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Stellmacher, G.; Wiehr, E.

doi:10.1023/a:1005237823016

Cited by 33 publications

(52 citation statements)

References 10 publications

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“…The pressure-sensitive ratio of both lines is in agreement with our former observations (Stellmacher & Wiehr 2000).Comparison with model calculations by Gouttebroze and Heinzel (2002) for the optically thin case τ (Hβ) ≤ 1.0 (which is generally valid for quiescent prominences) shows that our data is compatible with a gas-pressure of 0.1 < P g < 1.0 dyn/cm 2 . In parallel we observed with the Gregory-Coude Telescope (GCT) on Tenerife spectra of the near infrared lines Ca ii 8542Å and He i 10830Å (hereafter referred to as Ca IR and He IR) simultaneously in the 5th and the 4th grating order of the spectrograph.…”

Section: Ground-based Observationssupporting

confidence: 92%

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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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Section: Ground-based Observationssupporting

confidence: 92%

“…The observed emission relation (Fig. 3) shows that each prominence is characterized by a well-defined relation; for the fainter prominence E/70N the slope is steeper than for the brighter one E/42N ('branching', cf., Engvold, 1978;Stellmacher and Wiehr, 1995).…”

Section: Ground-based Observationsmentioning

confidence: 99%

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2003

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“…They fixed the other parameters (slab thickness 2000 km, microturbulent velocity 5 km s −1 , altitude 10 000 km). As will be shown in the next section, these computations suffered from some inaccuracies, especially Landman & Illing (1977) 0.375 de Boer et al (1998) 0.425 Stellmacher & Wiehr (2000) 0.63 (faint prominence) 0.28 (bright prominence) concerning the ionization of calcium, but they produced new qualitative results which are confirmed by the present computations. In particular, they found that, at low temperatures, r is greater for P = 1 dyn cm −2 than for P = 0.1 dyn cm −2 .…”

Section: Introductionsupporting

confidence: 77%

“…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 . …”

supporting

confidence: 67%

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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“…Furthermore, what is causing filaments to oscillate and the ever present flowing of the plasma? Also, further high-resolution, multi-wavelength investigations shall be encouraged (Stellmacher & Wiehr, 2000).…”

Section: Discussionmentioning

confidence: 99%