\begin{table}%t8
    \caption{Electron density in \cmtrois. For \object{BD+30~3639} a
      $T_{{\rm e}}=8500$ K has been used, and for \nsix~$T_{{\rm e}}=8200$ K.}
    \label{den}
%\centerline
{\begin{tabular}{l @{\hspace{5pt}}c @{\hspace{10pt}}c @{\hspace{7pt}}c @{\hspace{10pt}}c c @{\hspace{7pt}}c @{\hspace{7pt}}c}
      \hline
      \hline
      Ion & {\it IP} & Lines & \multicolumn{2}{c}{\bd}& 
      &\multicolumn{2}{c}{\nsix}\\ \cline{4-5} \cline{7-8}
      & (eV)  & used (nm) & Ratio & $N_{{\rm e}}$ &  & Ratio& $N_{{\rm e}}$\\ 
      \hline
\ion{S}{iii} & 34.8 & 18~700/33~500 & 5.0 & 10~200  & & 2.6  & 3400\\
\ion{O}{ii}  & 35.1 & 372.6/372.9     & 2.5 & 11~300  & & 2.4  & 9300$^\dagger$\\
\ion{Cl}{iii}& 39.6 & 553.8/551.8     & 3.1 & 48~000  & & 1.4  & 6600\\
      \hline   
    \end{tabular}}
$^\dagger$Uncertain density.
\end{table}