Space Science Reviews

, Volume 210, Issue 1–4, pp 183–226 | Cite as

The Physics and Diagnostic Potential of Ultraviolet Spectropolarimetry

  • Javier Trujillo Bueno
  • Egidio Landi Degl’Innocenti
  • Luca Belluzzi


The empirical investigation of the magnetic field in the outer solar atmosphere is a very important challenge in astrophysics. To this end, we need to identify, measure and interpret observable quantities sensitive to the magnetism of the upper chromosphere, transition region and corona. This paper provides an overview of the physics and diagnostic potential of spectropolarimetry in permitted spectral lines of the ultraviolet solar spectrum, such as the Mg ii \(h\) and \(k\) lines around 2800 Å, the hydrogen Lyman-\(\alpha\) line at 1216 Å, and the Lyman-\(\alpha\) line of He ii at 304 Å. The outer solar atmosphere is an optically pumped vapor and the linear polarization of such spectral lines is dominated by the atomic level polarization produced by the absorption and scattering of anisotropic radiation. Its modification by the action of the Hanle and Zeeman effects in the inhomogeneous and dynamic solar atmosphere needs to be carefully understood because it encodes the magnetic field information. The circular polarization induced by the Zeeman effect in some ultraviolet lines (e.g., Mg ii \(h\) & \(k\)) is also of diagnostic interest, especially for probing the outer solar atmosphere in plages and more active regions. The few (pioneering) observational attempts carried out so far to measure the ultraviolet spectral line polarization produced by optically pumped atoms in the upper chromosphere, transition region and corona are also discussed. We emphasize that ultraviolet spectropolarimetry is a key gateway to the outer atmosphere of the Sun and of other stars.


Spectropolarimetry Sun: chromosphere Sun: transition region Sun: corona 



This is the last paper that our friend Egidio Landi Degl’Innocenti wrote with us before he unexpectedly passed away on 12 February 2017. We are deeply grateful to Egidio for the extraordinary scientific legacy that he has left to us and to future generations of scientists. Financial support by the Spanish Ministry of Economy and Competitiveness through projects AYA2014-60476-P and AYA2014-55078-P is gratefully acknowledged, as well as the computing grants provided by the Barcelona Supercomputing Center (National Supercomputing Center, Barcelona, Spain). L.B. gratefully acknowledges the Swiss National Science Foundation through grant 200021-163405.


  1. E. Alsina Ballester, L. Belluzzi, J. Trujillo Bueno, The transfer of resonance line polarization with partial frequency redistribution in the general Hanle-Zeeman regime. Astrophys. J. (2016a in press) Google Scholar
  2. E. Alsina Ballester, L. Belluzzi, J. Trujillo Bueno, The magnetic sensitivity of the Mg ii \(k\) line to the joint action of Hanle, Zeeman and magneto-optical effects. Astrophys. J. 831, L15 (2016b) ADSCrossRefGoogle Scholar
  3. L.H. Auer, D. Rees, J.O. Stenflo, Resonance line polarization. Line wing transfer calculations including excited state interference. Astron. Astrophys. 88, 302 (1980) ADSGoogle Scholar
  4. E.H. Avrett, Two-component modeling of the solar IR CO lines, in Infrared Tools for Solar Astrophysics. What’s Next? ed. by J.R. Kuhn, M.J. Penn. Singapore (World Scientific, Singapore, 1995), p. 303 Google Scholar
  5. S. Bashkin, J.O. Stoner Jr., Atomic Energy Levels and Grotrian Diagrams (North-Holland, Amsterdam, 1975) Google Scholar
  6. L. Belluzzi, J. Trujillo Bueno, The polarization of the solar Mg II h & k lines. Astrophys. J. 750, L11 (2012) ADSCrossRefGoogle Scholar
  7. L. Belluzzi, J. Trujillo Bueno, The transfer of resonance line polarization. Astron. Astrophys. 564, A16 (2014) ADSCrossRefGoogle Scholar
  8. L. Belluzzi, J. Trujillo Bueno, J. Štěpán, The scattering polarization of the Ly\(\alpha\) lines of H I and He II taking into account PRD and \(J\)-state interference effects. Astrophys. J. 755, L2 (2012) ADSCrossRefGoogle Scholar
  9. L. Belluzzi, E. Landi Degl’Innocenti, J. Trujillo Bueno, Isotropic inelastic and superelastic collisional rates in a multiterm atom. Astron. Astrophys. 551, A84 (2013) CrossRefGoogle Scholar
  10. V. Bommier, Master equation theory applied to the redistribution of polarized radiation in the weak radiation field limit. III. Theory for the multilevel atom. Astron. Astrophys. 591, 59 (2016) ADSCrossRefGoogle Scholar
  11. V. Bommier, S. Sahal-Bréchot, The Hanle effect of the coronal L-alpha line of hydrogen—theoretical investigation. Sol. Phys. 78, 157 (1982) ADSCrossRefGoogle Scholar
  12. V. Bommier, J.L. Leroy, S. Sahal-Bréchot, Determination of the complete vector magnetic field in solar prominences, using the Hanle effect. Astron. Astrophys. 100, 231 (1981) ADSGoogle Scholar
  13. V. Bommier, E. Landi Degl’Innocenti, J.L. Leroy, S. Sahal-Bréchot, Complete determination of the magnetic field vector and of the electron density in 14 prominences from linear polarization measurements in the HeI D3 and H-alpha lines. Sol. Phys. 154, 231 (1994) ADSCrossRefGoogle Scholar
  14. E.S. Carlin, R. Manso Sainz, A. Asensio Ramos, J. Trujillo Bueno, Scattering polarization in the Ca II infrared triplet with velocity gradients. Astrophys. J. 751, 5 (2012) ADSCrossRefGoogle Scholar
  15. M. Carlsson, B. Stein, Formation of solar calcium H and K bright grains. Astrophys. J. 481, 500 (1997) ADSCrossRefGoogle Scholar
  16. M. Carlsson, V. Hansteen, B. Gudiksen, J. Leenaarts, B. De Pontieu, A publicly available simulation of an enhanced network region of the Sun. Astron. Astrophys. 585, A4 (2016) ADSCrossRefGoogle Scholar
  17. R. Casini, R. Manso Sainz, Line formation theory for the multiterm atom with hyperfine structure in a magnetic field. Astrophys. J. 624, 1025 (2005) ADSCrossRefGoogle Scholar
  18. R. Casini, R. Manso Sainz, Frequency redistribution of polarized light in the \(\varLambda \)-type multi-term polarized atom. Astrophys. J. 824, 135 (2016) ADSCrossRefGoogle Scholar
  19. R. Casini, S.M. White, P. Judge, Magnetic diagnostics of the solar corona: Unifying optical and radio techniques. Space Sci. Rev. (2017 this issue) Google Scholar
  20. W. Curdt, H. Tian, L. Teriaca, U. Schühle, P. Lemaire, The Lyman-\(\alpha\) profile and center-to-limb variation of the quiet Sun. Astron. Astrophys. 492, L9 (2008) ADSCrossRefGoogle Scholar
  21. B. De Pontieu, A. Title, J.R. Lemen et al., The Interface Region Imaging Spectrograph (IRIS). Sol. Phys. 289, 2733 (2014) ADSCrossRefGoogle Scholar
  22. T. del Pino Alemán, R. Manso Sainz, J. Trujillo Bueno, Non-coherent continuum scattering as a line polarization mechanism. Astrophys. J. 784, 46 (2014) ADSCrossRefGoogle Scholar
  23. T. del Pino Alemán, R. Casini, R. Manso Sainz, Magnetic diagnostics of the solar chromosphere with the Mg ii \(h\)\(k\) lines. Astrophys. J. 830, L24 (2016) ADSCrossRefGoogle Scholar
  24. M. Derouich, F. Auchière, J.C. Vial, M. Zhang, Hanle signatures of the coronal magnetic field in the linear polarization of the hydrogen Ly-\(\alpha\) line. Astron. Astrophys. 511, 7 (2010) ADSCrossRefGoogle Scholar
  25. S. Fineschi, Space-based instrumentation for magnetic field studies of solar and stellar atmospheres, in Magnetic Fields Across the Hertzsprung-Russell Diagram, ed. by G. Mathys, S.K. Solanki, D.T. Wickramasinghe. ASP Conf. Ser., vol. 248 (2001), p. 597 Google Scholar
  26. S. Fineschi, R.B. Hoover, A.B.C. Walker Jr., Hydrogen Lyman-alpha coronagraph/polarimeter. Proc. SPIE 1546, 402 (1992) ADSCrossRefGoogle Scholar
  27. S. Fineschi, R.B. Hoover, M. Zukic, K. Jongmin, A.B.C. Walker Jr., P.C. Baker, Polarimetry of the H I Lyman-\(\alpha\) for coronal magnetic field diagnostics. Proc. SPIE 1742, 423 (1993) ADSCrossRefGoogle Scholar
  28. S. Fineschi, A. van Ballegoijen, J.L. Kohl, Coronal magnetic field diagnostics with UV spectropolarimetry. ESA SP 446, 317 (1999) ADSGoogle Scholar
  29. J.M. Fontenla, E.H. Avrett, R. Loeser, Energy balance in the solar transition region. III. Helium emission in hydrostatic, constant-abundance models with diffusion. Astrophys. J. 406, 319 (1993) ADSCrossRefGoogle Scholar
  30. A.H. Gabriel, Measurements on the Lyman-\(\alpha\) corona. Sol. Phys. 21, 392 (1971) ADSCrossRefGoogle Scholar
  31. A.H. Gabriel, et al., Rocket observations of the ultraviolet solar spectrum during the total eclipse of 1970 March 7. Astrophys. J. 169, 595 (1971) ADSCrossRefGoogle Scholar
  32. G.E. Hale, On the probable existence of a magnetic field in sunspots. Astrophys. J. 28, 315 (1908) ADSCrossRefGoogle Scholar
  33. W. Hanle, Über magnetische Beeinflussung der Polarisation der Resonanzfluoreszenz. Z. Phys. 30, 93 (1924) ADSCrossRefGoogle Scholar
  34. W. Henze, J.O. Stenflo, Polarimetry in the Mg II \(h\) and \(k\) lines. Sol. Phys. 111, 243 (1987) ADSCrossRefGoogle Scholar
  35. W. Henze et al., Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot. Sol. Phys. 81, 231 (1982) ADSCrossRefGoogle Scholar
  36. I. Hubeny, D. Mihalas, Theory of Stellar Atmospheres (Princeton University Press, Princeton/Oxford, 2015) zbMATHGoogle Scholar
  37. D.G. Hummer, Non-coherent scattering: I. The redistribution function with Doppler redistribution. Mon. Not. R. Astron. Soc. 125, 21 (1962) ADSCrossRefzbMATHGoogle Scholar
  38. R. Kano, J. Trujillo Bueno, A. Winebarger et al., Discovery of scattering polarization in the hydrogen Lyman-\(\alpha\) line of the solar disk radiation. Astrophys. J. (2017, in press) Google Scholar
  39. A. Khan, E. Landi Degl’Innocenti, Solar coronal magnetic field diagnostics through polarimetric forward modelling of the Hanle effect. Astron. Astrophys. 532, 70 (2011) CrossRefGoogle Scholar
  40. A. Khan, E. Landi Degl’Innocenti, Spectropolarimetric signatures of anisotropic velocity distributions of optically thin coronal UV lines. Astron. Astrophys. 543, 158 (2012) CrossRefGoogle Scholar
  41. A. Khan, L. Belluzzi, E. Landi Degl’Innocenti, S. Fineschi, M. Romoli, Spectropolarimetric forward modelling of the lines of the Lyman-series using a self-consistent, global, solar coronal model. Astron. Astrophys. 529, 12 (2011) CrossRefGoogle Scholar
  42. K. Kobayashi, R. Kano, J. Trujillo Bueno et al., The Chromospheric Lyman-Alpha SpectroPolarimeter: CLASP, in The Fifth Hinode Science Meeting, ed. by L. Golub, I. De Moortel, T. Shimizu. Astronomical Society of the Pacific Conference Series, vol. 456 (2012), p. 233 Google Scholar
  43. J.L. Kohl et al., First results from the SOHO ultraviolet coronagraph spectrometer. Sol. Phys. 175, 613 (1997) ADSCrossRefGoogle Scholar
  44. E. Landi Degl’Innocenti, The determination of vector magnetic fields in prominences from the observations of the Stokes profiles in the D3 line of helium. Sol. Phys. 79, 291 (1982) ADSCrossRefGoogle Scholar
  45. E. Landi Degl’Innocenti, Polarization in spectral lines. III. Resonance polarization in the non-magnetic, collisionless regime. Sol. Phys. 91, 1 (1984) ADSGoogle Scholar
  46. E. Landi Degl’Innocenti, Atomic Spectroscopy and Radiative Processes (Springer, Milan, 2014) CrossRefGoogle Scholar
  47. E. Landi Degl’Innocenti, V. Bommier, A spectroscopic method for the solution of the \(180^{\circ}\) azimuth ambiguity in magnetograms. Astrophys. J. 411, L49 (1993) ADSCrossRefGoogle Scholar
  48. M. Landi Degl’Innocenti, E. Landi Degl’Innocenti, An analytical expression for the Hanle-effect scattering phase matrix. Astron. Astrophys. 192, 374 (1988) ADSzbMATHGoogle Scholar
  49. E. Landi Degl’Innocenti, M. Landolfi, Polarization in Spectral Lines (Kluwer, Dordrecht, 2004) CrossRefGoogle Scholar
  50. H. Lin, J.R. Kuhn, R. Coulter, Coronal magnetic field measurements. Astrophys. J. 613, 177 (2004) ADSCrossRefGoogle Scholar
  51. R. Manso Sainz, J. Trujillo Bueno, A possible polarization mechanism of EUV coronal lines, in Solar Polarization 5, ed. by S.V. Berdyugina, K.N. Nagendra, R. Ramelli. Astronomical Society of the Pacific Conference Series, vol. 405 (2009), p. 423 Google Scholar
  52. R. Manso Sainz, J. Trujillo Bueno, Scattering polarization and Hanle effect in stellar atmospheres with horizontal inhomogeneities. Astrophys. J. 743, 12 (2011) ADSCrossRefGoogle Scholar
  53. J.S. Morrill, C.M. Korendyke, High-resolution center-to-limb variation of the quiet solar spectrum near Mg II. Astrophys. J. 687, 646 (2008) ADSCrossRefGoogle Scholar
  54. T. Pereira, B. De Pontieu, M. Carlsson et al., An Interface Region Imaging Spectrograph first view on spicules. Astrophys. J. 792, L15 (2014) ADSCrossRefGoogle Scholar
  55. H. Peter, Magnetic field diagnostics and spatio-temporal variability of the solar transition region. Sol. Phys. 288, 531 (2013) ADSCrossRefGoogle Scholar
  56. H. Peter et al., Solar magnetism eXplorer (SolmeX). Exploring the magnetic field in the upper atmosphere of our closest star. Exp. Astron. 33, 271 (2012) ADSCrossRefGoogle Scholar
  57. D.J. Pinfield, F.P. Keenan, M. Mathioudakis, K.J.H. Phillips, W. Curdt, K. Wilhelm, Evidence for non-Maxwellian electron energy distributions in the solar transition region: Si III line ratios from SUMER. Astrophys. J. 527, 1000 (1999) ADSCrossRefGoogle Scholar
  58. N.E. Raouafi, S.K. Solanki, Effect of anisotropic velocity distribution on the linear polarization of coronal lines. Does the ion cyclotron exist in the inner corona? Astron. Astrophys. 412, 271 (2003) ADSCrossRefGoogle Scholar
  59. N.E. Raouafi, P. Lemaire, S. Sahal-Bréchot, Detection of the O VI 103.2 nm line polarization by the SUMER spectrometer on the SOHO spacecraft. Astron. Astrophys. 345, 999 (1999) ADSGoogle Scholar
  60. N.E. Raouafi, S.K. Solanki, T. Wiegelmann, Hanle effect diagnostics of the coronal magnetic field: A test using realistic magnetic field configurations, in Solar Polarization 5, ed. by S.V. Berdyugina, K.N. Nagendra, R. Ramelli. ASP Conf. Ser., vol. 405 (2009), p. 429 Google Scholar
  61. J.C. Raymond et al., Composition of coronal streamers from the SOHO ultraviolet coronagraph spectrometer. Sol. Phys. 175, 645 (1997) ADSCrossRefGoogle Scholar
  62. D. Roussel-Dupré, Skylab observations of H I Lyman-\(\alpha\). Astrophys. J. 256, 284 (1982) ADSCrossRefGoogle Scholar
  63. S. Sahal-Bréchot, M. Malinovski, V. Bommier, The polarization of the O VI 1032 Å line as a probe for measuring the coronal vector magnetic field via the Hanle effect. Astron. Astrophys. 168, 284 (1986) ADSGoogle Scholar
  64. S. Sahal-Bréchot, V. Bommier, N. Feautrier, Doppler redistribution of anisotropic radiation and resonance polarization in moving scattering media. I. Theory revisited in the density matrix formalism. Astron. Astrophys. 340, 579 (1998) ADSGoogle Scholar
  65. J.O. Stenflo, Applications of the Hanle effect in solar physics, in The Hanle Effect and Level-Crossing Spectroscopy, ed. by G. Moruzzi, F. Strumia (Plenum, New York, 1991), p. 237 CrossRefGoogle Scholar
  66. J.O. Stenflo, L. Stenholm, Resonance line polarization. II Calculations of linear polarization in solar UV emission lines. Astron. Astrophys. 46, 69 (1976) ADSGoogle Scholar
  67. J.O. Stenflo, H. Biverot, L. Stenmark, Ultraviolet polarimeter to record resonance-line polarization in the solar spectrum around 130—150 nm. Appl. Opt. 15, 1188 (1976) ADSCrossRefGoogle Scholar
  68. J.O. Stenflo, D. Dravins, N. Wihlborg et al., Search for spectral line polarization in the solar vacuum ultraviolet. Sol. Phys. 66, 13 (1980) ADSCrossRefGoogle Scholar
  69. J. Štěpán, J. Trujillo Bueno, PORTA: a three-dimensional multilevel radiative transfer code for modeling the intensity and polarization of spectral lines with massively parallel computers. Astron. Astrophys. 557, A143 (2013) CrossRefGoogle Scholar
  70. J. Štěpán, J. Trujillo Bueno, The Hanle and Zeeman polarization signals of the solar Ca ii 8542 Å line. Astrophys. J. 826, L10 (2016) ADSCrossRefGoogle Scholar
  71. J. Štěpán, J. Trujillo Bueno, J. Leenaarts, M. Carlsson, Three-dimensional radiative transfer simulations of the scattering polarization of the hydrogen Ly-\(\alpha\) line in a magnetohydrodynamic model of the chromosphere-corona transition region. Astrophys. J. 803, 65 (2015) ADSCrossRefGoogle Scholar
  72. J. Trujillo Bueno, Atomic polarization and the Hanle effect, in Advanced Solar Polarimetry. Theory, Observation and Instrumentation, ed. by M. Sigwarth. Astronomical Society of the Pacific Conference Series, vol. 236 (2001), p. 161 Google Scholar
  73. J. Trujillo Bueno, The generation and transfer of polarized radiation in stellar atmospheres, in Stellar Atmosphere Modeling, ed. by I. Hubeny, D. Mihalas, K. Werner. Astronomical Society of the Pacific Conference Series, vol. 288 (2003), p. 551 Google Scholar
  74. J. Trujillo Bueno, Polarized radiation observables for probing the magnetism of the outer solar atmosphere, in Solar Polarization 7, ed. by K.N. Nagendra, J.O. Stenflo, Z.Q. Qu, M. Sampoorna. Astronomical Society of the Pacific Conference Series, vol. 489 (2014), p. 137 Google Scholar
  75. J. Trujillo Bueno, E. Landi Degl’Innocenti, Linear polarization due to lower-level depopulation pumping in stellar atmospheres. Astrophys. J. 482, L183 (1997) ADSCrossRefGoogle Scholar
  76. J. Trujillo Bueno, E. Landi Degl’Innocenti, M. Collados, L. Merenda, R. Manso Sainz, Selective absorption processes as the origin of puzzling spectral line polarization from the Sun. Nature 415, 403 (2002) ADSCrossRefGoogle Scholar
  77. J. Trujillo Bueno, E. Landi Degl’Innocenti, R. Casini, V. Martí nez Pillet, The scientific case for spectropolarimetry from space: A novel diagnostic window on cosmic magnetic fields, in 39th ESLAB Symposium on Trends in Space Science and Cosmic Vision 2020, ed. by F. Favata, J. Sanz-Forcada, A. Giménez, B. Battrick. ESA Publications Division (ESA SP-588) (2005), p. 203 Google Scholar
  78. J. Trujillo Bueno, J. Štěpán, R. Casini, The Hanle effect of the hydrogen Ly-\(\alpha\) line for probing the magnetism of the solar transition region. Astrophys. J. 738, L11 (2011) ADSCrossRefGoogle Scholar
  79. J. Trujillo Bueno, J. Štěpán, L. Belluzzi, The Ly-\(\alpha\) lines of H i and He ii: a differential Hanle effect for exploring the magnetism of the solar transition region. Astrophys. J. 746, L9 (2012) ADSCrossRefGoogle Scholar
  80. J.C. Vial, P. Lemaire, G. Artzner, P. Gouttebroze, O vi (\(\lambda=1032~{\mathring{\mathrm{A}}}\)) profiles in and above an active region prominence, compared to quiet Sun center and limb profiles. Sol. Phys. 68, 187 (1980) ADSCrossRefGoogle Scholar
  81. T.N. Woods, G.J. Rottman, Solar ultraviolet variability over time periods of aeronomic interest, in Comparative Aeronomy in the Solar System, ed. by M. Mendillo, A. Nagy, J. Hunter Waite Jr. Geophys. Monograph Series, vol. 130 (American Geophysical, Union, Washington DC, 2002), p. 221 CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  • Javier Trujillo Bueno
    • 1
  • Egidio Landi Degl’Innocenti
    • 2
  • Luca Belluzzi
    • 3
    • 4
  1. 1.Instituto de Astrofísica de CanariasLa Laguna, TenerifeSpain
  2. 2.Dipartimento di Fisica e AstronomiaUniversità di FirenzeFirenzeItaly
  3. 3.Istituto Ricerche Solari LocarnoLocarno MontiSwitzerland
  4. 4.Kiepenheuer-Institut für SonnenphysikFreiburgGermany

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