\begin{table}%t3
%\centering
\par
\caption{\label{tbl:columndensities}Summary of column densities, $N$(H$_2$) in~cm$^{-2}$ in the broad and medium components in 20$''$ beam.}
\tiny
\begin{tabular}{l c c c}
\hline \hline \noalign{\smallskip}
Source & Broad Comp. & Medium Comp. \\ 
\hline\noalign{\smallskip}
IRAS~2A  &   $6\times10^{19}$\tablefootmark{a}   &   $2\times10^{20}$\tablefootmark{b}    \\ 
IRAS~4A  &    $4\times10^{20}$\tablefootmark{b}  &   $6\times10^{20}$\tablefootmark{c}   \\ 
IRAS~4B   &   $1\times10^{20}$\tablefootmark{b}   &   $2\times10^{20}$\tablefootmark{c} \\ 
\hline
\end{tabular}
\tablefoot{Obtained from \tablefoottext{a}{CO 6--5}, 
\tablefoottext{b}{CO 10--9}, 
\tablefoottext{c}{$^{13}$CO 10--9 spectra.} }
\vspace*{-4mm}
\end{table}