Interpretation of the Balmer-alpha line absorption in the exoplanet WASP-69 b

In this work, the absorption in the H$\alpha$ line of the exoplanet Wasp-69 b was simulated. A three-dimensional self-consistent multifluid magnetohydrodynamic (MHD) model of the atmosphere was used to calculate the characteristic distributions of density, velocity, and temperature of various components in the atmosphere of WASP-69 b. To obtain the profile of hydrogen atoms excited to the second energy level H($2\ell$), a Monte Carlo model of Ly$\alpha$ photon transport in the atmosphere, obtained by MHD simulation, was used. Three main sources were taken into account as the ``pumping'' of the atmosphere with Ly$\alpha$ photons in the model: the photons incident from the star, photons generated in the process of collisions of hydrogen atoms with electrons, and photons arising in the process of recombination of electrons and protons in the atmosphere of the planet. Modeling of the resonant scattering of Ly$\alpha$ photons on hydrogen atoms was performed in the approximation of partially coherent isotropic scattering. The calculations have shown that the population of the hydrogen excited to the second energy level due to the pumping by intra-atmospheric Ly$\alpha$ photons is insignificant and does not lead to absorption in the H$\alpha$ line, but such absorption can appear due to the pumping by stellar photons. Nevertheless, judging by the observed data obtained and their analysis, the absorption in this line was not detected, which may indicate a low intensity of the Ly$\alpha$ line radiation from the parent star.