\begin{table}%t2
\caption{\label{tab2}Offset positions of 2M1207~b from A on 27 April 2004, 5 February 2005 and 31 March 2005.}             
%\centering
\par
\begin{tabular}{lllllllllll}      
\hline\hline                     
             &  \multicolumn{4}{c}{\underline{\hspace{2.4cm}Observed\hspace{2.4cm}}}  &   \multicolumn{2}{c}{\underline{\hspace{0.9cm}If background\hspace{0.9cm}}}    &      &           \\
UT date      &    $\Delta\alpha$             & $\Delta\delta$              & Separation     &    PA           &    $\Delta\alpha$ (If BKG)             & $\Delta\delta$ (If BKG) & $\chi^2$ &   Probability\\ 
             &    (mas)                  &    (mas)                 &    (mas)       &  ($^{\circ}$)          &    (mas)                 &    (mas)   &   &         "B is BKG''     \\
 \hline
27/04/2004  &$629\pm4$         & $-447\pm5$       & $772\pm4$      &$125.4\pm0.3$    & --  &-- & --&--     \\
05/02/2005  &$626\pm5$         & $-446\pm4$       & $768\pm5$      &$125.4\pm0.3$    & $673\pm12$   & $-624\pm10$    &  20&$4$~e-5\\
31/03/2005  &$631\pm7$         & $-451\pm10$      & $776\pm8$      &$125.5\pm0.3$    & $695\pm13$   & $-421\pm14$    &  49&$<$$1~$e-9\\
\hline                  
\end{tabular}
\end{table}