\begin{table}%T4
\par
%\centering
\par
    \caption{H$_{2}$CO lines opacities derived from the H$_{2}$$^{13}$CO
      observations.}
    \label{table_opacities}
    \begin{tabular}{l l l l l l}
      \hline
      \hline
      &\multicolumn{3}{c}{o-H$_2$CO} & & \multicolumn{1}{c}{p-H$_2$CO}\\
      \cline{2-4}\cline{6-6}
      Transition & 2$_{1,2}$--1$_{1,1}$ &
      4$_{1,4}$--3$_{1,3}$ & 5$_{1,5}$--4$_{1,4}$ &
      &5$_{2,4}$--4$_{2,3}$ \\
      \hline
      \object{NGC~1333-IRAS~4A} & $\rm 1.0^{+0.7}_{-0.4}$ &
      $\rm 0.5^{+1.2}_{-0.4}$ & $\rm 1.2^{+9.9}_{-0.7}$ && $<$2\\
      \object{NGC~1333-IRAS~4B} & - & - & $\rm 0.9^{+1.3}_{-0.5}$ && $<$0.5\\
      \object{NGC~1333-IRAS~2} & $\rm 1.1^{+1.9}_{-0.6}$ & - &
      $\rm 5.5^{+11.1}_{-2.2}$ && $<$4\\
      \object{L1448-MM} & - & - & $<$2 && - \\
      \object{L1448-N} & $\rm 0.4^{+1.1}_{-0.3}$ & $<$0.1 & - && - \\
      \object{L1157-MM} & - & - & $<$1.4 && - \\
      \hline
    \end{tabular}
\end{table}