Solar Heii(304 �) and Si xi(303 �) line profiles

Cushman, G. W.; Rense, W. A.

doi:10.1007/bf00157275

Cited by 17 publications

(10 citation statements)

References 7 publications

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“…7 in ). The linewidth (FWHM ≃ 0.08 Å) is somewhat smaller than the value of 0.10 Å observed by Doschek et al (1974) and Cushman & Rense (1978), but is very similar to that computed by Fontenla et al (1993). Fontenla et al (2002) predict greater widths if significant flows are present.…”

Section: Results Using Maxwellian Collision Ratessupporting

confidence: 70%

Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation - II. Non-Maxwellian electron distributions

Smith¹

2003

Monthly Notices of the Royal Astronomical Society

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In solar extreme ultraviolet spectra the He i and He ii resonance lines show unusual behaviour and have anomalously high intensities compared with other transition region lines. The formation of the helium resonance lines is investigated through extensive non‐local thermal equilibrium radiative transfer calculations. The model atmospheres of Vernazza, Avrett & Loeser are found to provide reasonable matches to the helium resonance line intensities but significantly overestimate the intensities of other transition region lines. New model atmospheres have been developed from emission measure distributions derived by Macpherson & Jordan, which are consistent with SOHO observations of transition region lines other than those of helium. These models fail to reproduce the observed helium resonance line intensities by significant factors. The possibility that non‐Maxwellian electron distributions in the transition region might lead to increased collisional excitation rates in the helium lines is studied. Collisional excitation and ionization rates are recomputed for distribution functions with power‐law suprathermal tails that may form by the transport of fast electrons from high‐temperature regions. Enhancements of the helium resonance line intensities are found, but many of the predictions of the models regarding line ratios are inconsistent with observations. These results suggest that any such departures from Maxwellian electron distributions are not responsible for the helium resonance line intensities.

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Section: Results Using Maxwellian Collision Ratessupporting

confidence: 70%

Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation - II. Non-Maxwellian electron distributions

Smith¹

2003

Monthly Notices of the Royal Astronomical Society

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“…This figure also indicates the main contributors to this relatively broad-band channel: the closely spaced Si xi line at 303.3Å and He ii line at 303.8Å. Contribution of the Si xi line has been previously investigated by several authors, who have found it to be around 3-4% for the on-disk quiet Sun regions and more than 90% for the coronal emission (Cushman and Rense, 1978;Thompson and Brekke, 2000). Since plasma conditions in prominences are similar to that of the quiet Sun, helium emission is typically dominant in them.…”

Section: Observationsmentioning

confidence: 58%

Quiescent and Eruptive Prominences at Solar Minimum: A Statistical Study via an Automated Tracking System

Loboda

Богачев

2015

Sol Phys

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We employ an automated detection algorithm to perform a global study of solar prominence characteristics. We process four months of TESIS observations in the He ii 304Å line taken close to the solar minimum of 2008-2009 and focus mainly on quiescent and quiescent-eruptive prominences. We detect a total of 389 individual features ranging from 25 × 25 to 150 × 500 Mm 2 in size and obtain distributions of many their spatial characteristics, such as latitudinal position, height, size and shape. To study their dynamics, we classify prominences as either stable or eruptive and calculate their average centroid velocities, which are found to be rarely exceeding 3 km s −1 . Besides, we give rough estimates of mass and gravitational energy for every detected prominence and use these values to evaluate the total mass and gravitational energy of all simultaneously existing prominences (10 12 -10 14 kg and 10 29 -10 31 erg, respectively). Finally, we investigate the form of the gravitational energy spectrum of prominences and derive it to be a power-law of index −1.1 ± 0.2.

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“…Let us recall that this line corresponds to the 1s 2 1 S-1s2p 1 P 0 transition of parahelium. It has been measured in the solar chromosphere with different techniques (Dupree & Reeves 1971;Dupree et al 1973;Delaboudinière & Crifo 1976;Cushman & Rense 1978). The chromospheric profiles (Cushman & Rense 1978) were rather broad and even possibly self-reversed (1976).…”

Section: Some Features Of the 58433å Hei Linementioning

confidence: 99%

Oscillations in an active region filament: Observations and comparison with MHD waves

Régnier

Solomon

Vial

2001

A&A

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Abstract. During the MEDOC Campaign 4, on October 1999, observations of a solar active region filament were carried out by the SUMER/SoHO spectrometer. A time sequence of this filament has been obtained with a duration of 7 h 30 min and with a temporal resolution of 30 s. The Fourier analysis of the line-of-sight Doppler velocities measured in the 584.33Å HeI line allows us to detect oscillations in several ranges of periodicities (short periods: less than 5 min, intermediate periods: 6-20 min, and long periods: greater than 40 min). From a theoretical point of view, we consider the possible modes of oscillations of an active region filament. Following Joarder & Roberts (1993), we treat the filament as a plasma slab embedded in a uniform magnetic field inclined at an angle φ to the long axis of the slab. Solving the dispersion equations for Alfvén waves and magnetoacoustic waves, primary and secondary mode frequencies appear to be non-equidistant. For the comparison between the observed and calculated frequencies, we outline an identification method of the oscillation modes in the observed filament. This identification provides a diagnostic of the filament: the angle between the magnetic field and the long axis of the slab is estimated to be 18• , and the magnetic field strength B (G) is proportional to the square root of the density ρo (cm −3 ) in the slab, B ∼ 2.9 × 10 −5 √ ρo.

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Solar Heii(304 �) and Si xi(303 �) line profiles

Cited by 17 publications

References 7 publications

Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation - II. Non-Maxwellian electron distributions

Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation - II. Non-Maxwellian electron distributions

Quiescent and Eruptive Prominences at Solar Minimum: A Statistical Study via an Automated Tracking System

Oscillations in an active region filament: Observations and comparison with MHD waves

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