\begin{table}%t3
\caption{\label{tab:abslines}Wavelengths of absorption lines, all in \AA.}
\par
\small%\centerline
 {
\begin{tabular}{lcccc}
 \hline
 \hline
 Constituent                     & Oxygen   & Iron & Iron & Ref. \\
                                 & main line & main line & 2nd line & \\
 \hline
%&&&& \\[-8pt]
 Ferrous, Fe$^{2+}$              &         & 17.498 & 17.196 & a \\
 Olivine                         & 23.26   &        &        & b \\
\hline
%&&&& \\[-8pt]
 Ferric, Fe$^{3+}$               &          & 17.456 & 17.130 & a \\
 Hematite                        & 23.43    &        &        & b \\
 \hline
 Atomic \ion{O}{i}               & 23.508   &        &        &  c \\ 
 Atomic \ion{Fe}{i}              &          & 17.453 & 17.142 &  d \\ 
\hline
 Crab    & $23.466\pm 0.009$ & $17.396\pm 0.009$ & $17.120\pm 0.016$ & e \\
\hline
\end{tabular}}
\medskip
$^a$~\citet{vanaken2002}, corrected by $-0.019$~\AA\ following \citet{juett2006};
$^b$~\citet{vanaken1998};
$^c$~\citet{juett2004}, from Chandra spectra;
$^d$~\citet{behar2001}, HULLAC calculations;
$^e$~present work.
\end{table}