Extreme-ultraviolet limb spectra of a prominence observed from SKYLAB

Mariska, J. T.; Doschek, G. A.; Feldman, U.

doi:10.1086/157356

Cited by 30 publications

(21 citation statements)

References 12 publications

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“…To account for the observed emission intensity, therefore, the effective prominence width (i.e., column depth) would be smaller if the heating were steady rather than impulsive. Skylab slitspectrograph observations of a limb prominence yielded a column depth of around 1200 km at transition-region temperatures (Mariska et al 1979), which is comparable to our lower estimate. The observed prominence width typically is much larger, indicating small filling factors, which is consistent with their wispy appearance in high-resolution images.…”

Section: Differential Emission Measuresupporting

confidence: 86%

Condensation Formation by Impulsive Heating in Prominences

Karpen

Antiochos

2008

ApJ

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Our thermal nonequilibrium model for prominence formation provides an explanation for the well-observed presence of predominantly dynamic, cool, dense material suspended in the corona above filament channels. According to this model, condensations form readily along long, low-lying magnetic field lines when heating is localized near the chromosphere. Often this process yields a dynamic cycle in which condensations repeatedly form, stream along the field, and ultimately disappear by falling onto the nearest footpoint. Our previous studies employed only steady heating, as is consistent with some coronal observations, but many coronal heating models predict transient episodes of localized energy release (e.g., nanoflares). Here we present the results of a numerical investigation of impulsive heating in a model prominence flux tube and compare the outcome with previous steady-heating simulations. We find that condensations form readily when the average interval between heating events is less than the coronal radiative cooling time ($2000 s). As the average interval between pulses decreases, the plasma evolution more closely resembles the steady-heating case. The heating scale and presence or absence of background heating also determine whether or not condensations form and how they evolve. Our results place important constraints on coronal heating in filament channels and strengthen the case for thermal nonequilibrium as the process responsible for the plasma structure in prominences.

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Section: Differential Emission Measuresupporting

confidence: 86%

Condensation Formation by Impulsive Heating in Prominences

Karpen

Antiochos

2008

ApJ

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“…Preliminary results indicate that, contrary to the expectations, the prominence appears to contain hotter material at lower rather than at greater heights and, in addition, confirm earlier results (Feldman and Doschek 1977b;Mariska et al 1979;) that the line widths in a prominence are narrower than in quiet-Sun areas.…”

Section: Prominencessupporting

confidence: 78%

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

et al. 2007

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In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical considerations on the heating of the corona and the generation of the solar wind.

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“…Their widths smoothly increase with T f orm . We consider this increase to be real, since Mariska, Doschek, and Feldman (1979) found comparable widths ∆λ e /λ = 8 · 10 −5 and a similar increase with T f orm , which they interpreted as a discontinuity of the non-thermal velocities between cool and hot emitting material. This increase of line widths is particularly pronounced in prominence E/70N (Fig.…”

Section: The Broader 'Hot' Linesmentioning

confidence: 78%

“…If we apply the revised correction with broader instrumental profiles by Chae, Schühle, and Lemaire (1998), the resulting widths 5 · 10 −5 < ∆λ e /λ < 9 · 10 −5 are still significantly broader than those obtained by Mariska, Doschek, and Feldman (1979) from observations with the NRL slit spectrograph on Skylab (at a spectral resolution of 60 mÅ). Interestingly, their reduced widths of lines from neutral and singly charged atoms of typically ∆λ e /λ ≈ 3 · 10 −5 are very near to those of our Ca IR line (entered in Figs.…”

Section: Correction Of Narrow Lines For the Sumer Profilementioning

confidence: 88%

Untitled

2003

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We present a comprehensive set of spectral data from two quiescent solar prominences observed in parallel from space and ground: with the VTT, simultaneous two-dimensional imaging of Hβ 4862Å and Ca ii 8542Å yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Ca ii 8542Å and He i 10830Å were taken, their widths yielding 8000 < T kin < 9000 K and v nth < 8km/s. The intensity ratio of the helium triplet components gives an optical thickness of τ < 1.0 for the fainter and τ ≤ 2.0 for the brighter prominence. The τ 0 values allow to deduce the source function for the central line intensities and thus the relative population of the helium 3 S and 3 P levels with a mean excitation temperature T mean ex = 3750 K. With SUMER, we sequentially observed 6 spectral windows containing higher Lyman lines, 'cool' emission lines from neutrals and singly charged atoms, as well as 'hot' emission lines from ions like O iv, O v, N v, S v and S vi. The EUV lines show pronounced maxima in the main prominence body as well as 'sidelocations' where the 'hot' lines are enhanced with respect to the 'cool' lines. The line radiance of 'hot' lines blue-wards of the Lyman series limit (λ < 912Å) appear reduced in the main prominence body.This absorption is also visible in TRACE images of Fe ix/x 171Å as fine dark structure which covers only parts of the main ('cool') prominence body.The Lyman lines show a smooth decrease of line widths and radiance with increasing upper level k = 5 through 19. For 5 ≤ k ≤ 8 the level population follows a Boltzmann distribution with T ex > 6 · 10 4 K; higher levels k> 8 appear more and more overpopulated. The larger widths of the Lyman lines require high non-thermal broadening close to that of 'hot' EUV lines. In contrast, the He ii emission is more related to the 'cool' lines.

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Extreme-ultraviolet limb spectra of a prominence observed from SKYLAB

Cited by 30 publications

References 12 publications

Condensation Formation by Impulsive Heating in Prominences

Condensation Formation by Impulsive Heating in Prominences

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

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