\begin{table}%t3
\par
\caption {\label{tab_sun}Compilations of the solar chemical composition adopted in the computation 
of the EOS and gas opacities.}
%\centerline
 {\begin{tabular}{lccc}
\hline
\hline
Reference  & $Z_{\odot}$ & (C/O)$_{\odot}$ 
& (C/O)$^a$$_{{\rm crit},1}$\\
\hline
Anders \& Grevesse \cite{Anders89} (AG89) & 0.0194 & 0.427 & 0.958\\
Grevesse \& Noels \cite{Grevesse93}  (GN93) & 0.0173 & 0.479 & 0.952\\
Grevesse \& Sauval \cite{Grevesse98} (GS98) & 0.0170 & 0.490 & 0.947 \\
Holweger \cite{Holweger01} (H01)$^b$ 
  & 0.0149 & 0.718 & 0.937 \\
Lodders \cite{Lodders03}     (L03)       & 0.0132 & 0.501 & 0.929 \\ 
Grevesse et~al. \cite{Grevesse07}  (GAS07) & 0.0122 & 0.537 & 0.929 \\
Caffau et~al. \cite{Caffau09} (C09)$^c$
    & 0.0155 & 0.575 & 0.938 \\ 
\hline
\end{tabular}}
\par
\smallskip
$^a$ {This abundance ratio is defined by Eq.~(\ref{eq_crit1}).}
$^b$ {The elemental abundances are taken from Grevesse \& Sauval (\cite{Grevesse98}), but 
for  C, N, O, Ne, Mg, Si, and Fe that are modified following the revision by Howeger (2001).}
$^c$ {The elemental abundances are taken from Grevesse \& Sauval (\cite{Grevesse98}), but 
for N, O, and Ne following the revision by Caffau et~al. (\cite{Caffau08}, \cite{Caffau09}).}\\
For each  mixture
the solar total metallicity $Z_{\odot}$ (in mass fraction), 
the abundance ratios  (C/O)$_{\odot}$ and (C/O)$_{{\rm crit},1}$ are indicated for comparison.
The latter marks a critical boundary for the gas molecular chemistry in the range 
$3.2~\le~\log(T)~\le~3.6$. The C and O abundances are expressed as
number fractions.
\end{table}