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We have used the HARPS-North high resolution spectrograph ($\mathcal{R}$=115000) at TNG to observe one transit of the highly irradiated planetMASCARA-2b/KELT-20b. Using only one transit observation, we are able to clearlyresolve the spectral features of the atomic sodium (Na I) doublet and theH$\alpha$ line in its atmosphere, measuring absorption depths of0.17$\pm$0.03$\%$ and 0.59$\pm$0.08$\%$ for a 0.75 $\AA$ passband,respectively. These absorptions are corroborated with the transmission measuredfrom their respective transmission light curves, which show a largeRossiter-McLaughlin effect. In case of H$\alpha$, this absorption correspondsto an effective radius of $R_{\lambda}/R_P$=1.20$\pm$0.04. While the S/N of thefinal transmission spectrum is not sufficient to adjust different temperatureprofiles to the lines, we find that higher temperatures than the equilibriumare needed to explain the lines contrast. Particularly, we find that the Na Ilines core require a temperature of T=4210$\pm$180K and that H$\alpha$ requiresT=4330$\pm$520K. MASCARA-2b, like other planets orbiting A-type stars, receivesa large amount of UV energy from its host star. This energy excites the atomichydrogen and produces H$\alpha$ absorption, leading to the expansion andabrasion of the atmosphere. The study of other Balmer lines in the transmissionspectrum would allow the determination of the atmospheric temperature profileand the calculation of the lifetime of the atmosphere. In the case ofMASCARA-2b, residual features are observed in the H$\beta$ and H$\gamma$ lines,but they are not statistically significant. More transit observations areneeded to confirm our findings in Na I and H$\alpha$, and to build up enoughS/N to explore the presence of H$\beta$ and H$\gamma$ planetary absorptions.

Na I and H$\alpha$ absorption features in the atmosphere of MASCARA-2b/KELT-20b