Sr I 4607 Å谱线太阳盘心散射偏振的观测与模拟比较
Comparing Observed with Simulated Solar Disk Center Scattering Polarization in the Sr I 4607 Å line
AI总结：
通过重建方法比较观测与模拟的Sr I 4607 Å盘心散射偏振，发现两者在考虑系统误差和图像退化后高度一致，支持170 G平均磁场的光球模型。
摘要：
太阳磁场通过汉勒效应改变Sr I 4607 Å等谱线中的散射偏振，使其成为诊断小尺度混合极性光球磁场的一种潜在工具。近期，在太阳盘心处发现了Sr I 4607 Å散射偏振的观测证据。在此，我们研究了使该探测成为可能的重建方法的可靠性。为此，我们将该方法应用于从包含小尺度发电机贡献的磁流体动力学模拟快照中，通过详细的3D辐射转移计算得到的盘心处Sr I 4607 Å谱线辐射的线性偏振轮廓。重建方法系统地降低了散射振幅，根据噪声水平最高可降低至原来的二分之一。我们证明，这种降低可归因于两个系统性误差：第一，我们关于散射偏振对辐射场四极矩依赖关系的假设所依据的物理约束；第二，我们的方法在从观测强度图像准确确定辐射场张量符号方面的局限性。然而，一致地应用重建过程，并在考虑了由视宁度等造成的随时间变化的图像质量所导致的图像退化效应后，观测和合成的偏振信号表现出显著的一致性。因此，我们得出结论：太阳盘心处观测到的散射偏振与从平均磁场为170 G的可见表面的太阳光球磁流体动力学模型中涌现出的散射偏振一致。
英文摘要：
Solar magnetic fields alter scattering polarization in spectral lines like Sr I at 4607 Å via the Hanle effect, making it a potential diagnostic for small-scale mixed-polarity photospheric magnetic fields. Recently, observational evidence for scattering polarization in the Sr I 4607 Å at the solar disk center was found. Here, we investigate the reliability of the reconstruction method making possible this detection. To this end, we apply it to linear polarization profiles of the Sr I 4607 Å line radiation emerging at the disk center obtained from a detailed 3D radiative transfer calculation in a magneto-hydrodynamic simulation snapshot with a small-scale dynamo contribution. The reconstruction method systematically reduces the scattering amplitudes by up to a factor of two, depending on the noise level. We demonstrate that the decrease can be attributed to two systematic errors: first, the physical constraint that underlies our assumptions regarding the dependence of scattering polarization on the quadrupolar moment of the radiation field, and second, the limitations of our method in accurately determining the sign of the radiation field tensor from the observed intensity image. However, consistently applying the reconstruction process and after taking into account image degradation effects due to the temporally variable image quality, such as imposed by seeing, observed and synthesized polarization signals show remarkable agreement. We thus conclude that the observed scattering polarization at solar disk center is consistent with that emerging from magneto-hydrodynamic model of the solar photosphere with an average magnetic field of 170 G at the visible surface.
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