\begin{table}%t1
\caption{\label{T:widths}Line widths related to \ion{Fe}{15} (284~{\AA}).}
%\centerline
{
\begin{tabular}{lrcc}
\hline
\hline\noalign{\smallskip}
                   &                      &  {\it FWHM}  & Exponential~width
\\
                   && [km~s$^{-1}$] & [km~s$^{-1}$]  %\multicolumn{2}{c}{[km~s$^{-1}$]}
\\
\hline
instrumental width\tablefootmark{a} & $w_{\rm{instr}}$     &      59      &      35
\\
thermal width\tablefootmark{b}      & $w_{\rm{thermal}}$   &      45      &      27
\\
\multicolumn{2}{l}{
total width ~ $(w_{\rm{instr}}^2+w_{\rm{thermal}}^2)^{1/2}$}
                                          &      75      &      45
\\
\hline
\end{tabular}}
\tablefoot{\tablefoottext{a}{According to \cite{Doschek+al:2007}:  {\it FWHM} = 56~m{\AA}; at 284~{\AA}.}
\tablefoottext{b}{$w_{\rm{thermal}}^2=2k_{\rm{B}}T/\mu$  with line formation temperature ${\log}\ T[{\rm{K}}]=6.4$ and molecular weight $\mu=55.8~$amu.}}
\end{table}