\begin{table}%T2
%\centering
\small
\caption{Summary of absolute motion  (in [mas/yr]) for each field. The
          number of background galaxies  used to compute the reference
          point is also indicated. }  
\label{absPM}
\begin{tabular}{cccccc}
\hline\hline
field   & $\mu_{\alpha} \cos{\delta}$
                  & $\sigma_{ \mu_{\alpha} \cos{\delta} }$
                         & $\mu_{\delta}$
                                 & $\sigma_{\mu_{\delta}}$
                                        & $N_{\rm gal}$ \\[-3.2mm] \\
\hline
%&&&&\\
B       & $+$3.33  & 0.17 & $-$17.53 & 0.17 & 12 \\
C       & $+$3.14  & 0.73 & $-$17.18 & 0.73 &  8 \\
D       & $+$3.75  & 0.40 & $-$17.81 & 0.40 & 13 \\
\hline
average & $+$3.39  & 0.15 & $-$17.55 & 0.15 & 33 \\
%&&&&\\
\hline 
\end{tabular}
\end{table}