Obliquity Constraints for the Extremely Eccentric Sub-Saturn Kepler-1656 b
Huber, Daniel; Howard, Andrew W.; Petigura, Erik A.; Rubenzahl, Ryan A.; Weiss, Lauren M.; Wright, Jason T.; Winn, Joshua N.; Holden, Bradford; Dai, Fei; Angelo, Isabel; Laher, Russ R.; Fulton, Benjamin; Wang, Sharon X.; Halverson, Samuel; Roy, Arpita; Schwab, Christian; Isaacson, Howard; Stefánsson, Guđmundur; Gibson, Steven R.; Householder, Aaron; Shaum, Abby P.; Brodheim, Max; Deich, William; Hill, Grant M.; Lanclos, Kyle; Payne, Joel N.; Walawender, Josh; Petrovich, Cristobal
United States, Chile, Netherlands, Australia, China
Abstract
The orbits of close-in exoplanets provide clues to their formation and evolutionary history. Many close-in exoplanets likely formed far out in their protoplanetary disks and migrated to their current orbits, perhaps via high-eccentricity migration (HEM), a process that can also excite obliquities. A handful of known exoplanets are perhaps caught in the act of HEM, as they are observed on highly eccentric orbits with tidal circularization timescales shorter than their ages. One such exoplanet is Kepler-1656 b, which is also the only known nongiant exoplanet (<100 M ⊕) with an extreme eccentricity (e = 0.84). We measured the sky-projected obliquity of Kepler-1656 b by observing the Rossiter–McLaughlin effect during a transit with the Keck Planet Finder. Our data are consistent with an aligned orbit but are also consistent with moderate misalignment with λ < 50° at 95% confidence, with the most likely solution of