\begin{table}%t1
\caption{\label{Tab:Obs}Details of the imaging observations used in this~work.}
\par
\small%\centerline
 {
\begin{tabular}{llllll}
\hline
\hline
Date & $\lambda_{\rm central}$ [$\mu$m] & $\Delta\lambda$  [$\mu$m] & $N$ & NDIT & DIT [s]\\
\hline
03 May 2002 & 2.18 & 0.35 & 20 & 3 & 20 \\
10 May 2003 & 2.18 & 0.35 & 19 & 120 & 0.5\\
12 June 2004 & 2.06 & 0.06 & 96 & 1 & 30 \\
12 June 2004 & 2.24 & 0.06 & 99 & 1 & 30 \\
13 June 2004 & 2.33 & 0.06 & 119 & 1 & 30 \\
13 May 2005 & 2.18 & 0.35 & 103 & 60 & 0.5 \\
29 April 2006 & 1.66 & 0.33 & 32 & 28 & 2 \\
29 April 2006 & 2.18 & 0.35 & 32 & 28 & 2 \\
01 June 2006 & 2.18 & 0.35 & 80 & 3 & 10 \\
28 May 2008 & 2.18 & 0.35 & 35 & 4 & 10 \\
28 May 2008 & 2.18 & 0.35 & 20 & 2 & 20 \\
\hline
offset fields & & & & & \\
\hline
11 Aug. 2004 & 2.18 & 0.35 & 16 & 3 & 40\\
27 July 2005 & 2.18 & 0.35 & 8 & 4 & 15\\
28 May 2008 & 2.18 & 0.35 & 20 & 20 & 2\\
\hline
\end{tabular}}
\medskip
DIT is the detector integration time, NDIT is the number of integrations that were averaged on-line by the read-out electronics, $N$~is the number of (dithered) exposures (terminology of
ESO observations). The total integration time of each observation amounts to $N$~$\times$ NDIT~$\times$ DIT. The pixel scale of all observations is $0.027''$~per~pixel.
\end{table}