\begin{table}%t1
\caption{Comparison of the characteristic cyclotron time of some species with their heat exchange time with protons, in the lower corona.}\label{tab characteristic times} 
\small%\centerline
 {
\begin{tabular}{l c c c }
\hline
\hline
&&& \\[-8pt]
Species & $q/m^{{a}}$ & $\tau_{\rm c}$ (s)$^{{b}}$ & 
$\tau^{\rm \tiny E}$ (s)$^{{c}}$ \\
\hline
&&& \\[-8pt]
e$^{-}$ & 1758 & $4 \times 10^{-7}$ & 120 \\
p$^{+}$ & 1 & $6 \times 10^{-4}$ & 3 \\
\ion{Mg}{x} & 0.37 & $2 \times 10^{-3}$ & 1 \\
     \ion{Fe}{x} & 0.16 & $4 \times 10^{-3}$ & 2 \\
\hline
\end{tabular}}
\medskip
$^{{a}}$ Charge-to-mass ratio, normalized to the proton one. \ion{Mg}{x} and \ion{Fe}{x} are the ion species having the highest and lowest values of $q/m$, respectively, in the spectrum observed by SUMER. \\
$^{{b}}$ $\tau_{\rm c} = 2 \pi \frac{m}{q ~ B}$, with $q$ the charge and $m$ the mass of the particle, and $B$ the magnetic field. \\ 
$^{{c}}$ Heat exchange time with protons $\tau_{\rm \scriptsize ep}^{\rm \tiny E}$ and  $\tau_{\rm \scriptsize ip}^{\rm \tiny E}$ \citep[e.g.][ p.~68]{Wesson04}. \\ 
All these times are calculated with the following conditions: $B=1~{\rm Gauss}$, electron density  $n_{\rm e}=10^{14}~{\rm m}^{-3}$, and proton and electron temperatures both equal to $10^6$~K ($\beta \approx 0.35$). 
\end{table}