Search

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.

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

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.

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.

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.

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