% Documentation for UBVRI Photometric Standards Around the Celestial Equator
% (Landolt 1983)
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% Document Number: NSSDC/WDC-A-R\&S 88-27
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% Written: October 1988 by Wayne H. Warren Jr.
% TeX Ver: March 1991 by L.E. Brotzman
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\newcommand{\dmv}{Documentation for the Machine-Readable Version of the}
\newcommand{\cat}{UBVRI Photometric Standards Around the Celestial Equator}
\newcommand{\catref}{Landolt 1983}
\newcommand{\adc}{Astronomical Data Center}
\newcommand{\docnum}{NSSDC/WDC-A-R\&S 88-27}
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\begin{tabular}{c}
   {\LARGE \cat } \\
   {\Large (\catref)} \\
   \\
   Documentation for the Computer-Readable Version \\
   \\
   {\small Wayne H. Warren Jr.} \\
   {\small October 1988} \\
   \\
   {\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}
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\pagebreak

\begin{abstract}

The machine-readable version of this catalog of {\em UBVRI} standard stars, as
it is currently being distributed from the \adc , is described. The catalog
contains {\em UBVRI} photoelectric observations of 223 stars, mostly in an
approximate two-degree zone centered on the celestial equator. Most of the
stars are in Selected Areas 92-115 and fall in the magnitude range of about 7
to 12.5 in {\em V} and the color range $-0.3$ to $+2.0$ in {\em B-V}. The data
include equatorial coordinates, photoelectric magnitudes and colors, numbers of
observations, and computed internal errors.

\end{abstract}

\section{Introduction}

\subsection{Description}

The catalog of {\em \cat } (\catref) is intended to provide a uniform set of
new standards, available to various sizes of telescopes in both hemispheres, on
an internally consistent, homogeneous system. Such readily accessible standard
sequences are essential for the calibration of observations. The original {\em
UBV} system, as developed by Johnson and Morgan (1953), is still used
extensively and has become even more useful with its extension by the addition
of the {\em R} (7000 \AA) and {\em I} (9000 \AA) filters (Johnson {\em et al.}
1966). The photometric data presented in this catalog represent the first part
of an effort to provide {\em UBVRI} photoelectric photometric standard stars in
a magnitude range useful for a wide variety of telescopes and equipment.

For a more detailed description of the observing program, equipment used, and
photometric reductions, users of these data are referred to the source
reference.

This document describes the machine-readable version of the {\em \cat } as it
is currently being distributed from the \adc\ (ADC). It is only intended to
facilitate the processing and use of the data in the machine version. As
mentioned above, users should consult the source publication for additional
details. {\bf A copy of this document should be transmitted to any recipient of
the machine-readable catalog}.

\subsection{Source Reference}

Landolt, A. U. 1983, {\em Astron. J.} {\bf 88}, 439-460.

\pagebreak
\section{Structure}

\subsection{File Summary}

The machine version of the {\em \cat} 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 (as noted below) except that the last
block may be short. The first file contains the basic data of the catalog,
while the second contains remarks about particular stars, as flagged in the
individual records of the first file.

\begin{table}[htbp]
\centering
\begin{tabular}{|c|l|c|c|r|}
\hline
\multicolumn{5}{|c|}{UBVRI Photometric Standards Around the} \\
\multicolumn{5}{|c|}{Celestial Equator (Landolt 1983)} \\
\hline
     &                               & Record & Record &
                                     \multicolumn{1}{c|}{Number of} \\
File & \multicolumn{1}{c|}{Contents} & Format & Length &
                                     \multicolumn{1}{c|}{Records}   \\
\hline
  1  & Data    & Fixed & 125 & 223 \\
  2  & Remarks & Fixed & 132 & 262 \\
\hline
\end{tabular}
\caption{Summary Description of Catalog Files}
\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 (File 1 of 2)}
\label{s:cathd}

This file contains the principal data of the catalog, which are the {\em UBVRI}
photoelectric data and their errors, plus ancillary data consisting of primary
object identifiers and positions.

Table \ref{t:cattab} 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);
however, caution is advised when substituting format specifications, since many
data fields contain character data. Default (null) values are always blanks in
data fields for which primary suggested formats are given as A. No default
values are given for the integer and real data fields because all of these
contain valid data in this particular catalog. Alternate format specifications
are shown in parentheses.

\begin{table}[htbp]
\centering
\begin{tabular}{|c|c|c|c|l|}
\hline
        &        &    Suggested   & Default &                            \\
 Bytes  & Units  &      Format    &  Value  & \multicolumn{1}{c|}{Data}  \\
\hline
1-10    & ---    & A10            &  ---    & Star identification     \\
11      & ---    & A1             &  ---    & Supplemental BD letter  \\
12-14   & hours  & 1X,I2 (I3)     &  ---    & Right ascension         \\
15-17   & min    & 1X,I2 (I3)     &  ---    & RA                      \\
18-20   & sec    & 1X,I2 (I3)     &  ---    & RA                      \\
21      & ---    & 1X             &  ---    & Blank                   \\
22      & ---    & A1             &  ---    & Sign of declination     \\
23-24   & deg    & I2             &  ---    & Dec                     \\
25-27   & arcmin & 1X,I2 (I3)     &  ---    & Dec                     \\
28-30   & arcsec & 1X,I2 (I3)     &  ---    & Dec                     \\
31-37   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em V}                 \\
38-44   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em B-V}               \\
45-51   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em U-B}               \\
52-58   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em V-R}               \\
59-65   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em R-I}               \\
66-72   & mag    & 1X,F6.3 (F7.3) &  ---    & {\em V-I}               \\
73-75   & ---    & 1X,I2 (I3)     &  ---    & {\em n}                 \\
76-78   & ---    & 1X,I2 (I3)     &  ---    & {\em m}                 \\
79-80   & ---    & 2X             &  ---    & Blank                   \\
81-86   & mag    & F6.4           &  ---    & Mean error of {\em V}   \\
87-93   & mag    & 1X,F6.4 (F7.4) &  ---    & Mean error of {\em B-V} \\
94-100  & mag    & 1X,F6.4 (F7.4) &  ---    & Mean error of {\em U-B} \\
101-107 & mag    & 1X,F6.4 (F7.4) &  ---    & Mean error of {\em V-R} \\
108-114 & mag    & 1X,F6.4 (F7.4) &  ---    & Mean error of {\em R-I} \\
115-121 & mag    & 1X,F6.4 (F7.4) &  ---    & Mean error of {\em V-I} \\
122     & ---    & 1X             &  ---    & Blank                   \\
123-125 & ---    & A3             &  ---    & Notes flag(s)           \\
\hline
\end{tabular}
\caption{Data File Record Format}
\label{t:cattab}
\end{table}

\begin{definition}{23ex}

\item[Star identification] Catalog abbreviations are always given in bytes 1-2,
while numbers are contained in bytes 3-10. The abbreviations are defined in
Appendix I of the second catalog file.

\item[Supplemental BD letter] The letter ``a'' is given for Barnard's Star
(BD+04 3561a).

\item[Equatorial coordinates] Positions are for equinox 1985 at epoch. However,
proper motions have been accounted for in computing the 1985 coordinates for
the large proper-motion stars, so these positions are given for equinox {\bf
and} epoch 1985.0.

\item[V magnitude] Weighted {\em V} magnitude on the {\em UBVRI} photometric
system, as defined by stars in Landolt (1973) and Cousins (1976).

\item[B-V] Weighted {\em B-V} color on {\em UBVRI} system.

\item[U-B] Weighted {\em U-B} color on {\em UBVRI} system.

\item[V-R] Weighted {\em V-R} color on {\em UBVRI} system.

\item[R-I] Weighted {\em R-I} color on {\em UBVRI} system.

\item[V-I] Weighted {\em V-I} color on {\em UBVRI} system.

\item[n] The total number of observations used to compute the weighted means.

\item[m] The number of nights on which the star was observed.

\item[Mean error of V] The mean error of the mean magnitude, as defined by:

\[ <\epsilon> = \left[ \frac{\sum (x_{i} - \overline{x})^{2}}
                            {n(n - 1)} \right]^{1/2} , \]

where $x_{i}$ is an individual observation, $\overline{x}$ is the mean value,
and {\em n} is the number of observations. The mean error of a single
observation can be found by multiplying the appropriate error of the mean by
$\sqrt{n}$, since the mean error of a single observation is given by
\( \left[\sum(x_{i} - \overline{x})^{2}/(n - 1) \right]^{1/2} \).

The mean errors for the colors are computed in the same way.

\item[Notes flag(s)] Number(s) referring to notes given at the top of the
remarks file. These notes are distinct from the additional information given in
Appendix I, which follows the ``Notes'' section in the text file.

\end{definition}

\subsection{Notes (File 2 of 2)}
\label{s:nothd}

This file contains the notes to the main data table in an A132 Fortran~77
format, as indicated by the presence of notes flags in the final column of that
table (bytes 123-125). The file can only be processed as free text because it
contains a mixture of full lines of free text and star identifications. The
contents of Appendix I of the published paper follow the notes.

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

\subsection{Remarks and Modifications}

The machine-readable data table {\em \cat } was received on magnetic tape from
Dr. Arlo U. Landolt on 15 April 1986. As received, the table appeared
essentially as does Table IV of the published paper, with table headings and
the free-text notes at the end of the file. The following modifications to the
machine-readable file were made at the ADC in order to effect a uniformly
formatted data file, to isolate the table notes from the data, and to add the
additional information contained in Appendix I of the published paper:

\begin{enumerate}

\item The table headings and all blank lines were removed from the file, and
the notes were placed into a second file;

\item The colons in the RA field were changed to blanks;

\item The numerical star identifications were aligned, and the data field was
expanded to accommodate catalog identifiers at the beginning of the field.
Identifications such as ``SA'', ``HD'', and ``BD'' were then added to all
designations not already having them. The supplemental letter ``a'' was added
to BD+04 3561 (Barnard's Star) to distinguish it from BD+04 3561, which is not
included in this catalog;

\item Appendix I of the published paper, containing additional information
gleaned from the literature for the BD and HD stars, was computerized at the
ADC and added to the notes file.

\end{enumerate}

\subsection{Acknowledgments}

Appreciation is expressed to A. U. Landolt for providing the catalog on
magnetic tape and for reviewing and commenting on a preliminary version of this
document prior to its finalization for distribution with the machine-readable
catalog.

\subsection{References}

\begin{references}
\item Cousins, A. W. J. 1976, {\em Mem. Roy. Astron. Soc.} {\bf 81}, 25-36.
\item Johnson, H. L., Mitchell, R. I., Iriarte, B., and Wi\'{s}niewski, W. Z.
1966, {\em Commun. Lunar Planet. Lab.} {\bf 4}, 99 (No. 63).
\item Johnson, H. L. and Morgan, W. W. 1953, {\em Astrophys. J.} {\bf 117},
313-352.
\item Landolt, A. U. 1973, {\em Astron. J.} {\bf 78}, 959-981.
\item Landolt, A. U. 1983, {\em Astron. J.} {\bf 88}, 439-460.
\end{references}

\end{document}
