Browsing by Author "Stellmann, Jan-Patrick"

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, Delta lambda(D)/lambda(0), of H gamma and H delta of 1.05 +/- 0.03, which can hardly be attributed to saturation, since both are optically thin for the prominences observed: tau(gamma) <= 0.3, tau(delta) <= 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 b(2) 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 Tkin deduced from observed line radiances using models indicate low temperatures down to T-kin approximate to 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.

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 H beta 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 T(b) to be estimated from the spectral radiance at line center, where T(b) is found to be largely independent of the upper level number, in contrast to the (known) behavior of the Balmer lines.

Background Gadolinium-enhancing (GD+) lesions and T2 lesions are MRI outcomes for phase-2 treatment trials in relapsing-remitting Multiple Sclerosis (RRMS). Little is known about predictors of lesion development and regression-to-the-mean, which is an important aspect in early baseline-to-treatment trials. Objectives To quantify regression-to-the-mean and identify predictors of MRI lesion development in placebo cohorts. Methods 21 Phase-2 and Phase-3 trials were identified by a systematic literature research. Random-effects meta-analyses were performed to estimate development of T2 and GD+ after 6 months (phase-2) or 2 years (phase-3). Predictors of lesion development were evaluated with mixed-effect meta-regression. Results The mean number of GD+-lesions per scan was similar after 6 months (1.19, 95% CI: 0.87-1.51) and 2 years (1.19, 95% CI: 1.00-1.39). 39% of the patients were without new T2-lesion after 6 month and 19% after 2 years (95% CI: 12-25%). Mean number of baseline GD+-lesions was the best predictor for new lesions after 6 months. Conclusion Baseline GD-enhancing lesions predict evolution of Gd-and T2 lesions after 6 months and might be used to control for regression to the mean effects. Overall, proof-of-concept studies with a baseline to treatment design have to face a regression to 1.2 GD+ lesions per scan within 6 months.

We observed bright solar limb prominences with significant emission of NaD2 and Mgb(2) simultaneously with the Halpha, Hbeta, HeD3, He+ 4685, and the He-singl 5015 Angstrom lines, using the THEMIS telescope on Tenerife. We find that most prominences with significant NaD2 and Mgb(2) emissions show pronounced centrally reversed Ha profiles, and occasionally even of H; the strongest emissions reach integrated intensities Ebeta > 16 x 10(4) [erg/(cm(2) s str)]. The centrally reversed profiles are well reproduced by semi-infinite models. The source function reaches Salpha less than or equal to 36 x 10(4) [erg/(cm(2) s strAngstrom)] corresponding to an excitation temperature T-ex(alpha) approximate to3950 K; here, the optically thickness of Halpha amounts tau(alpha)(0) approximate to 10. The line widths of the NaD2, Mgb(2), and HeD3 profiles yield kinetic temperatures 7000 less than or equal to T-kin < 8000 K and non-thermal broadening v(tu) = 5 km s(-1).

High-spatial-resolution spectra of limb faculae show spatial displacements of line cores relative to the adjacent continuum at cos theta <0.35, confirming results from earlier photographic analyses. The observed displacements are geometric measures which probe the upper atmospheric layers of fluxtubes forming facular grains. We selected spectra with highest contrast and smallest width of the facular continuum streaks, in order to avoid clustered structures. The spatial displacements of Stokes-Q and -V maxima were also measured: we find Q-signals spatially located near the continuum, as is expected from their origin in line wings; V-signals - which should give evidence for the existence of horizontal fields - are not found, except for one case of a `hidden' pore.

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 Hbeta at 4862 Angstrom and Ca II at 8542 Angstrom show no significant spatial variation of their pressure-sensitive emission ratio. Slit spectra of the Ca II 8542 Angstrom and He I 10830 Angstrom lines obtained at the Gregory-Coude telescope yield 8000 K < T-kin < 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 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 Hbeta 4862 Angstrom and Ca II 8542 Angstrom yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Ca II 8542 Angstrom and He I 10830 Angstrom were taken, their widths yielding 8000 K< T-kin < 9000 K and 3 < v(nth) < 8 km s(-1). The integrated line intensities show a distinct relation E(He I) versus E(Ca II) for each prominence ('branching'). The intensity ratio of the helium triplet components is used for a simple estimate of the optical thickness, which is tau < 1.0 for the fainter prominence but reaches up to τ = 2.0 for the brighter one. The τ(0) values allow us to deduce the source function from the central line intensities and thus a mean excitation temperature T-ex(mean) = 3750 K, which determines the relative populations of the helium S-3 and P-3 levels. With SUMER, we sequentially observed six 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, S V, N V, O V, and SVI. The spatial variation of the EUV lines along the SUMER slit shows a pronounced maximum at the main prominence body and 'side-regions' where the 'hot' lines are significantly enhanced with respect to the 'cool' lines from neutral and singlyionized atoms. These selected locations were averaged over 7" and the resulting mean EUV lines were fitted by Gaussians yielding realistic widths and integrated line intensities. The intensities of 'hot' lines blue-wards of the Lyman series limit appear reduced in the main prominence body but enhanced in the 'side-regions'. This absorption is also visible in TRACE images of Fe IX/X 171 Angstrom as fine dark structure which covers only parts of the main ('cool') prominence body. The Lyman lines show a smooth decrease of both line widths and integrated emission, with increasing upper level k = 5 to k = 19; the widths are smaller for the prominence that yields lower T-kin from the ground-based spectra. The level populations along the line of sight follow for 5 less than or equal to k less than or equal to 8 a smooth Boltzmann distribution with T-ex > 6 x 10(4) 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 He II emission is more related to the 'cool' lines.

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 less than or equal to 1 arc sec. The resulting spatially high-resolution two-dimensional images in H beta, H alpha, 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 H alpha and H beta, 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 H beta, 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 less than or equal to 30% within one prominence may be interpreted in terms of a magnetic field with variations of less than or equal to5%. The brightness distribution in most prominences is not smooth but indicates preferred values, which are interpreted as superpositions of several fine structures.