Global 3D Simulation of the Upper Atmosphere of HD189733b and Absorption in Metastable He i and Lyα Lines

Abstract

Abstract A 3D fully self-consistent multifluid hydrodynamic aeronomy model is applied to simulate the hydrogen-helium expanding upper atmosphere of the hot Jupiter HD189733b, and related absorption in the Lyα line and the 10830 Å line of metastable helium. We studied the influence of a high-energy stellar flux, a stellar wind, and Lyα cooling to reproduce the available observations. We found that to fit the width of the absorption profile of the 10830 Å line the escaping upper atmosphere of the planet should be close to the energy-limited escape achieved with significantly reduced Lyα cooling at the altitudes with an H i density higher than 3 × 106 cm−3. Based on the performed simulations, we constrain the helium abundance in the upper atmosphere of HD189733b to be a rather low value of He/H ∼ 0.005. We show that under the conditions of a moderate stellar wind similar to that of the Sun the absorption of the Lyα line takes place mostly within the Roche lobe due to thermal broadening at a level of about 7%. For an order of magnitude stronger wind, a significant absorption of about 15% at high blueshifted velocities of up to 100 km s−1 is generated in the bowshock region, due to Doppler broadening. These blueshifted velocities are still lower than those (∼200 km s−1) detected in one of the observations. We explain the differences between the performed observations, though not in all of the details, by stellar activity and the related fluctuations of the ionizing radiation (in the case of the 10830 Å line), and the stellar wind (in the case of the Lyα line).