\begin{table}%t1
\caption{\label{linfit}Slopes obtained by linear regression ($y=a~x+b$) for $V$ magnitude and \ha EW data for all available data and several subsets. }
%\centerline
 {\small 
\begin{tabular}{crcrc}
\hline\hline
HJD--2400000 & $N$ & $a_{V \rm mag.}$ & $N$ & $a_{\rm EW}$ \\
\hline
all data  & 2465 & --$0.85 \pm 0.53$   & 382 & --$0.169 \pm 0.075$ \\
HJD~$<$~49000  & 1529 & $9.0 \pm 1.2$ & 206 & --$1.89 \pm 0.20$   \\
47750~$<$~HJD~$<$~48750 & 375& $60.4 \pm 7.7$ & 11 & $14.5 \pm 2.0$ \\
HJD~$>$~49000  &  936 & $0.8 \pm 1.5$ & 176 & --$0.94 \pm 0.14$  \\
\hline
\end{tabular}}
\medskip
The coefficients are expressed in units of micromagnitude per day and miliangstr\"om per day.
\end{table}