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

Abstract

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 a previous detection of Fe i in emission at 15.1σ; however, we are unable to reproduce published detections of Fe ii, Cr i, or Si i. We attribute the non-detection of Si i to the lack of lines in our bandpass, but the non-detections of Fe ii and Cr i are puzzling due to our much higher signal-to-noise ratio than previous works. Our search for the inversion agents TiO, VO, FeH, and CaH results in non-detections. Using injection-recovery testing we set 4σ upper limits upon the volume mixing ratios for these constituents as low as ∼ 1 × 10 −10 for TiO. For TiO, VO, and CaH, our limits are much lower than expectations from an equilibrium chemical model, while FeH is lower than the expectations only from a super-Solar metallicity model. We thus rule out TiO, VO, and CaH as the source of the temperature inversion in KELT-20 b, while FeH is disfavored only if KELT-20 b possesses a high-metallicity atmosphere.

The GAPS Programme at TNG

“…These authors also find that Fe ii and Cr i are only observable post-eclipse, and not pre-eclipse, despite achieving a similar total S/N across both phase ranges. Johnson et al (2022) were not able to confirm the detection of Fe ii and Cr i with PEPSI@LBT, but they did not investigate the reason for the discrepancy in detail, hypothesizing that it could be due to differences in analysis techniques. Therefore, even if additional work is required to understand results on KELT-20b, observations of this UHJ further reinforce the expectation that climate can induce phase-dependent signals in HRS phase curves.…”

Unifying High- and Low-resolution Observations to Constrain the Dayside Atmosphere of KELT-20b/MASCARA-2b

“…The thermal emission spectrum of KELT-20b has been previously observed with ground-based, high-resolution spectrographs by Borsa et al (2022), Yan et al (2022b), andJohnson et al (2022). Using data from HARPS-N, Borsa et al (2022) found a 6.8σ detection of Fe I, as well as 3σ detections of Fe II and Cr I.…”

“…Yan et al (2022b) used data from CARMENES and found Fe I at 7.5σ. Using PEPSI, Johnson et al (2022) found Fe I in emission at 15.1σ with nondetections of Fe II and Cr I, among others. All the detected species in the previous works were observed in emission, which indicates a thermal inversion in KELT-20b's atmosphere.…”

“…All the detected species in the previous works were observed in emission, which indicates a thermal inversion in KELT-20b's atmosphere. Johnson et al (2022) inferred upper limits on the abundances of their TiO, VO, FeH, and CaH nondetections with volume mixing ratios in the ∼10 −9 -10 −10 range, with the exception of FeH, for which they found at an upper limit of 3 × 10 −7 .…”

“…These parameters place it in the population of the ∼30 12 known transiting hot Jupiters orbiting early-type stars. KELT-20b is very highly for dayside emission atmospheric follow-up due to the apparent magnitude of the host star, the size of the planet relative to the host star, and the planet's highequilibrium temperature of ∼2250 K. Furthermore, the unambiguous detection of both iron (Borsa et al 2022;Johnson et al 2022;Yan et al 2022b) and water (Fu et al 2022) in the emission spectrum of this exoplanet, which is one of the coolest exoplanets with a detected thermal inversion, gives a special opportunity to unify ground-based, high-resolution, and spacebased, low-resolution observations of exoplanet atmospheres.…”