\begin{table}%t2
\caption{\label{tab_obs}Summary of the observational parameters.}
\vspace{-1mm}
\par
%\centerline
{\small
\begin{tabular}{lrrr}
\hline\hline
& DR21(C) & Sgr~B2(M) & NGC~6334 \\
\hline
RA (J2000) & 20h39m01.1s & 17h47m20.35s & 17h20m53.32s\\
Dec & 42$^\circ$19$'$43.0$''$ & $-28^\circ$23$'$03.0$''$ & $-35^\circ$46$'$58.5$''$\\
Mode & Load-chop$^2$ & DBS & DBS \\
$t\sub{int,source}$ & 150~s & 48~s & 48~s \\
$\sigma\sub{noise}^1$ & 0.07~K & 0.08~K & 0.08~K\\
\hline
\end{tabular}}
\vspace{-1mm}
\tablefoot{$^1$~At native WBS resolution (1.1~MHz = 0.30~\kms{}).\\ $^2$~OFF position = 20h37m10s, 42$^\circ$37$'$00$''$.}
\vspace{-3mm}\end{table}