Space environment and magnetospheric Poynting fluxes of the exoplanet $\tau$ Boötis b

Abstract

Context: The first tentative detection of a magnetic field on the Hot Jupiter type exoplanet $\tau$ Boötis b was recently reported by Turner et al. (2021). The magnetic field was inferred from observations of circularly-polarized radio emission obtained with the LOFAR telescopes. The radio emission is possibly a consequence of the interaction of the surrounding stellar wind with the planet's magnetic field. Methods: We perform magnetohydrodynamic simulations of the space environment around $\tau$ Boötis b and its interaction with the stellar wind using the PLUTO code. We study the magnetospheric energy fluxes and effects of different magnetic field orientations in order to understand the physical processes which cause energy fluxes leading to the observed radio emission given the proposed magnetic field strength in Turner et al. (2021). Furthermore we study the effect of stellar wind density and pressure on magnetospheric energy fluxes given the uncertainty of extrasolar stellar wind predictions. Results: We find in our simulations that the interaction is most likely super--Alfvénic and energy fluxes generated by the stellar wind--planet interaction are consistent with the observed radio powers. Magnetospheric Poynting fluxes are of the order of 1-8 $\times 10^{18}$ W for open, semi-open and closed magnetospheres. The Poynting fluxes are energetically consistent with the radio powers in Turner et al. (2021) for a magnetospheric Poynting flux-to-radio efficiency $>10^{-3}$ when the magnetic fields of the planet and star are aligned. In case of lower efficiency factors the magnetospheric emission scenario is according to the parameter space modeled in this study not powerful enough. In case of a magnetic polarity reversal of the host star towards an anti-aligned field configuration, expected radio powers in the magnetospheric emission scenario fall below the observable threshold.

Accepted for publication in Astronomy and Astrophysics (08.01.2023)

References in corpus (20)

• The On/Off Nature of Star-Planet Interactions
• Magnetic cycles of the planet-hosting star tauBootis
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Predicting low-frequency radio fluxes of known extrasolar planets
• Magnetic moment and plasma environment of HD 209458b as determined from Ly$\alpha$ observations
• Magnetic field strengths of hot Jupiters from signals of star-planet interactions
• Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars
• On the environment surrounding close-in exoplanets
• The search for radio emission from the exoplanetary systems 55 Cancri, $\upsilon$ Andromedae, and $\tau$ Boötis using LOFAR beam-formed observations
• On the diversity of magnetic interactions in close-in star-planet systems
• The shocking transit of WASP-12b: Modelling the observed early ingress in the near ultraviolet
• Planet-induced radio emission from the coronae of M dwarfs: the case of Prox Cen and AU Mic
• Radio emission from exoplanets: the role of the stellar coronal density and magnetic field strength
• A comprehensive statistical assessment of star-planet interaction
• How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability
• On possible types of magnetospheres of hot Jupiters
• The Rise of ROME. I. A Multiwavelength Analysis of the Star-Planet Interaction in the HD 189733 System
• MHD study of planetary magnetospheric response during extreme solar wind conditions: Earth and exoplanet magnetospheres applications
• Magnetic field and chromospheric activity evolution of HD75332: a rapid magnetic cycle in an F star without a hot Jupiter
• Radio emission in Mercury magnetosphere

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