Polarized Scattering of Light for Arbitrary Magnetic Fields With Level-Crossings From the Combination of Hyperfine and Fine Structure Splittings

Sowmya, K.; Nagendra, K. N.; Sampoorna, M.; Stenflo, J. O.

doi:10.1088/0004-637x/814/2/127

Cited by 6 publications

(4 citation statements)

References 16 publications

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“…With some minor changes in notation, this expression coincides with the one presented in Sowmya et al (2015). We recall that the 3-j and 6-j symbols couple different angular momenta, and their expressions can be found in Sects.…”

Section: Appendix C1: the Atomic Hamiltoniansupporting

confidence: 73%

The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields

Ballester

Belluzzi

Bueno

2022

A&A

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Aims. 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 without assuming local thermodynamical equilibrium, while accounting for scattering polarization, partial frequency redistribution (due to both the Doppler effect and elastic collisions), J-state interference, and hyperfine structure. The resulting radiative transfer code allows one to model the impact of magnetic fields of an arbitrary strength and orientation through the Hanle, incomplete Paschen-Back, and magneto-optical effects. We also evaluate the suitability of a series of approximations for modeling the scattering polarization in the wings of strong resonance lines at a much lower computational cost, which is particularly valuable for the numerically intensive case of three-dimensional radiative transfer. Methods. We examine the suitability of the considered approximations by using our radiative transfer code to model the Stokes profiles of the Mg ii h & k lines and of the H i Lyman-α line in magnetized one-dimensional models of the solar atmosphere. Results. Neglecting Doppler redistribution in the scattering processes that are unperturbed by elastic collisions (i.e., treating them as coherent in the observer's frame) produces a negligible error in the scattering polarization wings of the Mg ii resonance lines and a minor one in the Lyman-α wings, although it is unsuitable to model the cores of these lines. For both lines, the scattering processes that are perturbed by elastic collisions only give a significant contribution to the intensity component of the emissivity. Neglecting collisional as well as Doppler redistribution (so that all scattering processes are coherent) represents a rough but suitable approximation for the wings of the Mg ii resonance lines, but a very poor one for the Lyman-α wings. The magnetic sensitivity in the scattering polarization wings of the considered lines can be modeled by accounting for the magnetic field in only the η I and ρ V coefficients of the Stokes-vector transfer equation (i.e., using the zero-field expression for the emissivity).

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Section: Appendix C1: the Atomic Hamiltoniansupporting

confidence: 73%

The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields

Ballester

Belluzzi

Bueno

2022

A&A

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“…1 One is based on the Kramers-Heisenberg scattering formula. This approach was initially proposed by Stenflo (1994), and it has been recently extended to increasingly complex atomic models in the presence of arbitrary magnetic fields (e.g., Sowmya et al 2014Sowmya et al , 2015.…”

Section: Introductionmentioning

confidence: 99%

The Transfer of Resonance Line Polarization with Partial Frequency Redistribution in the General Hanle–Zeeman Regime

Ballester

Belluzzi

Bueno

2017

ApJ

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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 ρ V 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.

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“…Furthermore, interpretation of the polarization of the K I lines for magnetic fields with B > 5 Gauss faces a serious problem because of collisional effects, which are not known in the incomplete PB regime. Sowmya et al (2015Sowmya et al ( , 2019 examined Li I D1 and D2 lines within a collisionless model and encountered the incomplete PB regime at magnetic fields of as low as around 2 Gauss. If one were to consider the Li atoms in the incomplete PB regime and use zero-field collision rates, a similar inconsistency would be encountered.…”

Section: Challenges Of Modeling Polarized Lines In Strong Magnetic Fi...mentioning

confidence: 99%

Collisional effects in modeling solar polarized lines

Derouich,

Qutub

2024

A&A

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Rigorous implementation of the effects of collisions in modeling the formation of the polarized solar lines is of utmost importance in order to realistically analyze the available, highly sensitive solar spectropolarimetric observations. Indeed, even when an observation seems to fit well with theory, one can misinterpret results if important effects due to collisions are not correctly implemented in the modeling process. We point out inconsistencies in the models adopted to implement the Paschen Back effect together with collisional effects on the solar linear polarization formed by scattering of anisotropic radiation. Because the significance of these inconsistencies increases as polarization becomes increasingly responsive to collisions we investigate the range of hydrogen densities $n_H$ to which the polarization is sensitive We used the density matrix formalism in the tensorial irreducible basis, which was developed within the theory of atom-radiation interaction and of atomic collisions We solved the statistical equilibrium equations for multi-level atoms with hyperfine structure (HFS) in order to evaluate the collisional depolarization of levels of the D1-D2 lines of the K I atom. We find that collisions play a prominent role, particularly at hydrogen densities of between 1013 and 1016 cm$^ So far, analyses of polarized lines formed in the presence of solar magnetic field have incorporated, if at all, collisional rates calculated assuming zero magnetic field. This could be a good approximation in the Hanle regime but not in the Paschen Back regime. For typical quiet Sun magnetic fields, the latter regime could be reached, and level-crossing takes place in several atomic systems. Therefore, one must be careful when using collisional rates calculated in the zero-field case to interpret linear polarization formed in magnetized media.

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Polarized Scattering of Light for Arbitrary Magnetic Fields With Level-Crossings From the Combination of Hyperfine and Fine Structure Splittings

Cited by 6 publications

References 16 publications

The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields

The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields

The Transfer of Resonance Line Polarization with Partial Frequency Redistribution in the General Hanle–Zeeman Regime

Collisional effects in modeling solar polarized lines

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