\begin{table}%t3
\caption{Physical parameters of the \zabs~= 1.7301 and 1.6131~metal
  absorbers towards \object{HS~0747+4259} derived by the MCI procedure
  with the Haardt \& Madau and modified UV~background spectra (marked,
  respectively, by~HM96 and~S1 in Fig.~\ref{fig2}).  Column densities are given
  in~\cm.}\label{tbl_3}
%\centerline
{
\begin{tabular}{lcccc}
\hline
\hline
  &\multicolumn{2}{c}{\zabs~= 1.7301}& \multicolumn{2}{c}{\zabs~= 1.6131}\\
Parameter$^a$ & HM96 & S1 & HM96 & S1 \\
(1) & (2) & (3) & (4) & (5) \\
\hline
$U_0$& 1.0E--1 & 5.7E--2 & $\ga$2.8E--1 & $\ga$1.3E--1 \\
$N_{\rm H}$&1.9E20 & 9.5E19 & 5.7E19 & 2.5E19 \\
$\sigma_{v}$, \kms & 24.9 & 24.5 & 26.4 & 24.5 \\
$\sigma_{y}$& 0.72 & 0.68 & 0.53 & 0.64 \\
$Z_{\rm C}$&8.1E--7 & 1.6E--6 & 3.1E--6 & 6.1E--6 \\
$Z_{\rm N}$&$\ldots$ & $\ldots$ & $<$2.0E--6 & $<$4.8E--6 \\
$Z_{\rm O}$&2.8E--6 & 5.6E--6 & 1.8E--5 & 3.3E--5 \\
$Z_{\rm Si}$&1.4E--7 & 2.7E--7 & $\ldots$ & $\ldots$ \\
$[Z_{\rm C}]$&$-2.50$ &$-2.18$ & $-1.90$ & $-1.60$ \\
$[Z_{\rm N}]$&$\ldots$ & $\ldots$ & $<$$-1.5$ &$<$$-1.1$ \\
$[Z_{\rm O}]$&$-2.24$ & $-1.94$ & $-1.41$ &$-1.17$ \\
$[Z_{\rm Si}]$&$-2.37$ & $-2.11$ & $\ldots$ & $\ldots$ \\
$N$(H~{\sc i})&1.9E16 & $(1.9\pm0.4)$E16 & 7.3E14 & 
$(7.2\pm2.0)$E14 \\
$N$(C~{\sc iii}) &4.0E13 & $(3.9\pm0.8)$E13 &  3.6E12 & 
$(3.5\pm1.5)$E12 \\
$N$(O~{\sc iii}) &1.3E14 & $(1.3\pm0.4)$E14 & 3.9E13$^b$ & 3.0E13$^b$ \\
$N$(Si~{\sc iii}) &1.7E12&$(1.7\pm0.2)$E12&$\ldots$&$\ldots$ \\
$N$(C~{\sc iv}) &3.1E13&$(3.10\pm0.15)$E13&1.2E13 & $(1.1\pm0.1)$E13 \\
$N$(O~{\sc iv}) &2.3E14$^b$ &2.4E14$^b$ &$\ldots$ & $\ldots$ \\
$N$(Si~{\sc iv}) &9.0E11 &$(8.3\pm3.0)$E11 & $\ldots$ & $\ldots$ \\
$N$(N~{\sc v}) &$\ldots$ &$\ldots$ & $<$1.6E13 & $<$1.6E13 \\
$N$(O~{\sc vi}) &2.8E13 &$(4.0\pm1.0)$E13 & 1.3E14 & $(1.30\pm0.25)$E14 \\
$\langle T \rangle$, K & 4.0E4 & 3.9E4 & $\ga$4.7E4 & $\ga$4.5E4 \\
$n_{\rm H}$, \cmm & 3.2E--4 & 5.6E--4 & $\la$1.0E--4 & $\la$2.4E--4 \\ 
$L$, kpc & 200 & 56 & $\ga$190 & $\ga$35 \\
\hline
\end{tabular}}
\medskip
$^a\;Z_{\rm X} = N_{\rm X}/N_{\rm H}$; $[Z_{\rm X}] = \log~ (N_{\rm X}/N_{\rm H}) -
\log~ (N_{\rm X}/N_{\rm H})_\odot$; $^b$ calculated using the corresponding velocity and density distributions estimated from the metal profiles marked by the horizontal bold lines in Figs.~\ref{fig3} and~\ref{fig4}.
\end{table}