J2000 right ascension, $\alpha$ \\
  9-10 & min   &   I2      &  $\alpha$                        \\
 11-12 & sec   &   I2      &  $\alpha$                        \\
 13-15 & deg   &   I3      &  J2000 declination, $\delta$     \\
 16-19 & arcmin&   F4.1    &  $\delta$                        \\
 20-21 &  ---  &   A2      &  DM catalogue                    \\
 22-24 &  ---  &   I3      &  DM zone                         \\
 25-29 &  ---  &   I5      &  DM number                       \\
 30-31 &  ---  &   A3      &  Component                       \\
 32    &  ---  &   A1      &  Supplemental designation        \\
 33-38 &  ---  &   I6      &  HD number                       \\
 39    &  ---  &   I1      &  HD code                         \\
 40-44 &  ---  &   I5      &  GC number                       \\
\hline
\end{tabular}
\end{center}
\caption{SAO Sort Record Format}
\label{t:sao}
\end{table}

\begin{table}[ht]
\begin{center}
\begin{tabular}{|c|c|c|l|}            \hline
       &       & Suggested &          \\
 Bytes & Units &   Format  &  Data    \\ \hline
  1-2  & hours &   I2      &  J2000 right ascension, $\alpha$ \\
  3-4  & min   &   I2      &  $\alpha$                        \\
  5-6  & sec   &   I2      &  $\alpha$                        \\
  7-9  & deg   &   I3      &  J2000 declination, $\delta$     \\
 10-13 & arcmin&   F4.1    &  $\delta$                        \\
 14-19 &  ---  &   I6      &  SAO number                      \\
 20-21 &  ---  &   A2      &  DM catalogue                    \\
 22-24 &  ---  &   I3      &  DM zone                         \\
 25-29 &  ---  &   I5      &  DM number                       \\
 30-31 &  ---  &   A3      &  Component                       \\
 32    &  ---  &   A1      &  Supplemental designation        \\
 33-38 &  ---  &   I6      &  HD number                       \\
 39    &  ---  &   I1      &  HD code                         \\
 40-44 &  ---  &   I5      &  GC number                       \\
\hline
\end{tabular}
\end{center}
\caption{J2000 Sort Record Format}
\label{t:j2000}
\end{table}

\begin{table}[ht]
\begin{center}
\begin{tabular}{|c|c|c|l|}            \hline
       &       & Suggested &          \\
 Bytes & Units &   Format  &  Data    \\ \hline
  1-2  &  ---  &   A2      &  DM catalogue                    \\
  3-5  &  ---  &   I3      &  DM zone                         \\
  6-10 &  ---  &   I5      &  DM number                       \\
 11-12 &  ---  &   A3      &  Component                       \\
 13    &  ---  &   A1      &  Supplemental designation        \\
 14-15 & hours &   I2      &  J2000 right ascension, $\alpha$ \\
 16-17 & min   &   I2      &  $\alpha$                        \\
 18-19 & sec   &   I2      &  $\alpha$                        \\
 20-22 & deg   &   I3      &  J2000 declination, $\delta$     \\
 23-26 & arcmin&   F4.1    &  $\delta$                        \\
 27-32 &  ---  &   I6      &  SAO number                      \\
 33-38 &  ---  &   I6      &  HD number                       \\
 39    &  ---  &   I1      &  HD code                         \\
 40-44 &  ---  &   I5      &  GC number                       \\
\hline \end{tabular}
\end{center}
\caption{DM Sort Record Format}
\label{t:DM}
\end{table}

\section{Procedure}

A character-coded machine-readable version of the {\em Smithsonian Astrophysical
Observatory Star Catalog} (SAO, SAO Staff 1966) was prepared by T. A. Nagy
(1979) from a packed binary tape obtained from the Smithsonian Astrophysical
Observatory. In addition to certain format modifications, equatorial coordinates
in radians and cross identifications from the {\em Table of Correspondences
SAO/HD/DM/GC} (Morin 1973) were added to the converted version; however, the
known errata lists were not incorporated at that time. This version of the
catalog served as a starting point for the version described here. As a prelude
to creation of the 1984 version of the SAO, a new version of the {\em
SAO/HD/GC/DM Cross Index} was prepared (Roman, Warren and Schofield 1983), since
most of the changes and extensions for the SAO involved data in the Cross Index.
The original SAO did not use lower case letters, making some spectral types seem
strange. All capital letters that really should have been lower case in the
spectral types were changed.

Components were assigned according to the Washington Catalog of Visual Double
Stars (WDS, Worley and Douglas 1984), the successor to the Index Catalogue of
Visual Double Stars (IDS, Jeffers et al. 1963). For stars not in the WDS,
components were labeled according to visual magnitude. Supplemental (footnoted)
BD stars (Warren and Kress 1980) were identified and entered with lower case
letters. Corrections and additions to cross-identification data were made as
necessary. Some duplicate DM numbers actually referred to the same star for
which SAO data had been obtained from different source catalogs. In these cases,
only one record has been retained in this cross index. Many stars occur in two
DM catalogs (CD, CPD) in the southern hemisphere. The SAO gives numbers from
different catalogs for the components of some double stars; hence, although
there are no duplicate DM numbers, component confusion can occur. Although a
search for such systems was not exhaustive, the catalog was searched for
adjacent entries with declinations within 3 arcmin of each other. Most of these
entries proved to be double stars and were appended with letter designations as
if their DM numbers had been the same. These DM numbers were not changed.

An important subset of rather bright stars in the published SAO Catalog has no
DM numbers given. (Most of the stars in this subset were identified as FK3
double stars which were omitted from the FK4.) Many of these had been identified
by W. L. Stein, who supplied probable DM numbers. The positions for these stars
were compared manually with their positions in the various DM catalogs and many
additional identifications were made.

Although the {\em Henry Draper Extension} (Cannon 1925-1936) stars from {\em
Harvard Annals}, Volume 100, having DM numbers listed in the original catalog,
were included in the SAO, those listed with AG numbers only ({\em Astronomische
Gesellschaft}, zones +50 to +54 degrees, Harvard, Rogers 1892; zones +55 to +59
degrees, Helsingfors-Gotha, Kr\"{u}ger 1890) had not been cross identified and
inserted into the machine version. The {\em Yale Zone Catalogues} (YZ, Barney et
al. 1959a, 1959b), which identify stars by their AG numbers, but also give
corresponding DM numbers, were used to cross identify the AG stars. This was
accomplished by using the magnetic tape versions of the YZ and HD catalogs and
matching the stars by machine. A cross index of {\em Henry Draper Extension}
stars from {\em Harvard Annals}, Volume 112 (Cannon and Walton Mayall 1949) and
DM numbers (Bonnet 1978) was used to insert HDE numbers from the final HD
volume.

Since the GC (Boss 1937) numbers in the ``SAO-HD-GC-DM Cross Index'' had been
assigned by comparing with HD numbers in the GC, stars without HD numbers in the
Cross Index were missing GC identifications. The magnetic tape file of the GC
was therefore searched by DM number for all stars having no GC numbers in the
Cross Index. Additional GC numbers were found manually (by position) for the few
remaining stars without DM numbers. Fourteen GC stars were found not to be in
the SAO Catalog. HD numbers in the GC were then compared with their counterparts
in the Cross Index for stars in common, leading to the detection and correction
of a number of additional errors.

The catalog contains a numerical code appended to each HD number. The code
originally followed the convention of the ``Strasbourg Catalog of Stellar
Identifications'' (CSI, Ochsenbein et al. 1981) which assigned the numbers 1, 2,
... for individual components of multiple systems and the digit 9 if two
contiguous HD stars are included in the entry (the lower HD number is usually
given with code 9). Since the component codes were assigned to CSI entries
without regard to letter designations, and because letter designations have now
been added, the HD code was changed to a consistent indication of major
contamination of the spectral type of the component to which the entry applies
by the spectrum of another star (see Section 2.2). A visual magnitude difference
of 0.3 magnitude was used as the limit for which contamination was indicated.
Although photographic magnitudes would have been more appropriate, the visual
magnitudes in the SAO appeared to be more consistent.

Recently, Clayton A. Smith of the U.S. Naval Observatory, volunteered to provide
J2000.0 positions and proper motions for the SAO stars. Additional errors of
which we are aware (as of May 1991) have been corrected.

The astronomical data centers (ADC) have recently completed the preparation of
machine-readable versions of the three DM catalogs: the BD, the CD, and the CPD.
Using these versions, Mr. Barry Rappaport compared the positions of the stars in
the {\em Smithsonian Astrophysical Observatory Star Catalog} (SAO) with the
positions of the DM stars whose number had been assigned to each entry. A very
lengthy list of possible assignment errors resulted. Each of these has been
checked and the assignment corrected in those cases in which correction appeared
desirable. In many cases, the assignment in the printed SAO is probably
incorrect, but the evidence was not strong enough to warrant a change. As the
{\em Henry Draper Catalogue} numbers (HD) had been derived from the DM numbers,
those were also corrected as necessary.

\section{Acknowledgments}

We wish to express our appreciation to to D. Hoffleit, S. F. McLaughlin, R. E.
Reaves, P. C. Schmidtke and W. L. Stein for communicating errors. We also thank
the several people who pointed out additional errors, and Mr. Rappaport for
sending us the extensive list of possible problems in the DM numbers assigned in
the SAO. Especially significant was the work of T. Lederle (Astronomisches
Rechen-Institut, Heidelberg), who analyzed a large number of cross
identifications for Durchmusterung stars, provided a large list of possible
errors, and worked with us to improve the changes, which were then inserted into
the 1989 version. Finally, we thank C. A. Smith, especially, for providing the
J2000 positions.

\section{References}

\begin{references}

\item Argelander, F.W.A. 1859-1862, Bonner Sternverzeichniss, erste bis dritte
Sektion, Astronomischen Beobachtungen auf der Sternwarte des K\"{o}niglichen
Rhein., Friedrich-Wilhelms-Universit\"{a}t zu Bonn, B\"{a}nde 3-5.

\item Aitken, R. G. 1932, New General Catalogue of Double Stars within 120 deg
of the North Pole, Carnegie Institution of Washington Pub. 417 (Washington:
Carnegie Institution of Washington).

\item Becker, F. 1949, Bonner Durchmusterung, S\"{u}dlicher Teil,
Deklinations-Zonen -2 bis -22 Sternverzeichnis, zweite, berichtigte Auflage,
Ferd. Duemmlers Verlag, Bonn.

\item Becker, F. 1951, Bonner Durchmusterung, N\"{o}rdlicher Teil, Deklinations
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\item Bonnet, R. 1978, Bull. Inf. Cent. Donn\'{e}es Stellaires, No. 15, 115.

\item Boss, B. 1937, General Catalogue of 33342 Stars for the Epoch 1950,
Carnegie Institution of Washington Pub. 468 (Washington: Carnegie Institution of
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\item Cannon, A. J. and Pickering, E. C. 1918-1924, The Henry Draper Catalogue
Ann. Astron. Obs. Harvard Coll., 91-99.

\item Cannon, A. J. and Walton Mayall, M. 1949, The Henry Draper Extension, The
Annie J. Cannon Memorial Volume, Ann. Astron. Obs. Harvard College 112.

\item Gill, D. and 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).

\item Jeffers, H. M., van den Bos, W. H. and Greeby, F. M. 1963, Index Catalogue
of Visual Double Stars, 1961.0, Pub. Lick Obs. 21.

\item Kr\"{u}ger, A. 1890, Zonenbeobachtungen der Sterne zwischen 55 and 65 deg
n\"{o}rd. Decl. angestellt an der Sternwarten von Helsingfors und Gotha. I Band,
Enhaltd. Zonen 1-338 nebst den mittleren \"{O}rtern der Sterne f\"{u}r 1875
(Helsingfors: Kaiserl. Alexanders-Universit\"{a}t).

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

\item Morin, D. 1973, Table of Correspondences SAO/HD/DM/GC, Obs. de Meudon,
unpublished.

\item Nagy, T. A 1979, Documentation for the Machine-Readable Version of the
Smithsonian Astrophysical Observatory Catalog(ue) (EBCDIC Version), Systems and
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\item Ochsenbein, F., Bischoff, M. and Egret, D. 1981, Astron. Astrophys. Suppl.
43, 259.

\item Rogers, W. A. 1892, Catalogue of 8627 Stars, Ann. Astron. Obs. Harvard
College 15, Part II.

\item Roman, N. G., Warren, W. H. Jr. and Schofield, N. J. Jr. 1983,
Documentation for the Machine-Readable Version of the SAO-HD-GC-DM Cross Index,
Version 1983, NSSDC/WDC-A 83-17.

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

\item Smithsonian Astrophysical Observatory Staff 1966, Star Catalog. Positions
and Proper Motions of 258,997 Stars for the Epoch and Equinox of 1950.0, Pub. of
the Smithsonian Institution of Washington, D.C. No. 4652 (Washington:
Smithsonian Institution).

\item Stoy, R H. 1968, Cape Photographic Catalogue for 1950.0. Zone -80 to -90
degrees, Ann. Cape Obs. 22.

\item Thome, J. M. 1892-1932, C\'{o}rdoba Durchmusterung, Resultados del
Observatorio Nacional Argentino 16 (1892, Part I: -22 to -3 arcsec); 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).

\item Warren, W. H. Jr. and Kress, K. 1980, Astron. Data Center Bull. 1, 19.

\item Worley, C. E. 1980, Bull. Inf. Cent. Donn\'{e}es Stellaires, No. 18, 20.

\item Worley, C. E., and Douglas, G. G. 1984, U. S. Naval Observatory,
Washington, DC

\end{references}

\end{document}
