发表机构
Univ. de Toulouse, CNRS, IRAP; Leibniz Institute for Astrophysics Potsdam; Department of Physics, University of Oxford（图卢兹大学，法国国家科学研究中心，天体物理研究所; 波茨坦阿基米德天文研究所; 牛津大学物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用SPIRou近红外偏振观测搜索超热木星KELT-9b的磁场信号，在2025年凌星中发现边缘性圆偏振信号，但后续观测未重现，无法确证行星磁场。
AI 中文摘要
系外行星磁场控制着大气逃逸和环流，但在近距离行星中一直未被探测到。在超热木星KELT-9b中，预测大气发电机可产生400–4000 G的大气磁场。我们通过塞曼效应搜索原子谱线中的圆偏振信号，该信号会印在KELT-9b的透射光谱上。我们于2025年9月7日以及2026年7月3日和6日在CFHT用SPIRou观测了三次凌星，并应用最小二乘反卷积处理1398条原子谱线，以绘制凌星平均的斯托克斯V和零谱随轨道半振幅K_p和系统速度v_sys的变化。2025年的凌星在K_p = 219 ± 11 km s⁻¹、v = -34.0 ± 1.2 km s⁻¹处显示出V/I_c = 9.3 × 10⁻⁵的斯托克斯V信号，接近预期的行星速度。其误报概率为1.9 × 10⁻⁴，形式上属于边缘探测。2026年的两次凌星灵敏度相当，但在该位置均未显示信号，设定了4.9和6.0 × 10⁻⁵的3σ上限；2025年的振幅本应以4.9σ和4.0σ被恢复。2025年的信号对我们应用的测试具有稳健性，但最多只能算作边缘探测。在我们的斯托克斯V和零谱图中，其他位置也出现了强度相当的虚假信号，因此我们不能排除我们的边缘探测是多余噪声。十个月后该信号未被重现。
英文摘要
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. We search for the circular polarization in atomic lines that a magnetic field would imprint, through the Zeeman effect, on the transmission spectrum of KELT-9b. 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 orbital semi-amplitude $K_{\rm p}$ and systemic velocity $v_{\rm sys}$. The 2025 transit shows a Stokes $V$ signature of $V/I_c = 9.3 \times 10^{-5}$ at $K_{\rm p} = 219 \pm 11$ km s$^{-1}$, $v = -34.0 \pm 1.2$ km s$^{-1}$, close to the expected planetary velocity. Its false-alarm probability is $1.9 \times 10^{-4}$, formally a marginal detection. Both 2026 transits are of comparable sensitivity but neither exhibits a signal at that location, setting $3σ$ limits of $4.9$ and $6.0 \times 10^{-5}$; the 2025 amplitude would have been recovered at $4.9σ$ and $4.0σ$. 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 exclude that our marginal detection is excess noise. It is not reproduced ten months later.
Comments9 pages, 9 figures, accepted for publication in A&A
