\begin{table}%T4
\caption{Observed C and N enrichments in Saturn, and calculated enrichments in volatiles in the 
nominal model (CO$_2$:CO:CH$_4$ = 30:10:1 and N$_2$:NH$_3$ = 1). }\label{enrichissements}
%\centerline
{
\begin{tabular}{lcccc}
            \hline
            \hline
          \noalign{\smallskip}
    Species &  \multicolumn{2}{c}{Observed} & \multicolumn{2}{c}{Calculated}  \\
    & (1) & (2) & (1) & (2)  \\
   \noalign{\smallskip}
  \hline
    \noalign{\smallskip}
    C   &  $3.4 \pm 0.9$$^{a}$ & $8.8 \pm 1.7$$^{b}$ &  2.8  & 7.1 \\
    N   &  \multicolumn{2}{c}{$3.1 \pm 0.6$$^{c}$}         &  2.5  & 6.5 \\
    S   &   &                                                                               & 2.1    &  5.5 \\
    Ar  &    &   								    & 2.0   & 5.1 \\
   Kr  &    &  								    &  2.2  &  5.6 \\
   Xe &   &    								    &  2.6  &  6.7 \\
       \hline
     \end{tabular}}
\medskip
The observed values are taken from $^a$ Kerola et al. (\cite{Kerola97}); $^b$ Flasar et~al. (\cite{Flasar05}); and $^c$ Briggs \& Sackett (\cite{Briggs89}). Calculated enrichments are calibrated on the observed C enrichment with the same column label.
\end{table}