Reproduction package for "A strong H− opacity signal in the near-infrared emission spectrum of the ultra-hot Jupiter KELT-9b"

This is a basic reproduction package for the paper "A strong H− opacity signal in the near-infrared emission spectrum of the ultra-hot Jupiter KELT-9b" by [Jacobs, B.; Désert, J. -M.; Pino, L. et al. (2022)](https://doi.org/10.1051/0004-6361/202244533). Abstract: We present the analysis of a spectroscopic secondary eclipse of the hottest transiting exoplanet detected to date, KELT-9b, obtained with the Wide Field Camera 3 aboard the Hubble Space Telescope. We complement these data with literature information on stellar pulsations and Spitzer/Infrared Array Camera and Transiting Exoplanet Survey Satellite eclipse depths of this target to obtain a broadband thermal emission spectrum. Our extracted spectrum exhibits a clear turnoff at 1.4 μm. This points to H− bound-free opacities shaping the spectrum. To interpret the spectrum, we perform grid retrievals of self-consistent 1D equilibrium chemistry forward models, varying the composition and energy budget. The model with solar metallicity and C/O ratio provides a poor fit because the H− signal is stronger than expected, requiring an excess of electrons. This pushes our retrievals toward high atmospheric metallicities ([M/H] = 1.98−0.21+0.19) and a C/O ratio that is subsolar by 2.4σ. We question the viability of forming such a high-metallicity planet, and therefore provide other scenarios to increase the electron density in this atmosphere. We also look at an alternative model in which we quench TiO and VO. This fit results in an atmosphere with a slightly subsolar metallicity and subsolar C/O ratio ([M/H] = −0.22−0.13+0.17, log (C/O) = −0.34−0.34+0.19). However, the required TiO abundances are disputed by recent high-resolution measurements of the same planet.

本数据集为论文《超热木星（ultra-hot Jupiter）KELT-9b近红外发射光谱中的强氢负离子（H⁻）不透明度信号》（原作者：Jacobs, B.; Désert, J.-M.; Pino, L. 等 (2022)，DOI: 10.1051/0004-6361/202244533）的基础复现包。摘要：我们针对迄今已发现的最热凌日系外行星（transiting exoplanet）KELT-9b，对其光谱次级掩食（secondary eclipse）展开分析，观测数据由搭载于哈勃空间望远镜（Hubble Space Telescope）的广角相机3（Wide Field Camera 3, WFC3）获取。我们结合该目标的恒星脉动文献数据，以及斯皮策空间望远镜/红外阵列相机（Spitzer/Infrared Array Camera）与凌日系外行星巡天卫星（Transiting Exoplanet Survey Satellite, TESS）的掩食深度数据对上述观测进行补充，最终得到宽带热发射光谱。我们提取的光谱在1.4 μm处呈现清晰的光谱下降沿，这表明氢负离子（H⁻）的束缚-自由不透明度（bound-free opacity）塑造了该光谱的整体形态。为解释该光谱，我们对自洽的一维平衡化学正演模型开展网格反演（grid retrievals），调整模型的成分与能量预算参数。采用太阳金属丰度与碳氧比的模型拟合效果较差，因为氢负离子信号强度高于预期，需要额外的电子来源。这使得我们的反演结果指向高大气金属丰度（[M/H] = 1.98⁺₀.₁₉₋₀.₂₁）以及亚太阳碳氧比，偏差达2.4σ。我们对形成如此高金属丰度行星的可行性提出质疑，因此提出了其他可提升该大气电子密度的研究场景。我们还测试了淬灭TiO与VO的替代模型，该模型的拟合结果对应大气金属丰度略低于太阳、碳氧比为亚太阳水平的情况（[M/H] = -0.22⁺₀.₁₇₋₀.₁₃，log(C/O) = -0.34⁺₀.₁₉₋₀.₃₄）。但该模型所需的TiO丰度，与该行星的近期高分辨率观测结果存在争议。