Axisymmetric Simulations of Hot Jupiter-Stellar Wind Hydrodynamic Interaction

TL;DR

This study uses axisymmetric hydrodynamic simulations to explore how hot Jupiter atmospheres interact with stellar winds, revealing different flow regimes and their effects on hydrogen absorption spectra.

Contribution

It introduces axisymmetric simulations including charge exchange and ionization processes to analyze planetary wind regimes and hydrogen absorption features.

Findings

High-temperature regime shows a supersonic planetary wind forming a tail.

Low-temperature regime results in wind suppression and mass loss via viscous interaction.

Hot hydrogen absorption is dominated by the tail at large impact parameters.

Abstract

Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyman-alpha transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.