\begin{table}%t4
\caption{\label{abunds}The abundance pattern of the $\alpha$~Cen stars.}
\small%\centering
\par
\begin{tabular}{l r c c r c c r c}
\hline\hline
\multirow{2}{*}{element}&&\multicolumn{2}{c}{\acena}&&\multicolumn{2}{c}{\acenb}&&\multirow{2}{*}{$\Delta$}\\
%\cline{3-4}
 % \cline{6-7}
                  && [X/Fe]  &$\sigma$        &&[X/Fe]   & $\sigma$       &&                         \\\hline
Na                &&$+$0.14  &  --            &&$+$0.25  &  --        &&0.03             \\
Mg                &&\mezero  &  --            &&$+$0.04  &  --        &&0.03             \\
Si                &&\mezero  &0.06            &&\mezero  &0.05        &&0.05             \\
Ca                &&$+$0.03  &0.03            &&$+$0.09  &0.08        &&0.03             \\
Sc                &&\mezero  &0.02            &&$+$0.01  &0.07        &&0.06             \\
Ti        &&$-$0.01  &0.04            &&$+$0.19  &0.14        &&0.06             \\
V         &&$+$0.02  &0.05            &&$+$0.21  &0.09        &&0.07             \\
Cr        &&\mezero  &0.06            &&$+$0.06  &0.09        &&0.06             \\
Mn        &&$+$0.07  &0.01            &&$+$0.19  &0.06        &&0.04             \\
Co        &&\mezero  &0.06            &&$+$0.06  &0.07        &&0.07             \\
Ni        &&$+$0.10  &0.07            &&$+$0.11  &0.05        &&0.04             \\
Cu        &&$+$0.10  &  --            &&$+$0.10  &  --        &&0.04             \\
Y         &&$-$0.09  &0.05            &&$-$0.09  &0.08        &&0.07             \\
Ba        &&$-$0.13  &0.05            &&$-$0.16  &0.08 &&0.06
\\\hline
\end{tabular} 
\end{table}