% Documentation for UBVRI Photometric Standards Around the Celestial Equator % (Landolt 1983) % % Document Number: NSSDC/WDC-A-R\&S 88-27 % % Written: October 1988 by Wayne H. Warren Jr. % TeX Ver: March 1991 by L.E. Brotzman % \documentstyle [adc,11pt]{article} % \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} % \begin{document} % \setcounter{page}{0} \thispagestyle{empty} \null \vfil \vskip 1in \begin{center} \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} \end{center} \vfil \null \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}