\begin{table}%T2
%\centering
\small
\caption{Adopted velocity dispersions $\sigma_U$, $\sigma_V$,
  $\sigma_W$ and asymmetric drift~$v_{{\rm ad}}$ for the young thin 
  disk (YTD), the old thin disk (OTD) and for the thick disk
  \citep[from ][]{RRD2003}.}\label{t:pop}
\begin{tabular}{lrrrr}\hline\hline
Population  &$\sigma_U$ &$\sigma_V$
         &$\sigma_W$ 
         &$v_{\rm ad}$\\ 
         &$({\rm km~s^{-1}})$  &$({\rm km~s^{-1}})$
         &$({\rm km~s^{-1}})$  &$({\rm km~s^{-1}})$ \\ \hline
YTD (0.15--1 Gyr)   &19.8 &12.8 &8.0 &3.1\\
OTD (7--10 Gyr)   &43.1 &27.8 &17.5 &14.8\\
thick disk        &67   &51   &42   &53\\ \hline
\end{tabular}
\end{table}