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Marked velocity excesses of ions relative to neutrals are obtained from two time series of the neighboring emission lines He I 5015 and Fe II 5018 in a quiescent prominence. Their Doppler shifts show time variations of quasi-periodic character where the ions are faster than the neutrals 1.0 < V_macro(Fe II)/V_macro(He I) < 1.35 in series-A and, respectively, 6 pages, 11 figures

This paper presents observational evidence of the different dynamical behavior of neutral and ionized species in solar prominences. The analysis of a time-series of Sr ii 4078 A and Na D spectra in a quiescent prominence yields systematically larger Doppler shifts (line-of-sight velocities) for the ions V LOS(Sr ii) = 1.22 × V LOS(Na D). Both lines show a 30 minute oscillation of good coherence. Sixteen hours later the same prominence underwent marked morphological changes (with a rising dome), and the Sr ii velocity excess dropped to V LOS(Sr ii) = 1.11 ×V LOS(Na D). The same excess is found for the line pair Fe ii 5018 A and He i 5015 A. The widths of the ionic lines, mainly non-thermally broadened, are not related to the macro-velocities. The emission ratio of Na D and Sr ii, a measure of the electron density, yields n e = 4 × 1010 cm−3, shows no relation with the V LOS variation or with height above the limb, and seems to be reduced 16 hr later during the active phase. We apply a new wavelength reference from aureola spectra, which is independent of photospheric velocity fields.

Aims. We show that the line broadening in quiescent solar prominences is mainly due to non-thermal velocities.Methods. We have simultaneously observed a wide range of optically thin lines in quiescent prominences, selected for bright and narrow Mg b emission without line satellites from macro-shifts.Results. We find a ratio of reduced widths, Δλ D /λ 0 , of Hγ and Hδ of 1.05 ± 0.03, which can hardly be attributed to saturation, since both are optically thin for the prominences observed: τ γ ≤ 0.3, τ δ ≤ 0.15. We confirm the ratio of reduced widths of He 4772 (triplet) and He 5015 (singlet) of 1.1 ± 0.05 at higher significance and detect a width ratio of Mg b2 and Mg 4571 (both from the triplet system) of 1.3 ± 0.1.Conclusions. The discrepant widths of lines from different atoms, and even from the same atom, cannot be represented by a unique pair [T kin ; V nth ]. Values of T kin deduced from observed line radiances using models indicate low temperatures down to T kin ≈ 5000 K. Non-thermal velocities, related to different physical states of the respective emitting prominence region, seem to be the most important line broadening mechanism.

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 Hβ4862 A and Caii 8542 A yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Caii 8542 A and Hei 10830 A were taken, their widths yielding 8000 K 6×104 K, the levels k>8 appearing 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 Heii emission is more related to the `cool' lines.

High-spatial-resolution spectra of limb faculae show spatial displacements of line cores relative to the adjacent continuum at cos θ

Emission lines from quiescent prominences were observed simultaneously through narrow-band interference filters, thus integrating the total line intensities without the use of a spectrograph. Simultaneous exposures (50 ms) on three electronically connected CCD cameras at the 70 cm VTT on Tenerife assured almost identical influence of the Earth's atmosphere and a spatial resolution of ≤ 1 arc sec. The resulting spatially high-resolution two-dimensional images in Hβ, Hα, and Ca+8542, calibrated in units of the disk-center intensities, allow a two-dimensional mapping of emission ratios yielding relevant physical parameters. The emission relation between Hα and Hβ, which depends on the total optical thickness, confirms earlier photometric results from spectra, however, with a large sample of data points from six prominences. It demonstrates the saturation effects towards brighter prominences or prominence locations. The relation between Ca+8542 and Hβ, which depends on the gas pressure, is found to vary between different prominences but is nearly constant within one prominence. Its mean spatial variation of ≤ 30% within one prominence may be interpreted in terms of a magnetic field with variations of ≤5%. The brightness distribution in most prominences is not smooth but indicates preferred values, which are interpreted as superpositions of several fine structures.

We have determined absolute continuum intensities and brightness temperatures of individual facular grains at a spatial resolution limited by the φ=50 cm aperture of the SVST on La Palma. A facular region at θ≈57° was observed simultaneously in three narrow continuum windows at 450.5, 658.7, and 863.5 nm. We corrected for image degradation by the Earth's atmosphere using the speckle masking method. The brightness temperatures do not exactly follow the Planck law. The differences of Tblue−Tred=220 K and Tir−Tred=−42 K reflect the wavelength dependence of the continuum formation depth. The (red) temperatures of 250 facular grains show excesses between 250 and 450 K above their undisturbed neighborhood. The wavelength dependence of the relative intensity ratios Cλ= [Ifac/Iphot] λshow a large scatter around mean values of Cblue/Cred=1.075 and Cir/Cred=0.98. We determined the center-to-limb variation of the 863.5 nm continuum contrast for 0.17>cosθ>0.39 by measuring 270 grains in reconstructed facular images. The upper envelope of the data points increases linearly to 1.5 at cos θ=0.17. Application of the mean color dependence yields green contrasts up to C550=1.7, which is far higher than previously observed values. The behaviour for cos θ>0.17 is estimated from (unreconstructed) frame-selected best images taken over a time interval of 7 hours. Six distinct facular regions clearly discernible during the whole time interval indicate a slight contrast decrease towards the extreme limb. The observed quantities are useful for an adjustment of model calculations and for a discrimination of competing models.

Observational evidence of 3 and 5 min vertical oscillations of a filament on the disk are recorded. Wave activity was observed before, during and after a filament disappearance, inside and around the filament. Both an Hα brightening and, later, a blowing out of a faint soft X-ray (Yohkoh) loop system occuring in connection with a flare were noticed. The wave activity seems to be a dynamically important ingredient of this erupting prominence.Propagating MHD waves and convective structures bring their energy and momentum from the photosphere towards the chromosphere up to the coronal heights where they are partially reflected and/or dissipated. The transition from the laminar to the turbulent state of the whole prominence enhances the dissipation rate of the external waves inside this system, adding energy to produce the heating and lifting of the plasma. Internal plasma instabilities could trigger this transition in the framework of a prominence disappearance.

Two sets of H, He, and Ca+ emission lines were observed in a quiescent prominence simultaneously with the VTT and the Gregory telescope on Tenerife. At the same time, SUMER took two scans of low-ionized EUV emission lines.The emission ratios of Ca+–to–Balmer lines from ground vary little in the prominence, indicating a largely constant gas-pressure. In contrast, the ratio of He–to–Balmer from the ground shows the (known) increase toward the prominence borders, indicating higher temperature there. Similarly, the two-dimensional distributions of the ratios S IV/N II and C III/He I show pronounced bright prominence rims.The reduced He 537Å and He 584Å line widths are 2.6 and 3.6 times larger, respectively, than those of He D3 and He 3888Å. Explaining this by the optical thickness yields τ0 = 104 and τ0 = 2 · 105 for the two EUV lines. The total He 584 emission amounts to 13 watt/m2 ster in the main prominence body where the D3 line yields 4 watt/m2 ster; existing models, however, predict a factor 0.18.The widths of simultaneously observed optical lines with different atomic weights yield thermal and non-thermal broadening parameters of Tkin ≈ 8000 K and 2.5 < ξ < 6.5 km/s. The EUV lines, however, show line widths which correspond to much higher temperatures and non-thermal velocities. Assuming for each ion the corresponding ionization temperature, the line widths require non-thermal velocities of 15–40 km/s which is similar to values for the quiet corona.

We study spectral lines in exceptionally bright solar limb prominences with pronounced sodium and magnesium emission. We find that most prominences with significant NaD2 and Mgb2 emission show centrally reversed profiles of H-alpha and occasionally even of H-beta, which are are well reproduced by semi-infinite models. The maximum H-alpha source function corresponds to an excitation temperature of 3950 K, for pronounced central reversions 4000 K; the related optical thickness exceeds 10.0. The narrow widths of the NaD2 and Mgb2 profiles yield a non-thermal broadening of 5 km/s., 5 pages, 9 figures

Aims. We show how the observed hydrogen Balmer and Lyman emission lines constrain the modeling of quiescent solar prominences. Methods. We compare space observations of Lyman lines with ground-based observations of Balmer lines for quiescent solar prominences of comparable brightness defined by their Hβ emission. Results. The effective number densities of hydrogen atoms emitting from the same upper level u deduced from the corresponding emerging Lyman and Balmer line emissions show large differences that diminish with increasing level number and converge at the highest level numbers. Hydrogen atoms excited in u = 5 contribute 250 times less, and those in u= 8 still contribute 65 times less to the Lyman than to the corresponding Balmer emission, supporting the idea of distinct spatial origin of the emissions of both series. This is also indicated by the line widths. The high optical thickness of all Lyman members allows the brightness temperature Tb to be estimated from the spectral radiance at line center, where Tb is found to be largely independent of the upper level number, in contrast to the (known) behavior of the Balmer lines. peerReviewed

Two quiescent solar prominences were observed in July 2000 from SUMER aboard SOHO and from the two German solar telescopes at Tenerife. Two-dimensional images taken at the VTT simultaneously in the spectral lines Hβ at 4862 A and Ca II at 8542 A show no significant spatial variation of their pressure-sensitive emission ratio. Slit spectra of the Ca II 8542 A and He I 10830 A lines obtained at the Gregory-Coude telescope yield 8000 K < Tkin < 9000 K and 3 km/s < Vn–th < 8 km/s. Among the various spectral ranges observed with SUMER, we first investigate the Lyman emission lines, which were fitted by Gaussians yielding reliable spectral radiances and line widths for the series members 5 < k < 18. A determination of the level population gives for the lower series members a Boltzmann temperature of 60 000 K, the higher members being over-populated. This temperature indicates an origin of the Lyman lines from hot surroundings of the cool prominence body seen in the ground-based data; this also holds for the ‘hotter’ SUMER lines.

Simultaneously measured line intensities of Ca+ K and H, Hα, Hβ and He D3 are presented and compared with recent model calculations by Heasley and Milkey (1978). The model calculations are compatible with the observations. There is indication that the observed branching of the relation E(Ca+ K and H) ∼ E(Hβ) depends on the widths of the Ca+-lines.

We observe simultaneously the Ca II K, Ca II 8542 and H-beta emissions in solar prominences at high spatial and spectral resolution. We confirm a branching in the emission relations of Ca II and H-beta. This is related to non-thermal line broadening, which affects the Ca II lines much more than H-beta. The classical non-thermal (Maxwell) line broadening, determined by comparison of the width of hydrogen lines with those from calcium lines, is not sufficient to explain the Ca II widths. This indicates an additional broadening by large-scale motions of the unresolved prominence fine-structure.

A photometric and colorimetric analysis of a color picture of the very inner solar corona, near the South pole region, is performed. Dimensions and average electron densities of both chromospheric and very fine resolved coronal spikes are deduced. For the coronal spike a half width of 1″.67 is measured, the estimate of electron density yields ne = 1010 cm−3. Some conclusions are attempted on the light of a simultaneously observed spectrum of the same region which appeared to be a “disappearing coronal hole.” The observations seem to support the concept of a “striated” corona.

The intensity ratios E(Hα)/E(D3) and E(Hβ)/E(D3) in prominences depend on the total optical thickness in Hα of the layer. The emission of the He D3 line appears relatively enhanced in thin layers and in outer parts of the prominences.

Profile changes of five magnetically non-split lines going from the photosphere to faculae are investigated. The observations show that the profiles normalized to the continuum differ from those of the undisturbed photosphere only in the core. The outer parts of the profiles remain unchanged. Calculations using two recent facular models do not represent these observed profile changes. It is shown that a temperature increase in outer layers h≳ 250 km does explain the observations. The problem of photospheric magnetograph calibration for facula magnetic field measurements is discussed.

The dependence of the Li-abundance on the equivalent width of the Li-resonance doublet at λ 6708 A is calculated for different umbral models. The choice of the model strongly influences the deduced Li-abundance (up to a factor 8 or Δ log ɛ Li = 0.9) even when using recent umbral models. Detailed discussion of the observations and reduction with the most suitable umbral model (Stellmacher and Wiehr, 1970) leads to an abundance of log ɛ Li = 1.1±0.05 (in the log ɛ H = 12.0 scale).

Line asymmetries of five magnetically insensitive lines in penumbrae are investigated in detail.

In a recent paper Stellmacher and Wiehr (1973) discussed in detail the discrepancies between ‘continuum-’ and ‘line-profile facula models’. Their calculations show that continuum models (e.g. Kuz’minykh, 1962; Schmahl, 1967; Chapman 1970; Wilson, 1971) encounter the problem that the facula contrast increases towards the limb but decreases with wavelength λ. This discrepancy evidently cannot be due to NLTE effects since it concerns the continumm data.

Integrated total emissions of the lines Ca+H, Ca+K, Hα and Hβ observed simultaneously in quiescent prominences are discussed. While the total line emission calculated with the recent, most advanced prominence model by Heasley and Milkey (1978) fits well the observed means, the observed“fine-structure”of the emission relations is not reproduced. This“fine-structure”is best seen in Engvold’s (1978) data, where the observed brightness relation E(Ca+K) vers. E(Hα) shows a pronounced branching, (Figure 1).