The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines
The long-standing paradox of the linear polarization signal of the Na i D _1 line was recently resolved by accounting for the atom’s hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acf845 |
| _version_ | 1827766616662736896 |
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| author | Gioele Janett Ernest Alsina Ballester Luca Belluzzi Tanausú del Pino Alemán Javier Trujillo Bueno |
| author_facet | Gioele Janett Ernest Alsina Ballester Luca Belluzzi Tanausú del Pino Alemán Javier Trujillo Bueno |
| author_sort | Gioele Janett |
| collection | DOAJ |
| description | The long-standing paradox of the linear polarization signal of the Na i D _1 line was recently resolved by accounting for the atom’s hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for partial frequency redistribution (PRD) in scattering, which potentially neglects important angle–frequency couplings. This work aims at evaluating the suitability of a PRD-AA modeling for the D _1 and D _2 lines through comparisons with general angle-dependent (AD) PRD calculations in both the absence and presence of magnetic fields. We solved the radiative transfer problem for polarized radiation in a 1D semiempirical atmospheric model with microturbulent and isotropic magnetic fields, accounting for PRD effects and comparing PRD-AA and PRD-AD modelings. The D _1 and D _2 lines are modeled separately as a two-level atomic system with hyperfine structure. The numerical results confirm that a spectrally structured radiation field induces linear polarization in the D _1 line. However, the PRD-AA approximation greatly impacts the Q / I shape, producing an antisymmetric pattern instead of the more symmetric PRD-AD one while presenting a similar sensitivity to magnetic fields between 10 and 200 G. Under the PRD-AA approximation, the Q / I profile of the D _2 line presents an artificial dip in its core, which is not found for the PRD-AD case. We conclude that accounting for PRD-AD effects is essential to suitably model the scattering polarization of the Na i D lines. These results bring us closer to exploiting the full diagnostic potential of these lines for the elusive chromospheric magnetic fields. |
| first_indexed | 2024-03-11T11:44:29Z |
| format | Article |
| id | doaj.art-4b81331be8134c148785446390f6b75c |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T11:44:29Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-4b81331be8134c148785446390f6b75c2023-11-09T15:20:31ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195813810.3847/1538-4357/acf845The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D LinesGioele Janett0https://orcid.org/0000-0003-3247-6612Ernest Alsina Ballester1https://orcid.org/0000-0001-9095-9685Luca Belluzzi2https://orcid.org/0000-0002-8775-0132Tanausú del Pino Alemán3https://orcid.org/0000-0003-1465-5692Javier Trujillo Bueno4https://orcid.org/0000-0001-5131-4139Istituto ricerche solari Aldo e Cele Daccó (IRSOL), Faculty of Informatics, Universitá della Svizzera italiana (USI) , CH-6605 Locarno, Switzerland; Euler Institute, Università della Svizzera italiana (USI) , CH-6900 Lugano, SwitzerlandInstituto de Astrofísica de Canarias (IAC) , E-38205 La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, SpainIstituto ricerche solari Aldo e Cele Daccó (IRSOL), Faculty of Informatics, Universitá della Svizzera italiana (USI) , CH-6605 Locarno, Switzerland; Euler Institute, Università della Svizzera italiana (USI) , CH-6900 Lugano, Switzerland; Leibniz-Institut für Sonnenphysik (KIS) , D-79104 Freiburg i. Br., GermanyInstituto de Astrofísica de Canarias (IAC) , E-38205 La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, SpainInstituto de Astrofísica de Canarias (IAC) , E-38205 La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, Spain; Consejo Superior de Investigaciones Científicas , SpainThe long-standing paradox of the linear polarization signal of the Na i D _1 line was recently resolved by accounting for the atom’s hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for partial frequency redistribution (PRD) in scattering, which potentially neglects important angle–frequency couplings. This work aims at evaluating the suitability of a PRD-AA modeling for the D _1 and D _2 lines through comparisons with general angle-dependent (AD) PRD calculations in both the absence and presence of magnetic fields. We solved the radiative transfer problem for polarized radiation in a 1D semiempirical atmospheric model with microturbulent and isotropic magnetic fields, accounting for PRD effects and comparing PRD-AA and PRD-AD modelings. The D _1 and D _2 lines are modeled separately as a two-level atomic system with hyperfine structure. The numerical results confirm that a spectrally structured radiation field induces linear polarization in the D _1 line. However, the PRD-AA approximation greatly impacts the Q / I shape, producing an antisymmetric pattern instead of the more symmetric PRD-AD one while presenting a similar sensitivity to magnetic fields between 10 and 200 G. Under the PRD-AA approximation, the Q / I profile of the D _2 line presents an artificial dip in its core, which is not found for the PRD-AD case. We conclude that accounting for PRD-AD effects is essential to suitably model the scattering polarization of the Na i D lines. These results bring us closer to exploiting the full diagnostic potential of these lines for the elusive chromospheric magnetic fields.https://doi.org/10.3847/1538-4357/acf845Radiative transferSolar physicsSpectropolarimetrySolar atmosphere |
| spellingShingle | Gioele Janett Ernest Alsina Ballester Luca Belluzzi Tanausú del Pino Alemán Javier Trujillo Bueno The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines The Astrophysical Journal Radiative transfer Solar physics Spectropolarimetry Solar atmosphere |
| title | The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines |
| title_full | The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines |
| title_fullStr | The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines |
| title_full_unstemmed | The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines |
| title_short | The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines |
| title_sort | impact of angle dependent partial frequency redistribution on the scattering polarization of the solar na i d lines |
| topic | Radiative transfer Solar physics Spectropolarimetry Solar atmosphere |
| url | https://doi.org/10.3847/1538-4357/acf845 |
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