\begin{table}%t3
%\centering
\par
\caption{\label{ages}Ages and dust masses of the disks in planetary nebulae.}
\begin{tabular}{lrrl}
\hline\hline
\noalign{\smallskip}
  Nebula & Nebular Age & Dust Mass & Reference \\
       &     [yr]  &   [$M_{\odot}$]  \\ 
%\noalign{\smallskip}
\hline
\noalign{\smallskip}
CPD$-56\degr8032$ &  $10^2$         &  $3 \times 10^{-4}$ & 
(2), (3) \\
Ant nebula (Mz 3) & $10^3$         &   $1 \times 10^{-5}$ & 
(1), (4) \\
M~2-29          &  $5\times10^3$   & $ 10^{-6}$          &  This paper \\
Helix nebula     &  $1.1 \times 10^4$ & $4 \times 10^{-7}$  & 
(5), (6)\\
\hline
\end{tabular}
\par
\tablebib{(1) \citet{Chesneau2006}; (2) \citet{Chesneau2007}; (3) \mbox{\citet{deMarco1997}}; (4) \citet{Guerrero2004}; (5) \citet{Meaburn2008}; (6) \citet{Su2007}.}
\end{table}