Helium emission in the middle chromosphere

Livshits, M. A.; Akimov, L. A.; Belkina, I. L.; Dyatel, N. P.

doi:10.1007/bf00162455

Cited by 13 publications

(12 citation statements)

References 8 publications

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“…Direct collisional excitation at temperatures above 20 kK is a negligible source of lower level population in our model. We also confirm the conclusion by Livshits et al (1976) that the relative opacity of He i 1083 nm is electron density dependent: for a given mass density and coronal illumination the extinction coefficient is an increasing function of the electron density under typical chromospheric conditions. Our simulations are not representative for strongly magnetically active areas and phenomena, such as emerging flux regions, flares and plage.…”

Section: Discussionsupporting

confidence: 86%

“…Zirin 1975;Livshits et al 1976;Pozhalova 1988;Avrett et al 1994;Andretta & Jones 1997;Centeno et al 2008), but all either in a plane-parallel slab geometry or using one-dimensional plane-parallel atmospheres without an actual corona. Consequently the coronal radiation field in these calculations had to be prescribed, for which typically the data described in Tobiska (1991) has been used.…”

Section: Introductionmentioning

confidence: 99%

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The cause of spatial structure in solar He i 1083 nm multiplet images

Leenaarts¹,

Golding²,

Carlsson³

et al. 2016

A&A

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Context. The He i 1083 nm is a powerful diagnostic for inferring properties of the upper solar chromosphere, in particular for the magnetic field. The basic formation of the line in one-dimensional models is well understood, but the influence of the complex threedimensional structure of the chromosphere and corona has however never been investigated. This structure must play an essential role because images taken in He i 1083 nm show structures with widths down to 100 km. Aims. To understand the effect of the three-dimensional temperature and density structure in the solar atmosphere on the formation of the He i 1083 nm line. Methods. We solve the non-LTE radiative transfer problem assuming statistical equilibrium for a simple 9-level helium atom that nevertheless captures all essential physics. As a model atmosphere we use a snapshot from a 3D radiation-MHD simulation computed with the Bifrost code. Ionising radiation from the corona is self-consistently taken into account. Results. The emergent intensity in the He i 1083 nm is set by the source function and the opacity in the upper chromosphere. The former is dominated by scattering of photospheric radiation and does not vary much with spatial location. The latter is determined by the photonionisation rate in the He i ground state continuum, as well as the electron density in the chromosphere. The spatial variation of the flux of ionising radiation is caused by the spatially-structured emissivity of the ionising photons from material at T ≈ 100 kK in the transition region. The hotter coronal material produces more ionising photons, but the resulting radiation field is smooth and does not lead to small-scale variation of the UV flux. The corrugation of the transition region further increases the spatial variation of the amount of UV radiation in the chromosphere. Finally we find that variations in the chromospheric electron density also cause strong variation in He i 1083 nm opacity. We compare our findings to observations using SST, IRIS and SDO/AIA data.

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

The cause of spatial structure in solar He i 1083 nm multiplet images

Leenaarts¹,

Golding²,

Carlsson³

et al. 2016

A&A

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“…Zirin, 1975;Livshits et al, 1976). These lines should therefore provide useful probes of the lower and middle chromosphere, although in order to use the line intensities to calculate such parameters as electron density it is necessary to have information on the geometry of the emitting region.…”

Section: Introductionmentioning

confidence: 99%

“…These lines should therefore provide useful probes of the lower and middle chromosphere, although in order to use the line intensities to calculate such parameters as electron density it is necessary to have information on the geometry of the emitting region. Previous calculations have all been based on a homogeneous chromosphere, and yield Ne ~ 2-4 x 101~ cm -3 at h = 2000 km (Livshits et al, 1976;Milkey et al, 1973), although Livshits et al considered that the D3 emission occurred in small filaments, and that the calculated electron density represented an average value.…”

Section: Introductionmentioning

confidence: 99%

D3 spicules and the lower chromosphere

Marsh

1978

Sol Phys

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High resolution filtergrams of the solar limb in D3 and off-band Ha have been used to investigate the spatial structure of the D 3 chromosphere. It was found that spicules provide the major contribution to the intensity of the D3 emission band observed above the limb, with the remainder of the emission coming from a semi-homogeneous background component at low heights.The observations can be understood on the basis of the photoionization model, whereby it is found that helium is only slightly ionized at the height Of peak intensity in the D3 emission band, and that spicules are at least 3 times denser than their surroundings at this height.In coronal holes, the D3 emission is confined to isolated emission patches, and these patches contain a fine structure resembling normal chromospheric spicules.

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“…It is commonly accepted that the height distributions of surface brightness for all helium lines, including the HeI D3 line, are similar. The surface brightness increases with height first, reaches a maximum above the solar limb in the range of 1100 -1300 km [2−7] (sometimes it may extend to 1700 km [8] ) for quiet chromosphere and then decreases exponentially. Another possible maximum of the HeI D3 line surface brightness distribution at lower height is also reported [5,9,10] even though it remains unexplained.…”

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confidence: 99%

The calibration and initial results of the HeI D3 line flash spectrum obtained during the 2008 total solar eclipse

et al. 2009

Sci. China Ser. G-Phys. Mech. Astron.

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The flash spectra in the HeI D3 line were obtained during the 2008 total solar eclipse. This paper describes the instrument and the calibration of the obtained flash spectrum, and presents our initial results. The average integrated intensity is Eave = 8.13×10 13 erg·cm −1 · s −1 ·ster −1 at h = 1100 km, which confirms that the HeI D3 emission is negatively correlated with the solar activity. The surface brightness reaches a maximum of F ave = 8.25×10 5 erg·cm −2 ·s −1 ·ster −1 at about h ≈ (1290 ± 75) km and then decreases exponentially with height when h >1800 km with an exponential index β = 1.63×10 −8 cm −1 .total solar eclipse, flash spectrum, spectral line Total solar eclipse (TSE) provides an excellent opportunity to observe the high chromosphere and low corona in optically thin spectral lines (e.g., the HeI D3 line) and coronal forbidden lines (e.g., the Fe xiv 5303Å and Fe x 6374Å lines). Even though some lines are also observable during the non-eclipse time, they suffer from serious sky brightness, which may be comparable with the line intensity [1] . Therefore, solar physicists always congregate from all over the world to conduct various scientific observations whenever a TSE happens.Helium is the second abundant element in the solar atmosphere. However, due to the small optical thickness, among the spectral lines of helium in the optical waveband, only the HeI D3 line, the strongest line, most commonly used in TSE observations, shows weak emission close to the solar limb. This line is important to both solar physics and the study of the excitation mechanism of helium lines. It is commonly accepted that the height distributions of surface brightness for all helium lines, including the HeI D3 line, are simi-

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Helium emission in the middle chromosphere

Cited by 13 publications

References 8 publications

The cause of spatial structure in solar He i 1083 nm multiplet images

The cause of spatial structure in solar He i 1083 nm multiplet images

D3 spicules and the lower chromosphere

The calibration and initial results of the HeI D3 line flash spectrum obtained during the 2008 total solar eclipse

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