Star-planet magnetic interactions in photoevaporating exoplanets: enhanced power due to atmospheric escape

Abstract

Observations of periodic stellar activity near the transit phase of a close-in exoplanet provide evidence of star-planet magnetic interactions (SPMI), similar to the magnetic coupling between Jupiter and its moons. Comparing the power associated with SPMI signals to analytical theories offers a way to constrain exoplanetary magnetic fields, but models based on moon-magnetosphere analogs often underpredict observed energy fluxes. Unlike moons, many close-in exoplanets are extended, highly irradiated gas giants undergoing significant photoevaporation. However, it is not known how atmospheric escape influences the star-planet magnetic coupling. Here, we present three-dimensional radiation magneto-hydrodynamic simulations that simultaneously model planetary evaporation and SPMI in a hot Jupiter planet embedded in a magnetised stellar wind. Our simulations reveal the formation of magnetic structures known as Alfvén wings, which transport magnetic energy away from the planet. When the dayside mass-loss rate ${\dot{M}}_d$ of the planet lies below a threshold ${\dot{M}}_0$ defined by pressure balance between the planetary and stellar winds (${\dot{M}}_d\le {\dot{M}}_0$), the maximal power delivered to the star matches predictions from the Alfvén wing model. For higher escape rates, the planetary outflow opens additional magnetic flux, and the SPMI power increases proportionally with $({\dot{M}}_d/{\dot{M}}_0{)}^{1/2}$. Applying this scaling law to the HD18973 system, we find that a $50$ G planet could reproduce the observed power if ${\dot{M}}_d\sim 5\times 10^{11}$ g/s. Although this signal likely represents only a fraction of the total power, additional mechanisms could amplify the energy budget. These results show that photoevaporating exoplanets in sub-Alfvénic orbits constitute promising targets for SPMI observations.

18 pages, 14 figures, 4 tables. Version accepted for publication in MNRAS, after incorporating referee's comments

References in corpus (33)

• Atmospheric Escape from Hot Jupiters
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• The On/Off Nature of Star-Planet Interactions
• The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733
• Atmospheric escape from HD 189733b observed in HI Lyman-alpha: detailed analysis of HST/STIS September 2011 observations
• Magnetically controlled mass loss from extrasolar planets in close orbits
• Magnetic field strengths of hot Jupiters from signals of star-planet interactions
• Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b
• The search for radio emission from the exoplanetary systems 55 Cancri, $\upsilon$ Andromedae, and $\tau$ Boötis using LOFAR beam-formed observations
• Estimating the magnetic field strength in hot Jupiters
• Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune
• Coherent radio bursts from known M-dwarf planet host YZ Ceti
• One year of AU Mic with HARPS: II -- stellar activity and star-planet interaction
• Age dependence of wind properties for solar type stars: a 3d study
• Assessing magnetic torques and energy fluxes in close-in star-planet systems
• Effects of the stellar wind on the Ly-alpha transit of close-in planets
• Modelling the He I triplet absorption at 10830 Angstroms in the atmospheres of HD 189733 b and GJ 3470 b
• MOVES I. The evolving magnetic field of the planet-hosting star HD189733
• The Effects of Magnetic Fields on Observational Signatures of Atmospheric Escape in Exoplanets: Double Tail Structures
• The MOPYS project: A survey of 70 planets in search of extended He I and H atmospheres. No evidence of enhanced evaporation in young planets
• Using helium 10830 Å transits to constrain planetary magnetic fields
• The space weather around the exoplanet GJ 436 b. II. Stellar wind-exoplanet interactions
• MOVES V. Modelling star-planet magnetic interactions of HD 189733
• X-ray variability of HD 189733 across eight years of XMM-Newton observations
• Hydrodynamic atmospheric escape in HD 189733 b: Signatures of carbon and hydrogen measured with the Hubble Space Telescope
• Star-Planet Interactions: A Computational View
• Atmospheric escape in hot Jupiters under sub-Alfvénic interactions
• Star-Planet Interaction: Wave Structures and Wing-Wing Interaction
• Energetics of star-planet magnetic interactions: Novel insights from 3D modelling
• On stellar hotspots due to star-planet magnetic interactions: How much power can actually be transmitted to the chromosphere?
• Interaction of Trappist-1 exoplanets with coronal mass ejections: Joule heating, Poynting fluxes and the role of magnetic fields
• Induced-Flare Candidates from the TESS Mission