超冷矮星的统一正演模拟分析。I.方法和基准
Uniform Forward-Modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking
摘要：
我们提出了一个前向建模框架，使用贝叶斯推理工具海星和无云Sonora-Bobcat模型大气分析低分辨率（$R\approx80-250$）近红外（$1.0-2.5$ $μ$ m）光谱的T矮星。我们的方法推断有效温度，表面重力，金属丰度，半径和质量，并占模型插值和相关残差由于仪器效应和建模系统学的不确定性，产生更现实的参数后验比传统的（$χ^2$为基础的）光谱拟合分析。我们验证我们的框架，通过拟合模型大气本身，并找到派生和输入参数之间的可忽略不计的偏移。我们将我们的方法应用于三个著名的基准晚T矮星，HD 3651 B，GJ 570 D和Ross 458 C，使用太阳和非太阳金属丰度大气模型。我们还推导出这些基准的物理性质，使用它们的热光度，它们的主星的年龄和金属丰度，和Sonora-Bobcat演化模型。假设基于演化的参数更稳健，我们发现基于大气的正演模拟分析产生了两个结果。对于HD 3615 B和GJ 570 D，光谱拟合提供了准确的$T_{\rm eff}$和$R$，但低估了$\log{g}$（通过$\approx1.2$ dex）和$Z$（通过$\approx0.35$ dex），这可能是由于模拟钾谱线的系统学。对于Ross 458 C，光谱拟合提供了准确的$\log{g}$和$Z$，但高估了$T_{\rm eff}$（通过$\approx120$ K），低估了$R$（通过$\approx1.6\times$），这可能是因为我们的模型大气缺乏云，垂直温度梯度降低或不平衡过程。最后，这些基准的光谱推断质量都被大大低估了。
英文摘要：
We present a forward-modeling framework using the Bayesian inference tool Starfish and cloudless Sonora-Bobcat model atmospheres to analyze low-resolution ($R\approx80-250$) near-infrared ($1.0-2.5$ $μ$m) spectra of T dwarfs. Our approach infers effective temperatures, surface gravities, metallicities, radii, and masses, and by accounting for uncertainties from model interpolation and correlated residuals due to instrumental effects and modeling systematics, produces more realistic parameter posteriors than traditional ($χ^2$-based) spectral-fitting analyses. We validate our framework by fitting the model atmospheres themselves and finding negligible offsets between derived and input parameters. We apply our methodology to three well-known benchmark late-T dwarfs, HD 3651B, GJ 570D, and Ross 458C, using both solar and non-solar metallicity atmospheric models. We also derive these benchmarks' physical properties using their bolometric luminosities, their primary stars' ages and metallicities, and Sonora-Bobcat evolutionary models. Assuming the evolutionary-based parameters are more robust, we find our atmospheric-based, forward-modeling analysis produces two outcomes. For HD 3615B and GJ 570D, spectral fits provide accurate $T_{\rm eff}$ and $R$ but underestimated $\log{g}$ (by $\approx1.2$ dex) and $Z$ (by $\approx0.35$ dex), likely due to the systematics from modeling the potassium line profiles. For Ross 458C, spectral fits provide accurate $\log{g}$ and $Z$ but overestimated $T_{\rm eff}$ (by $\approx120$ K) and underestimated $R$ (by $\approx1.6\times$), likely because our model atmospheres lack clouds, reduced vertical temperature gradients, or disequilibrium processes. Finally, the spectroscopically inferred masses of these benchmarks are all considerably underestimated.
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