\begin{table}%t1
\caption{\label{tabla-masas}Stellar  masses  for all of the intensively studied pulsating  
         PG 1159 stars, including also one pulsating [WCE] star. All  
         masses are in solar units.}
%\centerline
 {
\begin{tabular}{lcccclc}
\hline 
\hline\\[-3.2mm]
Star & $\Delta \Pi_{\ell}^{\rm a}$ &$\overline{\Delta \Pi_{\ell}}$ & Approximate  & Period fit & Pulsations    & Spectroscopy\\
     &                             &                               &  formula     &            & (other works) & \\
\hline\\[-3.2mm]
\ngc       & 0.571$^{a}$        & 0.576$^{a}$ & 0.530$^{a}$ & ---             & 0.55$^{j}$ (asymptotic analysis) & 0.56 \\ %NGC1501
\rxj       & 0.568$^{b}$        & 0.560$^{b}$ & 0.525$^{a}$ & 0.565$^{b}$ & 0.56$^{h}$ (asymptotic analysis) & 0.72 \\ %RXJ2117
\pp        & 0.577--0.585$^{d}$ & 0.561$^{d}$ & 0.570$^{a}$ & 0.565$^{d}$ & 0.59$^{i}$ (asymptotic analysis) & 0.54 \\ %PG1159
\pr        & 0.627$^{a}$        & 0.578$^{a}$ & 0.609$^{a}$ & 0.589$^{a}$ & 0.61$^{e}$ (period fit)          & 0.55 \\ %PG2131
\pt        & 0.597$^{a}$        & 0.566$^{a}$ & 0.587$^{a}$ & 0.542$^{a}$ & 0.57$^{g}$ (asymptotic analysis) & 0.53 \\ %PG1707
\pg        & 0.625$^{c}$        & 0.567$^{c}$ & 0.593$^{a}$ & 0.566$^{c}$ & 0.69$^{f}$ (asymptotic analysis) & 0.53 \\ %PG0122
\hline
\end{tabular} }
\medskip
\par
Notes: $^{a}$ This work.   
$^{b}$ C\'orsico et~al. (\cite{Corsico07a}).  
$^{c}$ C\'orsico et~al. (\cite{Corsico07b}).  
$^{d}$ C\'orsico et~al. (\cite{Corsico08}).  
$^{e}$ Reed et~al. (\cite{Reed00}).  
$^{f}$ Fu et~al. (\cite{Fu07}).
$^{g}$ Kawaler et~al. (\cite{Kawaler04}).   
$^{h}$ Vauclair et~al. (\cite{Vauclair02}).
$^{i}$ Costa et~al. (\cite{Costa08}). 
$^{j}$ Bond et~al. (\cite{Bond96}).
\end{table}