\begin{table}%T6
\caption{\label{siirat}Extended diffuse emission regions around PNe that give a [\ion{S}{ii}] 
$\lambda6716$/$\lambda6731$ ratio larger than~1.4 (from Kingsburgh \& English 
1992).}
%\centerline
{
\begin{tabular}{lc}
\hline
\hline
PN & $I(\lambda6716)/I(\lambda6731)^a$\\
\hline
 NGC 3195   &  1.98::                                                         \\
 Fg 1       & $\rm 1.45^{1.56}_{1.34}$ \\
 Pb 8       & $\rm 1.40^{1.48}_{1.32}$ \\
 He 2-104   & $\rm 1.71^{1.92}_{1.50}$ \\
 He 2-141   & $\rm 1.62^{1.84}_{1.40}$ \\
 He 2-146   & $\rm 1.52^{1.67}_{1.37}$ \\            
 NGC 6072   & $\rm 1.61^{1.80}_{1.42}$ \\  
 Mz 2       & $\rm 1.44^{1.55}_{1.33}$ \\
 IC 4634    &  2.14::                                                         \\ 
 IC 4637    &  1.75::                                                         \\
\hline
\end{tabular}}
\smallskip
 $^a$  A "::" indicates an uncertainty larger than 20\%.
\end{table}