\begin{table}%t4
\caption{\label{tab4}Radii of planets  (in $\rjup$) in the mass range 20~$\mearth$$-$1~$\mjup$ for different levels of heavy element enrichment $Z$ (see text, Sect.~7.2, for the choice of the heavy material
distribution) and at different ages. 
%The orbital separation $a$ indidates whether the models are not irradiated ($a=10$~AU) or irradiated by a Sun at 0.045 AU.
}
\small%\centering
\par
\begin{tabular}{lcccc}
\hline
\hline 
$Z$ & $M_{\rm p}/\mearth$ & $R_{\rm 0.5 ~~Gyr}$  & $R_{\rm 1 ~~Gyr}$ & $R_{\rm 5 ~~Gyr}$\\
 \noalign{\smallskip} \hline
0.02 & 10. &  0.828 &  0.811 &  0.758 \\
  &  20. &  0.858 &  0.839 &  0.800 \\
  &  50. &  0.923 &  0.905 &  0.876 \\
  & 100. &  0.980 &  0.963 &  0.937 \\
  & 159. &  1.017 &  0.995 &  0.968 \\
  & 318. &  1.057 &  1.032 &  0.998 \\
0.10  &  10. &  0.779 &  0.763 &  0.716 \\
  &  20. &  0.813 &  0.797 &  0.762 \\
  &  50. &  0.878 &  0.862 &  0.836 \\
  & 100. &  0.935 &  0.919 &  0.896 \\
  & 159. &  0.971 &  0.951 &  0.926 \\
  & 318. &  1.012 &  0.990 &  0.958 \\
 0.50 &  10. &  0.598 &  0.586 &  0.555 \\
  &  20. &  0.632 &  0.621 &  0.598 \\
  &  50. &  0.683 &  0.665 &  0.635 \\
  & 100. &  0.717 &  0.697 &  0.670 \\
  & 159. &  0.739 &  0.718 &  0.690 \\
  & 318. &  0.781 &  0.756 &  0.721 \\
 0.90 &  10. &  0.382 &  0.375 &  0.357 \\
  &  20. &  0.420 &  0.414 &  0.403 \\
  &  50. &  0.503 &  0.474 &  0.439 \\
  & 100. &  0.543 &  0.512 &  0.469 \\
  & 159. &  0.568 &  0.538 &  0.492 \\
  & 318. &  0.607 &  0.578 &  0.524 \\
 \hline
 \end{tabular}
\end{table}