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Abstract KELT-20b is a well-studied (T_eq = 2262 K) ultrahot Jupiter, but its multidimensional atmospheric structure remains unconstrained. We performed high-resolution cross-correlation transmission spectroscopy (HRCCTS) on a single-transit time series of KELT-20b, observed with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope. Upon combining nineteen in-transit exposures, we detect FeI(11.9σ) and FeII(23.7σ) and tentatively detect NaI(3.4σ) and CrI(3.3σ). The full-transit velocity offsets of the strongest absorbers are ΔV_FeI = −1.0 ± 0.7 km s⁻¹and ΔV_FeII = 0.0 ± 0.5 km s⁻¹, which are mostly inconsistent with previously published values for KELT-20b, although the previous measurements are mostly inconsistent with each other. By correcting for discrepant systemic velocity solutions of up to 1.7 km s⁻¹between studies, our FeIIoffset becomes consistent with previous measurements (≤1.7σ), while FeIremains significantly less blueshifted than in earlier studies (≥2.2−4.5σ). We propose a set of detection criteria to improve future reproducibility in HRCCTS work. Phase-resolving the FeIand FeIIabsorption signatures into eight orbital phase bins reveals distinct dynamical regimes: FeIIexhibits a strong phase-dependent blueshift from ingress to egress along with significant limb asymmetry, while FeIshows weaker signals and a more modest blueshift with phase. These patterns indicate day-to-night winds and suggest scale height differences are a significant driver of limb asymmetry in KELT-20b. 

ABSTRACT We explore the prospects for Twinkle to determine the atmospheric composition of the nearby terrestrial-like planet LTT 1445 Ab, including the possibility of detecting the potential biosignature ammonia (NH3). At a distance of 6.9 pc, this system is the second closest known transiting system and will be observed through transmission spectroscopy with the upcoming Twinkle mission. Although LTT 1445 Ab has been suggested to be a candidate for a Hycean world, constraints on the interior composition based on its mass and radius suggests that the planet lacks a substantial water layer, and thus the proposed Hycean scenario is disfavoured. We use PETITRADTRANS and a Twinkle simulator to simulate transmission spectra for the more likely scenario of a cold Haber world for which NH3 is considered to be a biosignature. We study the detectability under different scenarios: varying hydrogen fraction, concentration of ammonia, and cloud coverage. We find that ammonia can be detected at an ∼3σ level for optimal (non-cloudy) conditions with 25 transits and a volume mixing ration of 4.0 ppm of NH3. We provide examples of retrieval analysis to constrain potential NH3 and H2O in the atmosphere. Our study illustrates the potential of Twinkle to characterize atmospheres of potentially habitable exoplanets. 

ABSTRACT Most ultra-hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe i with a significance of 17σ. We also report a tentative 4.3σ detection of Ni i. A nominally 4.5σ detection of Mg i emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg i cross-correlation template and the Fe i lines present in the spectrum. We cannot reproduce a recent detection of Cr i, while we do not have the wavelength coverage to robustly test past detections of Fe ii and Si i. Together with non-detections of molecular species like TiO, this suggests that Fe i is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability. 

We present a reanalysis of the K2-106 transiting planetary system, with a focus on the composition of K2-106b, an ultra-short-period, super-Mercury candidate. We globally model existing photometric and radial velocity data and derive a planetary mass and radius for K2-106b of Mp = 8.53 ± 1.02 M⊕ and = - + Rp 1.71 0.057 RÅ 0.069 , which leads to a density of r = - + 9.4 p 1.5 1.6 g cm−3 , a significantly lower value than previously reported in the literature. We use planet interior models that assume a two-layer planet comprised of a liquid, pure Fe core and an iron-free, MgSiO3 mantle, and we determine that the range of the core mass fractions are consistent with the observed mass and radius. We use existing high-resolution spectra of the host star to derive the Fe/Mg/Si abundances ([Fe/ H] = −0.03 ± 0.01, [Mg/H] = 0.04 ± 0.02, [Si/H] = 0.03 ± 0.06) to infer the composition of K2-106b. We find that K2-106b has a density and core mass fraction ( - + 44 %15 12 ) consistent with that of Earth (CMF⊕ = 32%). Furthermore, its composition is consistent with what is expected, assuming that it reflects the relative refractory abundances of its host star. K2-106b is therefore unlikely to be a super-Mercury, as has been suggested in previous literature. 

Abstract Recent observations have shown that the atmospheres of ultrahot 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 Feiin emission at 16.9σ. Our search for the inversion agents TiO, VO, FeH, and CaH results in non-detections. Using injection-recovery testing we set 4σupper limits upon the volume mixing ratios for these constituents as low as ∼1 × 10⁻⁹for 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.