\begin{table}%T3
\caption{\label{tab:cds}Column densities. Errors are given at 2$\sigma$.}
\small%\centerline
{
\begin{tabular}{p{0.2\linewidth}ll}
\hline\hline
\noalign{\smallskip}
Species & $N_{\rm obs}^a$   &   $N_{\rm norm}^b$  \\
               & ({\rm cm}$^{-2}$)  & ({\rm cm}$^{-2}$) \\
        \hline  
N{~\sc i}~& $\rm 14.20^{+0.12}_{-0.14}$ &           $\rm 13.96^{+0.22}_{-0.33}$      \\
O{~\sc i}~& $\rm 15.58^{+0.12}_{-0.09}$ &    $\rm 15.52^{+0.10}_{-0.09} $             \\ 
Si{~\sc ii}~& $\rm 15.06^{+0.19}_{-0.28}$ &         $\rm 15.00^{+0.13}_{-0.13} $           \\
P{~\sc ii}~& $\rm 12.78^{+0.22}_{-0.32}$ &            $\rm 12.94^{+0.16}_{-0.21} $             \\
Ar{~\sc i}~& $\rm 13.18^{+0.19}_{-0.29}$ &    $\rm 13.10^{+0.31}_{-0.79} $            \\
Fe{~\sc ii}~& $\rm 13.98^{+0.11}_{-0.13}$ &         $\rm 13.97^{+0.13}_{-0.18}$  \\
\hline
\end{tabular}}
\smallskip
 $^a$ $N_{\rm obs}$ is the column density calculated using local spectral continuum from the observation. \\
$^b$  $N_{\rm norm}$ is the column density calculated using the spectrum corrected from stellar absorption (Sect.~\ref{sec:stellar}). 
\end{table}