Enhanced Lidov-Kozai migration and the formation of the transiting giant planetWD1856+534 b

We investigate the possible origin of the transiting giant planet WD1856+534 b, the first strong exoplanet candidate orbiting a white dwarf, through high-eccentricity migration (HEM) driven by the Lidov-Kozai (LK) effect. The host system's overall architecture is a hierarchical quadruple in the '2+2' configuration, owing to the presence of a tertiary companion system of two M-dwarfs. We show that a secular inclination resonance in 2+2 systems can significantly broaden the LK window for extreme eccentricity excitation (e greater than or similar to 0.999), allowing the giant planet to migrate for a wide range of initial orbital inclinations. Octupole effects can also contribute to the broadening of this 'extreme' LK window. By requiring that perturbations from the companion stars be able to overcome short-range forces and excite the planet's eccentricity to e similar or equal to 1, we obtain an absolute limit of a(1) greater than or similar to 8 au (a(3)/1500 au)(6/7) for the planet's semimajor axis just before migration (where a(3) is the semimajor axis of the 'outer' orbit). We suggest that, to achieve a wide LK window through the 2+2 resonance, WD1856 b likely migrated from 30 au less than or similar to a(1) less than or similar to 60 au, corresponding to similar to 10-20 au during the host's main-sequence phase. We discuss possible difficulties of all flavours of HEM affecting the occurrence rate of short-period giant planets around white dwarfs.

Automated summary

This study investigates the possible origin of the transiting giant planet WD1856+534 b around a white dwarf through high-eccentricity migration driven by the Lidov-Kozai effect. It demonstrates the significance of secular inclination resonance in the system's overall architecture and the role of other factors in influencing planet migration.