\begin{table}%t4
\caption{\label{tab4}Mean values of (O$-$R) with their errors.}  
%\centering
\small                         
\begin{tabular}{c c c c}        
\hline\hline\noalign{\smallskip}                 
Reference catalog & $\Delta{\alpha}\cos{\delta}, {\rm mas}$ & $\Delta\delta, {\rm mas}$ & $N$ \\
 \hline 
   UCAC2 & $-4\pm5$ & $15\pm4$ & 130 \\     
   2MASS & $9\pm6$ & $27\pm6$   & 182 \\
\hline                                   
\end{tabular}
\end{table}