2025/03/10 by Calder Lenhart, Marshall C. Johnson, Lenhart, Calder +13
Earth and Planetary Sciences · Environmental Science · #Atmospheric Ozone and Climate #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Geological and Geophysical Studies #Methane Hydrates and Related Phenomena
paper · pdf · doi:10.48550/arxiv.2503.07719
openalex publication_date 2025/03/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
KELT-20b is a well-studied (Teq=2262 K) ultra hot 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 PEPSI on the LBT. Upon combining nineteen in-transit exposures, we detect Fe I (11.9σ) and Fe II (23.7σ) and tentatively detect Na I (3.4σ) and Cr I (3.3σ). The full-transit velocity offsets of the strongest absorbers are ΔVFe I = -1.0 ± 0.7 km s-1 and ΔVFe II= 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-1 between studies, our Fe II offset becomes consistent with previous measurements (≤ 1.7σ), while Fe I remains 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 Fe I and Fe II absorption signatures into eight orbital phase bins reveals distinct dynamical regimes: Fe II exhibits a strong phase-dependent blueshift from ingress to egress along with significant limb asymmetry, while Fe I shows 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.