\begin{table}%t1
\caption{The properties of the return currents. $\mathcal{F}_1$ stands for
the initial flux of the 10~keV beam, $\alpha$ is the mean relative number
of runaway return-current electrons in the Balmer lines formation region,
and $E_\RC$ stands for the typical energy of the return-current electrons in
these layers. Both $\alpha$ and $E_\RC$ are average quantities which
can roughly characterize the return-current properties in the region
of interest.}
\label{tab:alphas}
%\centering
\small
\begin{tabular}{ccc}
\hline \hline
&& \\[-8pt]
$\mathcal{F}_1 [10^{11}~{\rm erg~cm^{-2}~s^{-1}}]$ & $\alpha$ & $E_\RC [{\rm eV}]$\\
&& \\[-8pt]
\hline
   4  & 0.01 & 100 \\
   6  & 0.05 & 14  \\
   8  & 0.11 & 6   \\
   10 & 0.16 & 3.8 \\
\hline
\end{tabular}
\end{table}