\begin{table}%t2
%\centering
\small\caption{Four-step model-PN evolution. Integrated intensity of representative nebular emissions (relative to {\it I}(H$\beta)=100$), absolute H$\beta$ flux, 
and ionized mass for the adopted, spherically symmetric nebula (Table~\ref{t1}) powered by a hydrogen-burning post-AGB star of 0.605~$M_\odot$.}\label{t2}
\begin{tabular}{cccccc}
\hline\hline
$\lambda$ ($\rm\AA\/$)&Ion &&{\it I}($\lambda$)&\\
\cline {3-6}
&& {Sect. 4.4}& {Sect. 4.1}&{Sect. 4.2} &{Sect. 4.3}\\
&&{proto-PN + }&{early-PN}&{intermediate-PN}&{late-PN} \\
&&{"born-again'' low-exc.-PN}&&&\\
&&(very thick)&(nearly thin)& (thin)& (recombining) \\
&&$T_*=25~000$~K & $T_*=50~000$~K&$T_*=100~000$~K     & $T_*=150~000$~K  \\
&&$L_*$/$L_\odot=6500$& $L_*$/$L_\odot=6500$& $L_*$/$L_\odot=6500$& $L_*$/$L_\odot=1000$ \\
\hline
3425  &$[$Ne V$]$   & 0.0       & 0.0       & 4.1  & 14.7  \\
3726+29  &$[$O~II$]$& 133.3  & 231.2       & 73.8       &   587.5   \\
3968  &$[$Ne III$]$   &  0.02      & 15.2       & 49.8  & 64.9  \\
4686  &He~II   &  0.0      &  0.25      & 19.0  & 42.2  \\
4740  &$[$Ar IV$]$   &0.0        & 0.22       & 3.4  &2.9   \\
4861&H~I   & 100.0       & 100.0       &100.0   & 100.0  \\
5007  &$[$O~III$]$   & 5.5       &  490.0      &1510.0   &1312.2   \\
5876  &He~I   &   3.11     & 15.5       & 12.6  & 10.5  \\
6300  &$[$O I$]$   & 1.3       & 2.5       &0.1   & 26.3  \\
6563  &H~I   &  297.2      & 291.7       &285.7   & 288.4  \\
6584&$[$N~II$]$   &265.5        &  169.0      &37.3   &434.5   \\
6717+31  &$[$S~II$]$   &  43.1      & 24.4       &12.4   & 107.3  \\
7005  &$[$Ar V$]$   &  0.0      &  0.0      &0.77   & 1.05  \\
7135  &$[$Ar III$]$   & 1.6       & 17.4       & 21.0  & 30.7  \\
7320  &$[$O~II$]$   & 0.8       &  2.2      &1.0   & 9.8  \\
\\
$\log E$(H$\beta$)&(erg s$^{-1}$)&34.549& 35.057&35.019&34.321 \\
\\
$M_{\rm ion}$& ($M_\odot$)&0.10&0.38&0.40&0.07$^{*}$\\
&&&&&* excluding the ionized mass \\
&&&&&of the recombining halo\\
\hline
\end{tabular}
\end{table}