\begin{table} %t6
\par
\caption{Flux scale factors for optical spectra.}\label{tab6}
\small%\centerline
{
\begin{tabular}{lllll}
\hline\hline
Sample      & Years     & Aperture     &Point-source     &Extended source \\
            &           & (arcsec)     &Scale factor     &Correction      \\
            &           &              & ($\varphi$)           & G(g)$^a$  \\
\hline
  L(U,N)    &  1996--2005&   2.0~$\times$~6.0    &   1.000         &    0.000       \\
  GH,S-P    &  1996--2005&   2.5~$\times$~6.0    &   1.000         &    0.000       \\
  L(S)      &  2004--2006&   1.0~$\times$~6.0    &   0.950 $\pm$ 0.000  &   --0.391       \\
  L1(G)     &  1996--2003&   4.2~$\times$~19.8   &   1.035 $\pm$ 0.021  &    1.133 $\pm$ 0.037\\
  L1(G)     &  1996--2003&   8.0~$\times$~19.8   &   1.112 $\pm$ 0.005  &    1.623 $\pm$ 0.080\\
  L1(U)     &  2004--2006&   4.0~$\times$~9.45   &   0.962 $\pm$ 0.044  &    0.750 $\pm$ 0.150\\
\hline
\end{tabular}}
\smallskip
$^a$  In units $10^{-14}~\rm (erg~s^{-1}~cm^{-2}~\AA^{-1})$.
\end{table}