Modeling the Hα and He 10830 Transmission Spectrum of WASP-52b

Escaping atmosphere has been detected by the excess absorption of Ly α , H α and He triplet ( λ 10830) lines. Simultaneously modeling the absorption of the H α and He λ 10830 lines can provide useful constraints about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model combined with a non−local thermodynamic model and a new Monte Carlo simulation model to obtain the H(2) and He(2 3 S ) populations. The Monte Carlo simulations of Ly α radiative transfer are performed with assumptions of a spherical stellar Ly α radiation and a spherical planetary atmosphere, for the first time, to calculate the Ly α mean intensity distribution inside the planetary atmosphere, necessary in estimating the H(2) population. We model the transmission spectra of the H α and He λ 10830 lines simultaneously in hot Jupiter WASP-52b. We find that models with many different H/He ratios can reproduce the H α observations well if the host star has (1) a high X-ray and extreme-ultraviolet (XUV) flux ( F XUV ) and a relatively low X-ray fraction in XUV radiation ( β m ) or (2) a low F XUV and a high β m . The simulations of the He λ 10830 triplet suggest that a high H/He ratio (∼98/2) is required to fit the observation. The models that fit both lines well confine F XUV to be about 0.5 times the fiducial value and β m to have a value around 0.3. The models also suggest that hydrogen and helium originate from the escaping atmosphere, and the mass-loss rate is about 2.8 × 10 11 g s −1 .