\begin{table}%t8                                                            
\caption{Parameters representing the best-fit model.}\label{tab8}                               
%\centering
\small                                                         
\begin{tabular}{ll}                                                         
\hline\hline
Parameter & Value\\                                                         
\hline
{\it Ionizing source} &\\
{\it Model atmosphere} & Tlusty \\
$T_{\rm eff}  $ &47~500 K \\
Log $g$    & 3.75 \\
Luminosity & 1640 $L_{\odot}$\\
\\
{\it Nebula}    & \\
Density profile & See Fig.~\ref{fig-2}  \\
Abundance & H     \hskip 1.0cm He    \hskip 0.9cm C    \hskip 1.0cm N \\
          & 12.000\hskip 0.3cm 11.041\hskip 0.6cm 8.637\hskip 0.4cm 7.820 \\
          & O     \hskip 1.0cm Ne    \hskip 0.9cm Si   \hskip 0.9cm P \\
          & 8.586 \hskip 0.4cm 7.903\hskip 0.4cm 6.636 \hskip 0.5cm 5.380\\ 
          & S     \hskip 1.0cm Cl    \hskip 0.9cm Ar  \hskip 0.8cm Fe \\
          & 6.377 \hskip 0.4cm 4.903\hskip 0.6cm 6.114 \hskip 0.4cm 5.784\\
Size      &$20\arcsec$ (radius)\\
Distance  & 1.40~kpc\\
Dust grains & Silicates of single size $0.01~\mu$m; see Fig.~\ref{fig-5} \\
Inner radius & 6.283e15 cm ($\sim$$0.00203$~pc) \\
Outer radius & 4.189e17 cm ($\sim$$0.136$~pc)\\
Filling factor & 1.0\\
\hline
\end{tabular}
\end{table}