\begin{table}%T1
\caption{\label{parameters}Observed  molecules together with the observing
parameters. The critical densities~($n_{\rm cr}$) are computed for
temperatures between 50 and~100~K using the collisional coefficients
quoted in Sect.~4. The area mapped ($\Delta\alpha \times
\Delta\delta$)  in each transition and the sampling of the map are
reported in the last two lines. $B_{\rm eff}$ is the beam efficiency
of the telescope.  The symbol "--'' implies that only observations
towards the "key'' positions have been obtained.  }
%\centering
\par
\begin{tabular}{l|c|c|c|cc|cc|c}
     \hline\hline
      Transitions & \sothree\ & \sosix\ & \soiso\ &
\multicolumn{2}{|c|}{SO$_{2}$~$5_{1,5}\rightarrow 4_{0,4}$} &
\multicolumn{2}{|c|}{H$_2$S~$2_{2,0}\rightarrow 2_{1,1}$} & H$_2$S
$1_{1,0} \rightarrow 1_{0,1}$ \\
 \hline
  $\nu$ (GHz) & 99.299 &
219.949 & 97.715 & 135.696 & & 216.710 & & 168.762 \\ 
$E_{\rm up}$/k (K) &
9 & 35 & 9 & 15.6 & & 84 & & 24 \\ 
$n_{\rm cr}$ (cm$^{-3}$) & $10^{5}$
& $10^{6}$ & $10^{5}$ & $2 \times 10^{6}$ & & $10^{6}$ & & $2 \times
10^{6}$ \\ 
Telescope & SEST & SEST & IRAM & IRAM & IRAM & SEST & IRAM
& IRAM \\ 
$T_{\rm sys}$ (K) & 160 & 250 & 140 & 400 & 270 & 220 & 600 &
700 \\ 
Beam ($''$) & 51 & 24 & 26 & 18 & 18 & 25 & 11 & 14.5 \\ 
$B_{\rm eff}$ & 0.75 & 0.5 & 0.75 & 0.59 & 0.71 & 0.5 & 0.57 & 0.65 \\
$\Delta \nu$ (kHz) & 86 & 86 & 40 & 39 & 39 & 86 & 42 & 42 \\
$\Delta\alpha\times\Delta\delta$ ($\arcsec \times \arcsec $) & $280
\times 190$ & $288 \times 216$ & -- & $120\times100$ & -- &
$120\times100$ & -- & -- \\ 
sampling ($''$) & 24 & 24 & -- & 12 & -- & 24
& -- & -- \\ \hline
\end{tabular}
\end{table}