Optimal Spectral Lines for Measuring Chromospheric Magnetic Fields

Judge, P. G.; Bryans, P.; Casini, R.; Kleint, Lucia; Lacatus, D. A.; Paraschiv, Alin Rǎzvan; Schmit, D. J.

doi:10.3847/1538-4357/aca2a5

Cited by 6 publications

(3 citation statements)

References 58 publications

(57 reference statements)

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“…It be interesting to explore the kinds of observations presented here with other data sets, especially in regions of quiet Sun where, although the He I lines are weak, they can still be used to probe conditions at the coronal base (Harvey & Hall 1971;Rüedi et al 1996;Lagg et al 2004). In the case that the He I lines are too weak to explore at sufficiently high angular resolution, one might use the 854.2 nm line of Ca II, or if selected for flight, various lines of Mg II and Fe II in the UV region (259-281 nm) using the Chromospheric Magnetism Explorer instrument (Gilbert & CMEx Team 2023; see Judge et al 2021Judge et al , 2022 for reasons to observe in this region).…”

Section: Discussionmentioning

confidence: 99%

Magnetic Fields beneath Active Region Coronal Loops

Judge,

Kleint,

Kuckein

2024

ApJ

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We examine the hypothesis that multipolar magnetic fields advected by photospheric granules can contribute to heating the active chromosphere and corona. On 2020 September 28 the Gregor Infrared Spectrograph (GRIS) and HiFI+ instruments at the GREGOR telescope obtained data of NOAA 12773. We analyze Stokes profiles of spectral lines of Si i and He i, to study magnetic fields from the photosphere to the upper chromosphere. Magnetogram and EUV data from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly instruments on the Solar Dynamics Observatory spacecraft are coaligned and studied in relation to the GRIS data. At coronal loop footpoints, minor polarity fields comprise just 0.2% and 0.02% of the flux measured over the 40″ × 60″ area observed in the photosphere and upper chromosphere, centered 320″ from the disk center. Significantly, the minority fields are situated ≳12″ from bright footpoints. We use physical arguments to show that any unresolved minority flux cannot reach coronal footpoints adjacent to the upper chromosphere. Even if it did, the most optimistic estimate of the energy released through chromospheric reconnection is barely sufficient to account for the coronal energy losses. Further, dynamical changes accompanying reconnection between uni- and multipolar fields are seen neither in the He i data nor in narrowband movies of the Hα line core. We conclude that the hypothesis must be rejected. Bright chromospheric, transition region, and coronal loop plasmas must be heated by mechanisms involving unipolar fields.

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Section: Discussionmentioning

confidence: 99%

Magnetic Fields beneath Active Region Coronal Loops

Judge,

Kleint,

Kuckein

2024

ApJ

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“…Emission lines from various chlorine-like ions have been observed in a number of astrophysical sources, such as the solar corona [58], stellar chromospheres [59], or the interstellar medium [60]. The intensity ratios of these lines are typically temperatureand density-sensitive, and they can thus be utilized for the diagnostics of astrophysical plasma.…”

Section: Collision Strengths For Chlorine-like Ionsmentioning

confidence: 99%

Collision Strengths of Astrophysical Interest for Multiply Charged Ions

Fritzsche

Jiao

Wang

et al. 2023

Atoms

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The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their significance, however, little is known quantitatively about these processes for low- and medium-impact energies of, say, Ekin≲5000 eV of the free incident electron. To further explore the role of impact excitation, we here expanded Jac, the Jena Atomic Calculator, to the computation of distorted wave collision strengths for fine-structure-resolved, as well as configuration-averaged transitions. While we excluded the formation of dielectronic resonances, these tools can be readily applied for ions with a complex shell structure and by including the major relativistic contributions to these strengths. Detailed computations of the collision strengths are shown and explained for the impact excitation of lithium- and chlorine-like ions. When compared with other, well-correlated methods, good agreement was found, and hence, these tools will support studies of effective collision strengths for a wide range of electron impact energies, levels, and ionic charge states.

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“…Among these lines, two Fe II spectral lines stand out: a relatively weak emission line at 279.79 nm and an absorption line at 280.66 nm, just at the red edge of the CLASP2 spectral window. Recent investigations have suggested that the Fe II lines located blueward of the CLASP2 spectral region are of complementary interest for diagnosing the magnetism of the solar chromosphere (see Judge et al 2021Judge et al , 2022. A quantitative study of the polarization signals and magnetic sensitivity of the Fe II spectral lines in the near-UV region of the solar spectrum has been recently published by Afonso Delgado et al (2023a), but the Fe II lines located in the CLASP2 spectral region were not included in their work.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Information in the Near-ultraviolet Fe ii Lines of the CLASP2 Space Experiment

Afonso Delgado,

del Pino Alemán,

Trujillo Bueno

2023

ApJ

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We investigate theoretically the circular polarization signals induced by the Zeeman effect in the Fe ii lines of the 279.3–280.7 nm spectral range of the CLASP2 space experiment and their suitability to infer solar magnetic fields. To this end, we use a comprehensive Fe ii atomic model to solve the problem of the generation and transfer of polarized radiation in semiempirical models of the solar atmosphere, comparing the region of formation of the Fe ii spectral lines with those of the Mg ii h and k and the Mn i resonance lines. These are present in the same near-ultraviolet (near-UV) spectral region and allowed the mapping of the longitudinal component of the magnetic field (B L) through several layers of the solar chromosphere in an active region plage. We compare our synthetic intensity profiles with observations from the IRIS and CLASP2 missions, proving the suitability of our model atom to characterize these Fe ii spectral lines. The CLASP2 observations show two Fe ii spectral lines at 279.79 and 280.66 nm with significant circular polarization signals. We demonstrate the suitability of the weak-field approximation applied to the Stokes I and V profiles of these Fe ii lines to infer B L in the plage atmosphere. We conclude that the near-UV spectral region of CLASP2 allows us to determine B L from the upper photosphere to the top of the chromosphere of active region plages.

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Optimal Spectral Lines for Measuring Chromospheric Magnetic Fields

Cited by 6 publications

References 58 publications

Magnetic Fields beneath Active Region Coronal Loops

Magnetic Fields beneath Active Region Coronal Loops

Collision Strengths of Astrophysical Interest for Multiply Charged Ions

Magnetic Field Information in the Near-ultraviolet Fe ii Lines of the CLASP2 Space Experiment

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