Analysis of Transit Absorptions of HAT-P-18 b “Water World” in Metastable Helium

We presented an analysis of spectral observations of the exoplanet HAT-P-18 b transits performed to determine the physical and chemical parameters of its atmosphere. The main attention is paid to the interpretation of the absorption line of metastable helium at a wavelength of 1083 nm and molecular features in the spectrum. Using the method of numerical simulation with variation of parameters, it is shown that the composition of the atmosphere in terms of the abundance of heavy elements (O and C) is close to the solar one, which is confirmed by the detection of lines of CO and CO2 molecules.