\begin{table}%t2
\caption{\label{tab2}Number of Hipparcos ($H_{\rm P}$) and Tycho ($B_{\rm T}$, $V_{\rm T}$) photometric data 
and ground based radial velocity observations, their mean $S/N$ and standard error
for the three programme stars. Error for radial velocity is in km~s$^{-1}$.}
%\centering
\par
\begin{tabular}{lccccccccccc} 
\hline\hline\noalign{\smallskip}
&&
\multicolumn{2}{c}{\it Hip}&&
\multicolumn{3}{c}{\it Tyc}&&
\multicolumn{3}{c}{\it RV}\\ \cline{3-4} \cline{6-8} \cline{10-12} 
%\multicolumn{11}{c}{}\\
&&
$N$&$\sigma$($H_{\rm P}$)&&
$N$&$\sigma$($B_{\rm T}$)&$\sigma$($V_{\rm T}$)&&
$N$&$S/N$&$\sigma$({\it RV})\\
\noalign{\smallskip}\hline
%\multicolumn{11}{c}{}\\
V781 Tau &&  61 & 0.014 &&  81 & 0.18 & 0.15 && 41 & 35 &  8 \\
UV Leo   &&  96 & 0.015 && 150 & 0.21 & 0.17 && 29 & 30 & 10 \\
GK Dra   && 124 & 0.017 && 179 & 0.15 & 0.15 && 35 & 45 &  3 \\  
\hline
\end{tabular}
\end{table}