\begin{table}%t1
%\renewcommand\arraystretch{1.15}
\caption{Observational parameters. }
\label{tab:obs}
%\centerline
{
\begin{tabular}{lcccccc}
\hline\hline
Line & $\nu$\tablefootmark{a} & $B_{\rm eff}$\tablefootmark{b} & $F_{\rm eff}$\tablefootmark{c} &  {\it FWHM}\tablefootmark{d}   & $T_{\rm sys}$\tablefootmark{e} & rms \\
        & GHz   &                   &                  & arcsec& K  & mK \\
\hline
4--3\tablefootmark{f}    & 87.925    & 0.78  & 0.95 & 28.4 &100& 12--18\\
5--4\tablefootmark{g}     & 109.905   & 0.75  & 0.95 & 22.3 &180& 16--19 \\
6--5\tablefootmark{h}     & 131.885   & 0.69  & 0.93 & 18.8 &215& 28--34\\
\hline
\end{tabular}}\tablefoot{
\tablefoottext{a}{Frequency;}
\tablefoottext{b}{beam efficiency;}
\tablefoottext{c}{forward efficiency;}
\tablefoottext{d}{full width at half maximum of the telescope main beam;}
\tablefoottext{e}{{system} temperature;}
\tablefoottext{f}{$4_{0,4}$--$3_{0,3}$;}
\tablefoottext{g}{$5_{0,5}$--$4_{0,4}$;}
\tablefoottext{h}{$6_{0,6}$--$5_{0,5}$}. }
\end{table}