The Escape of the Hydrogen-rich Atmosphere of Exoplanets: Mass-loss Rates and the Absorption of Stellar Lyα

Abstract

Since the mass loss rates are the function of the mean density of the planet and the stellar irradiation, we calculated about 450 models covering planets with different densities and stellar irradiation. Our results show that the mass loss rates are dependent on the stellar irradiation and the mean density. However, the mass loss rates predicted by the energy-limited equation are higher than that of hydrodynamic model when the XUV integrated flux is higher than ∼2×10 4 erg/cm 2 /s. The overestimation can be revised if the kinetic and thermal energy of the escaping atmosphere is included in the energy-limited equation. We found that the heating efficiencies are proportional to the product of the gravitational potential of the planet and the stellar irradiation. The mean absorption radii of stellar irradiation are 1.1-1.2 R p for the Jupiter-like planets while they vary in the range of 1.1-1.7 R p for the planets with smaller sizes. We evaluated the absorption of stellar Lyα by planetary atmosphere and found that the deeper Lyα absorptions tend to locate in the high stellar irradiation and low planetary mean density regions, and vice versa. Moreover, planets with mass loss rates higher than 10 11 g/s are likely to exhibit obvious absorptions. Finally, we suggested that the absorption levels are related to the inherent properties of the exoplanets. The planets with larger sizes (or lower mean density) show strong Lyα absorptions.Neptune-like and Earth-like planets tend to have weak Lyα absorptions because of their small sizes (or high densities).Subject headings: planets and satellites: atmosphere -planets and satellites: composition -planets and satellites: physical evolution R J are Neptune-like planets, 0.6-1.0 R J are Saturn-like planets. Finally, the planets with radius larger than 1.0 R J are Jupiter-like planets. Koskinen et al. (2007) suggests that the exoplanets with a separation smaller than 0.15AU will produce significant mass loss. Hence, we selected those planets that their separation are less than 0.1 AU. The separations are in the range of 0.01-0.09AU for Earth-like and Neptune-like planets, 0.04-0.07 AU for Saturn-like planets and 0.02-0.08AUfor Jupiter-like planets. The host stellar masses of each system are in the range of 0.08-1.105 M (M is the mass of the Sun) for Earth-like, 0.15-1.223 M for Neptune-like, 0.816-1.3

Modeling H$α$ and He 10830 transmission spectrum of WASP-52b

“…This would be because the mean absorption radius of XUV flux is below 2 R P . Yan & Guo (2019) performed a statistical analysis of the mean absorption radius of the stellar XUV radiation and proposed that it is in the range of 1.1-1.7 R P for Jupiter-like planets. This work is consistent with that one.…”