\begin{table}%t4
%\centering
\par
\caption{Physical parameters of \gl~B based on predictions of the
evolutionary cooling sequences models of \citet{ber01} for
hydrogen- and helium-rich white dwarfs.
\label{tab:model}}
\begin{tabular}{lllll}     % 7 columns
\hline\hline\noalign{\smallskip} 
                      % To combine 4 columns into a single one
Model   & Mass &  $T_{\rm eff}$ &  &  Cooling age \\
        & ($M_{\odot}$)  & (K) &  $\log~(g)$ & (Gyr) \\
\noalign{\smallskip} \hline\noalign{\smallskip}
%\multicolumn{4}{c}{hydrogen- rich atmosphere} \\
%\noalign{\smallskip} \hline\noalign{\smallskip}
H-rich  & 0.4 & $5500\pm1000$ & $7.66\pm0.02$ & $1.4_{-0.42}^{+1.4}$ \\
\noalign{\smallskip}
& 0.5 & $6000\pm1000$ & $7.86\pm0.01$ & $1.8_{-0.6}^{+1.4}$ \\
\noalign{\smallskip}
& 0.6 & $7000\pm1000$  & $8.01\pm0.01$ & $1.5_{-0.4}^{+0.9}$ \\
%\noalign{\smallskip} \hline\noalign{\smallskip}
%\multicolumn{4}{c}{helium- rich atmosphere} \\
\noalign{\smallskip} %\hline\noalign{\smallskip}
He-rich & 0.4 & $6000\pm1000$ & $7.70\pm0.01$ & $1.6_{-0.6}^{+1.5}$ \\
\noalign{\smallskip}
& 0.5 & $7000\pm1000$ & $7.88\pm0.01$ & $1.3_{-0.34}^{+0.7}$ \\
\noalign{\smallskip}
& 0.6 & $8000\pm1000$ & $8.03\pm0.01$ & $1.2_{-0.29}^{+0.6}$ \\
\hline
\end{tabular}
\end{table}