The unprecedented medium-resolution (R _λ ∼ 1500–3500) near- and mid-infrared (1–18 μm) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 M _Jup) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: T _eff, log(g), [M/H], C/O, γ, f _sed, and R. Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a T _eff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

中文翻译：

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JWST 早期发布的直接观测系外行星系统的科学计划。 V. 自洽大气模型是否代表 JWST 光谱？展示 VHS 1256–1257 b

前所未有的中分辨率（右 _λ ∼ 1500–3500) 近红外和中红外 (1–18μm) JWST 为年轻 (140 ± 20 Myr) 低质量 (12–20中号 _Jup ) L–T 转变 (L7) 配套 VHS 1256 b 提供分子吸收目录的访问。在这项研究中，我们利用贝叶斯框架的正向建模方法对该数据集进行了全面分析，莫萨。我们探索了五种不同的大气模型来评估它们在估计关键大气参数方面的性能：时间 _有效，日志（G), [M/H], C/O,γ,F _sed和右。我们的研究结果表明，每个参数的估计都受到考虑的波长范围和为拟合选择的模型等因素的显着影响。这是由于模型中的系统误差以及准确复制 VHS 1256 b 复杂大气结构的挑战，特别是其云和尘埃分布的复杂性。为了传播这些系统不确定性对我们的大气特性估计的影响，我们引入了基于在不同光谱窗口上执行的独立拟合的创新拟合方法。我们最终得出了一个时间 _{考虑到目标的年轻年龄， eff}与目标的光谱类型一致，这通过我们对 log(G）。尽管数据质量出色，但对通常用作形成历史指标的化学丰度 [M/H] 和 C/O 进行可靠的估计仍然具有挑战性。尽管如此，JWST 的 VHS 1256 b 数据的开创性案例为未来获取亚恒星光谱铺平了道路，这些光谱将被系统分析，以直接比较这些物体的属性并纠正模型中的系统性。