The final orbital separation in common envelope evolution

In the majority of population synthesis calculations close binary stars, common envelope (CE) phase is modeled using a standard prescription based upon conservation energy, known as alpha prescription. this prescription, orbital separation secondary and giant core at end CE taken to be when becomes unbound. However, recent observations planetary nebulae with cores (BPNe), believed immediate products evolution, indicate periods that are significantly shorter than predicted by models We argue unbinding provides necessary, but not sufficient, condition escape merger during evolution. The spiral-in must also halted. This requires additional dynamical constraint frictional torque on reduced approximately zero. paper, we undertake preliminary examination effect adding in BPNe. assume will sufficiently enters region within where mass-radius profile flat. crudely estimate location function mass existing stellar AGB stars between 1 7 solar masses. calculate theoretical period distribution BPNe code incorporates along