\begin{table}%t3 
\caption{\label{tab_type}Birth rates of DWDs with various types and different
  formation channels. }
\small%\centering
\par
\begin{tabular}{lccccccc}
\hline\hline\noalign{\smallskip}
 &$\nu$ & $N$ & $N/N_{\rm gal}$ & $N_{\rm Resolved}$ &  \% \\
 \hline
 types of WD binaries\\
 He+He & $1.34\times10^{-2}$ &$1.06\times10^{8}$& 38.41\% & 19936 &59.21\%\\
 CO+He & $5.07\times10^{-3}$ &$4.11\times10^{7}$& 14.89\% & 12852 &38.17\%\\
 CO+CO & $1.15\times10^{-2}$ &$1.08\times10^{8}$& 39.13\% &  586 &1.74\%\\
 ONeMg & $2.13\times10^{-3}$ &$2.09\times10^{7}$& 7.57\%  & 296 &0.88\%\\
 \noalign{\smallskip}
 formation channels\\
 RLOF+CE&$9.86\times10^{-3}$ &$8.27\times10^{7}$& 29.96\% &  1061 &3.15\%\\
 CE+CE~& $2.12\times10^{-2}$ &$1.84\times10^{8}$& 66.67\% & 32609 &96.85\%\\
 other channels & $1.04\times10^{-3}$ &$9.3\times10^{6}$& 3.37\% & 0 &0\\
 \noalign{\smallskip}
 Total & $3.21\times10^{-2}$ &$2.76\times10^{8}$&         & 33670 & \\
 \hline 
\end{tabular}
\tablefoot{$\nu$ = current birth rate, $N$ = total
  number, \% = percentage of the type of DWDs making up the total resolved DWDs
  in the Galaxy, $N_{\rm Resolved}$~= number of resolved DWDs. We
  take the thin disc model with $Z=0.02$.} \vspace{4mm}
\end{table}