\begin{table}%t5
\caption{\label{shellmass}Derived shell masses based on the EFOSC2 data (dust) and the APEX CO~line data (gas).}
%%\centering

\par
\begin{tabular}{c c c c}
\hline\hline\noalign{\smallskip}
shell		& $R$ & $M_{\rm dust}$ & $M_{\rm gas}$ \\
                  & [cm] & [$M_{\odot}$] & [$M_{\odot}$]\\
\par
\hline\noalign{\smallskip}
3		& $1.7\times10^{17}$ & & $2\times10^{-3}$\\
4		& $1.9\times10^{17}$ & $5\times10^{-5}$ \\
\hline
\end{tabular}
\end{table}