\begin{table}%t1
%\centering
\par
\caption{\label{tbldustspec}Dust species used for fitting the ISO spectra with DUSTY.} 
\par
\begin{tabular}{c c c c } 
\hline\hline 
$f$-Number & Species & Formula &  Ref.\\ 
\hline 
$f_1$& Amorphous aluminum oxide& Al$_2$O$_3$                                 &  1\\
$f_2$ & astronomical silicate  &                          SiO$_4$             &  2\\
$f_3$ & Amorphous pyroxene (100K)& Mg$_x$Fe$_{1-x}$SiO$_3$                     &  3\\
$f_4$ & Amorphous melilite                      & Ca$_2$Al$_2$SiO$_7$            & 4\\
$f_5$ & Amorphous olivine        & Mg$_{0.1}$Fe$_{1.2}$SiO$_4$ &                  5,6\\
$f_6$& Crystalline magnesiowustite                      & Mg$_{0.1}$Fe$_{0.9}$O    & 7\\
$f_7$ & Amorphous Mg-Fe-silicate      & MgFeSiO$_4$                                 & 8\\
$f_8$ & Crystalline spinel                 & MgAl$_2$O$_4$                           & 9\\
\hline
\end{tabular}
\tablebib{(1) \citet{begemann97}; (2) \citet{ossenkopf92};  (3) \citet{henning97};  (4) \citet{mutschke98}; (5) \citet{jaeger94}; (6) \citet{dorschner95}; (7) \citet{henning95}; (8)~\citet{hanner88}; (9) \citet{posch99}.} \vspace*{2mm}
\end{table}