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\begin{document}

\section*{1. Introduction}

This is a brief description of the data entries in the
{\it Third Reference Catalogue of Bright Galaxies\/} (RC3)
by G.\ and A.\ de Vaucouleurs, H.G.\ Corwin, R.J.\ Buta,
G.\ Paturel, and P.\ Fouqu\'e.  It accompanies an ASCII
version of RC3.9b (dated 27 April 1994) distributed 
by H.\ Corwin.  Any problems relating to this particular 
distribution should be addressed directly to
\begin{verse}
Dr.\ Harold G.\ Corwin, Jr. \\
IPAC, M/S 100-22 \\
California Institute of Technology \\
Pasadena, CA 91125 \\
\end{verse}

Files included in this distribution are:
\begin{description}
\item[rc39b.*.gz] 23 files containing the RC3 data.  These have been
   compressed using the UNIX ``gzip'' command, and may be uncompressed 
   using ``gunzip rc39b.*''; no options are necessary.
\item[bintro.tex] this file, a brief introduction to RC3.  It may be
   processed using \LaTeX\ should you wish to have a printed copy of
   it.
\item[bugs.rc3] a complete list of known errors in the printed version
   of RC3. {\it All of these errors are corrected in the present 
   machine--readable version}.
\item[checkrc3.f] a short FORTRAN program written to check the 
   integrity of the RC3 ASCII files.  Run this on the 23 files after
   you have uncompressed them.  This program also includes ``read''
   and ``format'' statements to read every field in RC3.  You may use
   these if you wish in other programs to read the RC3 data.
\item[rc3colsall.txt] a list of the columns (byte numbers) in RC3 and the
   information included in them.
\item[rc3.toc] a list of the equinox 2000.0 right ascensions of the 
   first and last galaxies in each file.  The PGC numbers of these
   same galaxies are also included.
\end{description}

Please note that there are only 23,011 entries in the current version
of RC3.  Several Galactic objects and duplicate entries have been removed.
Details are in the ``bugs.rc3'' file.

Details of the reduction procedures, and Notes,
References, and Appendices are in Volume 1 of the printed
version of RC3, available from Springer-Verlag New York.
References here to page numbers are to this first volume
of RC3.  Volumes 2 and 3 (included in the current distribution)
are also be available from Springer-Verlag
should you wish to have a printed and bound version of the 
complete catalogue.

\section*{2. Use and Distribution}

You may use any of the data in RC3 in any way you wish.  We do
ask that you acknowledge RC3 and its authors in any publication
that results from your use of the Catalogue.  You may also 
freely distribute {\it unaltered\/} electromagnetic copies of 
RC3 to friends and 
colleagues as long as a copy of this documentation -- including
this notice -- accompanies the Catalogue.  
{\it The printed version of RC3 is protected by
copyright, and may not be reproduced in any manner without the
written permission of the copyright holder, Springer-Verlag New York, Inc.}

\section*{3. The Catalogue}

The data for each galaxy are found on four successive lines.
The entries are as follows:
\begin{description}
\item[{\bf Column 1}:]  Positions
   \begin{description}
   \item[{\bf Line 1}:]  {\bf RA}\ and {\bf DEC}\ = right ascension and 
    declination for the equinox 2000.0, precessed from the 1950.0 position in 
    Column 1, Line 4, given to 0.1 second of time and 1 arcsec when 
    available, and to 0.1 minute of time and 1 arcmin otherwise 
    (Section 3.1.a, page 11).
   \item[{\bf Line 2}:]  {\bf l}\ and {\bf b}\ = galactic longitude and 
    latitude in the IAU 1958 system (Blaauw \etal 1960); both to 0.$\supdeg$01.
   \item[{\bf Line 3}:]  {\bf SGL}\ and {\bf SGB}\ = supergalactic longitude 
    and latitude in the RC2 system (Section 3.1.b), both to 0.$\supdeg$01.
   \item[{\bf Line 4}:]  {\bf RA}\ and {\bf DEC}\ = right ascension and
    declination for the equinox 1950.0 (Section 3.1.a, page 11).
   \end{description}
\item[{\bf Column 2}:]  Names = commonly used designations for the
    galaxies (Section 3.2, page 12).
   \begin{description} 
   \item[{\bf Line 1}:]  Names (\eg LMC, SMC) or NGC and IC designations.
   \item[{\bf Line 2}:]  UGC (Nilson 1973), ESO (Lauberts 1982), 
    MCG (Voront\-sov-Vel\-ya\-mi\-nov \etal 1962--1974), UGCA (Nilson 1974),
    and CGCG (Zwicky \etal 1961--1968)  designations, given in that order of 
    preference.  
    MCG designations not listed here are given in UGC and ESO.
   \item[{\bf Line 3}:]  Other common designations (see Table 1, page 14, for a 
    complete list).
   \item[{\bf Line 4}:]  PGC (Paturel \etal 1989a,b) designation.  For
    cross identifications of various catalogues with PGC, see Appendix 10, 
    page 561.
   \end{description}
\item[{\bf Column 3}:]  Types and Luminosity Classes
   \begin{description} 
   \item[{\bf Line 1}:]  {\bf Type}\ = mean revised morphological type in the 
   RC2 system, coded as in RC2 (Section 3.3.a, page 13).
   \item[{\bf Line 2}:]  {\bf S$_{\rm T}$ and n$_{\rm L}$}\ = sources of 
   revised type estimates and number of luminosity class estimates. 
   \item[{\bf Line 3}:]  {\bf T}\ = mean numerical index of stage along the 
   Hubble sequence in the RC2 system (coded as explained in Section 3.3.c, 
   page 16), and its mean error.
   \item[{\bf Line 4}:]  {\bf L}\ = mean numerical luminosity class in the RC2
   system (coded as explained in Section 3.3.d, page 18), and its mean error.
   \end{description}
\item[{\bf Column 4}:]  Optical Diameters and Axis Ratios
   \begin{description}
   \item[{\bf Line 1}:]  {\bf log\,D$_{\rm 25}$}\ = mean decimal logarithm of
   the apparent major {\it isophotal\/} diameter measured at or reduced to
   surface brightness level $\mu_{\rm B}$ = 25.0 \bms, and its mean
   error, as explained in Section 3.4.a, page 21.  Unit of D is 0.1 arcmin to 
   avoid negative entries.  A few very uncertain diameters are flagged with
   question marks.
   \item[{\bf Line 2}:]  {\bf log\,R$_{\rm 25}$}\ = mean decimal logarithm of
   the ratio of the major isophotal diameter, D$_{\rm 25}$, to the minor 
   isophotal diameter, d$_{\rm 25}$, measured at or reduced to the surface 
   brightness level $\mu_{\rm B}$ = 25.0 \bms, and its mean error, as
   explained in Section 3.4.b, page 26.  A few very uncertain axis ratios are
   flagged with question marks.
   \item[{\bf Line 3}:]  {\bf log\,A$_{\rm e}$}\ = decimal logarithm of
   the apparent diameter (in 0.1 arcmin) of the ``effective aperture,'' the
   circle centered on the nucleus within which one-half of the total B-band flux
   is emitted, and its mean error, both derived as explained in Section 3.4.c,
   page 28.
   \item[{\bf Line 4}:]  {\bf log\,D$_{\circ}$}\ = decimal logarithm of the
   isophotal major diameter corrected to ``face-on'' (i = 0\deg),
   and corrected for galactic extinction to $A_{g}$\ = 0, but not
   for redshift, as explained in Section 3.4.d, page 29.
   \end{description}
\item[{\bf Column 5}:]  Major Axis Position Angle, Galactic and Internal 
Extinctions
   \begin{description}
   \item[{\bf Line 1}:]  {\bf p.\,a.}\ = position angle, measured in degrees
   from north through east (all $<$ 180\deg), taken when available from 
   UGC, ESO, and ESGC (and in a few cases from H\,{\small\sc I} data)  
   (Section 3.5.a, page 30).
   \item[{\bf Line 2}:]  {\it A$_{\rm g}$}\ = Galactic extinction in B-band
   magnitudes, calculated following Burstein and Heiles (1978a,b, 1982, 1984), 
   as explained in Section 3.5.b, page 30.
   \item[{\bf Line 3}:]  {\it A$_{\rm i}$}\ = internal extinction in B-band
   magnitudes (for correction to face-on), calculated from log\,R and T, as 
   explained in Section 3.5.c, page 31.
   \item[{\bf Line 4}:]  {\it A$_{21}$} = H\,{\small\sc I} line 
   self-absorption in
   magnitudes (for correction to face-on), calculated from log\,R and T 
   $\geq$ 1, as explained in section 3.5.d, page 32.
   \end{description}
\item[{\bf Column 6}:]  Optical and Infrared Magnitudes
   \begin{description}
   \item[{\bf Line 1}:]  {\bf B$_{T}$}\ = total (asymptotic) magnitude
   in the B
   system, and its mean error, derived by extrapolation from photoelectric 
   aperture-magnitude
   data, B$_{T}^{\rm A}$, and from surface photometry with photoelectric
   zero point, B$_{T}^{S}$, as explained in Section 3.6.a, page 32.  The 
   magnitude
   is followed by an ``M'' when it is the weighted mean of B$_{T}^{\rm A}$\
   and B$_{T}^{S}$, by a ``V'' when it is a V-band magnitude rather than a
   B-band magnitude, and by a ``v'' when the nucleus of the galaxy is 
   variable.  The magnitude is flagged with an asterisk (*) when deriving 
   B$_{T}^{\rm A}$\ would have required an extrapolation in excess of 0.75 mag.
   \item[{\bf Line 2}:]  {\bf m$_{\rm B}$}\ = photographic magnitude and its
   mean error from Ames (1930), Shapley and Ames (1932), CGCG, Buta and Corwin
   (1986), and/or Lauberts 
   and Valentijn (1989) reduced to the B$_{T}$\ system, as explained in
   Section 3.6.b, page 37.
   \item[{\bf Line 3}:]  {\bf m$_{\rm FIR}$}\ = far-infrared magnitude 
   calculated from ${\rm m}_{\rm FIR} = - 20.0 - 2.5 \log\,{\rm FIR}$, 
   where FIR is the far infrared continuum flux measured at 60 and 100 microns 
   as listed in the {\it IRAS Point Source Catalog\/} (1987). For galaxies 
   larger than
   8$'$\ in RC2 and for the Virgo cluster area, resolved by the IRAS beam,
   integrated fluxes are taken from Rice \etal (1988) or Helou \etal (1988).
   See Section 3.6.c, page 43, for details.
   \item[{\bf Line 4}:]  {\bf B$_{T}^{\rm\circ}$}\ = total ``face-on''
   magnitude corrected for Galactic and internal extinction, and for 
   redshift, as explained in Section 3.6.d, page 44.
   \end{description}
\item[{\bf Column 7}:]  Total Color Indices
   \begin{description}
   \item[{\bf Line 1}:]  {\bf (B$-$V)$_{T}$}\ = total (asymptotic) color
   index in the Johnson B$-$V system, and its mean error, derived by 
   extrapolation from photoelectric color-aperture data, and/or from surface 
   photometry with photoelectric zero point, as explained in Section 3.7.a,
   page 45.
   \item[{\bf Line 2}:]  {\bf (U$-$B)$_{T}$}\ = total (asymptotic) color
   index in the Johnson U$-$B system, and its mean error, derived by 
   extrapolation from photoelectric color-aperture data, and/or from surface 
   photometry with photoelectric zero point, as explained in Section 3.7.a,
   page 45.
   \item[{\bf Line 3}:]  {\bf (B$-$V)$_{T}^{\rm\circ}$}\ = total B$-$V
   color index corrected for Galactic and internal extinction, and for redshift,
   as explained in Section 3.7.b, page 47.
   \item[{\bf Line 4}:]  {\bf (U$-$B)$_{T}^{\rm\circ}$}\ = total U$-$B
   color index corrected for Galactic and internal extinction, and for redshift,
   as explained in Section 3.7.b, page 47.
   \end{description}
\item[{\bf Column 8}:]  Effective Color Indices and B-band Surface Brightness
   \begin{description}
   \item[{\bf Line 1}:]  {\bf (B$-$V)$_{e}$}\ = mean B$-$V color index,
   and its mean error, within the effective aperture A$_{e}$, derived
   by interpolation from photoelectric color-aperture data, as explained in
   Section 3.7.a, page 45.
   \item[{\bf Line 2}:]  {\bf (U$-$B)$_{e}$}\ = mean U$-$B color index,
   and its mean error, within the effective aperture A$_{e}$, derived
   by interpolation from photoelectric color-aperture data, as explained in
   Section 3.7.a, page 45.
   \item[{\bf Line 3}:]  {\bf m$'_{e}$}\ = mean B-band surface brightness in
   magnitudes per square arcmin (B-m/sm) within the effective aperture 
   A$_{e}$, and its mean error,
   as given by the relation ${\rm m}'_{e} = {\rm B}_{T} + 0.75 +
   5 \log\,{\rm A}_{e} - 5.26.$
   m$'_{e}$\ is statistically
   related to the effective mean surface brightness, $\mu'_{e}$\
   (RC2, p.\ 31; Olson and de Vaucouleurs 1981), with which it coincides
   when log\,R = 0 (i = 0\deg) (Section 3.8.a, page 49).
   \item[{\bf Line 4}:]  {\bf m$'_{25}$}\ = the mean surface brightness
   in magnitudes per square arcmin (B-m/sm)
   within the $\mu_{\rm B}$\ = 25.0 \bms\ elliptical isophote of major axis
   \D25 and axis ratio \R25, defined as in RC2 (Equation 21) by:
   $${\rm m}'_{25} = {\rm B}_{T} + \Delta {\rm m}_{25} +  5 \log\,{\rm D}_{25}
   - 2.5 \log\,{\rm R}_{25} - 5.26,$$
   where $\Delta {\rm m}_{25}$ = 2.5 log\,L$_{T}$/L$_{D_{25}}$ = B$_{25}$
   $-$ B$_{T}$
   is the magnitude increment contributed by the outer regions of a galaxy
   fainter than $\mu_{\rm B}$\ = 25.0 \bms. For details, see Section 3.8.b,
   page 50.
   \end{description}
\item[{\bf Column 9}:]  21-cm Magnitude and Linewidths, Hydrogen Index
   \begin{description}
   \item[{\bf Line 1}:]  {\bf m$_{21}$}\ = 21-cm emission line magnitude,
   and its mean error, defined by 
   m$_{21}$ = 21.6 $-$ 2.5 log\,S$_{\rm H}$, where
   S$_{\rm H}$\ is the measured neutral hydrogen flux density in units of
   10$^{-24}$\,W\,m$^{-2}$.  For details, see Section 3.9.a, page 51.
   \item[{\bf Line 2}:]  {\bf W$_{20}$}\ = neutral hydrogen line full width
   (in \kms) measured at the 20\% level (I$_{20}$/I$_{\rm max}$),
   and its mean error, as explained in Section 3.9.b, page 51.
   \item[{\bf Line 3}:]  {\bf W$_{50}$}\ = neutral hydrogen line full width
   (in \kms) measured at the 50\% level (I$_{50}$/I$_{\rm max}$),
   and its mean error, as explained in Section 3.9.b, page 51.
   \item[{\bf Line 4}:]  {\it HI} = corrected neutral hydrogen index,
   which is the difference m$_{21}^{\rm\circ} - $B$_{T}^{\rm\circ}$\
   between the corrected (face-on) 21-cm emission line magnitude and the
   similarly corrected magnitude in the B$_{T}$\ system.  Details are
   given in Section 3.9.c, page 52.\footnote{Since m$_{21}$\ and B$_{T}$
   are listed separately in columns 6 and 9, line 1, there is no need to 
   list the uncorrected index.}
   \end{description}
\item[{\bf Column 10}:]  Radial Velocities
   \begin{description}
   \item[{\bf Line 1}:]  {\bf V$_{21}$}\ = {\it cz}\ is the mean
   heliocentric radial velocity, and its mean error, in \kms\
   derived from neutral hydrogen observations, as explained in Section 3.10.a
   page 52.
   \item[{\bf Line 2}:]  {\bf V$_{opt}$}\ = {\it cz}\ is the mean
   heliocentric radial velocity, and its mean error, in \kms\
   derived from optical observations, as explained in Section 3.10.b, page 53.
   \item[{\bf Line 3}:]  {\bf V$_{GSR}$}\ = the weighted mean of the
   neutral hydrogen and optical velocities, corrected to the ``Galactic 
   standard of rest,'' as explained in Section 3.10.c, page 54.
   \item[{\bf Line 4}:]  {\bf V$_{\rm 3K}$}\ = the weighted mean velocity
   corrected to the reference frame defined by the 3\deg K microwave
   background radiation, as explained in Section 3.10.d, page 55.
   \end{description}
\end{description}
\end{document}
