\begin{table}%t1
%\centering
\par
\caption{Summary of the extended model atom. The iron-group ions (Fe)
are described by a relatively small number of super-levels, each 
representing a large number of true atomic energy levels (sub-levels). 
In the present work we also apply a smaller model atom, where
the iron-group ions are restricted to {\FeII}--{\FeX} with {\FeX}
represented by one auxiliary level.\label{tab:modelatom}}
\begin{tabular}{llllll}
\hline \hline 
\rule{0cm}{2.2ex} Ion & Levels && Ion & Super-levels & Sub-levels\\
\hline
\rule{0cm}{2.2ex}\HeI& 17            &&\FeII&   1  & 1\\
\HeII& 16                            &&\FeIII&  8  & 14~188\\
\HeIII& 1                            &&\FeIV&   18 & 30~122\\
\CI&2                                &&\FeV&    19 & 19~804\\
\CII& 32                             &&\FeVI&   18 & 15~155\\
\CIII& 40                            &&\FeVII&  16 & 11~867\\
\CIV& 54                             &&\FeVIII& 10 & 8669\\
\CV& 1                               &&\FeIX&   11 & 12~366\\
\OII& 3                              &&\FeX&    9  & 761\\      
\OIII& 33                            &&\FeXI&   9  & 1143\\
\OIV& 25                             &&\FeXII&  9  & 894\\
\OV& 36                              &&\FeXIII& 9  & 797\\
\OVI& 15                             &&\FeXIV&  9  & 589\\
\OVII& 1                             &&\FeXV&   7  & 253\\
\SiIII& 10                           &&\FeXVI&  6  & 31\\
\SiIV& 7                             &&\FeXVII& 1  & 1\\
\SiV& 1 &&&\\
\hline
\end{tabular} 
\end{table}