\begin{table}%t2
\caption{Atomic data. \label{tab2}}
%\centerline
{\begin{tabular}{llll}
\hline
\hline
Transition                & $\lambda _{\rm vac}$ & $f$    & Ref.\\
                          & (\AA )               &        &     \\
\hline
Si~{\sc ii}~$\lambda$1020   & 1020.6989 & 0.01680  & a \\
Si~{\sc ii}~$\lambda$1190   & 1190.4158 & 0.25000  & a \\
Si~{\sc ii}~$\lambda$1304   & 1304.3702 & 0.08630  & a \\
Si~{\sc ii}~$\lambda$1526   & 1526.7070 & 0.12700  & a \\
Si~{\sc ii}~$\lambda$1808   & 1808.0129 & 0.00208  & a \\
S~{\sc ii}~$\lambda$1250    & 1250.5840 & 0.00545  & a \\
S~{\sc ii}~$\lambda$1253    & 1253.8110 & 0.01090  & a \\
S~{\sc ii}~$\lambda$1259    & 1259.5190 & 0.01620  & a \\
Cr~{\sc ii}~$\lambda$2056   & 2056.2690 & 0.1050    & a \\
Cr~{\sc ii}~$\lambda$2062   & 2062.2361 & 0.0780   & a \\
Cr~{\sc ii}~$\lambda$2066   & 2066.1640 & 0.0515   & a \\
Fe~{\sc ii}~$\lambda$1143   & 1143.2260 & 0.01770  & a \\
Fe~{\sc ii}~$\lambda$1144   & 1144.9379 & 0.10600 & a \\
Fe~{\sc ii}~$\lambda$1608   & 1608.4508 & 0.05800  & a \\
Fe~{\sc ii}~$\lambda$1611   & 1611.2003 & 0.00136 & a \\
Fe~{\sc ii}~$\lambda$2249   & 2249.8768 & 0.00182  & a \\
Fe~{\sc ii}~$\lambda$2260   & 2260.7805 & 0.00244  & a \\
Fe~{\sc ii}~$\lambda$2344   & 2344.2130 & 0.11400 & a \\
Fe~{\sc ii}~$\lambda$2374   & 2374.4603 & 0.0313   & a \\
Ni~{\sc ii}~$\lambda$1370   & 1370.1320 & 0.0765   & b \\
Ni~{\sc ii}~$\lambda$1454   & 1454.8420 & 0.0300   & b \\
Ni~{\sc ii}~$\lambda$1709   & 1709.6042 & 0.0324   & b \\
Ni~{\sc ii}~$\lambda$1741   & 1741.5531 & 0.0427   & b \\
Ni~{\sc ii}~$\lambda$1751   & 1751.9157 & 0.0277   & b \\
Zn~{\sc ii}~$\lambda$2026   & 2026.1371 & 0.489    & a \\
Zn~{\sc ii}~$\lambda$2062   & 2062.6604 & 0.256    & a \\
\hline
\end{tabular}}
\par
\smallskip
 References: Vacuum wavelengths from Morton (2003).\\ Oscillator strengths: {\bf a)}~Morton (2003); {\bf b)}~Fedchak et~al. (2000).
\end{table}