\begin{table}
\caption{\label{error_table}The different RV precision indicators on the RV std, TW Hya, and Gl 86.}
%\centering
\par
\begin{tabular}{lccccc} 
\hline\hline\noalign{\smallskip}
 &  External dispersion  [m/s] & Intra-Night Dispersion [m/s] & Photon Noise [m/s] & (O--C) [m/s]  \\ \hline 
RV std   & 5.77   & 7.03  & 6.48  & ---  \\
TW Hya  & 54.57  & 12.12  & 12.10 & 7.93  \\
Gl 86  & 122.47  & 12.77  & 7.62 & 5.41 \\
\hline
\end{tabular}
\end{table}