\begin{table}%t1
  \caption{\label{tab:dim-quan}Dimensional and dimensionless parameters.}
  \small%\centering
\par
  \begin{tabular}{lll}
  \hline
  \hline\noalign{\smallskip}
    Description               &  Dimensional  & Dimensionless \\
  \hline
    Hill radius               & $R_{\rm h}$               & 1 \\
    Orbital frequency         & $\Omega$            & 1 \\
    Headwind velocity         & $v_{\rm hw}$     & $\zeta_{\rm w}$ \\
    Drag constant             & $K_{\rm drag}$   & $K_{\rm drag}' = 1/{\rm St}$ \\  
    Radius (proto)planet      & $R_{\rm p}$               & $\alpha_{\rm p}$ \\
    Stopping time             & $t_{\rm s}$            & ${\rm St}$ \\
    Collision rate            & $P_{\rm col}$    & $P$ \\
    Impact radii\tablefootmark{a}          & $b_\sigma$               & $b_\sigma$ \\
  \hline
  \end{tabular}
  \tablefoot{\tablefoottext{a}{For impact radii and velocities we intentionally use the same symbols, see also footnote~\ref{foot:foot1}.}}
\end{table}