Atmospheric escape in hot Jupiters under sub-Alfvénic interactions

Abstract

Hot Jupiters might reside inside the Alfvén surface of their host star wind, where the stellar wind is dominated by magnetic energy. The implications of such a sub-Alfvénic environment for atmospheric escape are not fully understood. Here, we employ 3-D radiation-magnetohydrodynamic simulations and Lyman-$\alpha$ transit calculations to investigate atmospheric escape properties of magnetised hot Jupiters. By varying the planetary magnetic field strength ($B_p$) and obliquity, we find that the structure of the outflowing atmosphere transitions from a magnetically unconfined regime, where a tail of material streams from the nightside of the planet, to a magnetically confined regime, where material escapes through the polar regions. Notably, we find an increase in the planet escape rate with $B_p$ in both regimes, with a local decrease when the planet transitions from the unconfined to the confined regime. Contrary to super-Alfvénic interactions, which predicted two polar outflows from the planet, our sub-Alfvénic models show only one significant polar outflow. In the opposing pole, the planetary field lines connect to the star. Finally, our synthetic Ly-$\alpha$ transits show that both the red-wing and blue-wing absorptions increase with $B_p$. Furthermore, there is a degeneracy between $B_p$ and the stellar wind mass-loss rate when considering absorption of individual Lyman-$\alpha$ wings. This degeneracy can be broken by considering the ratio between the blue-wing and the red-wing absorptions, as stronger stellar winds result in higher blue-to-red absorption ratios. We show that, by using the absorption ratios, Lyman-$\alpha$ transits can probe stellar wind properties and exoplanetary magnetic fields.

16 pages, 11 figures (including 2 in the appendix), 2 tables, accepted for publication in MNRAS

References in corpus (26)

• Atmospheric Escape from Hot Jupiters
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Magnetic moment and plasma environment of HD 209458b as determined from Ly$\alpha$ observations
• 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
• The long egress of GJ~436b's giant exosphere
• Magnetic field strengths of hot Jupiters from signals of star-planet interactions
• What Sustained Multi-Disciplinary Research Can Achieve: The Space Weather Modeling Framework
• Atmosphere Expansion and Mass Loss of Close-Orbit Giant Exoplanets heated by Stellar XUV. II. Effects of Planetary Magnetic Field, Structuring of inner Magnetosphere
• The search for radio emission from the exoplanetary systems 55 Cancri, $\upsilon$ Andromedae, and $\tau$ Boötis using LOFAR beam-formed observations
• Stellar Winds on the Main-Sequence I: Wind Model
• Estimating the magnetic field strength in hot Jupiters
• Planetary Magnetic Field Control of Ion Escape from Weakly Magnetized Planets
• Signatures of Strong Magnetization and Metal-Poor Atmosphere for a Neptune-Size Exoplanet
• Two regimes of interaction of a Hot Jupiter's escaping atmosphere with the stellar wind and generation of energized atomic hydrogen corona
• Effects of the stellar wind on the Ly-alpha transit of close-in planets
• Magnetic Field of the Eclipsing M Dwarf Binary YY Gem
• The dichotomy of atmospheric escape in AU Mic b
• The Effects of Magnetic Fields on Observational Signatures of Atmospheric Escape in Exoplanets: Double Tail Structures
• The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b
• On possible types of magnetospheres of hot Jupiters
• Star-Planet Interaction: Wave Structures and Wing-Wing Interaction
• A dynamo simulation generating Saturn-like small magnetic dipole tilts

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