\begin{table}%t6
\caption {\label{gruppi}Average  abundances of $s$-element process  poor and  rich
  stars. } %\centering
\par
\begin{tabular}{ l r r }
\hline\hline
Element   & $s$-process elements poor & $s$-process elements rich  \\\hline
 $[\rm  O/Fe]$ &  0.30~$\pm$~0.06  &  0.26~$\pm$~0.10 \\
 $[\rm Na/Fe]$ &  0.13~$\pm$~0.11  &  0.40~$\pm$~0.08 \\
 $[\rm Mg/Fe]$ &  0.36~$\pm$~0.04  &  0.45~$\pm$~0.03 \\
 $[\rm Al/Fe]$ &  0.26~$\pm$~0.11  &  0.46~$\pm$~0.10 \\
 $[\rm Si/Fe]$ &  0.42~$\pm$~0.01  &  0.44~$\pm$~0.01 \\
 $[\rm Ca/Fe]$ &  0.27~$\pm$~0.01  &  0.38~$\pm$~0.02 \\
 $[\rm Sc/Fe]$ &  0.04~$\pm$~0.02  &  0.04~$\pm$~0.02 \\
 $[\rm Ti/Fe]_{TiI}$  &  0.22~$\pm$~0.01  &  0.27~$\pm$~0.03 \\
 $[\rm Ti/Fe]_{TiII}$ &  0.33~$\pm$~0.02  &  0.36~$\pm$~0.03 \\
 $[\rm  V/Fe]$ & $-$0.10~$\pm$~0.04  & $-$0.09~$\pm$~0.03 \\
 $[\rm Cr/Fe]$ & $-$0.16~$\pm$~0.02  & $-$0.09~$\pm$~0.04 \\
 $[\rm Fe/H ]$ & $-$1.82~$\pm$~0.02  & $-$1.68~$\pm$~0.02 \\
 $[\rm Ni/Fe]$ & $-$0.09~$\pm$~0.01  & $-$0.06~$\pm$~0.01 \\
 $[\rm  Y/Fe]$ & $-$0.16~$\pm$~0.03  &  0.34~$\pm$~0.05 \\
 $[\rm Zr/Fe]$ &  0.20~$\pm$~0.03  &  0.60~$\pm$~0.04 \\
 $[\rm Ba/Fe]$ &  0.02~$\pm$~0.04  &  0.43~$\pm$~0.04 \\
\hline
\end{tabular}
\end{table}