\begin{table}%t4
%\centering
\par
\caption{\label{S} Normalized reflectivity gradients  $\left[\%(1000~\AA)^{-1}\right]$.}
\begin{tabular}{c  c }
\hline\hline
 Object or Group &  $S'$  \\
\hline
 Dead Comets     &   $7.2\pm 6$   \\
 Nuclei          &   $8.3\pm8.4$  \\
 D-types         &   $8.8\pm1.5$  \\
 Trojans         &   $9.6\pm2.7$  \\
 Centaurs        &   $17\pm15$    \\   
 TNOs            &   $22.9\pm5.4$ \\
(5201) Ferraz-Mello & $12.6\pm 3$      \\
\hline
\end{tabular}
\end{table}