\begin{table}%t4
\newcommand{\T}{\rule{0pt}{2.6ex}}
\newcommand{\B}{\rule[-1.2ex]{0pt}{0pt}}
\caption{Upper column density limits of amino acetonitrile
(H$_2$N~CH$_2$~CN) and oxiranecarbonitrile ($c$-C$_3$H$_3$~NO).} 
\label{aminooxicols}
%\centerline
{\begin{tabular}{lccccc}
\hline \hline
 & \multicolumn{2}{c}{\underline{H$_2$N~CH$_2$~CN}$^{a}$} & &
 \multicolumn{2}{c}{\underline{$c$-C$_3$H$_3$~NO}$^{a}$} \\
\T Source & $T_{\rm ex}$ & $N$ & & $T_{\rm ex}$ & $N$ \\
 & (K) & (cm$^{-2}$) & & (K) & (cm$^{-2}$) \\
\hline 
\T Orion KL & [150] & $<$$1.3 \times 10^{13}$ & & [40] & $<$$3.4 \times 10^{12}$  \\
W51 e1/e2 & [150] & $<$$3.5 \times 10^{13}$ & & [40] & $<$$9.5 \times 10^{12}$ \\
S140 & [150] & $<$$1.1 \times 10^{13}$ & & [40] & $<$$2.3 \times 10^{12}$ \\
\B W3(OH) & [150] & $<$$1.2 \times 10^{13}$ & ~~~ & [40] & $<$$2.3 \times 10^{12}$ \\
\hline
\end{tabular}}
\medskip
\par
$^{a}$ Upper limits are taken at 3$\sigma$ noise-level
over 5 \kms, assuming the $T_{\rm ex}$ given in square brackets. 
\end{table}