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

Rubenzahl, Ryan A. and Dai, Fei and Howard, Andrew W. and Chontos, Ashley and Giacalone, Steven and Lubin, Jack and Rosenthal, Lee J. and Isaacson, Howard and Batalha, Natalie M. and Crossfield, Ian J. M. and Dressing, Courtney and Fulton, Benjamin and Huber, Daniel and Kane, Stephen R. and Petigura, Erik A. and Robertson, Paul and Roy, Arpita and Weiss, Lauren M. and Beard, Corey and Hill, Michelle L. and Mayo, Andrew and Močnik, Teo and Murphy, Joseph M. Akana and Scarsdale, Nicholas (2021) TESS–Keck Survey. IV. A Retrograde, Polar Orbit for the Ultra-low-density, Hot Super-Neptune WASP-107b. Astronomical Journal, 161 (3). Art. No. 119. ISSN 1538-3881. doi:10.3847/1538-3881/abd177.

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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 be |λ| = 118⁺³⁸₋₁₉ degrees. 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Rubenzahl, Ryan A.0000-0003-3856-3143
Dai, Fei0000-0002-8958-0683
Howard, Andrew W.0000-0001-8638-0320
Chontos, Ashley0000-0003-1125-2564
Giacalone, Steven0000-0002-8965-3969
Lubin, Jack0000-0001-8342-7736
Rosenthal, Lee J.0000-0001-8391-5182
Isaacson, Howard0000-0002-0531-1073
Batalha, Natalie M.0000-0002-7030-9519
Crossfield, Ian J. M.0000-0002-1835-1891
Dressing, Courtney0000-0001-8189-0233
Fulton, Benjamin0000-0003-3504-5316
Huber, Daniel0000-0001-8832-4488
Kane, Stephen R.0000-0002-7084-0529
Petigura, Erik A.0000-0003-0967-2893
Robertson, Paul0000-0003-0149-9678
Roy, Arpita0000-0001-8127-5775
Weiss, Lauren M.0000-0002-3725-3058
Beard, Corey0000-0001-7708-2364
Hill, Michelle L.0000-0002-0139-4756
Mayo, Andrew0000-0002-7216-2135
Močnik, Teo0000-0003-4603-556X
Murphy, Joseph M. Akana0000-0001-8898-8284
Scarsdale, Nicholas0000-0003-3623-7280
Additional Information:© 2021 The American Astronomical Society. Received 2020 November 10; revised 2020 December 1; accepted 2020 December 4; published 2021 February 15. We thank Konstantin Batygin, Cristobol Petrovich, and Jerry Xuan for helpful comments and productive discussions on orbital dynamics, and Josh Winn for constructive feedback that improved this manuscript. R.A.R. and A.C. acknowledge support from the National Science Foundation through the Graduate Research Fellowship Program (DGE 1745301, DGE 1842402). C.D.D. acknowledges the support of the Hellman Family Faculty Fund, the Alfred P. Sloan Foundation, the David & Lucile Packard Foundation, and the National Aeronautics and Space Administration via the TESS Guest Investigator Program (80NSSC18K1583). I.J.M.C. acknowledges support from the NSF through grant AST-1824644. D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379), and the National Science Foundation (AST-1717000). E.A.P. acknowledges the support of the Alfred P. Sloan Foundation. L.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP Grant 80NSSC19K0597. We thank the time assignment committees of the University of California, the California Institute of Technology, NASA, and the University of Hawai'i for supporting the TESS–Keck Survey with observing time at the W. M. Keck Observatory. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We recognize and acknowledge the cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are deeply grateful to have the opportunity to conduct observations from this mountain. Facility: Keck I (HIRES). - Software: emcee (Foreman-Mackey et al. 2013), (Foreman-Mackey 2016), REBOUND/REBOUND/x (Rein & Liu 2012; Tamayo et al. 2019), SciPy (Virtanen et al. 2020), NumPy (Harris et al. 2020), Matplotlib (Hunter 2007).
Group:Astronomy Department
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1745301
NSF Graduate Research FellowshipDGE-1842402
Hellman Family Faculty FundUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Beatrice Watson Parrent FellowshipUNSPECIFIED
Subject Keywords:Exoplanet dynamics; Orbit determination; Radial velocity
Issue or Number:3
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet dynamics (490); Orbit determination (1175); Radial velocity (1332)
Record Number:CaltechAUTHORS:20210217-111259280
Persistent URL:
Official Citation:Ryan A. Rubenzahl et al 2021 AJ 161 119
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108091
Deposited By: Tony Diaz
Deposited On:18 Feb 2021 18:47
Last Modified:16 Nov 2021 19:08

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