\begin{table}%t6
\caption{Summary of the seismic inferences for PG~1159-035, 
PG~2131+066,  PG~1707+427 and  PG~0122+200 from $\chi^2$  period fits.
The values of the observed mean period  spacing were extracted from Table~\ref{tab6} of Kawaler et~al. (\cite{Kawaler04}).\label{tab6}}
\small
%\centerline
{\begin{tabular}{l|cc|cc|cc|cc}
\hline
\hline
Quantity & Model & PG~1159-035 & Model & PG 2131+066 & Model & PG 1707+427 & Model  & PG 0122+200 \\
\hline
\noalign{\smallskip}
$\overline{\Delta \Pi}$ [s]         & 21.21   & $21.5 \pm 0.1$   & $20.86$ & $21.6 \pm 0.4$       & 23.22   & $23.0  \pm 0.3$      & 20.92  & $21.10 \pm 0.4$   \\
$T_{\rm eff}$ [K]                   & 137~620  & $140~000 \pm 6000$   & 94~740   & $95~000 \pm 5000$      & 87~585   & $85~000 \pm 4500$     & 81~810  & $80~000 \pm 4000$  \\ 
$M_*/M_{\odot}$                     & 0.56   & $0.54 \pm 0.1$       & 0.60   & $0.55 \pm 0.1$         & 0.55    & $0.54  \pm 0.1$      & 
0.64   & $0.54  \pm 0.1$   \\
$\log g$ [cm/s$^2$]                 & 7.31    & $7.0 \pm 0.3$       & 7.71    & $7.5 \pm 0.3$         & 7.59    & $7.5   \pm 0.3$      &  7.89      & $7.5   \pm 0.3$   \\
$\log (L_*/L_{\odot})$                & 2.38    & $2.7 \pm 0.4$       & 1.37    & $1.6 \pm 0.3$         & 1.31    & $1.4   \pm 0.3$      & 0.96   & $1.3   \pm 0.3$   \\  
$R_*/R_{\odot}$                     & 0.0273  & --                 & 0.0179  & --                      & 0.02    & --                  &  0.015      & --               \\
$M_{\rm He}$ $[10^{-3} M_{\odot}]$  & $4.94$  & --                 & $5.29$  & --                      & $4.85$  & --                  & $5.65$ & --               \\   
distance [pc]                       & $482 \pm 44$         &  $800^{+ 600 {(a)}}_{- 400}$      & $716^{+ 185}_{-147}$ &  $681^{+ 170 {(b)}}_{-137}$    &   $697^{+ 180}_{-144}$       & $1300^{+ 1000 {(a)}}_{-600}$        &        &                   \\ 
\hline
\end{tabular}}
\par
\smallskip
References: 
$^{(a)}$ Werner et~al. (\cite{Werner91});
$^{(b)}$ Reed et~al. (\cite{Reed00}).
\end{table}