Global 3D simulation of the upper atmosphere of HD189733b and absorption in metastable HeI and Ly{\alpha} lines

TL;DR

This study uses 3D hydrodynamic simulations to analyze the upper atmosphere of HD189733b, focusing on hydrogen and helium absorption lines, and explores how stellar activity influences observed spectral features.

Contribution

It presents a self-consistent 3D model of the exoplanet's atmosphere, constrains helium abundance, and examines the effects of stellar wind and radiation on absorption profiles.

Findings

The upper atmosphere's escape rate is near energy-limited with reduced Lya cooling.

Helium abundance in the upper atmosphere is constrained to He/H~0.005.

Moderate stellar wind causes about 7% Lya absorption within the Roche lobe.

Abstract

A 3D fully self-consistent multi-fluid hydrodynamic aeronomy model is applied to simulate the hydrogen-helium expanding upper atmosphere of the hot Jupiter HD189733b, and related absorption in the Lya line and the 10830 A line of metastable helium. We studied the influence of a high-energy stellar flux, stellar wind, and Lya cooling to reproduce the available observations. We found that to fit the width of the absorption profile in 10830 A line the escaping upper atmosphere of planet should be close to the energy limited escape achieved with a significantly reduced Lya cooling at the altitudes with HI density higher than 3*10^6 cm^-3. Based on the preformed simulations, we constrain the helium abundance in the upper atmosphere of HD189733b by a rather low value of He/H~0.005. We show that under conditions of a moderate stellar wind similar to that of the Sun the absorption of Lya line takes place mostly within the Roche lobe due to thermal broadening at a level of about 7%. At an order of magnitude stronger wind, a significant absorption of about 15% at high blue shifted velocities of up to 100 km/s is generated in the bowshock region, due to Doppler broadening. These blue shifted velocities are still lower than those (~200 km/s) detected in one of the observations. We explain the differences between performed observations, though not in all the details, by the stellar activity and the related fluctuations of the ionizing radiation (in case of 10830 A line), and stellar wind (in case of Lya line).