Publications

PEPSI Investigation, Retrieval, and Atlas of Numerous Giant Atmospheres (PIRANGA). I. The Ubiquity of Fe I Emission and Inversions in Ultra Hot Jupiter Atmospheres

We present high-resolution optical emission spectroscopy observations of the ultra hot Jupiters (UHJs) TOI-1431b and TOI-1518b using the PEPSI spectrograph on the LBT. We detect emission lines from Fe I with a significance of 5.68σ and 7.68σ for TOI 1431b and TOI-1518b, respectively. We also tentatively detect Cr I emission from TOI-1431b at 4.32σ. For TOI-1518 b, we tentatively detect Ni I, Fe II, and Mg I at significance levels ranging from 3−4σ. Detection of emission lines indicates that both planets possess temperature inversions in their atmospheres, providing further evidence of the ubiquity of stratospheres among UHJs. By analyzing the population of hot Jupiters, we compare models that predict the distribution of planets in the temperature-gravity space, and find a recent global circulation model suite from Roth et al. (2024) provides a reasonable match to the observed onset of inversions at Teq∼2000 K. The ubiquity of strong Fe I emission lines among UHJs, together with the paucity of detections of TiO, suggest that atomic iron is the dominant optical opacity source in their atmospheres and can be responsible for the inversions.

Left: Phase coverage of the observations used in this work. The solid inner circle shows the stellar surface, while the middle and outer circles show the orbits of TOI-1518 b and TOI-1431 b, respectively, to scale. The observer is off the bottom of the page, and the vertical dashed lines show the line of sight, such that transit occurs in the lower intersection of the dashed lines and planetary orbits, and the secondary eclipse in the upper intersection. The planets orbit counter clockwise. The colored points show the portions of the orbit where we obtained data. Right: signal-to-noise ratio of our observations as a function of orbital phase. The PEPSI red and blue arms are shown as the solid and dotted lines, respectively. The SNR values shown are, for each spectrum, the 95th quantile per-pixel signal to-noise ratios.

Read more: Petz et al. 2025, AJ, in press; arXiv