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Hot Jupiter Formation Clues from Three Extreme Solar Systems with the Keck Planet Finder

Presentation #200.06 in the session RV and Extreme Precision RV.

Published onApr 03, 2024
Hot Jupiter Formation Clues from Three Extreme Solar Systems with the Keck Planet Finder

Hot Jupiters have been known to exist for decades, yet the mechanisms by which they formed and evolved are not well understood. Clues to these mysteries are encoded in the planets’ present-day obliquities, the angle between the star’s rotation axis and the planet’s orbital plane. Extreme solar systems are often excellent probes of formation physics, as their unique dynamical architectures pinpoint plausible mechanisms. We report on obliquity measurements of three uniquely extreme solar systems using a new Doppler spectrometer, the Keck Planet Finder (KPF). KPF is a fiber-fed, ultra-stabilized (< 30 cm/s single measurement Doppler stability), high resolution (R~98,000) optical (445-870 nm) EPRV system recently commissioned at the W. M. Keck Observatory. KPF achieves < 100 ppm instrumental line profile stability, enabling detailed studies of stellar obliquities using the Reloaded Rossiter-McLaughlin technique. With KPF, we measured the obliquities of: i) KELT-18 b, an ultra-hot Jupiter on a polar orbit that likely underwent high-eccentricity migration and orbit tilting by a binary stellar companion. We also detected center to limb variations. ii) Kepler-1656 b, a sub-Saturn with a distant outer companion that despite its highly eccentric orbit appears to be aligned, strongly constraining eccentricity-exciting mechanisms. iii) Kepler-1658 b, an inspiraling planet (tidal decay timescale of 2.5 Myr) around an evolved star which appears to be aligned; since orbital decay and realignment happen on similar timescales, this planet likely formed in an aligned orbit around its star, which was hotter than the Kraft Break when on the main sequence. Together, these systems constrain exoplanet formation physics from three unique dimensions and paint a fuller picture of how close-in exoplanets attain their orbits.

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