\begin{table}%t4
\caption{\label{tabper}Time periods found to fit the data.}
%\centering
\par
\begin{tabular}{cccc}
\hline\hline\noalign{\smallskip}
Data set  & $Tp\pm1-\sigma$ & Confidence & Method \\[0cm]
[points] & [Days] &  Level or $\chi^2$  &        \\[0cm]
\hline
 38    & 0.815 & 98\% & PDM \\
 38    & $0.8200\pm0.0037$ & $\chi^2_{34}=1.40$ & Sine first order \\
 38    & $0.8139\pm0.0032$ & $\chi^2_{32}=1.06$ & Sine + harmonic \\
 57    & 0.820 & 75\% & PDM \\
 57    & $0.8195\pm0.0008$ & $\chi^2_{53}=2.55$ & Sine first order \\
 57    & $0.8188\pm0.0005$ & $\chi^2_{51}=2.39$ & Sine + harmonic \\[1mm]
\hline
\end{tabular} 
\end{table}