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题名	太阳散射偏振性质研究
作者	李昊
学位类别	硕士
答辩日期	2014-04
授予单位	中国科学院研究生院（云南天文台）
授予地点	北京
导师	屈中权
其他题名	Scattering polarization property of Solar spectrum
学位专业	天体物理
中文摘要	太阳磁场的诊断对研究太阳物理有着重要的意义。而磁场的诊断通常 通过塞曼效应利用斯托克斯参量I，Q，U，和V 对磁场进行反演。塞曼效应 对通常只能对强磁场的进行诊断，而太阳宁静区存在的大量弱磁场很难被 直接诊断。近几十年来大量科学家进行着利用汉勒效应（Hanle effect）诊断 弱磁场的研究。而利用汉勒效应诊断弱磁场需要对偏振的产生机制有一个 完整的理解。直到近年来，利用对偏振的测量精度达到10?5ZIMPOL（Zurich Imaging Polarimeter）技术获得以斯托克斯Q/I表征的第二太阳光谱（Second solar Spectrum）展现丰富的散射偏振特征，促使了对偏振研究的蓬勃发展。 通过对第二太阳光谱的研究，可以使我们对偏振产生机制理解的更为透彻， 从而使利用汉勒效应诊断弱磁场逐渐成为可能。主要介绍了用量子电动力学 为基础的密度矩阵来研究偏振光谱产生的物理过程。我们使用的是由E.Landi Degl’Innocenti在平直光谱近似下得到的公式。我们采用了7个原子能级的Mg原 子模型，研究了MgI b线由散射产生的偏振轮廓Q/I和U/I在磁场中的变化。 MgI b 线非常适合用来研究下能级的汉勒效应，对亚高斯的磁场非常敏感，没 有考虑部分频率再分布以及辐射转移所带来的影响。研究的结果显示MgI三线 结构的Q/I和U/I 轮廓对磁场的敏感范围分为两段，由下能级汉勒效应主导 的0.001高斯到0.1 高斯，有上能级汉勒效应主导的1高斯到10高斯。在下能级 汉勒效应主导的磁场范围内，我们发现b4线的偏振度随着磁场强度的增加而增 加，这是由于各个能级的原子能级排列分量（atomic alignment）都通过统计 平衡方程耦合在一起，致使下能级的原子的排列分量的变化对上能级的原子 的排列分量有一定想。因此虽然b4线的下能级J为零没有原子能级的排列分量， 但是由于其他能级的反馈而使得上能级的排列分量发生变化导致偏振度增加， 使b4线的偏振度随磁场强度的增加而增加。研究结果表明，由邻边昏暗效应所 得到的不对称因子（anisotropy factor）不适合用来处理如Mg I b 线等强线的 谱线轮廓。连续谱可以十分明显的改变谱线的展宽。为了得到与观测结果相吻 合的MgI b谱线轮廓必须要考虑二向色性。MgI b线十分适合用来研究下能级极 化的汉勒效应，并且对亚高斯范围的磁场十分敏感非常适合用来诊断色球宁静 区的极弱磁场，另外汉勒效应不仅可以退偏振还可以使偏振度增加。
英文摘要	Diagnosing the magnetic field is very important in solar physics. The way to diagnose the magnetic field vector is usually through Zeeman effect for the strong magnetic field, but in the weak magnetic field region where Zeeman is less efficient and Hanle effect can provide a useful tool. Using Hanle effect to diagnose the weak magnetic field is popular in the literature these years which need a complete understanding of the polarization mechanisms. A series of International Solar Polarization Workshops which focus on exploring the magnetic field through the polarized radiation have been taken place every three years since the first one in St.Petersberg, Russia, in 1995. As the high polarimetric precision technology were applied through the ZIMPOL (Zurich Imaging Polarimeter), the so-called Second Solar Spectrum shows a great amount of rich and complicated structure of the linear polarization profile. That the linear polarization profile provide a playground for studying of Hanle effect. Through the effort of a lot of scientists, the theories to compute the Hanle effect were developed like the statistical equilibrium equations and radiative transfer equation in the density matrix form. These theories have make great success and solve many problems in the polarization profile formation and still face to some difficult. Here we review the basic theory in scattering polarization to deal with Second Solar Spectrum and Hanle. And we also focus on investigating the scattering induced fractional linear polarization Q/I and U/I of Mg I b triplet in presence of a magnetic field. It is found that the triplet is suitable to study the lower level Hanle effect and very sensitive to the sub-gauss magnetic field. We use the quantum theory under the flat-spectrum approximation developed by Landi Degl’Innocenti, E to the investigate the Hanle effect in the triplet, and adopt a seven-levels atomic model of magnesium, and the radiative transfer does not be considered and the partial frequency effect (PRD) is not taken into account. The fractional linear polarization profile Q/I and U/I at the triplet are presented. The triplet is sensitive to the magnetic field strength between 0.001 and 0.1 gauss corresponding to lower level Hanle effect and between 1 and 10 gauss corresponding to upper level Hanle effect. In the lower level Hanle effect region, as the magnetic strength is increased, the Q/I amplitude of b4 line is increased due to the coupling of atomic alignment in the statistical equations. And in the upper level Hanle effect region, the magnetic sensitivity is proportional to the the parameter ω(2) JuJ? introduced by Landi Degl’Innocenti. It is found that the most sensitive line is b4 and then followed by b2 line. First, the anisotropy factors obtained through the limb darkening of continuum is not suitable to treat the strong lines. Second, the dichroism contribution needs to be considered to fit the observational profile of triplet. Finally, when the weak magnetic is present, the atomic alignment can be increased due to the coupling in the statistical equilibrium equations. On the other hand, due to the dichroism contribution, the Hanle effect can influence the line wings but can not produce any observable signal because of the contribution of the continuum.
语种	中文
学科主题	天文学
页码	55
内容类型	学位论文
源URL	[http://ir.ynao.ac.cn/handle/114a53/5125]
专题	云南天文台_光纤阵列太阳光学望远镜研究组
推荐引用方式 GB/T 7714	李昊. 太阳散射偏振性质研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2014.

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