Analysis of non-thermal velocities in the solar corona

Contesse, L.; Koutchmy, S.; Viladrich, Christian

doi:10.5194/angeo-22-3055-2004

Cited by 10 publications

(15 citation statements)

References 20 publications

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“…5, the Fe XIV line is observed everywhere in the corona, even in the darkest regions of the deep polar CHs. This is clearly a result of the improved S/N compared to previous studies and especially compared to the Lyot coronagraph analysis (e.g., Contesse et al 2004) and even studies made in space (Mierla et al 2008). A part of the Fe XIV flux is seen in CH regions that come from distant regions, which contribute along the l.o.s.…”

Section: Discussion and Perspectivesmentioning

confidence: 74%

“…This F-component, which is not to be confused with the scattered light from the terrestrial atmosphere , is due to the dust surrounding the Sun and originates in heliospheric comets heated by the Sun, degrading asteroids, and meteorites and small micron size bodies orbiting close to the Sun. At ground-based facilities large aperture Lyot coronagraphs that work under the direct solar light are limited by the parasitic light of different origins, and solar F-lines are imprinted (e.g., Koutchmy et al 1983;Contesse et al 2004). Their spatial resolution is often too marginal for a deep spectroscopic analysis of barely resolved structures due to turbulent effects of the daytime seeing and inside the instrument where the solar disk is concentrated on the artificial Moon.…”

Section: Introductionmentioning

confidence: 99%

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New deep coronal spectra from the 2017 total solar eclipse

Koutchmy

Baudin

Abdi

et al. 2019

A&A

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Context. The origin of the high temperature of the solar corona, in both the inner bright parts and the more outer parts showing flows toward the solar wind, is not understood well yet. Total eclipses permit a deep analysis of both the inner and the outer parts of the corona using the continuum white-light (W-L) radiations from electrons (K-corona), the superposed spectrum of forbidden emission lines from ions (E-corona), and the dust component with F-lines (F-corona). Aims. By sufficiently dispersing the W-L spectrum, the Fraunhofer (F) spectrum of the dust component of the corona appears and the continuum Thomson radiation can be evaluated. The superposed emission lines of ions with different degrees of ionization are studied to allow the measurement of temperatures, non-thermal velocities, Doppler shifts, and abundances to constrain the proposed heating mechanisms and understand the origin of flows that lead to solar wind. Methods. We describe a slit spectroscopic experiment of high spectral resolution to provide an analysis of the most typical parts of the quasi-minimum type corona observed during the total solar eclipse of Aug 21, 2017 from Idaho, USA. Streamers, active region enhancements, and polar coronal holes (CHs) are measured well using deep spectra. Results. Sixty spectra are obtained during the totality with a long slit, covering ±3 solar radii in the range of 510 nm to 590 nm. The K+F continuum corona is exposed well up to two solar radii. The F-corona can be measured even at the solar limb. New weak emission lines were discovered or confirmed. The rarely observed Ar X line is detected almost everywhere; the Fe XIV and Ni XIII lines are clearly detected everywhere. For the first time hot lines are also measured inside the CH regions. The radial variations of the non-thermal turbulent velocities of the lines do not show a great departure from the average values. No significantly large Doppler shifts are seen anywhere in the inner or the middle corona. The wings of the Fe XIV line show some non-Gaussianity. Conclusions. Deep slit coronal spectra offered an opportunity for diagnosing several aspects of coronal physics during a well observed total eclipse without extended investments. The analysis of the ionic emission line profiles offers several powerful diagnostics of the coronal dynamics; the precise measurement of the F-continuum component provides insight into the ubiquitous dust corona at the solar limb.1

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Section: Discussion and Perspectivesmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

New deep coronal spectra from the 2017 total solar eclipse

Koutchmy

Baudin

Abdi

et al. 2019

A&A

Self Cite

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“…But the reason for the lack of change in FWHM of the green emission line remains to be explored. Contesse, Koutchmy, and Viladrich (2004) analyzed the spectra in the green line at several off-limb locations both in equatorial and polar corona up to 12 ′ heights above the limb. They did not find any decrease in the green-line width with height, and they observed higher values of line width in the polar regions.…”

Section: Discussionmentioning

confidence: 99%

Variation of Emission Line Width in Mid- and High-Latitude Corona

2012

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Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines We find that the FWHM of the red line increases with height and that of the green line decreases with height similar to that observed in equatorial regions. The line widths are found to be higher in polar regions for all of the observed emission lines except for the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored.

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“…Hassler et al 1990;Contesse et al 2004). But this supposes ionization equilibrium, while several authors think that the plasma above coronal holes is weakly collisional (Tu et al 1998;Banerjee et al 1998).…”

Section: Distinguishing Thermal and Non-thermal Doppler Effectsmentioning

confidence: 99%

Solar off-limb line widths: Alfvén waves, ion-cyclotron waves, and preferential heating

Dolla

Solomon

2008

A&A

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Context. Alfvén waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). Aims. We propose a method to constrain both the Alfvén wave amplitude and the preferential heating induced by ion-cyclotron resonance, above a partially developed polar coronal hole observed with the SUMER/SOHO spectrometer. Methods. The instrumental stray light contribution is first substracted from the spectra. By supposing that the non-thermal velocity is related to the Alfvén wave amplitude, it is constrained through a density diagnostic and the gradient of the width of the Mg x 625 Å line. The temperatures of several coronal ions, as functions of the distance above the limb, are then determined by substracting the non-thermal component to the observed line widths. Results. The effect of stray light explains the apparent decrease with height in the width of several spectral lines, this decrease usually starting about 0.1−0.2 R above the limb. This result rules out any direct evidence of damping of the Alfvén waves, often suggested by other authors. We also find that the ions with the smallest charge-to-mass ratios are the hottest ones at a fixed altitude and that they are subject to a stronger heating, as compared to the others, between 57 and 102 above the limb. This constitutes a serious clue to ion-cyclotron preferential heating.

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Analysis of non-thermal velocities in the solar corona

Cited by 10 publications

References 20 publications

New deep coronal spectra from the 2017 total solar eclipse

New deep coronal spectra from the 2017 total solar eclipse

Variation of Emission Line Width in Mid- and High-Latitude Corona

Solar off-limb line widths: Alfvén waves, ion-cyclotron waves, and preferential heating

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