\begin{table}%t5
   \caption{Adopted and derived modelling parameters of the two PPNe.\label{modeldata}}
%\begin{center}
{   \begin{tabular}{lcccccccc}
   \hline\hline
 IRAS No. & $D$     & $L$       & $f_{{\rm CO}}$       & $\dot{M}$               & $v_{\rm exp}$& $R_{\rm e}$      & $h$ & $^{12}$CO/$^{13}$CO \\
          & [kpc]   & [$L_{\odot}$]    & & [$M_{\odot}$~yr$^{-1}$]& [km~s$^{-1}$]   & [cm]                 &     &  \\
    \hline
16594-4656& 1.80$^a$& \phantom{0}4900& $1\times 10^{-3}$ & $1\times 10^{-5}$      & 14.0             & $2.9\times10^{17}$& 10.0&30 \\
17150-3224& 2.42$^b$& 11~000      & $2\times10^{-4}$    & $3\times 10^{-5}$      & 14.5             & $2.4\times 10^{17}$& \phantom{0}1.8& \phantom{0}7\\
%
  \hline\\[-3mm]
   \end{tabular}}
\parbox{13.5cm}{
$^a$ \citet{VDV_etal1989}.\\
$^b$ \citet{Bujarrabal_etal2001}.}
%\end{center}
\par
\end{table}