Metastable Helium Absorptions with 3D Hydrodynamics and Self-consistent Photochemistry. II. WASP-107b, Stellar Wind, Radiation Pressure, and Shear Instability
- Creators
- Wang, Lile
- Dai, Fei
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.
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.Attached Files
Published - Wang_2021_ApJ_914_99.pdf
Submitted - 2101.00045.pdf
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Additional details
- Eprint ID
- 109633
- Resolver ID
- CaltechAUTHORS:20210628-191053934
- Flatiron Institute
- Caltech Division of Geological and Planetary Sciences
- Created
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2021-06-28Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field