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Coronal Magnetometry with EUV Permitted Lines

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Pith's one-line read The authors calculate the linear polarization of many permitted EUV coronal lines and identify the most promising ones for measuring the orientation of the coronal magnetic field.

desk verdict A careful, useful extension of the 2009 polarization mechanism to a wide set of EUV coronal lines, with solid line-selection tables and one unquantified assumption worth a revision request. read the letter →

arxiv 2505.14084 v1 pith:K7Q56Z4Q submitted 2025-05-20 astro-ph.SR

Nataliia G. Shchukina , Javier Trujillo Bueno , Supriya Hebbur Dayananda , Rafael Manso Sainz , Andrii V. Sukhorukov This is my paper · ORCID
classification astro-ph.SR
keywords linescoronalpermittedsolarmagneticpolarizationfieldlinear
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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The reading

The Sun's outer atmosphere, the corona, is a million-degree plasma whose magnetic field is hard to measure. One technique uses spectral lines whose polarization depends on the magnetic field. Most useful lines are visible or infrared 'forbidden' lines, but they can only be observed above the solar limb. This paper studies permitted extreme-ultraviolet (EUV) lines, which can also be seen on the solar disk.

The polarization mechanism was proposed by Manso Sainz and Trujillo Bueno in 2009. Forbidden-line radiation from the bright solar disk pumps atomic alignment into the ground levels of ions like Fe X and Fe XI. Electron collisions then transfer some of that alignment to the upper levels of EUV permitted lines. When those upper levels decay, the emitted EUV light is linearly polarized, with a polarization direction that depends on the angle between the magnetic field and the line of sight.

The authors built a numerical code that solves the statistical equilibrium equations for the atomic density matrix, using CHIANTI atomic data and a one-dimensional model of the quiet solar corona. They computed the fractional alignment and the ratio of Stokes Q to I emission coefficients for many EUV lines of Fe X, Fe XI, Fe XIII, Fe XIV, Si IX, and Si X. They then selected lines that are bright enough and have polarization above one percent, and listed which ones are blended with other spectral lines.

The most promising lines are Fe X 174.531 Å and 177.240 Å and Fe XI 188.216 Å and 180.401 Å, with the Fe X 174.531 line being the only unblended one. The predicted polarization signals are sensitive to the magnetic field orientation but not its strength, because the relevant atomic levels are in the Hanle saturation regime.

Extended reading notes

Core claim

The permitted EUV lines listed in Table 2 have upper-level Hanle critical fields larger than 2000 G, so their linear polarization signals are sensitive to the orientation of the coronal magnetic field but not to its strength. For example, the Fe X 174.531 Å line has |epsilon_Q/epsilon_I| of about 4.7 percent at 1.5 solar radii in the adopted 1D model, and is the only unblended strong line among the top candidates.

Load-bearing premise

The assumption that the upper levels of the EUV lines are excited only by isotropic electron collisions, with no significant radiative excitation at EUV wavelengths. This is stated in Section 1 and used throughout the statistical equilibrium calculations. If EUV radiative pumping is not negligible, upper-level coherences could appear, changing the polarization signals and possibly introducing sensitivity to the magnetic field strength. The authors acknowledge this possibility, citing Seaton et al. 2025, and defer it to future work.

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Assumptions & free parameters 0 free parameters · 9 assumptions · 0 invented entities

No parameters are fitted to data in this paper. The abundances and proton-to-electron ratio are taken from prior literature and standard assumptions, and they do not affect the fractional polarization signals. The axioms listed are the load-bearing physical and modeling assumptions the calculations rest on; none are introduced ad hoc to force the target result, but several simplifications are stated as future work.

assumptions (9)
  • domain assumption Isotropic inelastic collisions cannot directly induce atomic level polarization.
    Used in Section 1 to argue that only radiation pumping can create alignment; standard in the field.
  • domain assumption The solar-disk radiation at EUV wavelengths is negligible for radiative excitation of the coronal ions.
    Stated in Section 1 and used throughout; the paper assumes only collisional excitation of upper levels. Acknowledged as a simplification.
  • domain assumption The lower levels of the EUV transitions are in the Hanle saturation regime because their critical fields are below 10^-5 G.
    Used in Section 2 to justify absence of coherences in the magnetic field reference frame, simplifying the statistical equilibrium equations.
  • domain assumption The upper levels of the selected EUV lines have Hanle critical fields above 2000 G, so no Hanle effect operates on them.
    Based on Eq. (5) and atomic data; used to conclude that polarization is sensitive only to field orientation, not strength.
  • domain assumption The coronal plasma is optically thin at EUV wavelengths, and emission is computed in the single-scattering limit in the plane of the sky.
    Stated in Section 2 and used in deriving emissivity coefficients and the simpler LOS-integrated values in Section 5.
  • domain assumption The radiation field illuminating the coronal ions is unpolarized and axially symmetric around the local vertical.
    Used in Section 2 to reduce radiation field tensors to J0_0 and J2_0 only; standard for a radially symmetric corona.
  • domain assumption The 1D spherically symmetric quiet-Sun coronal model of Del Zanna and DeLuca (2018) is representative.
    Used in Section 3.1 for temperature and density as a function of height; the paper acknowledges 3D models are the next step.
  • domain assumption Atomic data from CHIANTI v10 (level energies, collision strengths, Einstein coefficients) are accurate.
    Used in Section 3.3 for all model atoms; the paper does not independently verify these data.
  • domain assumption Proton collisions and elastic collisions with neutral hydrogen are negligible.
    Justified in Section 2 by rate estimates; used to omit these processes from the statistical equilibrium equations.

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Pith. "Pith review of Coronal Magnetometry with EUV Permitted Lines." pith.science (2026). https://pith.science/paper/K7Q56Z4Q

@misc{pith2026250514084,
  author       = {Pith},
  title        = {Pith review of: Coronal Magnetometry with EUV Permitted Lines},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/K7Q56Z4Q}},
  note         = {Machine review of arXiv:2505.14084}
}
read the original abstract

A major challenge in solar physics is to obtain empirical information on the magnetic field of the million-degree plasma of the solar corona. To this end, we need observables of the solar radiation sensitive to the coronal magnetic field. The most familiar observables are the polarization signals of visible and near-infrared forbidden lines of highly ionized species and some ultraviolet permitted lines, like hydrogen Lyman-{\alpha}. While the coronal radiation in these spectral lines can only be detected for off-limb line of sights, the coronal radiation from permitted extreme ultraviolet (EUV) lines can be observed also on the solar disk. These coronal lines are mainly collisionally excited, but it has been pointed out that some permitted EUV lines can actually be linearly polarized if their lower level carries atomic alignment, and that their linear polarization is sensitive to the orientation of the coronal magnetic field (see Manso Sainz & Trujillo Bueno 2009). Here we theoretically investigate the linear polarization in permitted EUV lines of a variety of ions: Fe X, Fe XI, Fe XIII, Fe XIV, Si IX, and Si X. To this end, we have developed a numerical code, which we have applied to investigate the linear polarization and magnetic sensitivity of many permitted EUV lines in a one-dimensional model of the solar corona, providing a list of the most promising lines to be further investigated for polarimetry with future space telescopes. Our next step will be to extend this work by using state-of-the-art three-dimensional coronal models.

Figures

Figures reproduced from arXiv: 2505.14084 by the authors.

Figure 1
Figure 1. Electron temperature (left panel) and electron density(right panel) as a function of the radial distance R/RSun, where RSun is the solar radius in spherically symmetric 1D coronal model of the quiet Sun (Del Zanna & DeLuca 2018). where Ne is the electron density in cm−3 , Te in K, kB is the Boltzmann constant, gℓ = 2Jℓ + 1 is the statistical weight of the lower level, ∆Eℓu is the transition energy, and the ther￾mall… view at source ↗
Figure 2
Figure 2. The fractional alignment σ 2 0(αJ) of the lower and highly excited levels (left panels) and the ratio of the Stokes Q and I emission coefficients εQ(ν, Θ)/εI (ν,Θ) (right panels) for selected EUV lines of the Fe X and Fe XI ions as a function of the radial distance R/RSun in the spherically symmetric coronal model of the quiet Sun of Del Zanna & DeLuca (2018). The top and bottom panels show the results for the Fe X … view at source ↗
Figure 3
Figure 3. The fractional alignment σ 2 0(αJ) of the lower and highly excited levels (left panels) and the ratio of the Stokes Q and I emission coefficients εQ(ν,Θ)/εI (ν, Θ) (right panels) for selected EUV lines of the Fe XIII and Si IX ions as a function of the radial distance R/RSun in the coronal model of Del Zanna & DeLuca (2018). The top and bottom panels show the results for the Fe XIII and Si IX ions, respectively. The… view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: Same as [PITH_FULL_IMAGE:figures/full_fig_p009_4.png]
Figure 5
Figure 5. Figure 5: Same as [PITH_FULL_IMAGE:figures/full_fig_p010_5.png]
Figure 6
Figure 6. Figure 6: Fractional alignment σ 2 0(αℓJℓ) of the first 2P 0 3/2 J1-level of the Fe X ground term (left panel) and of the second 3P e 1 J2-level of the Fe XIII ground term (right panel) as a function of the radial distance R/RSun in the spherically symmetric 1D quiet-Sun coronal…
Figure 7
Figure 7. Figure 7: The left and right panels show results for the Fe X and Fe XIII lines, respectively. Top panels: the density matrix elements ρ 0 0(αℓJℓ). Bottom panels: the term F(Ne, Te), the fractional alignment σ 2 0(αℓJℓ) (lower level) and the fractional alignment σ 2 0(αuJu) (upp…

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Works this paper leans on

43 extracted references · 38 canonical work pages

  1. [1]

    - [1] #1 = = ^ ^ ^ .\!\!^ d .\!\!^ h .\!\!^ m .\!\!^ s .\!\!^ @mss

    thebibliography [1] 20pt to REFERENCES 6pt =0pt -12pt 10pt plus 3pt =0pt =0pt =1pt plus 1pt =0pt =0pt -12pt =13pt plus 1pt =20pt =13pt plus 1pt \@M =10000 =-1.0em =0pt =0pt 0pt =0pt =1.0em @enumiv\@empty 10000 10000 `\.\@m \@noitemerr \@latex@warning Empty `thebibliography' environment \@ifnextchar \@reference \@latexerr Missing key on reference command E...

    2021

  2. [2]

    Allen , C. W. 1976, Astrophysical Quantities , 3rd edn. (University of London, Athlone Press)

    work page 1976

  3. [3]

    M., & Grevesse , N

    Asplund , M., Amarsi , A. M., & Grevesse , N. 2021, , 653, A141

    2021

  4. [4]

    J., & Scott , P

    Asplund , M., Grevesse , N., Sauval , A. J., & Scott , P. 2009, , 47, 481

    2009

  5. [5]

    E., Cohen , L., Feldman , U., & Doschek , G

    Behring , W. E., Cohen , L., Feldman , U., & Doschek , G. A. 1976, , 203, 521

    work page 1976

  6. [6]

    K., & Doschek , G

    Bhatia , A. K., & Doschek , G. A. 1995, Atomic Data and Nuclear Data Tables, 60, 97

    work page 1995

  7. [7]

    Casini , R., & Judge , P. G. 1999, , 522, 524

    work page 1999

  8. [8]

    2010, , 514, A41

    Del Zanna , G. 2010, , 514, A41

    work page 2010

Show all 43 references
  1. [9]

    2012a, , 537, A38

    ---. 2012a, , 537, A38

  2. [10]

    2012b, , 546, A97

    ---. 2012b, , 546, A97

  3. [11]

    A., & Mason , H

    Del Zanna , G., Berrington , K. A., & Mason , H. E. 2004, , 422, 731

    2004

  4. [12]

    Del Zanna , G., & DeLuca , E. E. 2018, , 852, 52

    2018

  5. [13]

    P., Young , P

    Del Zanna , G., Dere , K. P., Young , P. R., & Landi , E. 2021, , 909, 38

    2021

  6. [14]

    P., Young , P

    Del Zanna , G., Dere , K. P., Young , P. R., Landi , E., & Mason , H. E. 2015, , 582, A56

    2015

  7. [15]

    Del Zanna , G., & Mason , H. E. 2018, Living Reviews in Solar Physics, 15, 5

    2018

  8. [16]

    J., Badnell , N

    Del Zanna , G., Storey , P. J., Badnell , N. R., & Mason , H. E. 2012, , 541, A90

    2012

  9. [17]

    Del Zanna , G., & Supriya , H. D. 2025, , 537, 3781

    2025

  10. [18]

    P., Del Zanna , G., Young , P

    Dere , K. P., Del Zanna , G., Young , P. R., Landi , E., & Sutherland , R. S. 2019, , 241, 22

    2019

  11. [19]

    P., Del Zanna , G., Young , P

    Dufresne , R. P., Del Zanna , G., Young , P. R., et al. 2024, , 974, 71

    2024

  12. [20]

    E., Fludra , A., Bagenal , F., et al

    Gibson , S. E., Fludra , A., Bagenal , F., et al. 1999, , 104, 9691

    1999

  13. [21]

    G., Low , B

    Judge , P. G., Low , B. C., & Casini , R. 2006, , 651, 1229

    2006

  14. [22]

    E., Casini , R., & Nagaraju , K

    Khan , R., Gibson , S. E., Casini , R., & Nagaraju , K. 2024, , 971, 27

    2024

  15. [23]

    Laming , J. M. 2015, Living Reviews in Solar Physics, 12, 2

    2015

  16. [24]

    2004, Polarization in Spectral Lines , Vol

    Landi Degl'Innocenti , E., & Landolfi , M. 2004, Polarization in Spectral Lines , Vol. 307 ( Kluwer Academic Publishers ), doi:10.1007/978-1-4020-2415-3

    2004 doi

  17. [25]

    Y., Badnell , N

    Liang , G. Y., Badnell , N. R., Crespo L \'o pez-Urrutia , J. R., et al. 2010, , 190, 322

    2010

  18. [26]

    2009, in Astronomical Society of the Pacific Conference Series, Vol

    Manso Sainz , R., & Trujillo Bueno , J. 2009, in Astronomical Society of the Pacific Conference Series, Vol. 405, Solar Polarization 5: In Honor of Jan Stenflo, ed. S. V. Berdyugina , K. N. Nagendra , & R. Ramelli , 423

    2009

  19. [27]

    1978, Stellar atmospheres , 2nd edn

    Mihalas , D. 1978, Stellar atmospheres , 2nd edn. (W.H. Freeman & Co.)

    1978

  20. [28]

    E., Lemaire , P., & Sahal-Br \'e chot , S

    Raouafi , N. E., Lemaire , P., & Sahal-Br \'e chot , S. 1999, , 345, 999

    1999

  21. [29]

    E., Sahal-Br \'e chot , S., & Lemaire , P

    Raouafi , N. E., Sahal-Br \'e chot , S., & Lemaire , P. 2002, , 396, 1019

    2002

  22. [30]

    2020, , 295, 98

    Schad , T., & Dima , G. 2020, , 295, 98

    2020

  23. [31]

    2021, , 296, 166

    ---. 2021, , 296, 166

    2021

  24. [32]

    T., Reames , D

    Schmelz , J. T., Reames , D. V., von Steiger , R., & Basu , S. 2012, , 755, 33

    2012

  25. [33]

    B., Downs , C., Del Zanna , G., et al

    Seaton , D. B., Downs , C., Del Zanna , G., et al. 2025, arXiv e-prints, arXiv:2504.08996

    2025 arXiv

  26. [34]

    2012, , 755, 176

    Shchukina , N., Sukhorukov , A., & Trujillo Bueno , J. 2012, , 755, 176

    2012

  27. [35]

    2001, , 550, 970

    Shchukina , N., & Trujillo Bueno , J. 2001, , 550, 970

    2001

  28. [36]

    D., de Vicente , A., del Pino Alem \'a n , T., Trujillo Bueno , J., & Shchukina , N

    Supriya , H. D., de Vicente , A., del Pino Alem \'a n , T., Trujillo Bueno , J., & Shchukina , N. 2025, , in press, (see arXiv:2505.05962)

    2025 arXiv

  29. [37]

    D., Trujillo Bueno , J., de Vicente , A., & del Pino Alem \'a n , T

    Supriya , H. D., Trujillo Bueno , J., de Vicente , A., & del Pino Alem \'a n , T. 2021, , 920, 140

    2021

  30. [38]

    2023, , 944, 117

    Testa , P., Mart \' nez-Sykora , J., & De Pontieu , B. 2023, , 944, 117

    2023

  31. [39]

    2001, in Astronomical Society of the Pacific Conference Series, Vol

    Trujillo Bueno , J. 2001, in Astronomical Society of the Pacific Conference Series, Vol. 236, Advanced Solar Polarimetry -- Theory, Observation, and Instrumentation, ed. M. Sigwarth , 161

    2001

  32. [40]

    2022, , 60, 415

    Trujillo Bueno , J., & del Pino Alem \'a n , T. 2022, , 60, 415

    2022

  33. [41]

    M., van Ballegooijen , A

    V \'a squez , A. M., van Ballegooijen , A. A., & Raymond , J. C. 2003, , 598, 1361

    2003

  34. [42]

    L., & Raymond , J

    Withbroe , G. L., & Raymond , J. C. 1984, , 285, 347

    1984

  35. [43]

    R., Dere , K

    Young , P. R., Dere , K. P., Del Zanna , G., Landi , E., & Sutherland , R. 2019, in American Astronomical Society Meeting Abstracts, Vol. 234, American Astronomical Society Meeting Abstracts \#234, 314.02

    2019

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