The TESS–Keck Survey. IV. A Retrograde, Polar Orbit for the Ultra-low-density, Hot Super-Neptune WASP-107b

Abstract

We measured the Rossiter-McLaughlin effect of WASP-107b during a single transit with Keck/HIRES. We found the sky-projected inclination of WASP-107b's orbit, relative to its host star's rotation axis, to bedegrees. This confirms the misaligned/polar orbit that was previously suggested from spot-crossing events and adds WASP-107b to the growing population of hot Neptunes in polar orbits around cool stars. WASP-107b is also the fourth such planet to have a known distant planetary companion. We examined several dynamical pathways by which this companion could have induced such an obliquity in WASP-107b. We find that nodal precession and disk dispersal-driven tilting can both explain the current orbital geometry while Kozai-Lidov cycles are suppressed by general relativity. While each hypothesis requires a mutual inclination between the two planets, nodal precession requires a much larger angle, which for WASP-107 is on the threshold of detectability with future Gaia astrometric data. As nodal precession has no stellar type dependence, but disk dispersal-driven tilting does, distinguishing between these two models is best done on the population level. Finding and characterizing more extrasolar systems like WASP-107 will additionally help distinguish whether the distribution of hot-Neptune obliquities is a dichotomy of aligned and polar orbits or if we are uniformly sampling obliquities during nodal precession cycles.

Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. II. WASP-107b, Stellar Wind, Radiation Pressure, and Shear Instability

“…Specifically for WASP-107, Anderson et al (2017) reported a K6 host star with a mass of M * = 0.69 M e , a radius of R * = 0.66 R e , and an effective temperature of T *,eff = 4430 K. Planet b orbits its host on a near-circular but polar orbit (Dai & Winn 2017, C. Piaulet et al 2021Rubenzahl et al 2021). The semimajor axis is a = 0.055 au where the equilibrium temperature is T eq = 740 K; the transit light curve indicates a small impact parameter (b = 0.07 Dai & Winn 2017).…”

“…Dai & Winn (2017) suspected that the planet is on a polar orbit owing to the lack of repeating spot-crossing events. More recently, a Rossiter-McLaughlin measurement by Rubenzahl et al (2021) confirmed this suspicion and thus demands a dynamically hot formation and evolution pathway that may involve the nontransiting planet 107c (P ∼ 1100 days,M i sin Å M 110 ; C. Piaulet et al 2021). These reasons render WASP-107b a unique and interesting system.…”

Long-period Jovian Tilts the Orbits of Two sub-Neptunes Relative to Stellar Spin Axis in Kepler-129

“…Several exoplanets systems that host spin-orbit misaligned close-in small planets have been found to contain an distant giant planet, e.g., HAT-P-11 (Winn et al 2010;Yee et al 2018), π Men (Jones et al 2002;Kunovac Hodžić et al 2021), Kepler-56 (Huber et al 2013Otor et al 2016), andWASP-107 (Piaulet et al 2021;Rubenzahl et al 2021). Kepler-129 joins their ranks.…”

“…The alignment between solar spin and planetary orbital axes is considered to result from the protoplanetary disk where these planets formed and has been maintained throughout the history of the solar system (Kant 1755;de Laplace 1796). On the contrary, spin-orbit misalignment has been found in dozens of exoplanet systems (e.g., Winn et al 2010;Huber et al 2013;Bourrier et al 2018;Yee et al 2018;Kamiaka et al 2019;Rubenzahl et al 2021), suggesting a different formation pathway or the occurrence of dynamical events in those systems. Measuring the spin-orbit angle therefore helps to understand the formation and evolution of planetary systems.…”

TESS-Keck Survey. V. Twin Sub-Neptunes Transiting the Nearby G Star HD 63935

“…TKS is a consortium performing precise RV (PRV) followup of TESS planet candidates (Dalba et al 2020;Dai et al 2020;Rubenzahl et al 2021;Weiss et al 2021). One of our group's primary science goals is to measure a diverse set of planet masses at high enough precision to be suitable for atmospheric characterization (Batalha et al 2019), particularly with the James Webb Space Telescope (JWST), which is what led us to observe HD 63935.…”