\begin{table}%t2
\caption{Cen X-4 dynamical parameters.\label{param}}
%\centerline
{\begin{tabular}{cccc}
\hline\hline
Reference                   &   $\gamma$      & $K_2$           & $P$ \\
                            &  (km s$^{-1}$)  & (km s$^{-1}$)   &   (d)       \\
\hline
Cowley et~al. (\cite{Cowley88})          & $234\pm 8$      & $152\pm 10$     &    --     \\
McClintock \& Remillard (\cite{McClintock90})& $137\pm 17$     & $146\pm 12$     & 0.629063 \\
Torres et~al. (\cite{Torres02})          & $184.0\pm 1.9$  & $150.0\pm 1.1$  & $0.6290496\pm 0.0000021$\\ 
This paper                  & $196.0\pm 1.1$  & $145.8\pm1.0$   & $0.630\pm0.001$ \\
\hline
\end{tabular}}
\par
\smallskip
{The velocity values reported
here have been obtained by fixing $P$ to the value given by Torres et~al. (\cite{Torres02}). We also repeated the fit leaving all the parameters free,
obtaining the value given here.} 
\end{table}