\begin{table}%t3
\small
\caption{Positions of the five IRAM/MAMBO sources  in the map of GJ~628 at $\lambda = 1.2$~mm (Fig.~\ref{fig2}) and their nearest optical objects referenced in the USNO-B1.0 catalogue.}\label{tab3}
%\centerline
{\begin{tabular}{lcccrrr}  
\hline\hline 
\multicolumn{1}{c}{}  &  \multicolumn{4}{c}{ MAMBO }  &     \multicolumn{2} {c}{USNO-B1.0} \\
\hline\noalign{\smallskip}
     Name       &  $\alpha^a$        &   $\delta^a$                          &   Flux$^b$       & Star-source    & Object-source       &   Object~~~~~~   \\
                &  (J2000)           &  (J2000)                              &   density        & separation     & separation~~        &  magnitudes~~    \\
                &                    &                                       &   (mJy)          & ($''$) (AU)    &  ($''$)~~~~~~~~~~   &                  \\ 
\hline 
     MAMBO-W    &  16 30 07.5      &  $-12$ 39 42   &   3.6      & 154~~~ 660  &  3.0 ~ (1.0$\sigma$) &  $B = 20.03$ $R = 19.12$       \\
     MAMBO-NW   &  16 30 15.6      &  $-12$ 39 11   &   2.7      & 53 ~~~230   & 13.3 ~ (4.0$\sigma$) &  $B = 20.50$ $R = 17.90$     \\
     MAMBO-SW   &  16 30 13.9      &  $-12$ 39 59   &   2.0      & 90 ~~~390   &  10.1~ (3.0$\sigma$) &  $B = 19.27$ $R = 18.23$       \\
     MAMBO-NE   &  16 30 19.7      &  $-12$ 39 32   &   2.4      & 83 ~~~360   &  9.1 ~ (2.5$\sigma$) &  $B = 20.06$ $R = 18.30$    \\
     MAMBO-E    &  16 30 22.3      &  $-12$ 39 25   &   1.8      & 68 ~~~290   &  6.9 ~ (2.0$\sigma$) &  $B = 21.63$ $I = 18.61$ \\
\hline
\end{tabular}}
\smallskip
 $^a$  The coordinates uncertainties are $3.5''$ for MAMBO.  $^b$  Flux densities are the peak values unaffected by Gaussian smoothing of the map.
\end{table}