\begin{table}%t6
  \caption{Distance of the gas from the central star and total density
    of the observed medium, as determined by the best-fitting model
    using the Meudon PDR~Code.}\label{param_pdr}
%\centering
\small
\begin{tabular}{lcc}
\hline
\hline
Star        & Gas to star   & Gas  volume       \\ 
            & distance (pc) & density, $n_{\rm H}$ (cm$^{-3}$)     \\
\hline                                       
HD~176386   & 0.04         & 3000     \\ 
HD~250550   & 0.03         & 600      \\  
HD~85567    & 0.10         & 250       \\  
HD~259431   & 0.35         & 70      \\    
HD~38087    & 1.60         & 12      \\         
HD~76534    & 0.40         & 170     \\     
\hline
\end{tabular} 
\end{table}