The spectral line polarization encodes a wealth of information about the thermal and magnetic properties of the solar atmosphere. Modeling the Stokes profiles of strong resonance lines is, however, a complex problem both from the theoretical and computational point of view, especially when partial frequency redistribution (PRD) effects need to be taken into account. In this work, we consider a two-level atom in the presence of magnetic fields of arbitrary intensity (Hanle-Zeeman regime) and orientation, both deterministic and micro-structured. Working within the framework of a rigorous PRD theoretical approach, we have developed a numerical code which solves the full non-LTE radiative transfer problem for polarized radiation, in one-dimensional models of the solar atmosphere, accounting for the combined action of the Hanle and Zeeman effects, as well as for PRD phenomena. After briefly discussing the relevant equations, we describe the iterative method of solution of the problem and the numerical tools that we have developed and implemented. We finally present some illustrative applications to two resonance lines that form at different heights in the solar atmosphere, and provide a detailed physical interpretation of the calculated Stokes profiles. We find that in strong resonance lines sensitive to PRD effects the magneto-optical terms of the Stokes-vector transfer equation produce conspicuous U/I wing signals along with a very interesting magnetic sensitivity in the wings of the linear polarization profiles. We also show that the weak-field approximation has to be used with caution when PRD effects are considered.
Observations of the Joint Action of the Hanle and Zeeman Effects in the D2 Line of BaII
我们选择的高灵敏度光谱偏振观测在过去几年中获得的Ba II D2线与苏黎世成像偏振仪(ZIMPOL)连接到格雷戈里库德望远镜的IRSOL。测量数据是在靠近太阳边缘的几个磁场活动程度不同的区域收集的。我们观察到的斯托克斯轮廓显示了汉勒和塞曼效应联合作用的清晰特征,与理论预期非常好的定性一致。这条线的偏振测量表明,非常适合低太阳色球层的磁场诊断,从磁场强度低至1高斯的区域到具有KG磁场强度的强磁化区域。
The magnetic sensitivity of the Mg ii k line to the joint action of Hanle, Zeeman and magneto-optical effects
我们强调的主要结果的辐射转移调查的磁灵敏度的太阳Mg ii k共振线在2795.5埃,占汉勒和塞曼效应以及部分频率再分布(PRD)现象的共同作用。我们确认,在线中心,散射过程产生的线性极化信号是可测量的,并且它们是敏感的,通过汉勒效应,磁场的强度在5和50 G之间,大约。我们还表明,塞曼效应产生显着的圆偏振信号,特别是对于纵向磁场强于50 G,这可以用来估计通过熟悉的magnetographer公式的太阳色球的磁化。最新颖的结果是,磁光效应在线的翼中产生Q/I散射偏振图案的减小和U/I信号的出现(即,线偏振平面的旋转)。Q/I和U/I翼信号对弱(约5 G)和强磁场的敏感性扩大了Mg ii k线探测太阳安静和活动区域色球层的科学兴趣
1.5D investigation of the Hanle effect in the Ca I 4227 line using partial frequency redistribution. Comparison of synthetic Stokes profiles in Bifrost and MURaM-ChE rMHD models
Indian Institute of Astrophysics(印度天体物理研究所);Pondicherry University(本地治里大学);Max Planck Institute for Solar System Research(马普太阳系研究所);School of Space Research, Kyung Hee University(庆熙大学宇宙研究学院)
本研究通过Bifrost与MURaM-ChE rMHD模型,利用1.5维方法对比Ca I 4227线的Hanle效应,发现两者偏振轮廓差异源于热磁结构不同,MURaM-ChE线心磁化更弱。
The diagnostic capabilities of spectral lines in far ultraviolet (FUV) and extreme ultraviolet (EUV) wavelength range are explored in terms of their Hanle and Zeeman sensitivity to probe vector magnetic field in the solar corona. The temperature range covered is log$_{10}(T)=5.5-6.3$. The circular polarization signal due to longitudinal Zeeman effect is estimated for spectral lines in the wavelength range of 500 to 1600 Å. The Stokes $V/I$ signal for a FUV line is found to be in the order of 10$^{-4}$ for a longitudinal field strength of 10 Gauss, which further reduces to 10$^{-5}$ for wavelen…
Observations of scattering polarization and the Hanle effect in various spectral lines are increasingly used to complement traditional solar magnetic field determination techniques. One of the strongest scattering polarization signals in the photosphere is measured in the Sr I line at 4607.3 Å when observed close to the solar limb. Here, we present the first observational evidence of Hanle rotation in the linearly polarized spectrum of this at several limb distances. We observed with the Zurich IMaging POLarimeter, ZIMPOL, at the IRSOL observatory, with exceptionally good seeing conditions, al…
Observations of the forward scattering Hanle effect in the Ca i 4227 Å line
色球磁场是出了名的难以测量。色球谱线很宽,而磁场则产生微小的塞曼效应偏振。前向散射Hanle效应提供了一个有希望的诊断替代方案,它可以记录在色球线,如He i 10830和Ca i 4227线。利用IRSOL天文台的ZIMPOL偏振仪对太阳盘中心附近的Ca i 4227线上的Stokes矢量进行了偏振光谱观测,发现了一些有趣的前向散射Hanle效应特征,并成功地用偏振辐射转移进行了模拟。在这里,我们专注于观测方面,而一个单独的配套文件涉及的理论建模。
We present the Tenerife Inversion Code (TIC), which has been developed to infer the magnetic and plasma properties of the solar chromosphere and transition region via full-Stokes inversion of polarized spectral lines. The code is based on the HanleRT forward engine, which takes into account many of the physical mechanisms that are critical for a proper modeling of the Stokes profiles of spectral lines originating in the tenuous and highly dynamic plasmas of the chromosphere and transition region: quantum level population imbalance and interference (atomic polarization), frequency coherence eff…
Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar magnetic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting magnetic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but th…
Radiative transfer investigations of the solar Mg II h and k resonance lines around 280~nm showed that, while their circular polarization (Stokes V) signals arise from the Zeeman effect, the linear polarization profiles (Stokes Q and U) are dominated by the scattering of anisotropic radiation and the Hanle and magneto-optical (MO) effects. Using the unprecedented observations of the Mg II and Mn I resonance lines obtained by the Chromospheric LAyer Spectro-Polarimeter (CLASP2), here we investigate how the linear polarization signals at different wavelengths (i.e., at the center, and at the nea…
Synthetic polarimetric spectra from stellar prominences
在快速旋转的恒星中探测到的恒星磁场可以作为冷恒星日冕中磁性的探测器。我们已经合成的斯托克斯配置文件中产生的He I 10830和5876 A三胞胎在日珥围绕恒星旋转的时间演化。合成进行了HAZEL代码使用云模型,其中的突出的特点是位于一个固定的纬度和高度的板。它解释了散射极化和塞曼和汉勒效应。分析了几种不同日珥磁场强度和方向的情况。结果表明,当日珥在恒星盘外时,辐射特征在剖面上漂移。当日珥遮蔽恒星时,强度轮廓显示出吸收。由日珥引起的散射产生斯托克斯Q和U分布中的线偏振信号,当存在磁场时,该线偏振信号被汉勒效应修改。由于塞曼效应,当沿视线的磁场不为零时,Stokes V剖面显示具有非常低幅度的信号。估计的线偏振信号可能会被未来的分光偏振计MIRADAS检测到,将被附加到GTC望远镜。
Determining the Magnetization of the Quiet Sun Photosphere from the Hanle Effect and Surface Dynamo Simulations
安静的太阳光球的大部分被认为是显著磁化的,这是由于在亚分辨率尺度上普遍存在平均强度约<B>为100 G的缠结磁场。这一结论是通过详细的三维(3D)辐射转移模型的Hanle效应在Sr I 4607线,使用微湍流场近似,并假设的概率密度函数的磁场强度的形状是指数。在这里,我们放松这两个近似建模所观察到的散射极化的Hanle效应产生的磁场的三维光球模型产生的(国家的最先进的)磁对流模拟与表面发电机行动。我们发现,在Sr I 4607线中观察到的散射偏振振幅可以解释,只有在增强光球模型的磁场强度后,由一个相当大的比例因子,F=10,这意味着<B>= 130 G在上层光球。我们还认为,为了解释两个Hanle去极化的Sr I 4607线和塞曼信号中观察到的Fe I线,我们需要引入一个高度相关的比例因子,这样,随后<B>= 160 G在低光球和<B>= 130 G在上层光球。
Scattering polarization tends to dominate the linear polarization signals of the Ca II 8542 A line in weakly magnetized areas ($B \lesssim 100$ G), especially when the observing geometry is close to the limb. In this paper we evaluate the degree of applicability of existing non-LTE spectral line inversion codes (which assume that the spectral line polarization is due to the Zeeman effect only) at inferring the magnetic field vector and, particularly, its transverse component. To this end, we use the inversion code STiC to extract the strength and orientation of the magnetic field from syntheti…
Two Suggestions to See the Hidden Magnetism of the Solar Chromosphere
太阳磁场在出射的谱线辐射的偏振特征中留下了它们的指纹。这是通过各种相当不熟悉的物理机制发生的,而不仅仅是通过塞曼效应。特别是,磁场修改原子水平的偏振(人口不平衡和量子相干性),各向异性辐射泵浦过程中诱导的原子和分子的太阳大气。有趣的是,这种所谓的汉勒效应使我们能够在现有仪器的限制下“看到”塞曼效应所看不到的磁场。在这里,我认为,IR三重态的钙II和He I 10830的三重态将是非常合适的选择,通过光谱偏振观测从未来的空间望远镜,如JAXA的SOLAR-C任务的太阳色球层的磁性调查。
A numerical approach for modelling the polarisation signals of strong resonance lines with partial frequency redistribution. Numerical applications to two-term atoms and plane-parallel atmospheres
Validity of the CRD limit for modeling scattering polarization in the photospheric Sr I 4607 Å line
Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera italiana(瑞士意大利大学信息学院阿尔多和切莱达科太阳研究所);Euler Institute, Faculty of Informatics, Università della Svizzera italiana(瑞士意大利大学信息学院欧拉研究所)
本研究评估了CRD极限在Sr I 4607 Å谱线散射偏振建模中的有效性,发现除弱偏振信号外CRD均适用,PRD效应仅在信号低于0.3%时显著。
We present the theoretical framework and numerical methods we have implemented to solve the problem of the generation and transfer of polarized radiation in spectral lines out of local thermodynamical equilibrium, while accounting for scattering polarization, partial frequency redistribution, J-state interference, and hyperfine structure. The resulting radiative transfer code allows modeling the impact of magnetic fields of arbitrary strength and orientation through the Hanle, incomplete Paschen-Back, and magneto-optical effects. We also evaluate the suitability of a series of approximations f…
Polarized Line Formation in Multi-dimensional Media. IV. A Fourier Decomposition Technique To Formulate The Transfer Equation With Angle-Dependent Partial Frequency Redistribution
SolRaT: polarized spectral line modeling with multi-term and multi-level atoms
Institute of Physics of the National Academy of Sciences of Ukraine(乌克兰国家科学院物理研究所);Astronomical Observatory of the Taras Shevchenko National University of Kyiv(基辅塔拉斯舍甫琴科国立大学天文台)
This paper presents a numerical application of a self-consistent theory of partial redistribution in non-LTE conditions, developed in previous papers of the series. The code was described in a previous paper of this series. However, in that previous paper (number IV of the series), the numerical results were unrealistic. The present paper presents an approximation, which was able to restore the reliability of the outgoing polarization profiles. The convergence of the results is also proved. It is demonstrated that the step increment decreases like 1/N^a, with a > 1, so that the results series …
The sizable linear polarization signals produced by the scattering of anisotropic radiation in the core of the Ca I 4227 $\mathrm{Å}$ line constitute an important observable for probing the inhomogeneous and dynamic plasma of the lower solar chromosphere. Here we show the results of a three-dimensional (3D) radiative transfer complete frequency redistribution (CRD) investigation of the line's scattering polarization in a magneto-hydrodynamical 3D model of the solar atmosphere. We take into account not only the Hanle effect produced by the model's magnetic field, but also the symmetry breaking …
The Sun is the only star where we can resolve the intricate magnetism that all convective stars harbor. Yet, more than 99% of its visible surface along the solar cycle (the so-called quiet Sun) is filled with a tangled, unresolved magnetism. These "hidden" fields are thought to store enough magnetic energy to play a role in the heating of the Sun's outer atmosphere, but its field strength is still not constrained. Previous investigations based on the Hanle effect in atomic lines claim a strong magnetization of about 100 G, while the same effect in molecules show a factor of 10 weaker fields. T…
The Zeeman effect is of limited utility for probing the magnetism of the quiet solar chromosphere. The Hanle effect in some spectral lines is sensitive to such magnetism, but the interpretation of the scattering polarization signals requires taking into account that the chromospheric plasma is highly inhomogeneous and dynamic (i.e., that the magnetic field is not the only cause of symmetry breaking). Here we investigate the reliability of a well-known formula for mapping the azimuth of chromospheric magnetic fields directly from the scattering polarization observed in the \ion{Ca}{2}~8542~Å\, …
Measuring vector magnetic fields in solar prominences
我们目前的分光偏振观测在他我1083.0 nm多重的一个静止的,树篱日珥。这些数据是用特内里费岛红外线偏振计拍摄的,该偏振计安装在位于西班牙加那利群岛特内里费岛天文台(Observatorio del Teide)的德国真空塔望远镜上。所观察到的He I圆偏振和线偏振信号分别由塞曼效应和原子级偏振和汉勒效应主导。这些可观测量对视场的每个空间点处的磁场矢量的强度和方向敏感。我们确定的磁场矢量的日珥应用HAZEL反演代码所观察到的斯托克斯轮廓。我们简要讨论了检索的磁场矢量配置。
PORTA: A three-dimensional multilevel radiative transfer code for modeling the intensity and polarization of spectral lines with massively parallel computers
We take a broad look at the problem of identifying the magnetic solar causes of space weather. With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near UV part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, Hubble Space Telescope, and SKYLAB, along with 1D computations of the near-UV (NUV) spectrum and numerical experiments based on the MURaM radiation-MHD and HanleRT radiative transfer codes, we address multiple challenges. These cha…
Modeling the quantum interference signatures of the Ba II D2 4554 A line in the second solar spectrum
量子干涉效应在形成太阳谱线的线性偏振轮廓中起着至关重要的作用。在4554 A处的Ba II D2线是一个突出的例子,其中由于奇数同位素产生的F态干扰效应产生的偏振分布与没有F态干扰的偶数同位素的偏振分布非常不同。因此,有必要考虑不同同位素的贡献,以了解这条线的观测线性偏振分布。在这里,我们做辐射转移建模与部分频率重新分布(PRD)的观测,同时占干扰效应和同位素组成。发现Ba II D2极化曲线强烈受PRD机制支配。我们展示了如何一个完整的PRD治疗成功地再现的意见,而完全的频率重新分配(CRD)单独未能产生偏振配置文件,有任何相似之处,与所观察到的。然而,我们也发现线中心偏振对模式大气的温度结构是敏感的。为了获得一个很好的拟合所观察到的斯托克斯Q/I分布的线中心峰,一个小的修改的WAX模型的大气是必要的,通过降低线形成层的温度。由于Ba II D2线的温度敏感性,它可能不是太阳色球层Hanle磁场诊断的合适工具,因为目前还没有直接的方法将温度和磁场效应相互分离。