\begin{table}%t2
%%\centering
\par
\caption{\label{tab2}Parameters of the models fitted to the measured mid-eclipse
  time variations of NN~Ser, where $\equiv$ indicates a fixed
  parameter.} 
\begin{tabular}{c@{\hspace{2mm}}c@{\hspace{3mm}}cccccccccccc@{\hspace{3mm}}c@{\hspace{5mm}}c}
\hline \hline\noalign{\smallskip} 
Model & Planets &Number    & \pc\  & \pd\ &\pc/\pd\ & \ec\ & \ed\ & \ac\ & \ad\ & \omegac\ & \omegad\ & \massc~sin~$i_{\rm c}$ & \massd~sin~$i_{\rm d}$ & \chisq &\chisqr\ \\ 
&      & free par. & (yrs) & (yrs)&         &      &      & (AU) & (AU) & ($^\circ$)&($^\circ$)& (\mjup)&(\mjup)& & \\   
\hline  
1     & 1    & $2 + 5$  & 22.60 &      &         & $\ga$$ 0.65$&& 6.91 &      &  8.0     &          &  8.36 &      & 1052.3 & 23.38  \\ 
2a     & 2    & $2+8$ & 15.50 & 7.75 & $2.00$  &$\equiv 0.0$ &0.20    & 5.38 & 3.39 & &  74    &  6.91 & 2.28 & 32.9& 0.78\\
&      &          &$\pm 0.45$ & $\pm 0.35$ &$\pm 0.15$& &$\pm 0.02$&$\pm 0.20$&$\pm 0.10$& &$\pm 4$&$\pm 0.54$&$\pm 0.38$& & \\
2b     & 2    & $2 + 8$  & 16.73 & 6.69 & 2.50 &$\equiv 0.0$ & 0.23  & 5.66 & 3.07 &     &  73   &  5.92 & 1.60 & 33.8& 0.80\\
&      &          &$\pm 0.26$ & $\pm 0.40$ &$\pm 0.15$& &$\pm 0.04$&$\pm 0.06$&$\pm 0.13$& &$\pm 7$&$\pm 0.40$&$\pm 0.27$& & \\ 
 \hline 
\end{tabular} 
\vspace*{-3.5mm}
\end{table}