Measuring the Wilson depression of sunspots using the divergence-free condition of the magnetic field vector
Measuring the Wilson depression of sunspots using the divergence-free condition of the magnetic field vector
复制标题
利用磁场矢量的无发散条件测量太阳黑子的威尔逊凹陷
DOI：
10.1051/0004-6361/201833571
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发表时间：
2018
影响因子：
6.5
通讯作者：
S. Solanki
中科院分区：
文献类型：
--
作者：
B. Löptien;A. Lagg;M. Noort;S. Solanki
上下文威尔逊凹陷是太阳黑子本影和宁静太阳之间单位连续光学厚度的几何高度差。测量威尔逊凹陷对于理解太阳黑子的几何形状很重要。目前的方法受到系统效应的影响，或者需要对磁场的几何形状进行假设。这导致大的系统的不确定性派生威尔逊洼地。
目标。我们的目标是开发一个强大的方法来推导威尔逊抑郁症，只需要有关的磁场信息，可以从分光偏振，并不依赖于太阳黑子的几何形状或其磁场的假设。
方法.我们的方法是基于最大限度地减少来自分光偏振观测的磁场矢量的发散。我们只关注大空间尺度，以减少自由参数的数量。
结果我们测试了我们的方法的性能，使用来自两个太阳黑子模拟的合成Hinode数据。我们发现，我们的方法确定的两个点的最大值和本影平均威尔逊抑郁症通常位于从模拟获得的真实值的100公里之内。此外，我们将该方法应用于太阳黑子的日出观测。导出的威尔逊低压（约600 km）与通常从威尔逊效应获得的结果一致。我们还发现，从使用水平力平衡获得的威尔逊凹陷比我们发现的和我们直接从模拟中推导出的威尔逊凹陷小110-180公里。这表明磁压力和磁曲率力对威尔逊凹陷的贡献是相似的。
Context. The Wilson depression is the difference in geometric height of unit continuum optical depth between the sunspot umbra and the quiet Sun. Measuring the Wilson depression is important for understanding the geometry of sunspots. Current methods suffer from systematic effects or need to make assumptions on the geometry of the magnetic field. This leads to large systematic uncertainties of the derived Wilson depressions.
Aims. We aim to develop a robust method for deriving the Wilson depression that only requires the information about the magnetic field that is accessible from spectropolarimetry, and that does not rely on assumptions on the geometry of sunspots or on their magnetic field.
Methods. Our method is based on minimizing the divergence of the magnetic field vector derived from spectropolarimetric observations. We have focused on large spatial scales only in order to reduce the number of free parameters.
Results. We tested the performance of our method using synthetic Hinode data derived from two sunspot simulations. We find that the maximum and the umbral averaged Wilson depression for both spots determined with our method typically lies within 100 km of the true value obtained from the simulations. In addition, we applied the method to Hinode observations of a sunspot. The derived Wilson depression (∼600 km) is consistent with results typically obtained from the Wilson effect. We also find that the Wilson depression obtained from using horizontal force balance gives 110–180 km smaller Wilson depressions than both, what we find and what we deduce directly from the simulations. This suggests that the magnetic pressure and the magnetic curvature force contribute to the Wilson depression by a similar amount.