\begin{table}%t5
\caption{Galactic P-L relations by different authors. The
  coefficients $a$ and $b$ are given for a P-L relation of the form
  $M=a(\log P -1)+b$.}
\label{tab:PL:comparison}
%\centering
\par
\begin{tabular}{lcccccc}
\hline
\hline
 \multicolumn{1}{c}{Authors} &
 \multicolumn{2}{c}{$M_{B}$} &
 \multicolumn{2}{c}{$M_{V}$} &
 \multicolumn{2}{c}{$M_{I}$} \\
 & \multicolumn{1}{c}{$a$} & \multicolumn{1}{c}{$b$} &
   \multicolumn{1}{c}{$a$} & \multicolumn{1}{c}{$b$} &
   \multicolumn{1}{c}{$a$} & \multicolumn{1}{c}{$b$} \\
\hline
Kraft (\cite{Kraft:61})           &  -2.25  &  -3.58  & -2.54 & -4.21 & \nodata & \nodata \\
Sandage \& Tammann (\cite{Sandage:Tammann:68}) &  -2.50  &  -3.61  & -2.76 & -4.24 & \nodata & \nodata \\
Feast \& Walker (\cite{Feast:Walker:87})    & \nodata & \nodata & -2.78 & -4.24 & 
\nodata & \nodata \\
Madore \& Freedman (\cite{Madore:Freedman:91}) & \nodata & \nodata & -2.76 & -4.16 &  
-3.06  &  -4.87  \\
Gieren et~al. (\cite{Gieren:etal:93})     & \nodata & \nodata & -2.99 & -4.36 & 
\nodata & \nodata \\
Laney \& Stobie (\cite{Laney:Stobie:94})    & \nodata & \nodata & -2.87 & -4.07 &
 \nodata & \nodata \\
Feast \& Catchpole (\cite{Feast:Catchpole:97}) & \nodata & \nodata & -2.81 & -4.24 & 
\nodata & \nodata \\
Gieren et~al. (\cite{Gieren:etal:98})     & \nodata & \nodata & -2.77 & -4.06 &  -3.04 
 &  -4.77  \\
present paper              &  -2.76  &  -3.23  & -3.14 & -3.97 &  -3.41  &  -4.73  \\
\hline
\end{tabular}
\end{table}