Planets surviving common envelope evolution should be rare, massive, and orbit very close to their host star

Abstract: The discovery of exoplanets around white dwarfs uniquely informs our understanding of planetary survival through stellar evolution. Common Envelope (CE) evolution is one of the proposed mechanisms that could shape the orbital architecture of these planets around stellar remnants. In this work, we predict the occurrence rate and orbital separation/planet mass distributions for planets that could form around white dwarfs through CE evolution. We simulate populations of giant-planet systems, sampling initial conditions from observed mass and semi-major axis distributions for main sequence stars. We evolve the host star from main sequence to white dwarf to assess which planetary configurations could survive, and we predict the resulting post-CE planet population. Our results suggest that such planets should be rare, massive, and have very close orbital separations. We find that most of the surviving planets have masses of $>10\,M_{\rm{Jup}}$ and orbital separations $<1.4$ times the tidal disruption radius, $a_{disrupt}$ ($\lesssim0.006$ AU, also called the Roche limit), which is in contrast to high eccentricity migration, which produces planets with orbital separations $>2a_{disrupt}$. The properties of CE survivors from our simulations contrast with the known closely-orbiting planet WD 1856+534 b, suggesting a different mechanism may be responsible for its formation.