\begin{table}%t6
%\centering
\par
\caption {\label{tab:opacities2}Optical depths of the HN$^{13}$C $J=3\rightarrow 2$~line toward L1448-mm (0, 0) and (0, --10) 
derived from different isotopologue ratios for the ambient (amb.) and the 
precursor (prec.) components, and for different source morphologies.}
\begin{tabular}{llcccc}
\hline \hline
\multicolumn{6}{c}{(0, 0)} \\ \hline
 Ratio used& Component & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(HN$^{13}$C)  & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(HN$^{13}$C) \\ \hline
& &  \multicolumn{2}{c}{Source size $5\arcsec$}&\multicolumn{2}{c}{Extended source}\\ \cline{3-6}
H$^{15}$NC/HN$^{13}$C&Amb.&$\la$0.74&$\la$7.6&$\la$0.3&$\la$1.1 \\
&Prec.&$\sim1.1$&...&$\sim$0.4&$\sim$2.5\\
H$^{15}$N$^{13}$C/HN$^{13}$C&Amb.&$\la$1.6&...&$\la $0.6&$\la$320\\
&Prec.&$\sim$2.3&...& $\sim$0.8&$\sim $700\\\hline \hline
\par
\multicolumn{6}{c}{(0, --10)} \\ \hline
Ratio used & Component & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(HN$^{13}$C)  & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(HN$^{13}$C) \\ \hline
& & \multicolumn{2}{c}{Source size $5\arcsec$}&\multicolumn{2}{c}{Extended source}\\ \cline{3-6}
H$^{15}$N$^{13}$C/HN$^{13}$C&Amb.&$\sim$2.2&...&$\sim$0.8&$\sim$610\\
&Prec.& $\sim$2.2&...&$\sim$0.8&$\sim$610\\ \hline 
\par
\end{tabular}
\par
\end{table}