\begin{table}%t1
\caption{\label{table:obs}Observational parameters.}
%\centerline
 {
\begin{tabular}{c c c c c c c c c c c}
\hline\hline 
Molecule & Transition & Frequency & Instrument & $F_{\rm eff}$ & $\eta_{\rm MB}$$^a$ & \multicolumn{2}{c}{Resolution} & $F_{\rm throw}$ & $T_{\rm sys}$ & Obs. date\\
 & & [GHz] & & & & [\arcsec] & [km s$^{-1}$] & [MHz] & [K] & \\
\hline\\[-3.2mm]
N$_2$H$^+$ & $J=1{-}0$ & 93.173777$^b$ & 30 m/AB100 & 0.95 & 0.80 & 26.4 & 0.064 & 7.9 & 150--190 & 18--20 May 2007\\
N$_2$D$^+$ & $J=2{-}1$ & 154.217154$^c$ & 30 m/CD150 & 0.93 & 0.73 & 16 & 0.038 & 15.8 & 290--340 & 18--20 May 2007\\
\hline
\multicolumn{3}{c}{Continuum at 870~$\mu$m} & APEX/LABOCA & 0.97 & 0.73 & 18.6 & -- & -- & -- & 4 Aug. 2007\\
\hline 
\end{tabular} }
\medskip
\par
$^a$ $\eta_{\rm MB}=B_{\rm eff}/F_{\rm eff}$, where $B_{\rm eff}$ and $F_{\rm eff}$ are the beam and forward efficiencies, respectively. $^b$ Frequency taken from Caselli et~al. (1995). $^c$  Frequency taken from Gerin et~al. (2001).
\end{table}