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

Wang, Lile and Dai, Fei (2021) Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. II. WASP-107b, Stellar Wind, Radiation Pressure, and Shear Instability. Astrophysical Journal, 914 (2). Art. No. 99. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20210628-191053934

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Abstract

This paper presents simulations of the metastable helium (He*) observations of WASP-107b, so far the highest signal-to-noise ratio detection that is confirmed by three different instruments. We employ full 3D hydrodynamics coupled with coevolving nonequilibrium thermochemistry and ray-tracing radiation, predicting mass-loss rates, temperature profiles, and synthetic He* line profiles and light curves from first principles. We find that a stellar wind stronger than solar is demanded by the observed heavily blueshifted line profile and asymmetric transit light curve. Radiation pressure can be important for Lyα observations, but not He*. Our model finds that WASP-107b is losing mass at a rate of Ṁ ≃ 1.0 x 10⁻⁹ M_⊕ yr⁻¹. Although Ṁ varies by <1% given constant wind and irradiation from the host, shear instabilities still emerge from wind impacts, producing ~10% fluctuations of He* transit depths over hour-long timescales. The common assumption that He* transit depth indicates the fluctuation of Ṁ is problematic. The trailing tail is more susceptible than planet adjacency to the shear instabilities; thus, the line profile is more variable in the blueshifted wing, while the transit light curve is more variable after midtransit. We stress that the synergy between Lyα (higher altitudes, lower density) and He* (lower altitudes, higher density) transit observations, particularly simultaneous ones, yields better understanding of planetary outflows and stellar wind properties.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/abf1edDOIArticle
https://arxiv.org/abs/2101.00045arXivDiscussion Paper
ORCID:
AuthorORCID
Wang, Lile0000-0002-6540-7042
Dai, Fei0000-0002-8958-0683
Additional Information:© 2021. The American Astronomical Society. Received 2020 December 18; revised 2021 March 21; accepted 2021 March 24; published 2021 June 21. This work is supported by the Center for Computational Astrophysics of the Flatiron Institute and the Division of Geological and Planetary Sciences of the California Institute of Technology. L.W. acknowledges the computing resources provided by the Simons Foundation and the San Diego Supercomputer Center. We thank our colleagues (in alphabetical order) Philip Armitage, Zhuo Chen, Jeremy Goodman, Xinyu Li, Mordecai Mac-Low, Songhu Wang, and Andrew Youdin, for helpful discussions and comments. We particularly thank the anonymous referee for the constructive comments and suggestions.
Funders:
Funding AgencyGrant Number
Flatiron InstituteUNSPECIFIED
Caltech Division of Geological and Planetary SciencesUNSPECIFIED
Subject Keywords:Exoplanet atmospheres; Exoplanet evolution; Exoplanet astronomy; Astrochemistry; Hydrodynamical simulations; Astronomical simulations; Hydrodynamics
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet evolution (491); Exoplanet astronomy (486); Astrochemistry (75); Hydrodynamical simulations (767); Astronomical simulations (1857); Hydrodynamics (1963)
Record Number:CaltechAUTHORS:20210628-191053934
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210628-191053934
Official Citation:Lile Wang and Fei Dai 2021 ApJ 914 99
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109633
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:28 Jun 2021 21:45
Last Modified:28 Jun 2021 21:45

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