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arXiv 2006.13653astro-ph.SR
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Ca I 4227线散射偏振翼中磁光效应的观测指示

Observational indications of magneto-optical effects in the scattering polarization wings of the Ca I 4227 Å line

E. Capozzi, E. Alsina Ballester, L. Belluzzi, M. Bianda, S. K. Dhara, R. Ramelli

摘要:

H I Ly- $α$、Mg II K、Ca II K、Ca I 4227等强共振线在太阳强度谱中具有深而宽的吸收轮廓,在靠近太阳边缘的安静区观测时,显示出明显的线性散射偏振信号。这样的信号显示出特征性的三峰结构,在线芯和扩展的翼瓣中具有尖锐的峰。线芯峰通过Hanle效应对磁场的存在敏感,然而已知Hanle效应不在线翼中操作。最近的理论研究表明,与以前认为的相反,机翼线偏振信号通过磁光效应(MO)也对磁场敏感。我们寻找这个最近发现的物理机制中的散射极化翼的钙I 4227线的观测指标。我们进行了一系列的光谱偏振观测这条线使用苏黎世成像偏光仪(ZIMPOL)相机在格雷戈里Coudé望远镜IRSOL(瑞士)和在GREGOR望远镜在特内里费岛(西班牙)。总的线偏振度和线偏振角的空间变化在所观察的线的翼中是明显可感知的。我们提供了一个详细的讨论,我们的观测结果表明,检测到的变化总是发生在纵向磁场存在的区域,从而支持理论预测,它们产生的MO效应。

英文摘要:

Several strong resonance lines, such as H I Ly-$α$, Mg II k, Ca II K, Ca I 4227 Å\, which are characterized by deep and broad absorption profiles in the solar intensity spectrum, show conspicuous linear scattering polarization signals when observed in quiet regions close to the solar limb. Such signals show a characteristic triplet-peak structure, with a sharp peak in the line core and extended wing lobes. The line core peak is sensitive to the presence of magnetic fields through the Hanle effect, which however is known not to operate in the line wings. Recent theoretical studies indicate that, contrary to what was previously believed, the wing linear polarization signals are also sensitive to the magnetic field through magneto-optical effects (MO). We search for observational indications of this recently discovered physical mechanism in the scattering polarization wings of the Ca I 4227 Å line. We performed a series of spectropolarimetric observations of this line using the Zurich IMaging POLarimeter (ZIMPOL) camera at the Gregory-Coudé telescope of IRSOL (Switzerland) and at the GREGOR telescope in Tenerife (Spain). Spatial variations of the total linear polarization degree and of the linear polarization angle are clearly appreciable in the wings of the observed line. We provide a detailed discussion of our observational results, showing that the detected variations always take place in regions where longitudinal magnetic fields are present, thus supporting the theoretical prediction that they are produced by MO effects.

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