Neutral Hydrogen and Its Emission Lines in the Solar Corona

Vial, J. C.; Chane-Yook, Martine

doi:10.1007/s11207-016-0995-x

Cited by 11 publications

(10 citation statements)

References 43 publications

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“…The mean k/h ratio takes a value of 1.41 in both the tornadoes and in the rest of the prominence. This is a similar value as has been found previously (Schmieder et al 2014;Liu et al 2015;Levens et al 2016a;Vial et al 2016). The displacement of the k 3 feature from its stationary position at line centre gives an indication of how the frontmost layers of the prominence are moving along the line-of-sight.…”

Section: Resultssupporting

confidence: 89%

“…Under normal chromospheric conditions, where the Mg ii ions are collisionally excited, we would expect a k/h ratio of 2 and the plasma to be opti-cally thin. Previous prominence observations have shown typical k/h ratios of around 1.5 (Schmieder et al 2014;Liu et al 2015;Vial et al 2016;Levens et al 2016a), and NLTE models of Mg ii have found similar expected values (Heinzel et al 2014). Values lower than 2, as have been observed, suggest the presence of scattering in the emitting region, i.e.…”

Section: Mg II I K /I H Ratiosupporting

confidence: 61%

“…The Mg ii h and k lines are optically thick in prominences, evident from observed centrally reversed profiles (Paper 1). However they are not always reversed (Vial 1982;Schmieder et al 2014;Vial et al 2016), often showing non-reversed, singlepeaked profiles. This behaviour can be explained by different physical conditions in different regions of the prominence (Heinzel et al 2014(Heinzel et al , 2015.…”

Section: Plasma Diagnosticsmentioning

confidence: 99%

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Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes

Levens

Labrosse

Schmieder

et al. 2017

A&A

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Context. Understanding the close relationship between the plasma and the magnetic field is important to describe and explain the observed complex dynamics of solar prominences. Aims. We determine if a close relationship between plasma and magnetic field parameters measured in a well-observed solar prominence with high spatial resolution can be found. Methods. We select a prominence observed on 15 July 2014 from space (IRIS, Hinode, SDO) and from the ground (THEMIS). We perform a robust co-alignment of the data sets using a 2D cross-correlation technique. We derive the magnetic field parameters from spectropolarimetric measurements of the He i D 3 line taken by THEMIS. Line ratios and line-of-sight velocities from the Mg ii h and k lines observed by IRIS are compared with magnetic field strength, inclination and azimuth. Electron densities are calculated using Hinode/EIS Fe xii line ratios and also compared with THEMIS and IRIS data. Results. We find Mg ii k/h ratios of around 1.4 everywhere, similar to values found previously in prominences. We also find that the magnetic field is strongest (∼ 30 G) and predominantly horizontal in the tornado-like legs of the prominence. The k 3 Doppler shift is found to be between ± 10 km s −1 everywhere. Electron densities at a temperature of 1.5 × 10 6 K are found to be around 10 9 cm −3 . No significant correlations are found between the magnetic field parameters, and any of the other plasma parameters inferred from EUV spectroscopy, which may be explained by the large differences in the temperatures of the lines used in this study. Conclusions. This is the first time that a detailed statistical study of plasma and magnetic field parameters has been carried out at high spatial resolution in a prominence. Our results provide important constraints on future models of the plasma and magnetic field in these structures.

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Section: Resultssupporting

confidence: 89%

Section: Mg II I K /I H Ratiosupporting

confidence: 61%

Section: Plasma Diagnosticsmentioning

confidence: 99%

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Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes

Levens

Labrosse

Schmieder

et al. 2017

A&A

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“…In general, the Mg II k line profile in on-disk observations has a central reversal in the emission peak within an even broader absorption component, which are produced by a complex radiative transfer process (Leenaarts et al 2013a,b;Pereira et al 2013). In off-limb observations, as long as there is no spatial overlap of different features along the line of sight, the profile is simple with a single, Gaussian-shaped peak indicative of optically thin emission (e.g., Schmieder et al 2014;Liu et al 2015;Vial et al 2016). This is indeed the case for most parts of our observed prominence.…”

Section: Event 2: 2013 October 19mentioning

confidence: 51%

Helical Motions of Fine-Structure Prominence Threads Observed by Hinode and Iris

Okamoto

Liu

Tsuneta

2016

ApJ

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Fine-structure dynamics in solar prominences holds critical clues to understanding their physical nature of significant space-weather implications. We report evidence of rotational motions of horizontal helical threads in two activeregion prominences observed by the Hinode and/or IRIS satellites at high resolution. In the first event, we found transverse motions of brightening threads at speeds up to 55 km s −1 seen in the plane of the sky. Such motions appeared as sinusoidal space-time trajectories with a typical period of ∼390 s, which is consistent with plane-of-sky projections of rotational motions. Phase delays at different locations suggest propagation of twists along the threads at phase speeds of 90-270 km s −1 . At least 15 episodes of such motions occurred in two days, none associated with any eruption. For these episodes, the plane-of-sky speed is linearly correlated with the vertical travel distance, suggestive of a constant angular speed. In the second event, we found Doppler velocities of 30-40 km s −1 in opposite directions in the top and bottom portions of the prominence, comparable to the plane-of-sky speed. The moving threads have about twice broader line widths than stationary threads. These observations, when taken together, provide strong evidence for rotations of helical prominence threads, which were likely driven by unwinding twists triggered by magnetic reconnection between twisted prominence magnetic fields and ambient coronal fields.

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“…The coronal number density of ionized hydrogen can be inferred by measuring the electron density from the VL polarised emission detected with Metis. Under the hypothesis of ionisation equilibrium, the ratio between neutral and ionized hydrogen atoms depends on the electron temperature, for example, see Vial & Chane-Yook (2016). The T e radial profiles can be selected from the literature.…”

Section: Diagnostic Techniquesmentioning

confidence: 99%

Metis: the Solar Orbiter visible light and ultraviolet coronal imager

Antonucci

Romoli

Andretta

et al. 2020

A&A

Self Cite

136

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Aims. Metis is the first solar coronagraph designed for a space mission and is capable of performing simultaneous imaging of the off-limb solar corona in both visible and UV light. The observations obtained with Metis aboard the Solar Orbiter ESA-NASA observatory will enable us to diagnose, with unprecedented temporal coverage and spatial resolution, the structures and dynamics of the full corona in a square field of view (FoV) of ±2.9 • in width, with an inner circular FoV at 1.6 • , thus spanning the solar atmosphere from 1.7 R to about 9 R , owing to the eccentricity of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter mission profile, Metis will be able to observe the solar corona from a close (0.28 AU, at the closest perihelion) vantage point, achieving increasing out-of-ecliptic views with the increase of the orbit inclination over time. Moreover, observations near perihelion, during the phase of lower rotational velocity of the solar surface relative to the spacecraft, allow longer-term studies of the off-limb coronal features, thus finally disentangling their intrinsic evolution from effects due to solar rotation. Methods. Thanks to a novel occultation design and a combination of a UV interference coating of the mirrors and a spectral bandpass filter, Metis images the solar corona simultaneously in the visible light band, between 580 and 640 nm, and in the UV H i Lyman-α line at 121.6 nm. The visible light channel also includes a broadband polarimeter able to observe the linearly polarised component of the K corona. The coronal images in both the UV H i Lyman-α and polarised visible light are obtained at high spatial resolution with a spatial scale down to about 2000 km and 15000 km at perihelion, in the cases of the visible and UV light, respectively. A temporal resolution down to 1 second can be achieved when observing coronal fluctuations in visible light. Results. The Metis measurements, obtained from different latitudes, will allow for complete characterisation of the main physical parameters and dynamics of the electron and neutral hydrogen/proton plasma components of the corona in the region where the solar wind undergoes the acceleration process and where the onset and initial propagation of coronal mass ejections (CMEs) take place. The near-Sun multi-wavelength coronal imaging performed with Metis, combined with the unique opportunities offered by the Solar Orbiter mission, can effectively address crucial issues of solar physics such as: the origin and heating/acceleration of the fast and slow solar wind streams; the origin, acceleration, and transport of the solar energetic particles; and the transient ejection of coronal mass and its evolution in the inner heliosphere, thus significantly improving our understanding of the region connecting the Sun to the heliosphere and of the processes generating and driving the solar wind and coronal mass ejections. Conclusions. This paper presents the scientific objectives and requirements, the overall optical design of the Metis instrument, t...

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Neutral Hydrogen and Its Emission Lines in the Solar Corona

Cited by 11 publications

References 43 publications

Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes

Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes

Helical Motions of Fine-Structure Prominence Threads Observed by Hinode and Iris

Metis: the Solar Orbiter visible light and ultraviolet coronal imager

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