| Presenter: | Malali Sampoorna |
| Affiliation: | Indian Institute of Astrophysics |
| Title: | Scattering polarization in the presence of moderately strong solar magnetic fields -- the theory of Hanle-Zeeman scattering |
| Authors: | M. Sampoorna, K.N. Nagendra, J.O. Stenflo |
| Form: | talk |
| Abstract: | Hanle effect is a light scattering phenomenon on atomic bound states, in the presence of weak magnetic fields. The scattering theory of Hanle effect is well established and employed as a diagnostic tool to detect weak solar magnetic fields. In this case, the quantum ($m$-state) interference affects the scattering polarization. At the other extreme is the light scattering in strong (kilogauss) magnetic fields on the solar atmosphere. We refer to this as Zeeman scattering limit, that is characterized by a marginal $m$-state interference. The Hanle-Zeeman effect would have significance for line formation in the regions of the solar atmosphere, where field strengths range from few Gauss to Kilogauss levels. It is clear that a self-consistent theory that encompasses all regimes of the field strength is essential for practical radiative transfer computations required to model the solar magnetic fields. In this paper we present the polarized partial frequency redistribution (PRD) matrices derived from classical theory of Bommier and Stenflo (1999), which describes scattering under arbitrarily strong magnetic fields. We call them by the name `Hanle-Zeeman redistribution matrices’. We show that for the simplest case of a triplet ($J=0 \rightarrow 1 \rightarrow 0$) transition, the classical and quantum treatments (Bommier 1997) give identical laboratory frame redistribution matrices. We discuss the nature of these redistribution matrices by performing `single scattering experiments’ using an unpolarized incident beam. Providing laboratory frame PRD redistribution matrices is a starting point for the polarized radiative transfer computations. We incorporate our Hanle-Zeeman redistribution matrices in a line radiative transfer code, and compute the emergent Stokes profiles for simple theoretical models. We describe a very general form of the line transfer equation, which is necessary to handle the anisotropic Zeeman absorption as well as the Hanle-Zeeman scattering under PRD in a self-consistent manner. Some details of the numerical approach are presented along with the test cases, which may serve as benchmarks, for testing the complex line transfer codes developed to study the Hanle-Zeeman line formation. |
| Session: | 2. Polarization physics in magnetized media |
| Presentation date: | Monday 17th September |
| Presentation time: | 15:15:00 |