\begin{table}%t3
      \caption{Constraints on the ionisation structure of circumnuclear matter.}
         \label{tab3}
         %\centering
 \small
                 \begin{tabular}{p{0.25\linewidth}l}
\hline
\hline
Element       & Ranges on the ionisation states \\
\hline
Neon & NeX\\
Oxygen & O VII--O IX \\
Magnesium & Mg XI--Mg XII \\
Silicon & Si XII--Si XIV \\
Iron & Fe I--Fe X \\
            \hline
         \end{tabular}
   \end{table}