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

Abstract

Escaping atmosphere has been detected by the excess absorption of Lyα, Hα and He triplet (λ10830) lines. Simultaneously modeling the absorption of the Hα and He λ10830 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(23 S) populations. The Monte Carlo simulations of Lyα radiative transfer are performed with assumptions of a spherical stellar Lyα radiation and a spherical planetary atmosphere, for the first time, to calculate the Lyα mean intensity distribution inside the planetary atmosphere, necessary in estimating the H(2) population. We model the transmission spectra of the Hα and He λ10830 lines simultaneously in hot Jupiter WASP-52b. We find that models with many different H/He ratios can reproduce the Hα 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 λ10830 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 × 1011 g s−1.