The PEPSI Exoplanet Transit Survey. III: The detection of Fe I, Cr I and Ti I in the atmosphere of MASCARA-1 b through high-resolution emission spectroscopy

Hot giant planets like MASCARA-1 b are expected to have thermally inverted atmospheres, that makes them perfect laboratory for the atmospheric characterization through high-resolution spectroscopy. Nonetheless, previous attempts of detecting the atmosphere of MASCARA-1 b in transmission have led to negative results. In this paper we aim at the detection of the optical emission spectrum of MASCARA-1 b. We used the high-resolution spectrograph PEPSI to observe MASCARA-1 (spectral type A8) near the secondary eclipse of the planet. We cross-correlated the spectra with synthetic templates computed for several atomic and molecular species. We obtained the detection of FeI, Cr I and Ti I in the atmosphere of MASCARA-1 b with a S/N ~7, 4 and 5 respectively, and confirmed the expected systemic velocity of ~13 km/s and the radial velocity semi-amplitude of MASCARA-1 b of ~200 km/s. The detection of Ti is of particular importance in the context of the recently proposed Ti cold-trapping below a certain planetary equilibrium temperature. We confirm the presence of an the atmosphere around MASCARA-1 b through emission spectroscopy. We conclude that the atmospheric non detection in transmission spectroscopy is due to the high gravity of the planet and/or to the overlap between the planetary track and its Doppler shadow.

Atmospheric planetary signal obtained with the Ti I template. The left column shows the Kp–vsys bi-dimensional map, with the color bar encoding the significance of the detection. The cross in white dashes marks the position where the planetary signal is expected. The central (right) column shows the cut along the vertical (horizontal) direction in the map and corresponding to the peak detection, together with its gaussian best fit (blue dashed line).

Read more: G. Scandariato, F. Borsa, A.S. Bonomo, et al. 2023, A&A, in press (eprint arXiv:2304.03328)