\begin{table}%t2
\caption{Chemical compositions of the adopted evolutionary models.}\label{tab2}
%\centering
\small
\begin{tabular}{lccc}
\hline \hline
$Z$  & $Y$ & [$\alpha$/Fe] & [Fe/H]\\
\hline
0.0001 & 0.245 & 0.4 & $-$2.62\\
0.001  & 0.246 & 0.4 & $-$1.62\\
0.004  & 0.251 & 0.4 & $-$1.01\\
0.0001 & 0.245 & 0.0 & $-$2.27\\
0.001  & 0.246 & 0.0 & $-$1.27\\
0.004  & 0.251 & 0.0 & $-$0.66\\
\hline
\end{tabular}
\end{table}