Structure and spectrum of quiescent prominences. III - Application of theoretical models in helium abundance determinations

Heasley, J. N.; Milkey, R. W.

doi:10.1086/156072

Cited by 76 publications

(24 citation statements)

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“…The influence of hydrogen Lyman lines on Ca II to Ca III ionization is found to be very important for the determination of calcium-to-hydrogen line ratios. In particular, the intensities obtained for calcium lines at low pressures are significantly lower than those obtained by Heasley & Milkey (1978), which is the result of a greater Ca III/Ca II ratio. Our numerical results have been further checked against an approximate analytical model.…”

contrasting

confidence: 56%

Calcium to hydrogen line ratios in solar prominences

Gouttebroze

Heinzel²

2002

A&A

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Abstract.The ratio of Ca II 8542Å to Hβ line intensities has been used for a long time to diagnose the gas pressure in solar prominences. In this paper we reconsider the theoretical dependence of E(8542)/E(Hβ) on the gas pressure, as originally computed by Heasley & Milkey (1978), and extend this theoretical correlation to higher pressures. Firstly, we revise the formation of calcium lines in prominences, using in parallel two independently developed NLTE radiative transfer codes. Computations consist of two subsequent steps: (i) the formation of hydrogen spectrum (treated in a similar way as in Gouttebroze et al. 1993), and (ii) the formation of calcium lines, using the electron-density structure obtained in step (i). The influence of hydrogen Lyman lines on Ca II to Ca III ionization is found to be very important for the determination of calcium-to-hydrogen line ratios. In particular, the intensities obtained for calcium lines at low pressures are significantly lower than those obtained by Heasley & Milkey (1978), which is the result of a greater Ca III/Ca II ratio. Our numerical results have been further checked against an approximate analytical model. Secondly, we have performed an extended computation using a large grid of models covering different temperatures, gas pressures, geometrical thicknesses, microturbulent velocities and prominence altitudes. For temperatures lower than 10 000 K and pressures lower than 0.1 dyn cm −2 , the line ratio E(8542)/E(Hβ) undergoes only small variations, remaining between 0.2 and 0.3. At higher pressures (0.1 to 1 dyn cm −2 ), the behaviour of this ratio appears to be strongly dependent on temperature: rapidly increasing below 6000 K, moderately increasing between 6000 and 8000 K, and generally decreasing at higher temperatures. A comparison of the present models with recent observations of Stellmacher & Wiehr (2000) suggests the existence of cool prominence structures with temperatures around 6000 K and gas pressures higher than 0.1 dyn cm −2 .

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confidence: 56%

Calcium to hydrogen line ratios in solar prominences

Gouttebroze

Heinzel²

2002

A&A

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“…We have to assume here, of course, that the electron density inside a prominence remains proportional to that in its outer shell along the line of sight. Earlier studies of prominences have shown that their ionisation degree is typically in the range of 0.5-0.8 (Orrall and Schmahl, 1980;Kanno, Withbroe, and Noyes, 1981) and their helium abundance is around 0.1 (Heasley and Milkey, 1978). Therefore, suggesting that most of the prominence mass is due to the hydrogen atoms, and the low helium abundance will not imply a large error, we calculate the mean density of the prominence plasma by multiplying the inferred electron density by the proton mass.…”

Section: Estimation Modelsmentioning

confidence: 99%

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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“…The first detailed multilevel non-LTE prominence models were devised by Heasley, Mihalas, Milkey and Poland (see Heasley & Milkey 1978 and references therein). Lα and Lβ lines were computed assuming the complete frequency redistribution (CRD) taking place during the scattering process.…”

Section: Theoretical Non-lte Models Predicting the Lyman-spectrum Intmentioning

confidence: 99%

“…The first consistent treatment of partial frequency redistribution in Lα and Lβ was presented by Heinzel et al (1987), in the framework of 1D isothermal-isobaric models of Heasley & Milkey (1978). A new ingredient, which has been shown to be critical for calculating the correct line shapes within PRD, was the introduction of realistic (i.e., observed) incident line intensities.…”

Section: Theoretical Non-lte Models Predicting the Lyman-spectrum Intmentioning

confidence: 99%

SOHO/SUMER observations and analysis of the hydrogen Lyman spectrum in solar prominences

Heinzel

Schmieder

Vial

et al. 2001

A&A

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Abstract. The complete hydrogen Lyman spectrum in several prominences has been observed with the UV spectrometer SUMER on-board the SOHO, during the Joint Observing Programme 107, together with other space and ground-based observatories. Based on these observations, we are able to demonstrate, for the first time, that there exists a large variety of intensities and shapes of Lyman lines in different prominences and in various parts thereof. Therefore, no "canonical" Lyman spectrum can be considered for modelling purposes. However, we have identified at least two representative properties of the observed spectra: in one case (May 28, 1999 prominence) we detected high integrated intensities and no reversals in lines higher than Lα. Another prominence (June 2, 1999) exhibited quite similar integrated intensities, but all lines have rather strongly reversed profiles. This behaviour cannot be explained in terms of standard isothermal-isobaric models and we thus consider more general models which are in pressure equilibrium with the magnetic field and which have significant prominencecorona transition region (PCTR) temperature gradients. This type of model, recently suggested by Anzer & Heinzel (1999), is capable of explaining strong emission profiles without reversal. Based on extended non-LTE computations, we suggest that quite different Lyman spectra mentioned above may correspond to two types of PCTRs, one seen along the magnetic-field lines (unreversed profiles) and the other one seen across the field lines (reversed profiles). Finally, we again confirm the importance of partial-redistribution (PRD) scattering processes for Lyman lines in prominences. However, our analysis of new SUMER data also points to a critical role of the PCTR in radiative transport in these lines.

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Structure and spectrum of quiescent prominences. III - Application of theoretical models in helium abundance determinations

Cited by 76 publications

References 0 publications

Calcium to hydrogen line ratios in solar prominences

Calcium to hydrogen line ratios in solar prominences

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

SOHO/SUMER observations and analysis of the hydrogen Lyman spectrum in solar prominences

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