\begin{table}%t6
%\centering
\par
\caption{Inferred abundances from radiative transfer models assuming constant 
radial abundances.}
\label{trad}
\begin{tabular}{lrrrr} \hline\hline
Source & CN & NO & CO$^+$ & SO$^+$ \\ \hline 
AFGL 2591 & $2.3\times 10^{-08}$ & $3.1\times 10^{-08}$ & $1.6\times 10^{-10}$ & $5.8\times 10^{-11}$ \\
W3 IRS 5 & $3.6\times 10^{-09}$ & $1.7\times 10^{-08}$ & $3.9\times 10^{-11}$ & $7.0\times 10^{-11}$ \\
IRAS 16293 & $5.4\times 10^{-11}$ & ... & $1.5\times 10^{-12}$ & $\lesssim$$3.0\times 10^{-12}$ \\
N1333-I2 & $3.9\times 10^{-10}$ & $2.5\times 10^{-09}$ & $\lesssim$$7.5\times 10^{-12}$ & $<5.0\times 10^{-12}$ \\
N1333-I4A & $4.2\times 10^{-11}$ & $1.5\times 10^{-09}$ & $<$$1.3\times 10^{-12}$ & $<2.2\times 10^{-12}$ \\
L1448-C & $1.1\times 10^{-09}$ & ... & $<$$2.0\times 10^{-11}$ & $<$$1.4\times 10^{-11}$ \\
L483 & $1.5\times 10^{-09}$ & ... & $<$$7.0\times 10^{-12}$ & ... \\
L723 & $9.2\times 10^{-10}$ & ... & $<$$2.0\times 10^{-11}$ & $<$$4.3\times 10^{-11}$ \\
SMM4 & $1.6\times 10^{-10}$ & ... & $<$$1.0\times 10^{-12}$ & $<$$4.0\times 10^{-12}$ \\
V1057 Cyg & $5.4\times10^{-09}$ & ... & $<$$2.0\times 10^{-10}$  & $<$$5.0\times 10^{-11}$ \\ 
L1489 & $2.5\times10^{-09}$ & ... & ... & ... \\ \hline
\end{tabular}
\end{table}