Spectral Lines in FUV and EUV for Diagnosing Coronal Magnetic Field

Khan, Raveena; Nagaraju, K.

doi:10.1007/s11207-022-02024-2

Cited by 2 publications

(3 citation statements)

References 58 publications

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“…Because of the typical low levels of coronal polarization, spectropolarimetric observations are notoriously photon starved, and therefore it is critical to identify coronal diagnostics with significant photon fluxes. Among the Hanle sensitive lines of the EUV listed by Khan & Nagaraju (2022), Ne VIII 770 Å appears to be the brightest one. It has a line formation temperature of about 800,000 K, so it originates between the transition region (TR) and the lower solar corona (Fludra et al 2021).…”

Section: Magnetic Sensitivity Of Scattering Polarization In the Unsat...mentioning

confidence: 96%

“…Extensive theoretical studies have been performed in the FUV coronal lines, i.e., O VI 1032 Å (Sahal- Bréchot et al 1986;Trujillo Bueno et al 2017;Zhao et al 2019) and Lyα 1215 Å (Bommier & Sahal-Bréchot 1982;Fineschi et al 1991;Hebbur Dayananda et al 2021). Recently, Khan & Nagaraju (2022) have reported several electric-dipole (E1) transition lines in the UV with different sensitivity regimes to the unsaturated Hanle effect. These lines can be exploited as potential diagnostics of the coronal magnetic field vector (Fineschi et al 1993;Fineschi & Habbal 1995), possibly enabling the technique of differential Hanle effect (House & Smartt 1982;Stenflo et al 1998;Trujillo Bueno et al 2012), to make the coronal diagnostic more robust to model dependencies.…”

Section: Introductionmentioning

confidence: 99%

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Extreme-ultraviolet Polarimetric Diagnostics of the Solar Corona: The Hanle Effect of Ne viii 770 Å

Khan,

Gibson,

Casini

et al. 2024

ApJ

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Magnetic fields are the primary driver of the plasma thermodynamics in the upper solar atmosphere, especially in the corona. However, magnetic field measurements in the solar corona are sporadic, thereby limiting us from the complete understanding of physical processes occurring in the coronal plasma. In this paper, we explore the diagnostic potential of a coronal emission line in the extreme-ultraviolet, i.e., Ne viii 770 Å, to probe the coronal magnetic fields. We utilize 3D “Magnetohydrodynamic Algorithm outside a Sphere” models as input to the FORWARD code to model polarization in the Ne viii line produced as a result of resonance scattering, and we interpret its modification due to collisions and the magnetic fields through the Hanle effect. The polarization maps are synthesized both on the disk and off the limb. The variation of this polarization signal through the different phases of Solar Cycle 24 and the beginning phase of Solar Cycle 25 is studied in order to understand the magnetic diagnostic properties of this line owing to different physical conditions in the solar atmosphere. The detectability of the linear polarization signatures of the Hanle effect significantly improves with increasing solar activity, consistent with the increase in the magnetic field strength and the intensity of the mean solar brightness at these wavelengths. We finally discuss the signal-to-noise ratio requirements by considering realistic instrument designs.

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Section: Magnetic Sensitivity Of Scattering Polarization In the Unsat...mentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Extreme-ultraviolet Polarimetric Diagnostics of the Solar Corona: The Hanle Effect of Ne viii 770 Å

Khan,

Gibson,

Casini

et al. 2024

ApJ

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“…The spectral lines should possess non-zero polarizability to resonance scattering, good line radiance and a critical Hanle field (different for each line) that lies within the range of coronal field strengths. In our recently published work, 12 we reported these parameters and provided a list of expected spectral lines which are sensitive to the Hanle effect. To exploit the differential Hanle effect, 13 a minimum of two spectral lines are required to infer full vector information of the magnetic field unambiguously.…”

Section: Introductionmentioning

confidence: 99%

Design concepts of EUV polarimeter

Khan,

Nagaraju,

Phanindra

2023

Optics for EUV, X-Ray, and Gamma-Ray Astronomy XI

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The solar corona is a complex and dynamic region primarily controlled by the magnetic fields. Hence the routine measurement of these fields is crucial. Magnetic field information remains embedded in the polarization profiles of the spectral lines, which can be quantified through spectropolarimetry. Differential Hanle effect is a promising diagnostic tool to probe weak coronal magnetic fields and their vector properties. In a recent study we have found several combinations of spectral lines located in the wavelength range 100 to 1210 Å suitable for the above purpose whose critical Hanle field lies in the range of 0.01-200 Gauss. Since the background emission from the Sun’s underlying layers, such as the photosphere and the chromosphere, is almost negligible at these short wavelengths, the coronagraphic technique is not required to study the solar corona, thereby enabling both on-disk and off-limb measurements. Yet there is no EUV polarimeter built for solar observations. In this context we explored a few polarimeter concepts based on the configurations of two and three reflecting mirrors. The performances of these configurations are studied in terms of their throughput and polarizing power using Zemax software in the wavelength range 740-780 Å. They are also compared with different coating materials namely, BaF2, MgF2 and LiF. It is found that BaF2 has significantly higher throughput and polarizing power in the above stated wavelength range.

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Spectral Lines in FUV and EUV for Diagnosing Coronal Magnetic Field

Cited by 2 publications

References 58 publications

Extreme-ultraviolet Polarimetric Diagnostics of the Solar Corona: The Hanle Effect of Ne viii 770 Å

Extreme-ultraviolet Polarimetric Diagnostics of the Solar Corona: The Hanle Effect of Ne viii 770 Å

Design concepts of EUV polarimeter

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