\begin{table}%t2
\caption{\label{elem_ab}Elemental abundances with respect to total hydrogen nuclei.}
%\centering
\par
\begin{tabular}{lc}
\hline \hline \noalign{\smallskip}
Species & Abundance \\
\hline
He & 0.09  \\
N & $7.6\times 10^{-5}$ \\
O & $2.56\times 10^{-4}$ \\
F & $6.68\times 10^{-9}$ \\
C$^+$ & $1.2\times 10^{-4}$\\
S$^+$ & $8.0\times 10^{-8}$  \\
Si$^+$ & $0.0$ \\
Fe$^+$ & $1.5\times 10^{-8}$  \\
Na$^+$ & $2.0\times 10^{-7}$  \\
Mg$^+$ & $0.0$  \\ 
Cl$^+$ & $1.8\times 10^{-8}$ \\
P$^+$ & $1.17\times 10^{-7}$ \\
\hline
\end{tabular}
\end{table}