\begin{table}%t13
\caption{Fits with a finite number of ionization components to the iron column densities for the RGS~data (Steenbrugge et~al. \cite{steen}). The number of ionization components is indicated by~$N$. In the last column we give the significance according to an F-test of the added \mbox{component}.}\label{tab:11}
%\centering
\par
\begin{tabular}{lllll}
\hline \hline
$N$ & $\chi^2$/d.o.f. & log $\xi$ & log $N_{\rm H}$ & Sign.  \\
  &                 & 10$^{-9}$ W m & m$^{-2}$    &        \\
  \hline
1 & 79/15      & 0.22      & 25.2                 &        \\
2 & 22.9/13    & 2.50, 0.20 & 25.7, 25.2          & 98.8   \\
3 & 10.5/11    & 2.57, 1.61, 0.20 & 25.7, 25.1, 25.2 & 90.9  \\
4 & 7.2/9      & 2.57, 1.62, 0.65 & 25.7, 25.1, 25.0 & 72.7 \\
  &            & $-$0.03          & 25.0             &      \\
5 & 4.9/7      & 3.10, 2.48, 1.56 & 25.8, 25.6, 25.1 &  71.1\\
  &            & 0.65, $-$0.03    & 25.0, 25.0    &    \\
\hline
\end{tabular}
\end{table}