\documentstyle [adc,11pt]{article}
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\newcommand{\dmv}{Documentation for the Computer-Readable Version}
\newcommand{\cat}{BV Photometry of the Galactic Globular Cluster NGC 1851}
\newcommand{\abbr}{NGC1851}
\newcommand{\catref}{Walker (1992)}
\newcommand{\pcatref}{Walker, A. R.}
\parindent 0pt
\parskip 11pt
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\begin{document}
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\title{\cat}
\author{(\pcatref)}
\docauthor{Nancy G. Roman}
\docno{NSSDC/WDC-A-R\&S 93-11}
\date{March 1993}
\maketitle

\begin{abstract}

BV photometry is provided for 1,234 stars in the magnitude range 13 - 18 in an
annulus between 5 and 20 arc seconds from the center of NGC 1851 and for 1,247
stars in the magnitude range 18 - 23 at a distance of more than 240 arc seconds
from the center. For stars in the magnitude range 16 - 21, the errors in B$-$V
increase with magnitude from 0.005 mag. to 0.022 mag.

\end{abstract}

\section{Introduction and Source Reference}

\subsection{Introduction}

The authors were primarily interested in the shape of the color magnitude
diagram of the galactic globular cluster, NGC 1851. To prepare this diagram,
they obtained a number of CCD frames of the cluster in B and in V with exposures
ranging from 20s to 1500s. The longer exposures were taken at a distance of more
than 240 arc seconds from the center of the cluster.

\subsection {Source Reference}

\begin{references}

\item {\em A BV Color-Magnitude Diagram for the Galactic Globular Cluster NGC
1851} Walker, A. R. 1992, PASP, 104, 1063.

\end {references}


\section {Structure}

\subsection{File Structure}

The {\em \cat} as distributed here is in a single file. The stars in the
magnitude range 13.0 to 19.0 in an annulus between 5 and 20 arc seconds from the
center of the cluster have a blank or 1 in byte 1. The stars in the magnitude
range 18.0 to 24.0 at a distance of at least 240 arc seconds from the center
have a 2 or 3 in byte 1. The positions are given in pixels from the center of
the cluster. To aid in star identification, accurate (GSC) coordinates are given
for two bright stars in Table 1.

\pagebreak

\begin{table} [h]
\centering
\begin{tabular}{ r c c c c c c}
\hline
Ident & X   &  Y  &   V &   B-V  &     RA   &        DEC           \\
 &\multicolumn{2}{c}{(pixels)}& & &\multicolumn{2}{c}{(2000)}      \\
\hline                                                             \\
  7 & 608.8& 26.8 & 13.425&1.628 & 05 13 44.76 & -40 00 28.8       \\
 59 & 575.4&228.3 & 14.025&1.306 & 05 13 53.02 & -40 00 44.1       \\
\hline
\end{tabular}
\caption{Positions of Bright Stars}
\label{t:ps}
\end{table}

The pixel scale is 0.478 arcsec/pixel, with the orientation X increasing to the
north, and Y increasing to the east.

The median error of the B-V colors as a function of magnitude is given in Table
2.

\begin{table} [h]
\centering
\begin{tabular}{ c c }
\hline
Mag. Range & Med. Error \\
\hline
16-17      & 0.005      \\
17-18      & 0.009      \\
18-19      & 0.012      \\
19-20      & 0.016      \\
20-21      & 0.022      \\     \hline
\end{tabular}
\label{t:me}
\caption{Median Errors as a Function of Magnitude}
\end{table}

\subsection{File Format}

Table 3 gives a byte-by-byte description of the contents of the data file.

\begin{table}  [h]
\centering
\begin{tabular}{ c c c l }
\hline
&  &  &    \\
Bytes     & Unit   &Format & Item                              \\ \hline
 1 -  4   &        & I4    & Number           \\
 6 - 11   & pixel  & F6.1  & X coordinate     \\
13 - 18   & pixel  & F6.1  & Y coordinate     \\
20 - 25   & mag.   & F6.3  & V magnitude      \\
27 - 32   & mag.   & F6.3  & B$-$V color      \\
34 - 36   &        & A3    & Remark           \\
\hline
\end{tabular}
\caption{Format }
\label{T:form}
\end{table}

\section{Acknowledgments}

We thank Dr. Walker for forwarding to us a machine-readable version of the
catalog, including the data for the faint stars that are not in the published
reference.

\section{References}

\begin{references}

\item {\em A BV Color-Magnitude Diagram for the Galactic Globular Cluster
      NGC 1851} Walker, A. R. 1992, PASP, 104, 1063.

\end{references}

\end{document}
