\begin{table}%t2
%\centering
\par
\caption{Observational characteristics.} \label{tab2}
\begin{tabular}[t]{lllllll}
\hline\hline 
Name & Telescope & \multicolumn{2}{c}{Exposure times} & \multicolumn{3}{c}{Interference filter}  \\
     &           & Total  & per channel               & Central     & $FWHM$ & Transmission \\
     &           &        &                           & wavelenght  &      & at maximum \\
     &           & (hour) & (s)                  & (\AA)         &(\AA)   &            \\
\hline
 & & & & & & \\
HCG~10   & CFH 3.6~m & 1.6 & 240 & 6670 & 20& 0.80 \\
HCG~19   & ESO 3.6~m & 2 & 300 & 6656 & 22  & 0.70 \\
HCG~87   & ESO 3.6~m & 2 & 300 & 6763 & 30  & 0.73 \\
HCG~91   & ESO 3.6~m & 2 & 300 & 6722 & 16  & 0.57 \\
HCG~96   & ESO 3.6~m & 2 & 300 & 6763 & 30  & 0.73 \\
\hline
\end{tabular}
%\end{flushleft}
\end{table}