Bisector Analysis of Stokes Profiles: Effects Due to Gradients in the Physical Parameters
Bisector Analysis of Stokes Profiles: Effects Due to Gradients in the Physical Parameters
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斯托克斯轮廓的平分线分析：物理参数梯度的影响
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
T. Rimmele
中科院分区：
文献类型：
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作者：
K. Sankarasubramanian;T. Rimmele
利用λ6301.5和λ6302.5谱线的Stokes V剖面的不对称性，系统地研究了一个靠近盘中心的黑子。斯托克斯光谱是由国家太阳天文台（NSO）/高海拔天文台高级斯托克斯偏振仪（ASP）拍摄的。使用国家统计局低阶自适应光学系统记录了一组始终具有高分辨率的数据。我们发现以下结果从这个分析：（1）一个强大的相关性之间的重心（COG）的速度从强度分布与V-轮廓不对称性;（2）振幅不对称性是更敏感的变化，重心速度比面积不对称性;和（3）绘制面积与振幅不对称性的整个活动区的结果在双峰分布。活动区内的不同区域，如半影、本影、光桥和太阳黑子外的小尺度场，在该图中被清楚地分开。光桥和小规模的磁场周围观察到的太阳黑子表现出较大的振幅不对称性相比，面积不对称性，而半影显示较大的面积不对称性。相比之下，在本影中测量的斯托克斯V光谱显示出很小的面积和振幅不对称性。在本文中，我们使用平分线分析的V强度轮廓作为一种新的工具，以确定在一个更直接的方式在物理参数的梯度。由平分线法导出的梯度为研究非对称性所得到的物理图象提供了进一步和更直接的证据。对于光桥，我们发现，数据是一致的小对流细胞局限于低层大气的图片。半影中的不对称性是由Evershed速度的陡峭垂直梯度与视线倾斜角的梯度相结合造成的，证实了早期的观测结果。对于小规模的田野，图片与树冠效应一致。我们还比较了平均速度和磁场强度来自这个平分线分析的速度和磁场强度来自ASP反演，并找到这些独立的方法之间的良好协议。除了这些不对称性，我们还观察到非常不对称的V型轮廓，如单叶轮廓和多个反转，主要是在边缘侧半影的边缘。在这些区域中，我们还发现λ6301.5和λ6302.5的V曲线存在差异，这表明物理参数存在陡峭的梯度。从单次扫描得到的不对称性与从通过平均14次间隔7.5分钟的这种扫描获得的时间平均性质得到的不对称性很好地匹配。这表明，在统计意义上，斯托克斯V不对称性不随时间而变化，并描述了一个全球/一般性质的磁特征，如光桥，本影，半影，和小规模的领域。
The asymmetry of Stokes V profiles of the spectral lines λ6301.5 and λ6302.5 was utilized to systematically study a sunspot observed close to the disk center. The Stokes spectra were taken with the National Solar Observatory (NSO)/High Altitude Observatory Advanced Stokes Polarimeter (ASP). The NSO low-order adaptive optics system was used to record a data set of consistently high resolution. We find the following results from this analysis: (1) a strong correlation between the center-of-gravity (COG) velocity derived from the intensity profiles with the V-profile asymmetry; (2) the amplitude asymmetry is much more sensitive to changes in the COG velocity than the area asymmetry; and (3) plotting area versus amplitude asymmetry for the entire active region results in a bimodal distribution. Different areas within the active region, such as penumbra, umbra, light bridge, and small-scale fields outside the sunspot, are clearly separated in this plot. The light bridges and the small-scale magnetic fields surrounding the observed sunspot show larger amplitude asymmetry compared to the area asymmetry, whereas the penumbra shows larger area asymmetry. In comparison, the Stokes V spectra measured in the umbra show little area and amplitude asymmetry. In this paper, we use bisector analysis of the V intensity profile as a new tool to determine the gradients in the physical parameters in a more direct way. The gradients derived from the bisector method provide further and more direct evidence for the physical picture derived from the study of the asymmetries. For light bridges we find that the data is consistent with a picture of small convective cells confined to lower layers of the atmosphere. Asymmetries in the penumbra are caused by steep vertical gradients in the Evershed velocities in combination with the gradient in the line-of-sight inclination angle, confirming the earlier observations. For small-scale fields, the picture is consistent with the canopy effect. We also compare the average velocity and the magnetic field strength derived from this bisector analysis with the velocity and magnetic field strength derived from the ASP inversion and find excellent agreement between these independent methods. Apart from these asymmetries, we also observe extremely asymmetric V profiles, such as one-lobed profiles and multiple reversals, mostly at the edges of the limb-side penumbra. In these regions, we also find differences in the V profiles of λ6301.5 and λ6302.5 that suggest steep gradients in the physical parameters. The asymmetries derived from a single scan match well with the ones derived from the time-averaged properties obtained by averaging 14 such scans separated by 7.5 minutes. This suggests that, in a statistical sense, the Stokes V asymmetries do not vary with time and describe a global/general property of magnetic features found in regions such as light bridge, umbra, penumbra, and small-scale fields.