\begin{table}%t2 
\caption{\label{tab_birthrates}Birth rates, local densities and numbers of DWDs.  }
\small%\centering
\par
\begin{tabular}{lccccccc}
\hline\hline\noalign{\smallskip}
 &Bulge &Thin disc &Thick disc &Halo &Galaxy\\
 \hline\noalign{\smallskip}
 $\nu-\xi$&$8.0\times10^{-3}$  &\tablefootmark{a}$2.1\times10^{-2}$& $1.4\times10^{-3}$ &$1.7\times10^{-3}$&\tablefootmark{a}$3.21\times10^{-2}$\\
      &                    &\tablefootmark{b}$2.7\times10^{-2}$&                   &                      &\tablefootmark{b}$3.81\times10^{-2}$\\
 $N  $&$7.6\times10^{7}$ &\tablefootmark{a}$1.7\times10^{8}$& $1.2\times10^{7}$ &$1.9\times10^{7}$&\tablefootmark{a}$2.76\times10^{8}$\\
            &                 &\tablefootmark{b}$2.3\times10^{8}$ &                 &                      &\tablefootmark{b}$3.37\times10^{8}$\\
 $N_{\rm o}$&$8.0\times10^{5}$ &\tablefootmark{a}$2.1\times10^{6}$& $1.4\times10^{5}$ &$1.7\times10^{5}$&\tablefootmark{a}$3.21\times10^{6}$\\
           &                  &\tablefootmark{b}$2.7\times10^{6}$&                  &                      &\tablefootmark{b}$3.81\times10^{6}$\\
 $\xi$&$4.0\times10^{-4}$ &\tablefootmark{a}$1.4\times10^{-3}$&$1.1\times10^{-4}$ &$8.3\times10^{-4}$& \tablefootmark{a}$2.74\times10^{-3}$\\
             &                  &\tablefootmark{b}$1.5\times10^{-3}$&                    &                     &\tablefootmark{b}$2.84\times10^{-3}$\\
 $X$  &$5.4\times10^{6}$ &\tablefootmark{a}$1.1\times10^{7}$&$1.2\times10^{6}$ &$1.2\times10^{6}$& \tablefootmark{a}$1.88\times10^{7}$\\
           &                  &\tablefootmark{b}$1.1\times10^{7}$&                  &                     &\tablefootmark{b}$1.88\times10^{7}$\\
 $\rho_{\rm LD}$  &$-$ &\tablefootmark{a}$2.1\times10^{-4}$&$4.4\times10^{-6}$ &$4.1\times10^{-7}$& \tablefootmark{a}$2.2\times10^{-4}$\\
           &                  &\tablefootmark{b}$2.8\times10^{-4}$&                  &                     &\tablefootmark{b}$2.9\times10^{-4}$\\
\noalign{\smallskip}\noalign{\smallskip}
 SNe Ia &                 &              &                    &                    &   $\nu=$ \tablefootmark{a}$1.3\times10^{-3}$     \\
 resolved &   14800              &    \tablefootmark{a}$18870  $        &                    &                    &  \tablefootmark{a}$N_{\rm r}=$ 33~670     \\
          &                      &    \tablefootmark{b}$22670  $        &                    &                    &  \tablefootmark{b}$N_{\rm r}=$ 37~470     \\
\hline
\end{tabular}
\tablefoot{$\nu$ = current birth rate,
$\xi$ = current merger rate, $N$ = total number, $N_{\rm o}$ =
  the number for DWDs with a detectable component, 
  $X$ = merger number, $\rho_{\rm LD}$=local density of DWDs. The last  two rows represent the current birth rate of supernovae Ia 
  and the number of resolved DWDs detectable by LISA. Different thin disc
  models are denoted by \tablefoottext{a}{$Z=0.02$;} \tablefoottext{b}{$Z=0.001$.} Rates $\nu,\xi$
  are in yr$^{-1}$, $\rho_{\rm LD}$ in pc$^{-3}$. \\
 A DWD is
    deemed detectable for $10^8$~yr after the second star became a
    WD. This definition follows \citet{Iben97} and the values are given
    for comparison with \citet{Han98}.}
\end{table}