\begin{table}%t1
%%%\centering


\par
\caption{\label{data} { Data of observations}.} 
\begin{tabular}{llcccc}
\hline \hline
\multicolumn{1}{c}{Source} & \multicolumn{1}{c}{Observing date} &
\multicolumn{1}{c}{Instrument} &
\multicolumn{1}{c}{Mode} & \multicolumn{1}{c}{Filter } &
\multicolumn{1}{c}{Exposure} \\
\multicolumn{1}{c}{  } & \multicolumn{1}{c}{ } &
\multicolumn{1}{c}{  } &
\multicolumn{1}{c}{ } & \multicolumn{1}{c}{ } &
\multicolumn{1}{c}{(ksec)} \\
  \hline  
\Xvingt & May 1, 2001 & PN & Large Window & Medium & $\sim$$ 21.8$ \\
 & & MOS1/2 & Full Window & Medium & $\sim $24 \\ 
 & & RGS1/2 & Spectroscopy HER &  & $\sim$25\\
 & & OM & Imaging & UVW2 & $\sim$$ 20^{\dagger}$\\
\noalign{\smallskip}   \noalign{\smallskip}
\Pdeux & May 1, 2001 & PN & Extended Full Window & Medium & $\sim$18 \\
 & & MOS1/2 & Full Window & Medium & $\sim$22.8   \\ 
 & & RGS1/2 & Spectroscopy HER &   & $\sim$23 \\nedit aa
 & & OM & Imaging & Grism 1& $\sim$$20^{\dagger}$\\
\noalign{\smallskip}   \noalign{\smallskip}
\Qzero & June 25, 2002 & PN & Extended Full Window & Thin & $\sim$43.5 \\
 & & MOS1/2 & Full Window & Thin & $\sim$$50.3$ \\
 & & RGS1/2 & Spectroscopy HER & & $\sim$$23$ \\
\noalign{\smallskip}  \noalign{\smallskip}
\milleq & August 1, 2002 & PN & Extended Full Window & Thin & $\sim$37 \\
 & & MOS1/2 & Full Window & Thin & $\sim$39  \\
 & & RGS1/2 & Spectroscopy HER &  & $\sim$42 \\
 & & OM & Imaging & UVW2 & $\sim$$ 20^{\dagger}$ \\ 
\hline
\end{tabular}
 $^{\dagger}$ Divided into five exposures of $\sim$4~ksec each. 
 \end{table}