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

Abstract

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 Halpha and He 10830 transmission spectra of the hot Jupiter HAT-P-32b. A Monte Carlo simulation was applied to calculate the number of Lyalpha resonance scatterings, which is the main process for populating H(2). In the examined parameter space, only models with H/He geq 99.5/0.5, $(0.5 3.0)$ times the fiducial value of XUV $, and spectral index $ 0.3)$, can explain the Halpha and He 10830 lines simultaneously. We found a mass-loss rate of $ $ g s$^ $, consistent with previous studies. Moreover, we found that the stellar Lyalpha flux should be as high as $4 $ erg cm$^ $ s$^ $, 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.