Fe I 4377埃线作为太阳耀斑指示：光谱比分析的启示
The Fe I 4377 Å Line as a Solar Faculae Indicator: Insights from Spectral Ratio Analysis
AI总结：
该研究利用光谱比分析（SRA）结合HARPS-N观测，发现Fe I 4377埃线可可靠指示太阳耀斑，其填充因子与SDO测量值吻合，有助于减轻恒星活动对系外行星径向速度测量的影响。
AI中文摘要：
耀斑是径向速度测量中恒星活动噪声的主要来源，但其低对比度和广阔的表面分布使其在日盘积分观测中难以追踪。我们将光谱比分析（SRA）应用于HARPS-N太阳作为恒星的观测，以在自转时间尺度上分离和表征耀斑区域的光谱印记。所得SRA光谱显示出与谱线相关的相干变异性，对表面磁活动敏感，其中Fe I 4377埃线对耀斑覆盖表现出特别强的诊断响应。我们使用两种互补的合成框架解释观测到的信号：复合PHOENIX光谱，从中我们得出最佳拟合的耀斑温度对比度范围为200-400K；以及使用宁静太阳的MURaM模拟合成的MPS-ATLAS光谱，包含小尺度发电机和初始平均垂直磁场为100G、200G、300G的磁增强耀斑类似物。两种方法均以太阳动力学天文台（SDO）的日盘分辨图像测量的耀斑填充因子为基准。我们发现使用Fe I 4377埃线时，SDO测量的填充因子与SRA推断的填充因子吻合良好，跨模型和时间尺度的皮尔逊R系数为0.587-0.927。估计的填充因子追踪太阳活动周期，从低活动时的约1.5%上升至高活动时的约5.5%，与SDO测量的填充因子一致。这些结果表明，SRA提供了一种可靠追踪日盘积分光谱中表面磁活动的方法，这对于减轻活动对现代精度下系外行星质量和大气的径向速度表征的影响是必要的。
英文摘要：
Faculae are a dominant source of stellar activity noise in radial velocity measurements, yet their low contrast and broad surface distribution make them difficult to track in disc-integrated observations. We apply Spectral Ratio Analysis (SRA) to HARPS-N Sun-as-a-star observations to isolate and characterize the spectral imprint of facular regions over rotational timescales. The resulting SRA spectra show coherent, line-dependent variability sensitive to surface magnetic activity, with the Fe I 4377 Angstrom line exhibiting a particularly strong diagnostic response to facular coverage. We interpret the observed signatures using two complementary synthetic frameworks: composite PHOENIX spectra, from which we derive best-fit facular temperature contrasts in the range 200-400 K, and MPS-ATLAS spectra synthesized using MURaM simulations of the quiet Sun including a small-scale dynamo and magnetically-enhanced facular analogues with initial mean vertical magnetic fields of 100G, 200G, and 300G. Both approaches are benchmarked against facular filling factors measured from Solar Dynamics Observatory (SDO) disc-resolved images. We find good agreement between SDO-measured and SRA-inferred filling factors using the Fe I 4377 Angstrom line, with Pearson R coefficients of 0.587-0.927 across models and timescales. The estimated filling factors track the solar activity cycle, rising from ~1.5% at lower activity to ~5.5% at higher activity, consistent with SDO-measured filling factors. These results demonstrate that SRA offers a means to reliably track surface magnetic activity in disc-resolved spectra, which is necessary for mitigating the effects of activity on RV characterization of exoplanet masses and atmospheres at modern precision.
