Nodal Precession and Tidal Evolution of KELT-9 b and WASP-33 b

Hot Jupiters provide important insights into planetary formation, migration, atmospheric composition, and star-planet tidal interactions. Of special interest are Hot Jupiters with strongly misaligned orbits to their host stars’ spin axis, which generally induces strong nodal precession of the planetary orbits, measurable via the Doppler Tomography technique. Here we present new results for the nodal precession of KELT-9 b, derived from new PEPSI/LBT observations and archival data covering a time span of 7 years. We measure the stellar gravitational quadrupole moment, J2, the stellar oblateness and spin rate, and true spin-orbit misalignment to a high degree of accuracy. We confirm the validity of our methodology by also analyzing the previously studied WASP-33 system, using new PEPSI/LBT observations and archival data covering a time span of 11 years. We conclude that both KELT-9 b and WASP-33 b will cease to transit their host stars by the end of the 21^st century. Based on their tidal dynamics, we estimate the expected remaining life spans of both planets as well as speculate on their likely dynamical origins.