Modeling H$\hat{I}\pm$ and He 10830 transmission spectrum of WASP-52b

Abstract

Escaping atmosphere has been detected by the excess absorption of Ly$\hat{I}\pm$, H$\hat{I}\pm$ and He triplet (10830$\tilde{\mathrm{A}}$) lines. Simultaneously modeling the absorption of the H$\hat{I}\pm$ and He 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$\hat{I}\pm$ radiative transfer are performed with assumptions of a spherical stellar Ly$\hat{I}\pm$ radiation and a spherical planetary atmosphere, for the first time, to calculate the Ly$\hat{I}\pm$ mean intensity distribution inside the planetary atmosphere, necessary in estimating the H(2) population. We model the transmission spectra of the H$\hat{I}\pm$ and He 10830 lines simultaneously in hot Jupiter WASP-52b. We find that models with many different H/He ratios can reproduce the H$\hat{I}\pm$ observations well if the host star has (1) a high X-ray/extreme ultraviolet (XUV) flux ($F_{\mathrm{XUV}}$) and a relatively low X-ray fraction in XUV radiation (${\hat{I}}_m^2$), or (2) a low $F_{\mathrm{XUV}}$ and a high ${\hat{I}}_m^2$. The simulations of He 10830 $\tilde{\mathrm{A}}$ triplet suggest that a high H/He ratio ($\sim$ 98/2) is required to fit the observation. The models that fit both lines well confine $F_{\mathrm{XUV}}$ to be about 0.5 times the fiducial value and ${\hat{I}}_m^2$ 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$\times 10^{11}$ g s${}^{-1}$.

Accepted for publication in ApJ, 48 pages