\begin{table}%t9
    \caption{Electron temperature in K. For \object{BD+30~3639} a
      $N_{{\rm e}}=11~000$~\cmtrois\ has been used, and for \nsix~$N_{{\rm e}}=5000$ \cmtrois.}
    \label{tem}
  %\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 & $T_{{\rm e}}$ &  & Ratio& $T_{{\rm e}}$\\ 
      \hline
\ion{N}{ii}  & 14.5 & 658.3/575.4   & 77.8 & 8400  & & 69.4 & 9500 \\
\ion{N}{ii}  & 14.5 & 654.8/575.4   &      &       & & 28.8 & 8800 \\
\ion{S}{iii} & 23.3 & 18~700/631.2 & 20.5 & 8600$^\dagger$ & & 48.4 & 7800 \\
\ion{O}{iii} & 35.1 & 500.7/436.3   &      &       & & 387  & 7800 \\
\ion{Ne}{iii}& 40.9 & 15~500/386.9 &      &       & & 4.0  & 8000 \\
\ion{Ar}{iii}& 27.6 & 8900/519.2    &      &       & & 531  & 7500$^\dagger$ \\
      \hline   
    \end{tabular}}
$^\dagger$Large error.  
\end{table}