14:00 〜 14:15
[PAE17-08] Three types of the atmospheric escape driven by EUV photoionization
キーワード：ホットジュピター、大気散逸
Hot Jupiters are gaseous planets at close distances from their host stars, and the formation and evolutionary processes are important for understanding those of planetary systems in general, including planets in the Solar System.
Ly-alpha transit observations show that the upper atmospheres heated by the intense radiation from the stars may escape in some close-in planets. The photoionization heating of hydrogen atoms by Extreme-Ultraviolet (>13.6 eV; EUV) has been considered as a dominant heating process, and many radiation hydrodynamic simulations have been performed. In the case of the strong EUV flux from the host, the flow is so-called recombination limited. The energy-conversion efficiency becomes lower than the case of the energy limited, where the injected photo-energy mostly goes into the gas kinetic plus thermal energy. However, the underlying physics that separates these two regimes is unclear. It is important for understanding the physics of close-in planets that could potentially show the signs of atmospheric escape regardless of whether Ly-alpha absorption has been undetected to date.
We find that the EUV-driven escape can be classified into three regimes according to the following two conditions. The first is that the photoheating timescale is equal to the gravitational timescale, which is related to the gravitational deceleration reducing the escape. The second is the condition where the characteristic temperature is equal to the equilibrium temperature determined by the heating and cooling. This condition determines whether the photoheating is rapid enough to heat the gas to the equilibrium temperature. We can classify the escape into three regimes using these two conditions.
These conditions can be written by the ratio of the flux to the critical flux F0/Fcr and the ratio of the planetary radius to the hill radius xi. We classify the detected close-in planets in the xi-F0/Fcr plane and find that the Ly-alpha detected planets cluster in F0/Fcr>10 and non-detected planets are in F0/Fcr<10. In this talk, we also discuss the radiation hydrodynamic simulations of some observed close-in planets.
Ly-alpha transit observations show that the upper atmospheres heated by the intense radiation from the stars may escape in some close-in planets. The photoionization heating of hydrogen atoms by Extreme-Ultraviolet (>13.6 eV; EUV) has been considered as a dominant heating process, and many radiation hydrodynamic simulations have been performed. In the case of the strong EUV flux from the host, the flow is so-called recombination limited. The energy-conversion efficiency becomes lower than the case of the energy limited, where the injected photo-energy mostly goes into the gas kinetic plus thermal energy. However, the underlying physics that separates these two regimes is unclear. It is important for understanding the physics of close-in planets that could potentially show the signs of atmospheric escape regardless of whether Ly-alpha absorption has been undetected to date.
We find that the EUV-driven escape can be classified into three regimes according to the following two conditions. The first is that the photoheating timescale is equal to the gravitational timescale, which is related to the gravitational deceleration reducing the escape. The second is the condition where the characteristic temperature is equal to the equilibrium temperature determined by the heating and cooling. This condition determines whether the photoheating is rapid enough to heat the gas to the equilibrium temperature. We can classify the escape into three regimes using these two conditions.
These conditions can be written by the ratio of the flux to the critical flux F0/Fcr and the ratio of the planetary radius to the hill radius xi. We classify the detected close-in planets in the xi-F0/Fcr plane and find that the Ly-alpha detected planets cluster in F0/Fcr>10 and non-detected planets are in F0/Fcr<10. In this talk, we also discuss the radiation hydrodynamic simulations of some observed close-in planets.