We present new V– and R– passband CCD photometry of UU Sge and V477 Lyr , the eclipsing binary nuclei of the planetary nebulae Abell 63 and Abell 46 , respectively .
We have performed a simultaneous analysis of VR light–curves and estimated the effective temperatures for the primary and secondary stars to be 78 000 \pm 3000 and 6136 \pm 240 \mathrm { K } for UU Sge , 49 500 \pm 4500 and 3874 \pm 350 \mathrm { K } for V477 Lyr .
We have also reanalysed the previously measured radial velocities and combined the results with those obtained from the analysis of the light curves to derive absolute parameters of the components .
The secondary stars have larger radii than expected from their main–sequence counterparts at the same masses .
We have determined the post–common envelope ages and the thermal time scales of the systems and examined the possible reasons of expanded radius of the secondary components , together with some selected post-common envelope binaries .
We conclude that the secondary components of the nuclei of the planetary nebulae are still out of thermal equilibrium along with two post-common envelope systems : HS 1136+6646 and RE 1016-053 .
For other systems , magnetic activity has been suggested as the more plausible reason for their expanded radii .
We have also estimated the common–envelope efficiency parameters of UU Sge and V477 Lyr .