Two-colour photometry of the binary planetary nebula nuclei UU Sagitte and V477 Lyrae: oversized secondaries in post-common-envelope binaries

Abstract

We present new V and R-passband CCD photometry of UU Sge and V477 Lyr, the\neclipsing binary nuclei of the planetary nebulae Abell 63 and Abell 46,\nrespectively. We have performed a simultaneous analysis of VR light-curves and\nestimated the effective temperatures for the primary and secondary stars to be\n78 000 $\\pm$ 3000 and 6136 $\\pm$ 240 K for UU Sge, 49 500 $\\pm$ 4500 and 3874\n$\\pm$ 350 K for V477 Lyr. We have also reanalysed the previously measured\nradial velocities and combined the results with those obtained from the\nanalysis of the light curves to derive absolute parameters of the components.\nThe secondary stars have larger radii than expected from their main--sequence\ncounterparts at the same masses. We have determined the post--common envelope\nages and the thermal time scales of the systems and examined the possible\nreasons of expanded radius of the secondary components, together with some\nselected post-common envelope binaries. We conclude that the secondary\ncomponents of the nuclei of the planetary nebulae are still out of thermal\nequilibrium along with two post-common envelope systems: HS 1136+6646 and RE\n1016-053. For other systems, magnetic activity has been suggested as the more\nplausible reason for their expanded radii. We have also estimated the\ncommon--envelope efficiency parameters of UU Sge and V477 Lyr.\n