\begin{table}%t4
\caption{\label{knownso}Previously known \so~candidates in our survey.}
           \small
%\centerline
{    
\begin{tabular}{l c c c l}     
\hline    
\hline    
Object                                   & $z'$            & $i'-z'$       & $I^{{a}}$ & Reference\\
\hline
S~Ori~13                               & 15.66~$\pm$~0.21  & 1.05~$\pm$~0.30 & 16.05 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~14                               & 15.92~$\pm$~0.21  & 1.26~$\pm$~0.29 & 16.35 & B\'ejar et al$.$ (\cite{bejar99})\\
S~Ori~19                               & 16.11~$\pm$~0.21  & 1.08~$\pm$~0.29 & 16.62 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~23                               & 16.43~$\pm$~0.21  & 1.14~$\pm$~0.29 & 16.88 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~24                               & 16.48~$\pm$~0.20  & 1.10~$\pm$~0.29 & 16.90 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~28                               & 16.74~$\pm$~0.21  & 1.24~$\pm$~0.29 & 17.23 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~J053922.2$-$024552               & 16.78~$\pm$~0.21  & 1.08~$\pm$~0.29 & 17.05 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~32	                         & 16.89~$\pm$~0.21  & 1.26~$\pm$~0.29 & 17.40 & B\'ejar et al$.$ (\cite{bejar06})\\
KNJ2005 72                               & 17.01~$\pm$~0.21  & 1.31~$\pm$~0.29 & 17.82 & Kenyon et al$.$ (\cite{kenyon05})\\
KNJ2005 70                               & 17.13~$\pm$~0.21  & 1.29~$\pm$~0.29 & 17.81 & Kenyon et al$.$ (\cite{kenyon05})\\
KNJ2005 71                               & 17.26~$\pm$~0.21  & 1.12~$\pm$~0.29 & 17.82 & Kenyon et al$.$ (\cite{kenyon05})\\
S~Ori~38	                         & 17.34~$\pm$~0.24  & 1.32~$\pm$~0.35 & 17.70 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~J053926.8$-$022614               & 17.69~$\pm$~0.21  & 1.15~$\pm$~0.30 & 18.25 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~J053918.1$-$025257$^{{b}}$& 17.99~$\pm$~0.21  & 1.66~$\pm$~0.29 & 18.64 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~J053948.1$-$022914               & 18.06~$\pm$~0.21  & 1.20~$\pm$~0.30 & 18.52 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~42	                         & 18.33~$\pm$~0.21  & 1.70~$\pm$~0.30 & 19.04 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~44	                         & 18.94~$\pm$~0.21  & 1.29~$\pm$~0.29 & 19.39 & B\'ejar et al$.$ (\cite{bejar99})\\
S~Ori~45	                         & 18.99~$\pm$~0.21  & 1.58~$\pm$~0.30 & 19.49 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~J053929.4$-$024636               & 19.12~$\pm$~0.21  & 1.68~$\pm$~0.29 & 19.73 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~J053946.5$-$022423               & 19.09~$\pm$~0.21  & 1.59~$\pm$~0.29 & 20.14 & B\'ejar et al$.$ (\cite{bejar01})\\
S~Ori~52	                         & 19.76~$\pm$~0.21  & 1.78~$\pm$~0.29 & 20.55 & B\'ejar et al$.$ (\cite{bejar06})\\
S~Ori~53	                         & 20.42~$\pm$~0.22  & 1.85~$\pm$~0.31 & 20.96 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~J053956.8$-$025315               & 20.49~$\pm$~0.21  & 1.86~$\pm$~0.30 & 21.25 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~J053858.6$-$025228               & 21.28~$\pm$~0.24  & 1.98~$\pm$~0.35 & 22.17 & Caballero et al$.$ (\cite{caballero04})\\
S~Ori~67         	                 & 22.05~$\pm$~0.22  & 1.78~$\pm$~0.35 & 23.04 & B\'ejar et al$.$ (\cite{bejar06})\\
\hline
\end{tabular}}
\smallskip
 $^{{a}}$ $I$-band magnitude from the literature.
 $^{{b}}$ It is detected in both Palomar and Calar surveys. We provide the mean $i'$ and $z'$ photometry. The $i'$ magnitudes differ by 0.3~mag suggesting photometric variability and supporting the conclusions on the source variable nature reported by Caballero et al$.$ (\cite{caballero04}). 
 %\vspace*{2mm}
\end{table}