\begin{table}%t1
\caption{Equivalent widths ({\it EW}s, in units of~m\AA) of various absorption lines observed in 1999, 2004 and 2006. The values of 1999 are taken unchanged from \citet{Israelian-etal-1999}. A~$^{+}$~sign indicates values actually quoted by the authors from the work by \citet{Shahbaz-etal-1999}. Horizontal lines delimitate groups of lines for which only one {\it EW} can be measured.}\label{table_ew}
%\centering
\small
\begin{tabular}{cl|ccc}\hline \hline
Line & Ion & 1999 & 2004 & 2006 \\ 
     &     & (m\AA) & (m\AA) & (m\AA) \\ \hline
5167.32 & Mg I & --  & 940 $\pm$ 70 & 890 $\pm$ 65 \\ \hline
5172.68 & Mg I & --  & 420 $\pm$ 50 & 475 $\pm$ 45 \\ \hline
5183.60 & Mg I & --  & 510 $\pm$ 50 & 505 $\pm$ 50 \\ \hline
6633.42 & Fe I &                   &              &              \\
6633.75 & Fe I & 105 $\pm$ 15      & $\la$100 & $\sim$100 \\
6634.12 & Fe I &                   &              &              \\ \hline
6663.24 & Fe I & 80 $\pm$ 15 $^{+}$& $\sim$100 & $\sim$100 \\
6663.44 & Fe I &                   &              &              \\ \hline
6677.99 & Fe I &130 $\pm$ 15 $^{+}$& $\ga$100 & $\la$100 \\ \hline
6749.03 & Cr I & 80 $\pm$ 15 $^{+}$& $\sim$100 & 180 $\pm$ 60 \\ 
6750.16 & Fe I &                   &              &              \\ \hline
7771.95 & O I  &               & &               \\
7774.17 & O I  & 1050 $\pm$ 80 & & 1190 $\pm$ 100 \\
7775.39 & O I  &               & &               \\ \hline
7780.56 & Fe I & 90 $\pm$ 15   & &  160 $\pm$ 30 \\ \hline
8446.24 & O I  &               & &               \\
8446.35 & O I  & 530 $\pm$ 50  & &  460 $\pm$ 60 \\
8446.75 & O I  &               & &               \\ \hline
8467.15 & Ti I &               & &               \\
8468.40 & Fe I &               & &  560 $\pm$ 110 \\
8468.50 & Ti I &               & &               \\ \hline
8693.93 & S I  & 230 $\pm$ 25  & &  $\sim$100 \\
8694.62 & S I  &               & &               \\ \hline
8728.01 & Si I & 250 $\pm$ 25  & &  $\ga$100 \\
8728.59 & Si I &               & &               \\ \hline
8736.02 & Mg I & 200 $\pm$ 20  & &  150 $\pm$ 60 \\
8736.03 & Mg I & & & \\ \hline
\end{tabular}
\end{table}