\begin{table}%t5
%\centering
\par
\caption {\label{tab:opacities1}Optical depths of the H$^{13}$CO$^+$ $J=3\rightarrow 2$~lines 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.} 
\par
%\centerline
 {
\begin{tabular}{llcccc}
\hline \hline
\multicolumn{6}{c}{(0, 0)} \\ \hline
 Ratio used&  Component  & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(H$^{13}$CO$^+$)  & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(H$^{13}$CO$^+$) \\ \hline
& &  \multicolumn{2}{c}{Source size $5\arcsec$}&\multicolumn{2}{c}{Extended source}\\ \cline{3-6}
HC$^{18}$O$^+$/H$^{13}$CO$^+$&Amb.&$\la $2.4&...&$\la$0.9&$\la$16\\ 
&Prec.&$\la$0.25&$\la$2.1&$\la$0.09&$\la$0.59\tablefootmark{a}\\
H$^{13}$C$^{18}$O$^+$/H$^{13}$CO$^+$&Amb.&$\la$1.1&...& $\la $0.4&$\la$290\\
&Prec.&$\la $0.11&$\la$67&$\la$0.04&$\la$24\\ \hline \hline
\multicolumn{6}{c}{(0, --10)} \\ \hline
 Ratio used&  Component & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(H$^{13}$CO$^+$)  & $T_{\rm B,rare}/T_{\rm B,32}$& $\tau_{32}$(H$^{13}$CO$^+$) \\ \hline
& & \multicolumn{2}{c}{Source size $5\arcsec$}&\multicolumn{2}{c}{Extended source}\\ \cline{3-6}
HC$^{18}$O$^+$/H$^{13}$CO$^+$&Amb.&$\la$3.1&...& $\la$1.1&...\\
&Prec.& $\la$0.85&$\la $16 &$\la$0.3&$\la$2.8\\
H$^{13}$C$^{18}$O$^+$/H$^{13}$CO$^+$&Amb.&$\la$1.4&...&$\la$0.5&$\la$390\\
&Prec. &$\la$0.38&$\la$280&$\la$0.1&$\la$83\\ \hline
\end{tabular}}
\tablefoot{
\tablefoottext{a}{This value of $\tau$(H$^{13}$CO$^+$) was estimated 
assuming $R=\frac{40}{577}$, rather than $R=\frac{69}{577}$ (see text for explanation).}}
\par
\end{table}