\begin{table}%t4
\small\caption{\CO\ column density and abundance from ($J=1$--0) and ($J=2$--1) transitions.}\label{tab:depl}
%\centerline
{\begin{tabular}{lccccc}
\hline\hline\noalign{\smallskip}
Source  &  \multicolumn{1}{c}{$T_{\rm ex}$} &\multicolumn{1}{c}{$N_{\rm C^{18}O}$} & \multicolumn{1}{c}{$N({\rm H_2}$)$^{a}$} & \multicolumn{1}{c}{$\chi_{\rm C^{18}O}^{b}$} & \multicolumn{1}{c}{$\eta^{c}$} \\
\hline\noalign{\smallskip}
&  \multicolumn{1}{c}{K} &\multicolumn{1}{c}{$10^{16} (10^{15})~\rm cm^{-2}$} & \multicolumn{1}{c}{$10^{23}$~cm$^{-2}$} & \multicolumn{1}{c}{10$^{-8}$} & \multicolumn{1}{c}{}  \\
\hline
G8.13+0.25     &  11.8    & 1.6     (0.1)     &  2.6     & 6.2     & 2.7 \\
G8.68-0.37     &  8.5     & 2.4     (0.9)     &  7.9     & 3.0     & 5.6 \\
G8.71-0.37     &  4.2     & 1.8     (0.5)     &  3.5     & 5.2     & 3.2 \\
G10.15-0.34    &  19.1    & 2.1     (0.4)     &  3.8     & 5.4     & 3.1 \\
G10.21-0.31    &  8.4     & 1.4     (0.2)     &  2.2     & 6.4     & 2.7 \\
G10.21-0.32    &  8.0     & 2.6     (0.3)     &  7.4     & 3.6     & 4.8 \\
G10.61-0.33    &  9.1     & 1.0     (0.3)     &  2.7     & 3.8     & 4.5 \\
G11.11-0.12P1  &  6.4     & 0.6     (0.1)     &  1.1     & 5.5     & 3.1 \\
G11.11-0.12P3  &  6.9     & 0.5     (0.3)     &  0.8     & 6.2     & 2.7 \\
G11.11-0.12P4  &  6.6     & 0.5     (0.2)     &  1.4     & 3.5     & 4.8 \\
G12.19-0.12    &  11.6    & 1.2     (0.2)     &  2.4     & 5.1     & 3.3 \\
G13.18+0.06    &  15.7    & 1.2     (0.6)     &  6.3     & 1.8     & 9.3 \\
G15.01-0.67    &  32.5    & 6.0     (0.4)     &  16.6    & 3.6     & 4.7 \\
G15.01-0.69    &  52.2    & 4.5     (0.6)     &  11.6    & 3.9     & 4.4 \\
G15.03-0.65    &  51.7    & 5.5     (0.6)     &  14.2    & 3.9     & 4.4 \\
G18.17-0.30    &  14.3    & 1.5     (0.8)     &  3.3     & 4.6     & 3.7 \\
G18.21-0.34    &  10.9    & 0.7     (0.4)     &  2.5     & 3.0     & 5.8 \\
G23.41-0.23    &  8.4     & 3.4     (0.8)     &  9.3     & 3.6     & 4.7 \\
G23.42-0.23    &  9.0     & 3.1     (0.3)     &  3.8     & 8.0     & 2.1 \\
G23.44-0.18    &  9.2     & 3.0     (0.5)     &  7.7     & 3.9     & 4.3 \\
G27.29+0.15    &  8.8     & 1.2     (0.2)     &  1.7     & 6.9     & 2.5 \\
G27.31+0.18    &  8.3     & 0.5     (0.2)     &  1.7     & 2.7     & 6.3 \\
G28.34+0.06P1  &  4.8     & 1.3     (0.5)     &  1.5     & 8.6     & 2.0 \\
G28.34+0.06P2  &  8.7     & 1.4     (0.5)     &  7.8     & 1.8     & 9.6 \\
G29.97-0.05    &  9.3     & 1.3     (0.7)     &  2.6     & 4.8     & 3.5 \\
G79.34+0.33    &  8.4     & 0.7     (0.1)     &  2.1     & 3.5     & 4.9 \\
G81.74+0.59    &  16.0    & 1.8     (0.2)     &  4.7     & 3.8     & 4.4 \\
\hline
\end{tabular}}
\smallskip
$^a$ ${\rm H_2}$ column density derived from the 850 $\mu$m dust continuum flux measured using SCUBA.  The dust temperature is assumed to be equal to the gas temperature derived from \AMM\ (1,~1) and (2,~2) measurements as given in Table~\ref{tab:nh2d_ratio}.   $^b$ abundance of \CO\ relative to H$_2$.  $^c$ depletion factor compared to the canonical value of 1.7$\cdot 10^{-7}$ \citep{frerking1982:co}. 
\end{table}