{ "abstract": "Context. Exoplanetary magnetic fields govern atmospheric escape and circulation but have eluded detection in close-in planets. In the ultra-hot Jupiter KELT-9b, atmospheric dynamo is predicted to generate atmospheric fields of 400−4000 G.\n\nAims. We searched for the circular polarization in atomic lines that a magnetic field would imprint, through the Zeeman effect, on the transmission spectrum of KELT-9b.\n\nMethods. We observed three transits with SPIRou at the CFHT, on 07 September 2025 and 03 and 06 July 2026, and applied least squares deconvolution to 1398 atomic lines to map the transit-averaged Stokes V and null spectra against the orbital semi-amplitude, K p , and systemic velocity, v sys .\n\nResults. The 2025 transit shows a Stokes V signature of V / I c = 9.3 × 10 ⁻⁵ at K p = 219 ± 11 km s ⁻¹ , v = −34.0 ± 1.2 km s ⁻¹ , close to the expected planetary velocity. Its false-alarm probability is 1.9 × 10 ⁻⁴ , and thus it is formally a marginal detection. Both 2026 transits are of comparable sensitivity but neither exhibits a signal at that location, setting 3 σ limits of 4.9 and 6.0 × 10 ⁻⁵ ; the 2025 amplitude would have been recovered at 4.9 σ and 4.0 σ .\n\nConclusions. The 2025 signature is robust to the tests we applied to it but qualifies as a marginal detection at best. Spurious signals of comparable strengths occur elsewhere in our Stokes V and null maps, and we cannot rule out that our marginal detection is excess noise. It is not reproduced ten months later.", "abstract_shown": true, "affiliations": [ "Univ. de Toulouse, CNRS, IRAP", "Leibniz Institute for Astrophysics Potsdam", "Department of Physics, University of Oxford", "Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur", "Canada France Hawai‘i Telescope Corporation (CFHT)", "Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal", "LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS", "Department of Physics & Astronomy, McMaster University", "Department of Physics and Trottier Space Institute, McGill University", "Univ. Grenoble Alpes, CNRS, IPAG", "Institut d’Astrophysique de Paris, CNRS, UMR 7095, Sorbonne Université", "Laboratório Nacional de Astrofísica", "Centro de Astrobiología (CAB), CSIC-INTA", "Weltraumforschung und Planetologie, Physikalisches Institut, University of Bern" ], "article_type": null, "arxiv": null, "author_total": 26, "authors": [ { "affs": [ 0 ], "name": "A. Lavail", "orcid": "0000-0001-8477-5265" }, { "affs": [ 0 ], "name": "F. Debras", "orcid": "0000-0002-3113-4840" }, { "affs": [ 0 ], "name": "D. Roge Royo" }, { "affs": [ 0 ], "name": "A. López Ariste", "orcid": "0000-0002-1097-8307" }, { "affs": [ 0 ], "name": "N. W. Borsato", "orcid": "0000-0002-4085-6001" }, { "affs": [ 0 ], "name": "J.-F. Donati", "orcid": "0000-0001-5541-2887" }, { "affs": [ 0 ], "name": "P. Petit", "orcid": "0000-0001-7624-9222" }, { "affs": [ 1 ], "name": "J. D. Alvarado-Gómez", "orcid": "0000-0001-5052-3473" }, { "affs": [ 0 ], "name": "L. Jouve" }, { "affs": [ 0 ], "name": "C. Moutou", "orcid": "0000-0002-2842-3924" }, { "affs": [ 0 ], "name": "A. Carmona", "orcid": "0000-0003-2471-1299" }, { "affs": [ 2 ], "name": "B. Klein", "orcid": "0000-0003-0637-5236" }, { "affs": [ 3 ], "name": "J. V. Seidel" }, { "affs": [ 4 ], "name": "L. Arnold", "orcid": "0000-0002-0111-1234" }, { "affs": [ 5 ], "name": "E. Artigau" }, { "affs": [ 0 ], "name": "C. Baruteau", "orcid": "0000-0002-2672-3456" }, { "affs": [ 6 ], "name": "E. Chabrol", "orcid": "0009-0002-1437-2860" }, { "affs": [ 7 ], "name": "R. Cloutier", "orcid": "0000-0001-5383-9393" }, { "affs": [ 5 ], "name": "N. J. Cook", "orcid": "0000-0003-4166-4121" }, { "affs": [ 8 ], "name": "N. B. Cowan", "orcid": "0000-0001-6129-5699" }, { "affs": [ 9 ], "name": "X. Delfosse", "orcid": "0000-0001-5099-7978" }, { "affs": [ 10 ], "name": "N. Heidari", "orcid": "0000-0002-2370-0187" }, { "affs": [ 11, 10 ], "name": "E. Martioli" }, { "affs": [ 12 ], "name": "A. Masson", "orcid": "0000-0002-2250-941X" }, { "affs": [ 13 ], "name": "J. P. Wardenier", "orcid": "0000-0003-3191-2486" }, { "affs": [ 9 ], "name": "V. Yariv", "orcid": "0009-0005-2775-1589" } ], "bibtex": "https://research.draconitic.com/paper/84wn132jvyfj6.bib", "cited_by": 0, "doi": "10.1051/0004-6361/202663128", "fulltext_url": null, "id": "84wn132jvyfj6", "issns": [ "0004-6361", "1432-0746" ], "landing_url": "https://www.aanda.org/10.1051/0004-6361/202663128", "language": null, "licence": "CC-BY-4.0", "licence_label": "CC BY 4.0", "licence_source": "article", "licence_url": "https://creativecommons.org/licenses/by/4.0", "metadata_licence": null, "native_subjects": [ [ "openalex", "3103|Stellar, planetary, and galactic studies" ] ], "openalex": "W7223785025", "pdf_url": null, "pmcid": null, "pmid": null, "published": "2026-10-27", "publisher": "EDP Sciences", "ris": "https://research.draconitic.com/paper/84wn132jvyfj6.ris", "sources": [ { "first_seen": "2026-10-30T12:18:18Z", "native_id": "10.1051/0004-6361/202663128", "source": "crossref", "url": "https://www.aanda.org/10.1051/0004-6361/202663128" } ], "subjects": [ { "field": "astronomy", "origin": "openalex:3103|Stellar, planetary, and galactic studies", "subfield": "stellar" } ], "title": "SPIRou near-infrared spectropolarimetry of the ultra-hot Jupiter KELT-9b: Tentative detection of the planet’s magnetic field", "title_text": "SPIRou near-infrared spectropolarimetry of the ultra-hot Jupiter KELT-9b: Tentative detection of the planet’s magnetic field", "type": "peer-reviewed", "updated_at": "2026-10-30T12:18:18Z", "url": "https://research.draconitic.com/paper/84wn132jvyfj6", "venue": "Astronomy & Astrophysics", "versions": [] }