\begin{table}%t6
%\centering
\par
\caption {Gas and total mass determination from X-ray data. Column~(1): cluster name; Cols.~(2,~3): gas and total mass calculated by means of the $\beta$-model; Cols.~(4,~5): gas and total mass calculated by means of the S\'{e}rsic model; Col.~(6): gas fraction ($M_{\rm{gas}}/M_{\rm{tot}}$) calculated by means of the best model. Values in bold represent the best model for the cluster. \label{TabMassDet}}
\begin{tabular}{c c c  c c c}
\hline\hline
&\multicolumn{2}{c}{$\beta$-model}&\multicolumn{2}{c}{S\'{e}rsic} \\
\cline{2-5}
 Cluster&  $M_{\rm gas}$ ($10^{14} ~M_{\odot}$) & $M_{\rm tot}$ ($10^{14} ~M_{\odot}$) &  $M_{\rm gas}$($10^{14}~ M_{\odot}$) & $M_{\rm tot}$($10^{14} ~M_{\odot}$) & $f_{\rm gas}$ \\
        &  ($<$$ r_{500}$) &  ($< $$r_{500}$) &  ($<$$ r_{500}$) &  
        ($ <$$ r_{500}$) &  ($ <$$ r_{500}$)  \\
\hline
A496  & 1.074 $\pm$ 0.040 & 1.997 $\pm$ 0.012 & {\bf 0.330 $\pm$ 0.040} & {\bf 3.270 $\pm$ 0.19} & 0.10 $\pm$ 0.014\\
A1689 & 3.79 $\pm$ 0.17   &  10.87 $\pm$ 0.20 & {\bf 1.672 $\pm$ 0.080} & {\bf 11.14 $\pm$ 0.46} & 0.150 $\pm$ 0.010\\
A2050 & {\bf 0.568 $\pm$ 0.079} & {\bf 4.974 $\pm$ 0.094} & --  & -- & 0.114 $\pm$ 0.016\\
A2631 & {\bf 0.84 $\pm$ 0.16} & {\bf 11.78 $\pm$ 0.58} &  --  & --  & 0.072 $\pm$ 0.014\\
A2667 & 1.789 $\pm$ 0.047     & 7.06 $\pm$ 0.14 & {\bf 1.132 $\pm$ 0.066} & {\bf 11.63 $\pm$ 0.24} & 0.0973 $\pm$ 0.0060\\
\hline	
\end{tabular} 
\end{table}