\begin{table}%t1
\par
\caption {Exposure times, image quality and detection limits of the\protect
reduced HAWK-I data. 
\label{table:observations}} 
%\centerline
 {\begin{tabular}{c c c c} 
\hline\hline
Filter & Exposure time$^{{a}}$ & Image quality & Detection limit$^{{b}}$ \\
       & (s)     & (\arcsec)     & (Vega magnitudes)\\
\hline
$J$      & 10~560         & 0.47          & 24.9 \\
$K$s     & 10~740         & 0.32          & 23.2 \\
\hline
\end{tabular}}
\par
\smallskip
$^{a}$ All quantities refer to the central part of the
mosaic, where exposure times are greatest;
$^{b}$ the detection limit is the 5~sigma point source detection limit within an aperture that has a
diameter equal to twice the image quality.
\end{table}