Abstract
Abstract We use results of shallow-water magnetohydrodynamics to place estimates on the minimum magnetic field strengths required to cause atmospheric wind variations (and therefore westward-venturing hotspots) for a data set of hot Jupiters (HJs), including HAT-P-7b, CoRoT-2b, Kepler-76, WASP-12b, and WASP-33b, on which westward hotspots have been observationally inferred. For HAT-P-7b and CoRoT-2b our estimates agree with past results; for Kepler-76b we find that the critical dipolar magnetic field strength, over which the observed wind variations can be explained by magnetism, lies between 4 G and 19 G; for WASP-12b and WASP-33b westward hotspots can be explained by 1 G and 2 G dipolar fields, respectively. Additionally, to guide future observational missions, we identify 61 further HJs that are likely to exhibit magnetically driven atmospheric wind variations and predict these variations are highly likely in ∼40 of the hottest HJs.
Highlights
Equatorial temperature maxima in the atmospheres of hot Jupiters (HJs) are generally found eastward of the substellar point (e.g., Harrington et al 2006; Cowan et al 2007; Knutson et al 2007, 2009)
For HAT-P-7b and CoRoT-2b our estimates agree with past results; for Kepler-76b we find that the critical dipolar magnetic field strength, over which the observed wind variations can be explained by magnetism, lies between 4 G and 19 G; for WASP-12b and WASP-33b westward hotspots can be explained by 1 G and 2 G dipolar fields respectively
We have applied the theory developed in Hindle et al (2021) to a dataset of HJs to estimate the critical magnetic field strengths Bdip,crit and Bφ,crit, beyond which strong toroidal fields cause westward hotspots
Summary
Equatorial temperature maxima (hotspots) in the atmospheres of hot Jupiters (HJs) are generally found eastward (prograde) of the substellar point (e.g., Harrington et al 2006; Cowan et al 2007; Knutson et al 2007, 2009). Thermal phase curve measurements from Spitzer have found westward hotspots on the UHJ WASP-12b (Bell et al 2019) and the cooler CoRoT-2b (Dang et al 2018); and optical phase curve measurements from TESS found westward brightspot offsets on the UHJ WASP-33b (von Essen et al 2020) Three explanations for these observations have been proposed: cloud asymmetries confounding optical measurements (Demory et al 2013; Lee et al 2016; Parmentier et al 2016); non-synchronous rotation (Rauscher & Kempton 2014); and magnetism (Rogers 2017). These conditions can be used to constrain the magnetic field strengths of UHJs
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