http://arxiv.org/abs/2005.08676
Atmospheric escape is an important process that controls the long-term evolution of close-in planets. We perform radiation hydrodynamics simulations of photo-evaporation of exoplanets’ atmospheres to study the effect of photoelectric heating by far-ultraviolet (FUV) radiation. Specifically, we consider a close-in hot Jupiter around a hot A-star. Hot main-sequence stars emit not only extreme ultraviolet radiation but also FUV radiation, and thus can drive strong atmospheric escape by photoelectric heating. We show that the planetary atmosphere escapes at a rate of $\dot{M}\sim10^{14}\,\mathrm{g/s}$ if the atmosphere contains heavy elements and dust grains with the level of ten percent of the solar metallicity. Close-in planets around hot stars can lose a significant fraction of the atmosphere during the long-term evolution. We also explore the metallicity dependence of the FUV driven escape. The mass-loss rate increases with increasing the atmosphere’s metallicity because of the enhanced photoelectric heating, but the stellar FUV flux decreases with increasing stellar metallicity. The net dependence nearly cancels if we assume the same or similar metallicities for the planet and the host star. We derive an accurate estimate for the mass-loss rate as a function of FUV flux and metallicity, and of the planet’s characteristics. The FUV driven atmospheric escape may be a key process to understand and explain the so-called sub-Jovian desert.
H. Mitani, R. Nakatani and N. Yoshida
Tue, 19 May 20
89/92
Comments: 9 pages, 6 figures, submitted to ApJ
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