\begin{table}%t1
\caption{\label{tab1}Derived $M_{\rm H}/M_{\rm WD}$ in ZZ Ceti stars.}
%\centerline
{
\begin{tabular}{lccc}
\hline\hline
 Object & Number of modes & $M_{\rm H}\times 10^{-4}~M_{\rm WD}$ &Ref.\\
\hline
 G~226-29 &  3 &  $\approx$1.0 & 1\\
 L~19-2 &  11 &  $\approx$1.0 &  2\\
 R~548 & 7 & 1.5 &3\\
 GD~165 &  8 &  $\approx$2.0 &  4\\
  G~29-38 &  19 &  0.005 &  5\\
 G~117-B15A &  3 &  $\approx$1.0 & 6\\
  GD~154 &  3 &  $2\times 10^{-6}$ & 7\\
 BPM~37093 &  8 &  0.02--0.6  &  8\\
 \hline
\end{tabular}}
\smallskip
Notes: The number of modes is obtained after subtracting the linear combinations and harmonics from the power spectra. Its does include multiplet
components induced by rotational splitting (except in the case of G~29-38 where the indicated  number is the total number of multiplets).
 This number is the sum of all the modes observed during various observing seasons. 
References: 1)~Kepler et~al. (\cite{kepler95}); 2)~Bradley (\cite{bradley93}, \cite{bradley01}); 3)~Bradley (\cite{bradley98}); 4)~Bergeron et~al. 
(\cite{bergeron93}), Bradley (\cite{bradley01}); 5)~Kleinman et~al. (\cite{kleinman98}); 6)~Robinson et~al. (\cite{robi95}), Bradley (\cite{bradley98}); 7) Pfeiffer et~al. (\cite{pfeiffer96}); 8)~Kanaan et~al. (\cite{kana05}), 
Metcalfe et~al. (\cite{metc04}), but see also Fontaine \& Brassard (\cite{fontaine04}).
\end{table}