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Constraints on the magnetic field strength of HAT-P-7 b and other hot giant exoplanets

Lookup NU author(s): Professor Tamara Rogers

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by Nature Publishing Group, 2017.

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Abstract

Observations of infrared and optical light curves of hot Jupiters have demonstrated that the peakbrightness is generally offset eastward from the substellar point [1,2]. This observation is consistentwith hydrodynamic numerical simulations that produce fast, eastward directed winds which advectthe hottest point in the atmosphere eastward of the substellar point [3,4]. However, recent continuousKepler measurements of HAT-P-7 b show that its peak brightness offset varies significantly intime, with excursions such that the brightest point is sometimes westward of the substellar point[5]. These variations in brightness offset require wind variability, with or without the presence ofclouds. While such wind variability has not been seen in hydrodynamic simulations of hot Jupiteratmospheres, it has been seen in magnetohydrodynamic (MHD) simulations [6]. Here we showthat MHD simulations of HAT-P-7 b indeed display variable winds and corresponding variabilityin the position of the hottest point in the atmosphere. Assuming the observed variability in HATP-7 b is due to magnetism we constrain its minimum magnetic field strength to be 6G. Similarobservations of wind variability on hot giant exoplanets, or lack thereof, could help constrain theirmagnetic field strengths. Since dynamo simulations of these planets do not exist and theoreticalscaling relations [7] may not apply, such observational constraints could prove immensely useful.

Publication metadata

Author(s): Rogers T

Publication type: Article

Publication status: Published

Journal: Nature Astronomy

Year: 2017

Volume: 1

Online publication date: 15/05/2017

Acceptance date: 06/04/2017

Date deposited: 16/06/2017

ISSN (electronic): 2397-3366

Publisher: Nature Publishing Group

URL: https://doi.org/10.1038/s41550-017-0131

DOI: 10.1038/s41550-017-0131

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