\begin{table}%t1 \caption{\label{table overview frequencies}All molecular transitions are observed with the Odin satellite except the $^{13}$CO(1$-$0)~map which is observed with the Onsala 20-m telescope.} \small%\centerline { \begin{tabular}{ll r r l r} \hline \hline %&&&&& \\[-8pt] Species &Transition&Freq. & $E_{\rm u}^a$&$n_{\rm crit}^b$&Int. time \\ &&[MHz]&[K]& [\cmcub]& [h]\\ \hline %&&&&& \\[-8pt] H$_2$O & 1$_{1,0}$--1$_{0,1}$ & 556~936.0 &61&$3\times10^{8~~c}$ & 41 \\ H$_2^{18}$O & 1$_{1,0}$--1$_{0,1}$ & 547~676.4 &60& $3\times10^{8~~c}$ & 91\\ CO & 5--4 & 576~267.9 &83& $2\times10^{5~~c}$ & 9 \\ $^{13}$CO & 5--4 & 550~926.3 & 79 &$2\times10^5$ & 9 \\ $^{13}$CO & 1--0 & 110~210.4 &5& $7\times10^2$ & 2 min/pos \\ NH$_{3}$ & 1$_0$--0$_{~0}$ & 572~498.1 &29& $5\times10^{7~~c}$ & 16 \\ \hline \end{tabular}} \medskip $^{{a}}$ Upper state energy; $^{{b}}$ critical density calculated for a temperature of 40~K; $^{{c}}$ can be considerably reduced because of radiative trapping. \end{table}