The PEPSI Exoplanet Transit Survey (PETS). II. A Deep Search for Thermal Inversion Agents in KELT-20 b/MASCARA-2 b with Emission and Transmission Spectroscopy

Recent observations have shown that the atmospheres of ultra hot Jupiters (UHJs) commonly possess temperature inversions, where the temperature increases with increasing altitude. Nonetheless, which opacity sources are responsible for the presence of these inversions remains largely observationally unconstrained. We used LBT/PEPSI to observe the atmosphere of the UHJ KELT-20 b in both transmission and emission in order to search for molecular agents which could be responsible for the temperature inversion. We validate our methodology by confirming previous detections of Fe I in emission at 16.9 σ. Our search for the inversion agents TiO, VO, FeH, and CaH results in nondetections. Using injection-recovery testing we set 4σ upper limits upon the volume mixing ratios for these constituents as low as ∼1×10−9 for TiO. For TiO, VO, and CaH, our limits are much lower than expectations from an equilibrium chemical model, while we cannot set constraining limits on FeH with our data. We thus rule out TiO and CaH as the source of the temperature inversion in KELT-20 b, and VO only if the line lists are sufficiently accurate.

Shifted and combined CCFs for emission from Fe I. We detect the Fe I emission at a significance of 16.9σ, reproducing previous results. We were able to recover the signal near the expected planetary radial velocity. Yan et al. (2022b) obtained a 7.7σ detection, and Borsa et al. (2022) at 7.1σ with the Calar Alto 3.5m and the TNG 3.6m, respectively.

Read more: Marshall et al. 2023, AJ, in press (arXiv:2205.12162)