\begin{table}%T6
%\centering
\small
\caption{Properties of the core sample.} 
\label{tab:core} 
\begin{tabular}{lrr}\hline \hline 
 X-ray sources ($t_{\rm{PN}}>6$~ks, $ML >10$) & & 170\\ 
%\hline 
 Optically identified X-ray counterparts & & 158\\ 
 Spectroscopically classified optical counterparts&  & 110\\ 
 \hline 
\end{tabular} 
\end{table}