The escape of hydrogen-rich atmosphere of exoplanet: Mass loss rates and the absorptions of stellar Lyman $alpha$. (arXiv:1906.05520v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yan_D/0/1/0/all/0/1">Dongdong Yan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guo_J/0/1/0/all/0/1">Jianheng Guo</a>
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 $sim$2$times$10$^{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 Ly$alpha$ by planetary atmosphere and found that the deeper
Ly$alpha$ 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 Ly$alpha$ absorptions. Neptune-like and Earth-like
planets tend to have weak Ly$alpha$ absorptions because of their small sizes
(or high densities).
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 $sim$2$times$10$^{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 Ly$alpha$ by planetary atmosphere and found that the deeper
Ly$alpha$ 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 Ly$alpha$ absorptions. Neptune-like and Earth-like
planets tend to have weak Ly$alpha$ absorptions because of their small sizes
(or high densities).
http://arxiv.org/icons/sfx.gif
