\begin{table}%t9
\caption{\H\ and \D\ total column densities ($N({\rm N_2H^+})$ and $N({\rm N_2D^+})$),
deuterium fractionation ($D_{\rm frac}$), and \H\ chemical abundance relative to H$_2$
($X_{\rm N_2H^+}$).
$X_{\rm N_2H^+}$ has been calculated from the molecular hydrogen column density
given in Col.~8 of Table~\ref{tab_dust}.}
\label{tab_dfrac}
%\centerline
{\small
\begin{tabular}{ccccc}
\hline \hline
Source & $N({\rm N_2H^+})$ & $N({\rm N_2D^+})$ & $D_{\rm frac}$ & $X_{\rm N_2H^+}$ \\
       & ($\times 10^{13}$~\cmq )  & ($\times 10^{11}$~\cmq )  &  &  ($\times 10^{-10}$) \\
\hline
05345+3157  &   3.14~$\pm$~0.07 &   3.2~$\pm$~0.9 &   0.010~$\pm$~0.007 & 1.5 \\
05373+2349  &   4.34~$\pm$~0.06 &   2.8~$\pm$~0.8 &   0.006~$\pm$~0.001 & 1.9 \\
18144+3157  &   9.75~$\pm$~0.08 &  $\leq$4.8   &   $\leq$0.004     &  2.1 \\
18511+0146  &   6.47~$\pm$~0.01 &  2.5~$\pm$~0.4  &   0.004~$\pm$~0.001 & 5.0 \\
18517+0437  &   6.48~$\pm$~0.02 &  $\leq$6.7     &   $\leq$0.01    & 8.1 \\
19092+0841  &   1.9~$\pm$~0.5 &  $\leq$5.3     &   $\leq$0.028    & 0.7 \\
20126+4104  &   7.62~$\pm$~0.01 &  4.9~$\pm$~0.7  &    0.006~$\pm$~0.001  & 0.8 \\
20216+4107  &   1.4~$\pm$~0.2 &  2.8~$\pm$~0.5  &   0.020~$\pm$~0.007 & 0.8 \\
20343+4129$^{a}$  &   2.2~$\pm$~0.1 &  4.4~$\pm$~0.7  &   0.020~$\pm$~0.005 & 0.4 \\
20343+4129$^{b}$  &   2.9~$\pm$~0.1 &   5.4~$\pm$~0.8  &   0.02~$\pm$~0.01 & 0.5 \\
22172+5549 &   1.226~$\pm$~0.006  &  2.1~$\pm$~0.4  &   0.017~$\pm$~0.004 & 0.4 \\
\hline
\end{tabular}
}
\footnotesize
$^{a}$  Peak at ($-$8\arcsec , 4\arcsec ).
$^{b}$  Peak at (13\arcsec , 0\arcsec ).
\normalsize
\end{table}