Nicholas Saunders (University of Hawai'i) - CU Boulder APS Friday Lunch Seminar 02/23/24

Orbital Evolution of Giant Planets After the Main Sequence

Nicholas Saunders (University of Hawai'i)

Giant planets on close-in orbits (hot Jupiters) are a rare result of planetary system formation, but their orbital properties are sensitive to otherwise invisible processes that govern the formation of all planets. Despite their relatively long observational history, it remains unclear how hot Jupiters arrive at such small separations from their host stars. The alignment between the stellar spin-axis and the orbital plane of planets (the obliquity) is a key diagnostic for understanding planet formation. Observations have revealed a dichotomy in the obliquities of hot Jupiters orbiting stars on either side of the Kraft break (6250 K), but the pathway and timescale for spin-orbit alignment and its relation to overall planetary system evolution remains unclear. Subgiant stars which have recently crossed the Kraft break as they cool and evolve away from the main sequence provide an ideal opportunity to investigate this spin-orbit dichotomy, potentially revealing the pathway and timescale for spin-orbit alignment. Here, I will present a spin-orbit obliquity analysis of several new hot Jupiters we recently discovered using the ‘giants’ pipeline developed to identify new evolved planetary systems in TESS full-frame images. We find that hot Jupiters orbiting subgiants that crossed the Kraft break are well aligned with the spin-axis of their host stars, indicating efficient tidal realignment after the emergence of a stellar convective envelope. Through a focused study of evolved hot Jupiter systems, we can shed light on the star-planet interactions that influence the formation and evolution of planetary systems in general.