Post-common envelope binary stars: Radiative Levitation and Blue Large-Amplitude Pulsators

Following the recent discovery of a new class of pulsating star, the blue large-amplitude pulsators (BLAPs), pulsation stability analysis was carried out on evolutionary models of post-common envelope (CE) ejection stars of 0.3 and 0.46 solar masses. These models subsequently evolve to become a low-mass helium white dwarf and a core helium-burning extreme horizontal-branch star respectively. We investigate the effects of atomic diffusion, particularly radiative levitation, on the pulsation behaviour of the models. We find that when the models have effective temperatures comparable to those of BLAPs, the inclusion of radiative levitation allows sufficient enhancement of heavy metals to produce opacity-driven fundamental mode pulsations with periods similar to those observed in BLAPs. Common envelope evolution is a phase of close binary evolution which may lead to the formation of exotic stellar objects, such as hot subdwarf stars. The effects of mixing processes such as atomic diffusion and especially radiative levitation have been shown to play a significant role in the post-common-envelope phase of evolution. Following the discovery of blue large-amplitude pulsators (BLAPs), further models of post red giant branch stars that have undergone a common envelope (CE) ejection were constructed and analysed for pulsation stability. Here we present analysis of post-CE objects of 0.3 and 0.46 solar masses that ultimately evolve to become a low mass white dwarf and a hot subdwarf star respectively. The role that atomic diffusion and radiative levitation play on the presence of pulsations in such models was examined. It is found that the inclusion of radiative levitation allows sufficient enhancement of heavy metals to produce opacity-driven fundamental mode pulsations with periods comparable to that of the newly discovered class of pulsating stars, the blue large-amplitude pulsators (BLAPs).