\begin{table}%t1
\caption{\label{obs}Data set used in this work.}
\small%\centering
\par
\begin{tabular}{cccc}
\hline\hline 
 Epoch(date) & Exp. time & Filt & Go\\
\hline
I (17 July 2003)&$\rm 2\times 1142~s+4\times 1185~s$&{\it F814W}&9815 \\
II (13 July 2005)&$\rm 2\times 1200~s+4\times 1264~s$&{\it F814W}&10471 \\
\hline
\end{tabular}
\end{table}