Stellar Wind Effect on the Atmospheric Escape of Hot Jupiters and their Ly-$\alpha$ and H$\alpha$ transits

TL;DR

This study uses radiation-hydrodynamics simulations to explore how stellar winds influence atmospheric escape and observable transit signals of hot Jupiters, highlighting the importance of both Ly-$ ext{α}$ and H$ ext{α}$ lines.

Contribution

It provides a self-consistent model of planetary outflows interacting with stellar winds, revealing their impact on transit signatures and atmospheric mass-loss rates.

Findings

Strong stellar winds confine planetary outflows, reducing Ly-$ ext{α}$ transit depth.

Wind effects on H$ ext{α}$} are minimal due to the lower atmospheric contribution.

Atmospheric mass-loss rate remains roughly unaffected by wind strength.

Abstract

Atmospheric escape of close-in exoplanets can be driven by high energy radiation from the host star. The planetary outflows interacting with the stellar wind may generate observable transit signals that depend on the strength of the stellar wind. We perform detailed radiation-hydrodynamics simulations of the atmospheric escape of hot Jupiters with including the wind from the host star in a self-consistent, dynamically coupled manner. We show that the planetary outflow is shaped by the balance between its thermal pressure and the ram pressure of the stellar wind. We use the simulation outputs to calculate the Lyman-$\alpha$ and H$\alpha$ transit signatures. Strong winds can confine the outflow and decrease the Lyman-$\alpha$ transit depth. Contrastingly, the wind effect on H$\alpha$ is weak because of the small contribution from the uppermost atmosphere of the planet. Observing both of the lines is important to understand the effect of the UV radiation and wind from the host. The atmospheric mass-loss rate is approximately independent of the strength of the wind. We also discuss the effect of the coronal mass ejections on the signatures. We argue that around M dwarfs the effect can be significant in every transit.