Article

The Warm Neptune GJ 3470b Has a Polar Orbit

Guðmundur StefánssonDepartment of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA; [email protected]Suvrath MahadevanCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USACristóbal PetrovichInstituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, ChileJoshua N. WinnDepartment of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA; [email protected]Shubham KanodiaCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USASarah MillhollandDepartment of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA; [email protected]Marissa ManeyHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USACaleb I. CañasCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAJohn P. WisniewskiHomer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019, USAPaul RobertsonDepartment of Physics & Astronomy, The University of California, Irvine, Irvine, CA 92697, USAJoe P. NinanCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAEric B. FordCenter for Astrostatistics, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAChad F. BenderSteward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USACullen H. BlakeDepartment of Physics and Astronomy, University of Pennsylvania, 209 S 33rd Street, Philadelphia, PA 19104, USAH. M. CeglaDepartment of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UKWilliam D. CochranCenter for Planetary Systems Habitability, The University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USAScott A. DiddamsDepartment of Physics, 390 UCB, University of Colorado, Boulder, CO 80309, USAJiayin DongCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAMichael EndlCenter for Planetary Systems Habitability, The University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USAConnor FredrickDepartment of Physics, University of Colorado, 2000 Colorado Avenue, Boulder, CO 80309, USASamuel HalversonJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USAFred HeartyCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USALeslie HebbDepartment of Physics, Hobart and William Smith Colleges, 300 Pulteney Street, Geneva, NY 14456, USATeruyuki HiranoAstrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanAndrea S. J. LinCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USASarah E. LogsdonNSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Avenue, Tucson, AZ 85719, USAEmily LubarDepartment of Astronomy, The University of Texas at Austin, 2515 Speedway, Austin, TX 78712, USAMichael W. McElwainExoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAAndrew J. MetcalfDepartment of Physics, University of Colorado, 2000 Colorado Avenue, Boulder, CO 80309, USAAndrew MonsonCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAJayadev RajagopalNSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Avenue, Tucson, AZ 85719, USALawrence W. RamseyCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USAArpita RoyDepartment of Physics and Astronomy, Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, USAChristian SchwabDepartment of Physics and Astronomy, Macquarie University, Balaclava Road, North Ryde, NSW 2109, AustraliaHeidi SchweikerNSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Avenue, Tucson, AZ 85719, USARyan C. TerrienCarleton College, One North College Street, Northfield, MN 55057, USAJason T. WrightCenter for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA, 16802, USA

2022en

ABI

Abstract

Abstract The warm Neptune GJ 3470b transits a nearby ( d = 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>98</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>15</mml:mn> <mml:mspace width="0.33em"/> <mml:mo>◦</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> and a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.85</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.27</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>km</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ψ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>9</mml:mn> <mml:mspace width="0.33em"/> <mml:mo>◦</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>0.0022</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.0011</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">m</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>day</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere.

Identifiers

DOI: 10.3847/2041-8213/ac6e3c

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Cited by 20 references

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