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

被引:0
作者
Yan, Dongdong [1 ,2 ,3 ]
Guo, Jianheng [1 ,2 ,3 ]
机构
[1] Chinese Acad Sci, Yunnan Observ, POB 110, Kunming 650011, Yunnan, Peoples R China
[2] Univ Chinese Acad Sci, Sch Astron & Space Sci, Beijing, Peoples R China
[3] Chinese Acad Sci, Key Lab Struct & Evolut Celestial Objects, Kunming 650011, Yunnan, Peoples R China
基金
中国国家自然科学基金;
关键词
planets and satellites: atmospheres; planets and satellites: composition; planets and satellites: physical evolution; HYDRODYNAMIC ESCAPE; RECOMBINATION COEFFICIENTS; CHARGE-TRANSFER; ATOMIC DATA; HD; 209458B; PLANET; IONS; WATER; SIMULATIONS; RESONANCE;
D O I
10.3847/1538-4357/ab29f3
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Because mass-loss rates are the function of the mean density of a 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 those predicted by the hydrodynamic model when the integrated extreme ultraviolet flux is higher than similar to 2 x 10(4) erg cm(-2) s(-1). The overestimation can be revised if the kinetic and thermal energies 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 Jupiter-like planets, while they vary in the range of 1.1-1.7 R-p for planets with smaller sizes. We evaluated the absorption of stellar Ly alpha by the planetary atmosphere and found that the deeper Ly alpha absorptions tend to be located 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(-1) are likely to exhibit obvious absorptions. Finally, we suggest that the absorption levels are related to the inherent properties of exoplanets. The planets with larger sizes (or lower mean density) show strong Ly alpha absorptions. Neptune-like and Earth-like planets tend to have weak Ly alpha absorptions because of their small sizes (or high densities).
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页数:13
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