\begin{table}%t1
\caption{Constraints on model parameters$^a$.}
\label{tab_conv}
\small%%\centerline
\par
 {
\begin{tabular}{l|l}
\hline\hline
Parameter  &  Constraints                \\
\hline                         
$E(B-V)$     & \ha/\hb; (No freedom: $E(B-V)$ = 0.04) \\
$R_{\rm i}$ & No freedom $R_{\rm i}$ = 2.85 $\times$ $10^{20}$~cm \\
$f^{\rm cov}$  & Absolute $I$(\hb) = 5.6 $\times$ 10$^{-14}$\ergcs \\
$L1$, $L2$ & Cluster SED; $f^{\rm cov} \leq 1.0$; $Q_{\rm abs}$/$Q$ $\sim$ 0.37\\
$T1$, $T2$ & $\delta_4 \leq 1.0$; (log~($Q_{\rm He}$/$Q$) $\sim$ $-$0.5) \\
$\delta_4$ & \heii\la4686 \\
\cline{1-2}
He & He/H = 0.08; \hei\la5876? \\
C  & \ciii\la1909  \\
N  & \nii\la6584   \\
O  & \oiii\la5007  \\
Ne & \neiii\la3869 \\
Mg &  Mg/Ar = 10.; \mgi\la4571?  \\
Al &  Al/Ar = 1.; \aliii\la1855? \\
Si &  Si/Ar = 10.; \sit\la1883?  \\  
S  &  S/Ar = 4.37; $\langle$\siii$\rangle$? \\
Ar & \ariii\la7135 \\ 
Fe & \feiii\la4658 \\
\cline{1-2} 
\multicolumn{2}{l}{One-component constant density run ($N0$, $N1$):} \\
\Nh            & $r$(\sii) = \sii\la6716/\sii\la6731 ($\pm$) \\
$\tau_{\rm m}$ & \oii\la3727 \\
$\epsilon$     & $R_{\rm f}$ = 4.75 $\times$ $10^{20}$ cm \\
\cline{1-2} 
\multicolumn{2}{l}{One-component model with Eq.~(1) ($M1$):} \\
$\epsilon = 1.0$ & No freedom \\
$P_{\rm out}$  & $r$(\sii) \\
$\tau_{\rm c}$ & \oii\la3727 \\
$P_{\rm in}$   & $R_{\rm f}$ = 4.75 $\times$ $10^{20}$ cm \\
\cline{1-2} 
\multicolumn{2}{l}{Two-component model ($M2, M3, M4$) added freedoms:} \\
$f^{\rm cov}_1$ & $f^{\rm cov}_2$ $>$ 0; $f^{\rm cov}$ = $f^{\rm cov}_1$ + $f^{\rm cov}_2$ $<$ 1 \\
$f^{\rm cov}_2$ & $\tau_{\rm m}$(2) $<$ $\tau_{\rm c}$; global 3D geometry \\
$\tau_{\rm m}$(2) & Fine tuning $I$(\hb) for given $f^{\rm cov}_i$\\
& \\[-8pt]
\hline
\end{tabular}}
\medskip
$^a$ Question marks attached to dismissed constraints (see text).
\end{table}