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Title: Magnetospheres of hot Jupiters: hydrodynamic models and ultraviolet absorption
Authors: Alexander, Richard
Wynn, Graham A.
Mohammed, H.
Nichols, Jonathan D.
Ercolano, B.
First Published: 31-Dec-2015
Publisher: Oxford University Press (OUP)
Citation: Monthly Notices of the Royal Astronomical Society, 2016, 456 (3): 2766-2778.
Abstract: We present hydrodynamic simulations of stellar wind–magnetosphere interactions in hot Jupiters such as WASP-12b. For fiducial stellar wind rates, we find that a planetary magnetic field of a few G produces a large magnetospheric cavity, which is typically 6–9 planetary radii in size. A bow shock invariably forms ahead of the magnetosphere, but the pre-shock gas is only mildly supersonic (with typical Mach numbers of ≃1.6–1.8) so the shock is weak. This results in a characteristic signature in the ultraviolet (UV) light curve: a broad absorption feature that leads the optical transit by 10–20 per cent in orbital phase. The shapes of our synthetic light curves are consistent with existing observations of WASP-12b, but the required near-UV optical depth (τ ∼ 0.1) can only be achieved if the shocked gas cools rapidly. We further show that radiative cooling is inefficient, so we deem it unlikely that a magnetospheric bow shock is responsible for the observed near-UV absorption. Finally, we apply our model to two other well-studied hot Jupiters (WASP-18b and HD 209458b), and suggest that UV observations of more massive short-period planets (such as WASP-18b) will provide a straightforward test to distinguish between different models of circumplanetary absorption.
DOI Link: 10.1093/mnras/stv2867
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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