\begin{table}%t6
\caption{Fine-structure line intensities$^a$ and X-rays.}\label{tab_fs}
\small%%\centerline
\par
 {
\begin{tabular}{lccccccc}
\hline\hline
&&&&&&& \\[-8pt]
 Line$^b$  & Obs. & \multicolumn{2}{c}{$M2$} & \multicolumn{2}{c}{$M2_{\rm X}$} & \multicolumn{2}{c}{$M2_{\rm X2}$} \\
\cline{1-8}
&&&&&&& \\[-8pt]
\hi\ colls.$^c$ &   --  &  no  &  yes &   no & yes &   no & yes \\
{\cii}$\:$158.  &   --  &  2.1 &  2.1 &  124 & 119 &  224 & 204 \\
{\oi}$\:$63.2   &   --  &  4.7 &  4.6 &  274 & 210 &  624 & 450 \\
{\neii}12.8     &   9  &  1.9 &  3.6 &  1.9 & 5.5 &  2.0 &  16 \\
{\sid}$\:$34.8  &157$^d$&  21 &   22 &   37 &  80 &   55 & 190 \\
{\arii}$\:$7.0  &   --  &  1.2 &  1.3 &  1.4 & 2.2 &  2.2 & 7.9 \\
{\feii}$\:$26.0 &  34  &  3.4 &  4.8 &  5.8 &  38 &  9.3 & 108 \\
{\feii}$\:$35.3 &   --  &  0.8 &  1.4 &  1.1 & 9.5 &  1.7 &  33 \\
\hline
\end{tabular}}
\medskip
$^a$ In units \hb\ = 1000. 
$^b$ Wavelengths in $\mu$m. 
$^c$ Inelastic collisions of \sid, \feii, \neii\ and \arii\ with \hi\ omitted ("no'') or included ("yes''). 
$^d$ The re-calibrated \sid\ flux is 68 after Sect.~\ref{disc_ir_oiv}. 
\end{table}