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 H alpha and He 10830 transmission spectra of the hot Jupiter HAT-P-32b. A Monte Carlo simulation was applied to calculate the number of Ly alpha 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 similar to 3.0) times the fiducial value of F-XUV, and spectral index beta(m) = (0.16 similar to 0.3), can explain the H alpha and He 10830 lines simultaneously. We found a mass-loss rate of similar to(1.0 similar to 3.1) x 10(13) g s(-1), consistent with previous studies. Moreover, we found that the stellar Ly alpha flux should be as high as 4 x 10(5) 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.