\begin{table}%t4
%\centering
\par
\caption{Linear relation between $f_{{\rm grad}}$ and the
logarithm of the period: $f_{{\rm grad}} = S \log P + ZP$ for
the \ion{Fe}{i} 4896.439 \AA\ spectral line.
\label{Tab_Results_fgrad}}
\begin{tabular}{lccc}
\hline \hline 
\par
                       &  S      & ZP     &
                       $\chi_{{\rm red}}^2$ \\
\hline
 O      & $-0.003 \pm$ 0.005   & 0.997 $\pm$ 0.006  & 2 \\
 O + C  & $-0.003 \pm$ 0.004 & 0.996 $\pm$ 0.005 &
 3 \\
\hline 
\end{tabular}
\end{table}