\begin{table}%t3
%\centering
\par
\caption{\label{t:rgs_a}Relevant absorption edges in the RGS spectrum of \mbox{\cy.} 
The energy, the corresponding wavelength, and the optical depth~($\tau$) were obtained 
from the data. The
equivalent total hydrogen column 
density \nh\ was derived from the ISM abundances of Wilms et~al. (2000). These are to be compared with the best-fit 
$\mbox{\nh} =(2.20\pm 0.02)\times 10^{21}\ {\rm cm}^{-2}$, measured by RGS. Errors are given at 90\% confidence level.}
\begin{tabular}{lcccc}
\hline
\hline
\multicolumn{1}{c}{Element} &
\multicolumn{1}{c}{Energy} &
\multicolumn{1}{c}{Wavelength} &
\multicolumn{1}{c}{$\tau$} &
\multicolumn{1}{c}{ $N_{\rm H}$} \\
& keV & \AA\ & & $10^{21}\ {\rm cm}^{-2}$\\
\hline
N K-shell & 0.409 (fixed)	& 30.31 & $0.15\pm0.06$ & $2.7\pm1.1$\\
O K-shell &   0.543 (fixed)  &  22.83  &  0.81$\pm0.10$ &  $2.8\pm0.8$\\
Fe L-shell &  $0.706\pm0.01$ & $17.56\pm0.02$ & $0.13\pm0.01$ & $2.8\pm0.2$\\             
Ne K-shell & $0.869^{+0.02}_{-0.06}$ & $14.26^{+0.10}_{-0.03}$ & $0.06\pm0.03$ & $1.8\pm0.9$ \\
\hline 
\end{tabular}
\end{table}