\begin{table}%t2
\caption{\label{tab2}Length of spectra and corresponding rotational periods.}
%\centering
\small
\begin{tabular}{c c c c} 
\hline \hline
 Spectrum & $\mu$Hz (days) & $\mu$Hz (days) & $\mu$Hz (days)    \\  
 \hline
 Total spectrum & 4.00 (2.9) &  4.45 (2.6)   &   --   \\
 First 78 days & 4.00 (2.9)  & 4.45 (2.6) & 4.90 (2.4)   \\
 Second 78 days & 4.00 (2.9)  & 4.58 (2.5) &  5.04 (2.4)   \\
 First 52 days& 4.00 (2.9)  & 4.45 (2.6)   & 4.90 (2.4)    \\ 
 Second 52 days& 3.77 (3.1) &  4.45 (2.6)  &   --  \\ 
 Third 52 days & 4.00 (2.9)  &--   &  5.12 (2.3)       \\ 
 \hline
\end{tabular}
\end{table}