\begin{table}%t6
%\centering
\par
\caption{\label{TT1}CLOUDY models for the three quasars: (1)
 $U=\frac{Q(H)}{4\pi r^{2} n c}$\ where~$Q(H)$ is the number of 
 hydrogen ionizing photons, $r$ is the distance of the gas to the 
 continuum source, $n$ is the gas number density and~$c$
 the speed of light.}
\begin{tabular}{lccc}
\hline \hline  
Para             &     PG    & PG    &   PG  \\
 meter                            & 1001+054  & 2112+059 & 1535+547 \\   \hline  
$N_{\rm H}$ [${\rm cm}^{-2}$] & 10$^{23.3}$ & 10$^{22.8}$ & 10$^{22.5}$ \\
$\rm U^{(1)}$             & 10$^{2.7}$ & 10$^{1.7}$ & 10$^{1.8}$ \\ 
$\alpha_{{\rm OX}}$     & --1.72 & --1.63 & --1.72 \\
$\alpha_{{\rm UV}}$     & {--0.5} & {--0.5} & {--0.5}\\
$\alpha_{{\rm X}}$      &    {--0.95}& {--0.95} & {--0.95} \\  
\hline 
\end{tabular}
\end{table}