A possibly solar metallicity atmosphere escaping from HAT-P-32b revealed by Hα and He absorption

This paper presents a hydrodynamic simulation that couples detailed non-local thermodynamic equilibrium (NLTE) calculations of the helium and hydrogen level populations to model the Hα and He 10830 transmission spectra of the hot Jupiter HAT-P-32b. A Monte Carlo simulation was applied to calculate the number of Lyα resonance scatterings, which is the main process for populating H(2). In the examined parameter space, only models with H/He ≥ 99.5/0.5, (0.5 ~ 3.0) times the fiducial value of F_XUV, and spectral index β_m = (0.16 ~ 0.3), can explain the Hα and He 10830 lines simultaneously. We found a mass-loss rate of ~(1.0 ~ 3.1) × 10¹³ g s⁻¹, consistent with previous studies. Moreover, we found that the stellar Lyα flux should be as high as 4 × 10⁵ erg cm⁻² s⁻¹, indicating high stellar activity during the observation epoch of the two absorption lines. Despite the fact that the metallicity in the lower atmosphere of HAT-P-32b may be super-solar, our simulations tentatively suggest it is close to solar in the upper atmosphere. Understanding the difference in metallicity between the lower and upper atmospheres is essential for future atmospheric characterisations.