\begin{table}
%\section{Comparison to observations}
%%\centering
\par
\caption{Comparison of best-fitting models with observed radial column densities for AFGL~$2591$.}\label{tob}
%\centerline
{
\begin{tabular}{llllllllrll} \hline\hline
Species & Model 6 & Observed & Data & Reference & $L_{{\rm X}}$ 
& $T_{{\rm X}}$ & $N_{{\rm H,in}}$ & $G_{{\rm 0,in}}$ & Time & \\ 
 & [cm$^{-2}$] & [cm$^{-2}$] & & & [erg s$^{-1}$] & [K] & [cm$^{-2}$] & & [yr] & \\  \hline
HCN & 3.8E+16 & 1.2E+16 & submm - JCMT & Bm01 & 3.0E+32 & 5.0E+07 & 4.0E+22 & 0 & 2.4E+04 & \\
HCN & 3.8E+16 & 4.0E+16 & IR - ISO & LvD & 8.0E+31 & 5.0E+07 & 5.0E+22 & 0 & 7.5E+04 & \\
HNC & 4.6E+15 & 9.6E+14 & submm - JCMT & Do & 5.0E+29 & 1.0E+08 & 5.0E+22 & 0 & 5.6E+03 & \\
HC$_3$N & 9.2E+13 & 1.8E+15 & submm - JCMT & Do & 1.0E+30 & 5.0E+07 & 5.0E+22 & 0 & 1.4E+05 & \\
HCO$^+$ & 3.5E+15 & 9.6E+14 & submm - JCMT & vdT99 & 7.0E+30 & 3.0E+07 & 4.0E+22 & 0 & 1.8E+04 & \\
HCS$^+$ & 1.7E+13 & 1.8E+13 & submm - JCMT & vdT03 & 9.0E+31 & 2.0E+07 & 3.0E+22 & 10 & 1.0E+04 & \\
H$_3^+$ & 1.8E+14 & 2-3E+14 & IR - UKIRT & Mc & 2.0E+32 & 3.0E+08 & 7.0E+22 & 0 & 5.6E+03 &  \\
H$_2$O & 6.4E+17 & 3.5E+18 & IR - ISO & Bmv & 1.0E+30 & 7.0E+06 & 2.0E+22 & 0 & 4.2E+04 & \\
H$_2$S & 5.3E+12 & 7.3E+14 & submm - JCMT & vdT03 & 5.0E+30 & 3.0E+07 & 3.0E+22 & 0 & 5.6E+03 & \\
H$_2$CO & 2.1E+15 & 3.8E+14 & submm - JCMT & vdT00 & Model 0 & & & 0 & 3.2E+05 & (4.8E+14) \\
H$_2$CS & 2.3E+13 & 2.8E+13 & submm - JCMT & vdT03 & 2.0E+32 & 2.0E+08 & 3.0E+22 & 10 & 1.0E+05 & \\
C$_2$H & 3.8E+14 & 1.9E+14 & submm - JCMT & Do & 6.0E+31 & 1.0E+08 & 5.0E+22 & 0 & 1.0E+05 & \\
C$_2$H$_2$ & 3.3E+14 & 2.0E+16 & IR - ISO & LvD & Model 0 & & & 0 & 5.6E+04 & (1.0E+15) \\
CH$_4$ & 2.6E+16 & 2.5E+17 & IR - UKIRT & Do &  7.0E+32 & 7.0E+07 & 5.0E+22 & 0 & 3.2E+05 & (3.7E+16) \\
CH$_3$OH & 3.4E+13 & 2.8E+15 & submm - JCMT & vdT00 & 5.0E+31 & 1.0E+07 & 1.0E+23 & 0 & 1.3E+04 & \\
CH$_3$CN & 2.6E+14 & 1.8E+15 & submm - JCMT & Do & 1.0E+30 & 5.0E+07 & 1.0E+22 & 0 & 3.2E+05 & (9.5E+14) \\
CO$_2$ & 2.0E+16 & 2.5E+16 & IR - ISO & Bm03 & 3.0E+32 & 3.0E+07 & 3.0E+22 & 0 & 2.4E+05 & \\
CS & 1.9E+15 & 9.6E+14 & submm - JCMT & vdT03 & 6.0E+31 & 1.0E+08 & 3.0E+22 & 10 & 2.4E+05 & \\
CN & 5.6E+14 & 4.5E+15 & submm - JCMT & Do & 5.0E+32 & 5.0E+07 & 5.0E+22 & 0 & 1.8E+04 & \\
OCS & 8.8E+14 & 9.6E+14 & submm - JCMT & vdT03 & 6.0E+31 & 5.0E+07 & 3.0E+22 & 0 & 1.4E+05 & \\
NH$_3$ & 5.7E+15 & 1.9E+15 & cm - Effelsberg & Do & 5.0E+30 & 1.0E+08 & 7.0E+22 & 0 & 1.0E+04 & \\
N$_2$H$^+$ & 4.9E+13 & 4.7E+13 & submm - JCMT & St & 7.0E+31 & 1.0E+08 & 3.0E+22 & 0 & 1.0E+04 & \\
SO & 1.8E+16 & 9.6E+14 & submm - JCMT &  vdT03 & Model 1 & & & 10 & 5.6E+04 & (1.6E+15) \\
SO$_2$ & 2.7E+15 & 1.9E+14 & submm - JCMT &  vdT03 & 5.0E+32 & 3.0E+07 & 3.0E+22 & 0 & 1.0E+04 & (6.9E+14) \\
NS & 2.4E+12 & 4.7E+11 & submm - JCMT &  vdT03 & 6.0E+31 & 3.0E+07 & 3.0E+22 & 10 & 5.6E+03 & (2.0E+12) \\ \hline
\end{tabular}}
\medskip
The column density of a model with the parameters 
$L_{{\rm X}}$, $T_{{\rm X}}$, $N_{{\rm H,in}}$, 
$G_{{\rm 0,in}}$ and time given in Cols.~6$-$10 match 
the observed column density. If no model was found to give a good fit, 
the best fitted model is presented with the column density given 
in brackets at the end of the line.
\\
References: Bm$01$ Boonman et~al. ($2001$), Bm$03$ Boonman et~al. ($2003$b), 
Bmv Boonman \& van Dishoeck ($2003$), Do Doty et~al. ($2002$), 
LvD Lahuis \& van Dishoeck ($2000$), Mc McCall et~al. ($1999$), 
St Stark et~al. ($1999$), vdT$99$ van der Tak ($1999$), 
vdT$00$ van der Tak ($2000$), vdT$03$ van der Tak ($2003$).
\end{table}