SI III line ratios in the sun

Dufton, P. L.; Hibbert, A; Kingston, A E; Doschek, G. A.

doi:10.1086/161458

Cited by 42 publications

(59 citation statements)

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“…These enhancements should be observable, but in general, no compelling evidence for enhanced Án ¼ 1 line intensities in ions other than those of helium exists in the literature. In one case, the Si iii 1313 8 Án ¼ 1 line was found to be enhanced in observations analyzed by Dufton et al (1983). These authors suggested that the enhancement may be due to nonthermal electrons present in the transition region (see also Dufton, Kingston, & Keenan 1984;Keenan et al 1989;Pinfield et al 1999).…”

Section: áN ! 1 Transitions In Other Atomic Systemsmentioning

confidence: 91%

On the Formation of the Resonance Lines of Helium in the Sun

Pietarila

Judge

2004

ApJ

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To investigate the cause of anomalously bright resonance lines of helium in the Sun, we have studied the magnitude of the enhancements and some proposals made to explain them. Calculations in new semiempirical solar models indicate that the resonance lines of helium are enhanced by factors of 2-5 for He i and between 2 and 9 for He ii, depending on the elemental abundances assumed. These enhancements are substantially less than earlier work has suggested, with the differences arising from radiative transfer not only in helium lines but also in lines of less abundant elements. Photon scattering, even with small line center optical depths (of order unity or less) throughout the transition region, is shown to significantly modify line intensities and their center-to-limb variation. This effect has important consequences both for our analysis and also for the analysis of solar EUV lines in general, including emission measure analyses. We have re-examined some proposals to explain the enhancements based on the ''ionizing plasma'' picture. The proposals include explicit heating (the ''burst'' picture) and heating via advection (diffusive and/or flowing models and the ''velocity redistribution'' [VR] proposal). We argue that the original VR mechanism must be modified to include kinetic effects for helium atoms, which reduce the effects of VR. The VR mechanism also naturally predicts helium lines that are blueshifted relative to lines less sensitive to VR, which contradicts observations for the He i 584 8 line. Ionizing plasma models also potentially lead to enhancement of Án ! 1 transitions (n is the principal quantum number) in other atoms and ions. Existing observational evidence for enhanced Án ! 1 transitions in other ions is weak. We conclude that the ionizing plasma scenarios are not the sole cause of the helium enhancement. Instead, in a companion paper, we propose that the thermodynamic properties of noble gases in the upper chromosphere will lead to enhancement of their spectral lines if cross-field diffusion into coronal plasma is important. Finally, we show that, surprisingly, multifluid flows of the kind computed by Fontenla and colleagues can reproduce observed intensities of several lines of C and Si and may contain a resolution to the helium enhancement problem.

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Section: áN ! 1 Transitions In Other Atomic Systemsmentioning

confidence: 91%

On the Formation of the Resonance Lines of Helium in the Sun

Pietarila

Judge

2004

ApJ

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“…The theoretical energy levels come from Baluja & Hibbert (1980). Oscillator strengths and A values come from Dufton et al (1983a). Since only a few transitions are treated in that paper, we have been performed new calculations for all the possible transition in the adopted atomic model.…”

Section: Fe XVIImentioning

confidence: 99%

CHIANTI - an atomic database for emission lines

Dere

Landi

Mason

et al. 1997

Astron. Astrophys. Suppl. Ser.

1,979

1,669

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Abstract. A comprehensive set of accurate atomic data is required for analyses of astrophysical and solar spectra. CHIANTI provides a database of atomic energy levels, wavelengths, radiative data and electron excitation data for ions which are abundant in cosmic plasmas. The most recent electron excitation data have been assessed and stored following the method of Burgess & Tully (1992). The current version is essentially complete for specifying the emission spectrum at wavelengths greater than 50Å. A list of observed lines in the spectral region between 50 and 1100Å has been compiled and compared with the lines predicted by the CHIANTI database. The CHIANTI database reproduces the vast majority of lines observed at these wavelengths. CHIANTI includes IDL (Interactive Data Language) routines to calculate optically thin synthetic spectra for equilibrium conditions. IDL routines to calculate theoretical line intensities required for electron density or temperature diagnostics and emission measure studies are also included. The CHIANTI atomic database and supporting IDL routines are available by anonymous FTP.

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“…They assumed the Maxwellian distribution, although they did not include the influence of the radiation field on the diagnostics and they did not diagnose T , therefore, they had to assume its value. Dufton et al (1983) have derived the range of the electron densities under the assumption of two values of log(T /K) = 4.5 and 4.7 as log(N e /cm −3 ) = 9.0-10.4 for CH, log(N e /cm −3 ) = 9.0-10.3 for QS, and log(N e /cm −3 ) = 8.8-11.3 for AR. Similar results have been derived by Keenan et al (1989a) and Doschek et al (1998).…”

Section: Diagnosed Plasma Parameters and Discussionmentioning

confidence: 99%

“…The modified software and extended database allow us to calculate the electron excitation rates, the excitation equilibrium and synthetic spectra under the assumption of κ-distributions (Dzifčáková 2006) by the method described in Dzifčáková & Mason (2008). Atomic data were taken from Dufton & Kingston (1989), Dufton et al (1983), Martin et al (1995), and Baluja & Hibber (1980). The 20-level model of Si iii is included in CHIANTI 6.0 (Dere et al 2009).…”

Section: Ionization and Excitation Equilibriummentioning

confidence: 99%

“…Dufton et al (1983) have derived the electron densities from the Si iii line ratios observed by Skylab and have reported the discrepancies in electron densities caused by enhanced intensity of the 1313 Å line. Dufton & Kingston (1989) have supposed the non-Maxwellian electron distribution of Shoub (1983) to explain the intensity of the 1313 Å line in data obtained with the high-resolution telescope and spectrograph onboard Spacelab 2.…”

Section: Introductionmentioning

confidence: 99%

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Diagnostics of theκ-distribution using Si III lines in the solar transition region

Dzifčáková

Kulinová

2011

A&A

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Aims. The solar transition region satisfies the conditions for appearance of the non-thermal κ-distribution. We aim to prove the occurrence of the non-thermal κ-distribution in the solar transition region and diagnose its parameters. Methods. The intensity ratios of Si iii lines observed by SUMER in 1100-1320 Å region do not correspond to the line ratios computed under the assumption of the Maxwellian electron distribution. We computed a set of synthetic Si iii spectra for the electron κ-distributions with different values of the parameter κ. We had to include the radiation field in our calculations to explain the observed line ratios. We propose diagnostics of the parameter κ and other plasma parameters and analyze the effect of the different gradient of differential emission measures (DEM) on the presented calculations. Results. The used line ratios are sensitive to T , density and the parameter κ. All these parameters were determined from the SUMER observations for the coronal hole (CH), quiet Sun (QS) and active region (AR) using our proposed diagnostics. A strong gradient of DEM influences the diagnosed parameters of plasma. The essential contributions to the total line intensities do not correspond to single T but a wider range of T , and they originate in different atmospheric layers. The amount of the contributions from these atmospheric layers depends on the gradient of DEM and the shape of the electron distribution function. Conclusions. The κ-distribution is able to explain the observed Si iii line spectrum in the transition region. The degree of nonthermality increases with the activity of the solar region, it is lower for CH and higher for the AR. The DEM influences the diagnosed T and N e but it has only little effect on the diagnostics of the parameter κ.

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SI III line ratios in the sun

Cited by 42 publications

References 0 publications

On the Formation of the Resonance Lines of Helium in the Sun

On the Formation of the Resonance Lines of Helium in the Sun

CHIANTI - an atomic database for emission lines

Diagnostics of theκ-distribution using Si III lines in the solar transition region

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