\begin{table}%t4
\caption{\label{tab4}HC$_3$N LVG models and resulting reduced $\chi^2$ values (see Sect.~4.1.1)$^{a}$.}
\par
%\centerline
{
\begin{tabular}{lrrrr}
\hline \hline
 Model   & $T_{\rm CMB}$   & $n$(H$_2$)   &\multicolumn{2}{c}{$\chi^2_{\rm red}$}\\
 & (K) &  (cm$^{-3}$) & $f_{\rm c} \propto \nu^{0.0}$   & $f_{\rm c} \propto \nu^{0.5}$ \\   
\hline
 A1      &     5.14        &      0       &        8.1                      &       4.1                        \\
 A2      &     6.00        &      0       &        6.0                      &       2.4                        \\
 A3      &     8.00        &      0       &        3.3                      &       0.8                        \\
 A4      &    10.00        &      0       &        2.0                      &       0.5                        \\
 A5      &    12.00        &      0       &        1.4                      &       0.6                        \\
 A6      &    15.00        &      0       &        1.0                      &       1.0                        \\
 A7      &    20.00        &      0       &        0.8                      &       1.7                        \\
 A8      &    25.00        &      0       &        0.9                      &       2.2                        \\
 A9      &    30.00        &      0       &        1.0                      &       2.6                        \\
 A10     &    50.00        &      0       &        1.4                      &       3.6                        \\
         &                 &              &                                 &                                  \\
 B1      &     5.14        &      0       &        8.1                      &       4.1                        \\
 B2      &     5.14        &    500       &        5.4                      &       2.1                        \\
 B3      &     5.14        &   1000       &        3.3                      &       0.8                        \\
 B4      &     5.14        &   1500       &        1.7                      &       0.3                        \\
 B5      &     5.14        &   1700       &        1.0                      &       0.2                        \\  
 B6      &     5.14        &   2000       &        0.8                      &       0.3                        \\  
 B7      &     5.14        &   2500       &        0.4                      &       0.7                        \\  
 B8      &     5.14        &   2700       &        0.4                      &       1.0                        \\
 B9      &     5.14        &   3000       &        0.5                      &       1.6                        \\  
 B10     &     5.14        &   4000       &        2.1                      &       4.0                        \\  
 B11     &     5.14        &   5000       &        4.9                      &       7.0                        \\  
\hline
\end{tabular}}
 \medskip
\par
 $^a$  Assumed kinetic temperature: $T_{\rm kin} = 80$~K. For the reduced $\chi^2$ values with the frequency independent continuum source coverage factor $f_{\rm c} = 0.3$, see Col.~4. Accounting for the maximal frequency dependence of $f_{\rm c}$, $f_{\rm c} = 0.2 \times (\nu/26$~GHz)$^{0.5}$, the corresponding reduced $\chi^2$ values are given in the last column. 
A comparison of the results summarized in the last two columns provides a good measure of the uncertainties involved. 
\end{table}