The impact of coronal mass ejections and flares on the atmosphere of the hot Jupiter HD189733b

Abstract

High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. For the exoplanet HD189733b, multiple observations in the Ly-$\alpha$ line have shown that atmospheric evaporation is variable, going from undetected to enhanced evaporation in a $1.5$-year interval. Coincidentally or not, when HD189733b was observed to be evaporating, a stellar flare had just occurred 8h prior to the observation. This led to the question of whether this temporal variation in evaporation occurred due to the flare, an unseen associated coronal mass ejection (CME), or even the effect of both simultaneously. In this work, we investigate the impact of flares (radiation), winds, and CMEs (particles) on the atmosphere of HD189733b using 3D radiation hydrodynamic simulations of atmospheric evaporation that self-consistently include stellar photon heating. We study four cases: first- the quiescent phase of the star including stellar wind, second- a flare, third- a CME, and fourth- a flare that is followed by a CME. Compared to the quiescent case, we find that the flare alone increases the evaporation rate by only 25%, while the CME leads to a factor of 4 increase in escape rate. We calculate Ly-$\alpha$ synthetic transits and find that the flare alone cannot explain the observed high blueshifted velocities seen in the Ly-$\alpha$ observation. The CME, however, leads to an increase in the velocity of the escaping atmosphere, enhancing the transit depth at high blueshifted velocities. While the effects of CMEs show a promising potential to explain the blueshifted line feature, our models are not able to fully explain the blueshifted transit depths, indicating that they might require additional physical mechanisms.

Accepted for publication in MNRAS, 14 pages, 9 figures

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