Sorting a mess I: Addressing velocity-axis correlation of cross-correlation functions. A census of atomic and ionised species in KELT-9b's atmosphere
Abstract
Ultra-hot Jupiters (UHJs) are the most extreme class of close-in gas giants. We combine 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 its atmosphere using cross-correlation. We introduce an agnostic strategy to mitigate velocity-axis correlation bias in parameter uncertainties. A forward model of the cross-correlation function (CCF) and a Monte Carlo bootstrap of flux uncertainties measure the CCF-derived velocity profiles of individual species and assess their time dependence. The stellar reference frame is determined, yielding Vsys = -17.99 +/- 0.04 km s^-1 and v sin i = 110.54 +/- 0.05 km s^-1. All previously reported species are recovered except Tb II; the combined analysis detects 29 species, including 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 sigma threshold in the bootstrap Mahalanobis significance test. The collective Doppler shifts show a blueshift of Delta Voffset = -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 when all species are homogenised. These results provide a catalogue of detections and retrieved Doppler parameters for a companion study of KELT-9b.
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BibTeX
@misc{borsato2026sorting,
title = {{Sorting a mess I: Addressing velocity-axis correlation of cross-correlation functions. A census of atomic and ionised species in KELT-9b's atmosphere}},
author = {Nicholas W. Borsato and Brian Thorsbro and Jens Hoeijmakers and Daniel B. Zucker and Stefan Pelletier and Bibiana Prinoth},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10695},
eprint = {2609.10695},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.10695},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Sorting a mess I: Addressing velocity-axis correlation of cross-correlation functions. A census of atomic and ionised species in KELT-9b's atmosphere
AU - Nicholas W. Borsato
AU - Brian Thorsbro
AU - Jens Hoeijmakers
AU - Daniel B. Zucker
AU - Stefan Pelletier
AU - Bibiana Prinoth
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.10695
UR - https://arxiv.org/abs/2609.10695
AB - Ultra-hot Jupiters (UHJs) are the most extreme class of close-in gas giants. We combine 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 its atmosphere using cross-correlation. We introduce an agnostic strategy to mitigate velocity-axis correlation bias in parameter uncertainties. A forward model of the cross-correlation function (CCF) and a Monte Carlo bootstrap of flux uncertainties measure the CCF-derived velocity profiles of individual species and assess their time dependence. The stellar reference frame is determined, yielding Vsys = -17.99 +/- 0.04 km s^-1 and v sin i = 110.54 +/- 0.05 km s^-1. All previously reported species are recovered except Tb II; the combined analysis detects 29 species, including 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 sigma threshold in the bootstrap Mahalanobis significance test. The collective Doppler shifts show a blueshift of Delta Voffset = -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 when all species are homogenised. These results provide a catalogue of detections and retrieved Doppler parameters for a companion study of KELT-9b.
ER -