\begin{table}%T1
\par
\caption{\label{tab_observation}Summary of the used HIFI observational data.}
\vspace{-1mm}
\small%\centering
\par
\begin{tabular}{lrrlrr}
\hline\hline\noalign{\smallskip}
Transition & $\nu\sub{line}$  &  {\it HPBW} & Observing mode\tablefootmark{1} &  $t\sub{int,source}$ &
rms \\
& $[$GHz$ $]  & $''$ & & $[$s$]$ & $[$K$]$ \\
\hline
HCO$^+$~6--5 & 535.062 & 40 &  OTF map & 16 & 0.04 \\
HCO$^+$~12--11 & 1069.694 & 21 & FSW spectral scan & 150 & 0.1 \\
$^{13}$CO~10--9 & 1101.350 & 21 & LC spectral scan & 270 & 0.08 \\
C$^{18}$O 10--9 & 1097.163 & 21 & LC spectral scan & 270 & 0.08 \\
\CII{} & 1900.537 & 12 & DBS raster map & 14 & 1 \\
& & 20 & convolved+binned & 112 & 0.2 \\
& & 40 & convolved+binned & 420 & 0.1 \\
\hline
\end{tabular} 
\vspace{-2mm}
\tablefoot{\tablefoottext{1}{DBS = dual-beam-switch, OTF = On-The-Fly, FSW = frequency-switch, 
LC = load-chop, OFF position = 20h37m10s, 42$^\circ$37$'$00$''$.}}
\vspace*{-6mm}
\end{table}