\begin{table}%t1
%\centering
\par
  \caption {\label{T:area_period}Main periodicities (in days) of the area covered by coronal holes (CH), quiet sun (QS), and active regions (AR).   }
    \begin{tabular}{c c c  c c c  c c c} \hline\hline
  \multicolumn{3}{c}{Area in $\%$} & \multicolumn{3}{c}{Mean 17.1 nm}& \multicolumn{3}{c}{Mean 19.5 nm}  \\ \hline
  CH & QS & AR &     CH & QS & AR &    CH & QS & AR \\
   26.9 & 26.2 & 26.2&
   26.8  & 26.6  & 27.6 &
   28.4  & 26.9  & 26.5 \\                  
\par
  % area
  &  & 495&  
  % mean 171
  416 & &  &
  % mean 195
    & &  \\
 \hline \hline
\multicolumn{3}{c}{Sum 17.1 nm}& \multicolumn{3}{c}{Sum 19.5 nm}&\\
\hline
 CH & QS & AR &     CH & QS & AR & &&\\
27.1  &27.2  &26.0 
   & 27.1 & 28.3 & 25.9\\  \hline
  \end{tabular}
\end{table}