\begin{table}%t3
\caption{Astrometric measurements of AB~Pic~A and~b and confidence level estimation that AB~Pic~b is not a stationary background object.}\label{tab3}
%\centering
\par
\begin{tabular}{llll}     
\hline\hline              
UT date      &    Separation     &    Position angle         &  Confidence\\
             &    (mas)          &  ($^\circ$)         & level \\
\hline
 17/03/2003             & $5460\pm14$       & $175.33\pm0.18$         & --  \\
 05/03/2004             & $5450\pm16$       & $175.13\pm0.21$        &3.0$\sigma$  \\
 25/09/2004             & $5450\pm14$       & $175.30\pm0.20$        &4.7$\sigma$  \\
\hline
\end{tabular}
\end{table}