Sorting a mess

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Abstract
Ultra-hot Jupiters (UHJs) represent the most extreme class of close-in gas giants, with KELT-9b being the most extreme example known. For this study, we combined 13 transit observations of KELT-9b from six high-resolution spectrographs spanning 316–960 nm to conduct a census of atomic and ionised species in the planet’s atmosphere using the cross-correlation technique. The primary objective is to introduce an agnostic strategy to mitigate velocity-axis correlation bias in parameter uncertainties during cross-correlation analysis. By employing a forward model of the cross-correlation function (CCF) alongside a Monte Carlo bootstrap of flux uncertainties, the individual CCF-derived velocity profiles of each species in the planet’s atmosphere were measured, and potential time dependence in these velocity profiles was assessed. The stellar reference frame was determined, yielding a systemic velocity of V sys = −17.99 ± 0.04 km s −1 and a projected rotational velocity of v sin i = 110.54 ± 0.05 km s −1 , which is consistent across all instruments and observing nights. The combined planetary absorption profiles provide insight into the collective motion of all detectable gas species in the atmosphere. All previously reported species were recovered except for Tb II, and the combined analysis detects 29 species, including additional absorbers C I, Si I, K I, V II, Co I, Zr II, La II, Pr II, and Nd II. All 29 recovered species exceed the conventional 5 σ threshold in the bootstrap Mahalanobis significance test. The collective Doppler shifts display a blueshift of ∆ V offset = −8.02 ± 0.17 km s −1 relative to the stellar rest frame, indicating a net day-to-night wind, with no explicit time dependence observed when all species are homogenised. These results constitute a catalogue of detections and retrieved Doppler parameters, forming a foundation for a companion study of KELT-9b that would allow for the most significant detections to be analysed and the differences across individual species to be compared.
Funding Information
  • Wenner-Gren Foundation
  • Agence Nationale pour la Recherche (ANR-24-CE49-3397 ORVET)

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