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Polarimetric Observations of the Sun

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Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 460))

Abstract

Probing the magnetism of the solar atmosphere requires measuring the polarisation state of the light in different wavelength bands. Since the physical conditions of the solar plasma change dramatically from the optically thick photosphere which is the main contributor to the emitted radiation in visible wavelengths to the optically thin outer solar atmosphere, several polarisation mechanisms contribute to the continuum and spectral line polarisation throughout the solar atmosphere. This chapter presents an overview of the main sources of light polarisation in the Sun along with some recent investigations of the polarisation produced in the solar atmosphere.

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Notes

  1. 1.

    He employed a rudimentary but efficient polarisation analyser to separate the different polarisation states, pretty much the same strategy we follow nowadays.

  2. 2.

    Already in 1802, William Wollaston detected solar Fraunhofer lines.

  3. 3.

    Microturbulence accounts for plasma motions taking place at spatial scales smaller than the photon mean free path.

  4. 4.

    The anisotropy is caused by the solar limb-darkening and local inhomogeneities.

  5. 5.

    Notice that for strong fields the He I infrared triplet in the incomplete Paschen-Back regime (Socas-Navarro et al. 2004).

  6. 6.

    Mainly due to electron–ion and H free–free absorption.

  7. 7.

    A full review of the quiet Sun magnetic fields can be found in Bellot Rubio and Orozco Suárez (2019).

  8. 8.

    Roughly speaking, a longitudinal magnetogram is a map of the line-of-sight component of the magnetic field taken at the Stokes V  wing of a magnetic sensitivity spectral line.

  9. 9.

    The reader is referred to del Toro Iniesta and Ruiz Cobo (2016) for detailed review on the inversion of the radiative transfer equation in solar physics.

  10. 10.

    Spectro-Polarimeter for INfrared and Optical Regions, at the Dunn Solar Telescope in Sacramento Peak Observatory.

  11. 11.

    Filaments are prominences as seen against the brighter solar disc.

  12. 12.

    It is generally accepted that prominence plasma is supported against gravity by collisions and magnetic tension force. For comprehensive reviews go to, e.g., Parenti (2014).

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Acknowledgements

This work has been supported by Spanish Ministry of Science, Innovation and Universities through the project RTI2018-096886-B-C51. The author acknowledges support from a Ramón y Cajal fellowship RYC-2016-20150 by the spanish Ministerio de Economía, Industria y Competitividad. He also thanks J. C. del Toro Iniesta, L. R. Bellot Rubio, and J. Trujillo Bueno for comments that greatly improved the manuscript. IAA-CSIC acknowledges financial support from the Spanish Research Agency (AEI/MCIU) through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709).

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Correspondence to David Orozco Suárez .

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Suárez, D.O. (2019). Polarimetric Observations of the Sun. In: Mignani, R., Shearer, A., Słowikowska, A., Zane, S. (eds) Astronomical Polarisation from the Infrared to Gamma Rays. Astrophysics and Space Science Library, vol 460. Springer, Cham. https://doi.org/10.1007/978-3-030-19715-5_6

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