\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}