\begin{table}%t4
\caption{\label{tdthp}p-\DTHP\ column density upper limits.}
\small%\centerline
 {
\begin{tabular}{lccccccccc}
\hline\hline
Source &  $\Delta {v}_{\rm res}$ & $T_{\rm sys}$ & $t_{\rm int}$ &
          $T_{\rm rms}$$^{{a}}$ &
          $T_{\rm R}$ &  $\eta_{\rm b}$ &  $T_{\rm ex}$$^{{b}}$ & $N$(p-\DTHP) &
          p/o$^{{c}}$\\
Name   & (\kms ) & (K) & (min) & (K) & (K) & &  (K) & (10$^{13}$ cm$^{-2}$) & \\
\hline
B~1 & 0.083 & 3950 & 251 & 0.068 & $<$0.20 & 0.4  &  11.9 & $<$0.9 & $<$1.0 \\
NGC~1333--\DCOP & 0.083 & 3300 & 91 & 0.068 & $<$0.20 & 0.4  & 12.6 & $<$0.9 & $<$2.6 \\
NGC~2264G--VLA2 & 0.021 & 1436 & 93 & 0.045 & $<$0.14 & 0.4 & 14.4 & $<$0.2 & $<$0.7 \\
L~183 & 0.042 & 1770 & 42 & 0.084 & $<$0.25 & 0.4 & 6.9 & $<$7.9 & $<$3.2 \\
16293E$^{{d}}$ & 0.10 & ... & 103 & 0.19 & 0.85 & 0.60 & 10.7 &  1.2 \p\ 0.5 & 1.0 \\
L~1544$^{{e}}$ & 0.021 & ... & 230 & 0.18 & $<$0.54 & 0.4 & 7.6 & $<$2.5 &
$<$0.8 \\
\hline
\end{tabular}}
\medskip
$^{{a}}$ In radiation temperature units;
$^{{b}}$ excitation temperature assuming a critical density of 10$^5$~\percc\ for the observed \DTHP\ transition;
$^{{c}}$ p/o~$\equiv$ \mbox{$N$(para-\DTHP )/$N$(ortho-\HTDP)};
$^{{d}}$ data from \cite{vpy04}. The column density has been estimated using the method described in the text;
$^{{e}}$ data from \cite{vcc06}.  The column density has been estimated using the method described in the text, with the parameters listed in Table~\ref{tcolumn}.
\end{table}