\begin{table}%t1
\caption{Number of stars, light curves and age of the open clusters used in the
 present analysis.}
\label{tab-cluster}
%\centerline
{
\begin{tabular}{l c c c }
\hline
\hline
Cluster      & Stars & Light curves & Age (Myr) \\
\hline
\object{IC~2602}          & 31 & 38      & 25--35$^a$   \\
\object{IC~4665}          & 10 & 10      & 30--70$^{b,b1}$  \\
\object{IC~2391}          & 16 & 20      & 48--58$^c $  \\
\object{$\alpha$ Persei}  & 72 & 134     & 60--75$^d$   \\
\object{Pleiades}         & 57 & 97      & 110--120$^d$ \\
\object{Hyades}           & 23 & 23      & 500--650$^e$  \\
Field                     & 55 & 539     & ZAMS to 650$^f$\\
\hline
\end{tabular}}
\medskip
$^a$ Patten et~al. (\cite{Patten1996a}); $^b$ Giampapa et~al. (\cite{Giampapa1998}); $^{b1}$
 Tsch\"ape \& R\"udiger (\cite{Tschape2001}); $^c$ Barrado y Navascu\'es et~al. (\cite{Barrado1999});   $^d$ Basri \& Martin (1999); $^e$~Lebreton et~al. (\cite{Lebreton2001}); $^f$ stars from Zero Age Main Sequence to Hyades age.
\end{table}