Author name code: wiehr ADS astronomy entries on 2022-09-14 author:"Wiehr, Eberhard" ------------------------------------------------------------------------ Title: Velocity Difference of Ions and Neutrals in Solar Prominences Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H.; Bianda, M. Bibcode: 2021ApJ...920...47W Altcode: 2021arXiv210813103W Marked velocity excesses of ions relative to neutrals are obtained from two time series of the neighboring emission lines He I 5015 Å and Fe II 5018 Å in a quiescent prominence. Their Doppler shifts show time variations of quasi-periodic character where the ions are faster than the neutrals, 1.0 ≤ Vmacro(Fe II)/Vmacro(He I) ≤ 1.35 in series A and ≤1.25 in series B. This "ratio excess" confirms our earlier findings of a 1.22 ion velocity excess, but the present study shows a restriction in space and time of typically 5 Mm and 5 minutes. The ratio excess is superposed by a time- and velocity-independent "difference excess" of -0.3 ≤ Vmacro(Fe II)-Vmacro(He I) ≤ +0.7 km s-1 in series A (also indicated in series B). The high repetition rate of 3.9 s enables the detection of high-frequency oscillations with several damped 22 s periods in series A. These show a ratio excess with a maximum of 1.7. We confirm the absence of a significant phase delay of He neutrals with respect to the Fe ions. Title: Evidence for the Two-fluid Scenario in Solar Prominences Authors: Wiehr, E.; Stellmacher, G.; Bianda, M. Bibcode: 2019ApJ...873..125W Altcode: 2019arXiv190401536W 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 Å 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 Å and He I 5015 Å. 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. Title: The Na I and Sr II Resonance Lines in Solar Prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2017SoPh..292...83S Altcode: 2017arXiv170502475S We estimate the electron density, ne, and its spatial variation in quiescent prominences from the observed emission ratio of the resonance lines Na I 5890 Å (D2) and Sr II 4078 Å. For a bright prominence (τα≈25 ) we obtain a mean ne≈2 ×1010cm−3; for a faint one (τα≈4 ) ne≈4 ×1010cm−3 on two consecutive days with moderate internal fluctuation and no systematic variation with height above the solar limb. The thermal and non-thermal contributions to the line broadening, Tkin and Vnth, required to deduce ne from the emission ratio Na I/Sr II cannot be unambiguously determined from observed widths of lines from atoms of different mass. The reduced widths, Δ λD/λ0, of Sr II 4078 Å show an excess over those from Na D2 and Hδ 4101 Å, assuming the same Tkin and Vnth. We attribute this excess broadening to higher non-thermal broadening induced by interaction of ions with the prominence magnetic field. This is suggested by the finding of higher macro-shifts of Sr II 4078 Å as compared to those from Na D2. Title: The Electron Density in a Quiescent Prominence Authors: Wiehr, E.; Stellmacher, G.; Bianda, M. Bibcode: 2016CEAB...40...79W Altcode: We estimate the electron density, n_e, from the emission ratio of the Na I D_2 and Sr II 4078 Å resonance lines. For a quiescent prominence, we find a range 1.7≤ n_e≤3.4\cdot 10^{10}cm^{-3} with significant differences between neighboring structures but not with height above the solar limb. After seven hours of moderate evolutionary changes, the prominence shows the same n_e range. Title: Non-thermal line-broadening in solar prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2015A&A...581A.141S Altcode: 2016arXiv160507923S
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, ΔλD/λ0, 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: τγ ≤ 0.3, τδ ≤ 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 [Tkin; Vnth]. Values of Tkin deduced from observed line radiances using models indicate low temperatures down to Tkin ≈ 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. Title: The Temperature of Quiescent Prominences Authors: Wiehr, E.; Stellmacher, G. Bibcode: 2015CEAB...39...35W Altcode: We simultaneously observed in solar prominences faint metallic emission lines together with Hγand two He I lines from the singlet and triplet systems, respectively. We find that the reduced widths ΔλD/λ0 are not linearly related to the square-root of the inverse atomic mass, as is expected from the Doppler formula. Instead, each emission line is individually broadened. The gradients in the VD2(1/μ) diagrams correspond to unrealistically high Tkin≥104 K, which contradict values deduced from line radiance observations yielding temperatures down to at most 5000 K. A scenario of down-falling gas clumps by Low et al. (2012) offers a plausible explanation for these discrepancies. Title: The Hot Skin of Prominence Structures Authors: Wiehr, E.; Stellmacher, G.; Ramelli, R.; Bianda, M. Bibcode: 2013CEAB...37..487W Altcode: We observe various emission lines in solar prominences and compare the widths of He II 4686 Å, He I 4472 Å (triplet) and He I 5015 Å (singlet) with those of the optically thin Hγ and Mg b_2 lines. The latter two yield a thermal line broadening of 9000<T_{kin}<11 000 K, which fits the width of He I 5015 Å (singlet). However, He I 4471 Å (triplet) shows an excess of 1.1 indicating an excitation of the triplet in 1.2 times hotter prominence regions. He II 4686 Å is 1.65 times broader and thus emitted in 2.73 times hotter regions of the prominence-corona transition layer, PCTR. The linear radiance relations He tripl/He II=50 and Hγ/He tripl=11.8 suggest a PCTR between each fine-structure thread and the surrounding hot coronal gas. Title: Helium Emissions Observed in Ground-Based Spectra of Solar Prominences Authors: Ramelli, R.; Stellmacher, G.; Wiehr, E.; Bianda, M. Bibcode: 2012SoPh..281..697R Altcode: 2012SoPh..tmp..221R; 2012arXiv1208.2153R The only prominent line of singly ionized helium in the visible spectral range, He II 4686 Å, is observed together with the He I 5015 Å singlet and the He I 4471 Å triplet line in solar prominences. The Na D2 emission is used as a tracer for He II emissions which are sufficiently bright to exceed the noise level near 10−6 of the disk-center intensity. The prominences thus selected are characterized by small non-thermal line broadening and almost absent velocity shifts, yielding narrow line profiles without wiggles. The reduced widths [ΔλD/λ] of He II 4686 Å are 1.5 times broader than those of the He I 4471 Å triplet and 1.65 times broader than those of the He I 5015 Å singlet. This indicates that the He lines originate in a prominence-corona transition region with outwards increasing temperature. Title: A retrospective of the GREGOR solar telescope in scientific literature Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.; Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.; Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa, M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T.; Wiehr, E.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..810D Altcode: 2012arXiv1210.3167D In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the ``historical'' context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes. Title: The Spatial Structure of the Evershed effect Authors: Wiehr, E. Bibcode: 2012arXiv1210.2553W Altcode: The line profile asymmetry defining the Evershed effect in sunspot penumbrae, disappears abruptly at the outer sunspot boundary over a horizontal distance of less than 500 km immediately at the outermost ends of the dark penumbral continuum structures ('filaments'). This is indicated from the non-magnetic lines Ni I 5435.9 (g=0.5) and Fe I 5434.5 (g=0), which loose their profile asymmetries at the same spatial location although formed at a vertical height distance of 300 km. The widely accepted 'canopy' picture conflicts with this finding which, in contrary, suggests that the gas motion associated with the Evershed effect disappears together with the continuum intensity drop at the outer sunspot (penumbral) border. Corresponding downflows must then be smaller than the spatial resolution presently achieved (i.e., <0.5 arcsec) and located at the immediate outer sunspot border. It is suggested that this location marks the sharp threshold of the equipartition between kinetic and magnetic energy density at the outer penumbral boundary. Title: The Area Coverage of Small-scale Solar Magnetic Structures in a Quiet Region Authors: Wiehr, E.; Bovelet, B. Bibcode: 2009CEAB...33...19W Altcode: Inter-granular structures, IgS, are segmented with the `multiple-level tracking' pattern recognition algorithm, MLT 4 in a 149 '' x 117 '' G-band image taken at disc centre of the non-active Sun. From the total of 7593 IgS, the non-magnetic ones are identified in the scatterplot of continuum and G-band brightness which is known to show a magnetic and a non-magnetic branch. The overlap regime of both is largely disentangled applying an intrinsic Ca II H contrast criterion.

For the thus obtained 2995 magnetic IgS, the MIgS, we obtain a number density of 0.32 MIgS/Mm^2. Their sizes, provided by MLT 4 in pixel counts independent of the shape, yield a total area contribution of 2.0%. Superimposing the MIgS to the simultaneously observed Hα image, we find a preferred location at the foot points of the dark fibrils, which are known to mark the network boundaries. A substantial amount of the MIgS is, however, located in the fibril voids, and thus in the inter-network. Title: Balmer and Lyman Emission Lines in Solar Prominences Authors: Wiehr, E.; Stellmacher, G. Bibcode: 2009CEAB...33...99W Altcode: Space observations of Lyman lines are compared with ground-based observations of Balmer lines for quiescent solar prominences of comparable brightness defined by their Hβ emission. The integrated spectral line radiances of the Lyman and the Balmer emissions show differences which diminish with increasing upper level u and converge toward highest level numbers. Lyman lines emitted from u=5 originate from 250 times less emitters than the corresponding Balmer lines from the same upper level. For u=8 this difference still amounts to a factor of 65, supporting the idea of a distinct origin of the emissions of both hydrogen series. Title: On the origin of the Balmer and Lyman emission lines in solar prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2008A&A...489..773S Altcode: 2012arXiv1209.6264S 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. Title: The quiet Sun's magnetic flux estimated from Ca II H bright inter-granular G-band structures Authors: Bovelet, B.; Wiehr, E. Bibcode: 2008A&A...488.1101B Altcode: 2012arXiv1208.2160B Aims: We determine the number density and area contribution of small-scale inter-granular Ca II bright G-band structures in images of the quiet Sun as tracers of kilo-Gauss magnetic flux-concentrations.
Methods: In a 149 arcsec × 117 arcsec G-band image of the disk center at the activity minimum, 7593 small inter-granular structures were segmented with the “multiple-level tracking” pattern recognition algorithm. The scatterplot of the continuum versus the G-band brightness shows the known magnetic and non-magnetic branches. These branches are largely disentangled by applying an intrinsic Ca II H excess criterion. The thus obtained 2995 structures contain 1152 G-band bright points (BP) and 1843 G-band faint points (FP). They show a tendency toward increasing size with decreasing G-band excess, as expected from the “hot wall” picture. Their Ca II H and G-band brightness are slightly related, resembling the known relation of Ca II and magnetic field strength. The magnetic flux density of each individual BP and FP is estimated from their G-band brightness according to MHD model calculations.
Results: The entity of BP and FP covers the total FOV with a number density of 0.32 / Mm2 and a total area contribution of 2.0%. Their individual calibrations yield a mean flux density of 20 Mx/cm2 in the entire FOV and 13 Mx/cm2 for inter-network regions. Title: Multiple-Scale Pattern Recognition Applied to Faint Intergranular G-band Structures Authors: Bovelet, B.; Wiehr, E. Bibcode: 2007SoPh..243..121B Altcode: Small-scale solar magnetic flux concentrations are studied in two-dimensional G-band images at very high spatial resolution and compared with Ca II H enhancements. Among 970 small-sized G-band intergranular structures (IgS), 45% are co-spatial with isolated locations of Ca II H excess and thus considered as magnetic (MIgS); they may be even twice as frequent as the known G-band bright points. The IgS are recognized in the G-band image by a new algorithm operating in four steps: (1) A set of equidistant detection levels yields a pattern of primary "cells"; (2) for each cell, the intrinsic intensity profile is normalized to its brightest pixel; (3) the cell sizes are shrunk by a unitary single-intensity clip; (4) features in contact at an appropriate reference level are merged by removal of the respective common dividing lines. Optionally, adjoining structures may be excluded from this merging process (e.g., chains of segmented IgS), referring to the parameterized number and intensity of those pixels where enveloping feature contours overlap. From the thus recognized IgS pattern, MIgS are then selected by their local Ca II H contrast and their mean G-band-to-continuum brightness ratio. Title: Imaging of the He D3/Hβ Emission Ratio in Quiescent Solar Prominences Authors: Hirzberger, J.; Wiehr, E.; Stellmacher, G. Bibcode: 2007ASPC..368..321H Altcode: Quiescent solar prominences have been observed simultaneously in profile-integrated He D3 and Hβ emission with the SST on La Palma. The two-dimensional ratio maps of the He D3 and Hβ intensities are used to study temporal variations of intrinsic prominence parameters. Sub-areas with substantial variation of the intensity distribution indicate the evolution of prominence structures. When the emission ratio remains unchanged, the evolving threads are of largely equal physical state. Other regions which show a temporal varying emission ratio indicate substancial evolution of the intrinsic physical conditions. We propose that distance variation between the threads affects different penetration of the EUV irradiation required for populating of the He triplet system. Title: Two-dimensional imaging of the He D_3/Hbeta emission ratio in quiescent solar prominences . Authors: Stellmacher, G.; Wiehr, E.; Hirzberger, J. Bibcode: 2007MmSAI..78..108S Altcode: Simultaneous prominences spectroscopy with THEMIS in the emission lines H-alpha, H-beta, HeD3, NaD2, Mgb2 and He(singlet)5015 lead to an extended study of two-dimensional images simultaneously in H-beta and HeD3. The spatial variation of the integrated line intensities and their ratio shows mainly two characteristics: (a) A constant emission ratio (even) in regions with substantial intensity variations; this can be explained by a varying number of superposing threads with equal physical states. (b) A varying emission ratio (often) tightly related to intensity changes; this indicates a superposition of threads with different physical states (most likely the gas-pressure). We also observe temporal changes of the emission ratio which seem to be too fast for a variation of the gas-pressure; here, we suppose a change of the packing density of threads along the line-of-sight which affects the penetration of ionizing UV radiation required for the He triplet excitation. Title: Two-Dimensional Mapping of the He D3/Hβ Emission Ratio in Solar Prominences Authors: Wiehr, Eberhard; Stellmacher, Goetz; Hirzberger, Johann Bibcode: 2007SoPh..240...25W Altcode: Solar prominences have been simultaneously observed in the integrated light of the He D3 and the Hβ emissions on two successive days, using the SST on La Palma with its tip-tilt mirror locked on a nearby white-light limb facular grain. The spatial and the temporal variation of the integrated line intensities and their ratio shows mainly two characteristics: (A) Constant emission ratio (even) in regions with substantial intensity variations and (B) varying emission ratio (often) tightly related to intensity structures of the prominence. (A) May be explained by a different number of superposing threads along the line of sight having very similar physical state. (B) Indicates threads with different intrinsic physical states; these may depend on the gas pressure or the inner structure of each thread, i.e., the "packing density," affecting the penetration of ionizing EUV radiation, which affects the He I level populations and thus the rate of the triplet excitation. Title: Two-dimensional imaging of the HeD3/H[Beta] emission ratio in quiescent solar prominences Authors: Wiehr, E.; Stellmacher, G.; Hirzberger, J. Bibcode: 2007msfa.conf..261W Altcode: We extend our earlier studies of two-dimensional prominence imaging by simultaneous observations of the HeD3 and H[Beta] emissions at the 1m SST on La Palma. The observed small spatial variations of the HeD3/H[Beta] ratio indicate rather homogeneous physical conditions within prominences. Sub-regions do exist which show a largely uniform ratio in spite of substantial spatial intensity variations. Here, the fine-structures will exhibit almost uniform physical conditions. In other regions with variations of the ratio parallel to the emissions, the structures will have different intrinsic physical state. Title: Influence of the magnetic field on the velocity of the high frequency waves in the solar chromosphere Authors: Andjic, A.; Wiehr, E. Bibcode: 2006POBeo..80..367A Altcode: High frequency acoustic waves are thought to be the source of the mechanical heating of the chromosphere. The observed velocity interval of high frequency wave propagation starts with 3.7± 0.4 km/s but the upper limit cannot be observed with the temporal resolution achieved in this work. Three areas of the Sun with the various activities are observed. Only events with the amplitudes larger than 50% of the maximum one were analysed in this work. The magnetic field has an influence on the propagation of high frequency waves. In the quiet Sun area only 49% of the observed events are connected with the magnetic field, while in areas with the magnetic structures 70% of the observed wave features are connected with the magnetic field. Title: The flux-gap between bright and dark solar magnetic structures Authors: Puschmann, K. G.; Wiehr, E. Bibcode: 2006A&A...445..337P Altcode: The upper size limit of solar small-scale magnetic flux concentrations ("G-band bright points", BP) is reconsidered from speckle-reconstructed images taken at the 1-m SST on La Palma. The size-histogram shows a sharp drop towards 250 km diameter, variation of the noise filter threshold diminishes that value due to segmentation of the elongated structures. A further artificial segmentation of still elongated (i.e. not round) BP indicates that the upper limit may well be below 200 km diameter, corresponding to a flux smaller than 2.5×1017 Mx which is more than 40 times smaller than that of smallest dark (mini-) pores. BP with diameters of 130 km would already yield to a flux gap of two orders of magnitude. The drop of BP numbers between the histogram maximum and the 90 km resolution limit achieved is found to depend on the low-pass filtering and is thus probably virtual. Higher spatial resolution data will still increase the flux gap between bright and dark solar magnetic flux concentrations which might be a signature of differently deep rooting in the solar atmosphere. Title: The Size of Small-Scale Solar Magnetic Regions Authors: Wiehr, E.; Puschmann, K. G. Bibcode: 2005ESASP.596E..20W Altcode: 2005ccmf.confE..20W No abstract at ADS Title: Spectropolarimetry of a sunspot at disk centre Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E. Bibcode: 2005A&A...440..345S Altcode: The magnetic, thermal and velocity structure of a sunspot at the solar disk centre (θ=2°) is investigated by inverting the full Stokes profiles of three infrared lines. A single magnetic component atmosphere is assumed with height gradients of the physical quantities. Since the line-of-sight (LOS) is perpendicular to the solar surface, differential optical or projection effects do not interfere, as often is the case for the usual observations at oblique LOS. We find a symmetric configuration of the field and flow and the downward motion that increases with radial distance by up to 3 km s-1 near the outer penumbral border. The magnetic field is found to be highly axially symmetric without any indication of azimuthal vortices. A tight relation between field strength and inclination is obtained with a gradient of 35°/1000 G independent of height. The penumbra shows "spines" hosting a pronounced negative correlation between field strength and inclination in the sense that steeper and stronger magnetic fields are related to brightenings in the line cores but not in the continuum. We discuss the dependence of the obtained results on different assumptions of parasitic light, and present indications of its overestimation by the inversion code. Title: Solar limb faculae Authors: Hirzberger, J.; Wiehr, E. Bibcode: 2005A&A...438.1059H Altcode: We observe solar limb faculae at an unprecedented spatial resolution with the new 1 m Swedish Solar Telescope SST on La Palma. Speckle-reconstructed images are used to study 4475 limb facular grains simultaneously in the 430 nm G-band and the 587.5±1.5 continuum up to only 1'' from the limb (cos θ=0.05). No systematic contrast decrease is found even a few arcsec from the solar limb. The facular grains appear to be “projected” on the limb-side neighboring granules; approaching the disc center, the corresponding features occur as inter-granular G-band bright points. Independently, we took spectra with the French-Italian THEMIS telescope on Tenerife and find that the known “line-gap effect” from disc center disappears near the limb. Here, the facular continuum is enhanced whereas the normalized profiles are unchanged with respect to the undisturbed neighborhood. Title: Solar prominences with Na and Mg emissions and centrally reversed Balmer lines Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2005A&A...431.1069S Altcode: 2012arXiv1210.5643S We observed bright solar limb prominences with significant emission of NaD2 and Mgb2 simultaneously with the Hα, Hβ, HeD3, He^+4685, and the He^singl 5015 Å lines, using the THEMIS telescope on Tenerife. We find that most prominences with significant NaD2 and Mgb2 emissions show pronounced centrally reversed Hα profiles, and occasionally even of Hβ; the strongest emissions reach integrated intensities Eβ>16×{}104 [ erg/(cm2 s str)] . The centrally reversed profiles are well reproduced by semi-infinite models. The source function reaches Sα≤{}36 × {}104 [ erg/(cm2 s str Å)] corresponding to an excitation temperature T_exα≈3950 K; here, the optically thickness of Hα amounts τ^0α≈{}10. The line widths of the NaD2, Mgb2, and HeD3 profiles yield kinetic temperatures 7000≤{}T_kin<8000 K and non-thermal broadening v_tu=5 km s-1. Title: Brightness and size of small-scale solar magnetic flux concentrations Authors: Wiehr, E.; Bovelet, B.; Hirzberger, J. Bibcode: 2004A&A...422L..63W Altcode: The new 1 m Swedish Solar Telescope SST on La Palma allows to observe inter-granular G-band bright points (igBP) in solar active regions at an unprecedented spatial resolution. The igBP are reasonably assumed to be small-scale magnetic flux-concentrations. A sample of more than 1500 igBP shows tight relations of diameter and brightness in the G-band and in the continuum; it covers a diameter range of 100 km to 300 km, with a most frequent value near 160 km. Features larger than 300 km formerly reported, evidently result from insufficient spatial resolution; that upper diameter limit is close to the typical width of inter-granular lanes, and suggests a ``gap'' to small pores. The lack of igBP with sizes below 130 km is discussed not to arise from the finite spatial resolution of the 1 m telescope. Title: Riesenkonvektion unter Sonnenflecken Authors: Wiehr, Eberhard; Bovelet, Burkart Bibcode: 2004S&W....43d..22W Altcode: No abstract at ADS Title: Observational Aspects of Doppler Oscillations in Solar Prominences Authors: Wiehr, E. Bibcode: 2004ESASP.547..185W Altcode: 2004soho...13..185W No abstract at ADS Title: Polarimetry of a sunspot at disk centre Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E. Bibcode: 2004IAUS..223..237S Altcode: 2005IAUS..223..237S No abstract at ADS Title: Dynamics of the solar active region finestructure Authors: Bovelet, B.; Wiehr, E. Bibcode: 2003A&A...412..249B Altcode: We investigate the dynamical behavior of the finestructure in a sunspot's surroundings and its penumbra from a speckle-reconstructed 60 min time series taken at the 45 cm Dutch Open Telescope (DOT) on La Palma. In the 1 nm spectral window containing the G-band, we determine the area of each feature and its time evolution by means of pattern recognition, particularly adapted to separate bright granular edges from inter-granular G-band bright points (BP). The evolution of each individual BP shows a stronger variation of the area than of the intensity. We analyze the horizontal motions of BP as a function of their distance from the sunspot center. Within a 6 Mm ring around the outer sunspot border, most BP (4/5) move radially outwards; they are faster than the minority (1/5) of inward moving BP. The difference of both velocities indicates a radial outward drift which decreases from about 0.3 km s-1 at the outer penumbral border to zero at about 20 Mm distance (28\arcsec) from the sunspot center; a spatial range that we interpret as the extension of the sunpot ``moat''. This finding supports the idea of giant rolls in deep layers measured by helio-seismic tomography and predicted by theory. Inside the penumbra, we find a 4/5 majority of penumbral bright structures (PBS) to move inwards with a mean velocity of 0.8 km s-1. The 1/5 minority of outward moving PBS is almost entirely located in the outer penumbra; their mean velocity of 0.8 km s-1 is equally found for penumbral dark structures (PDS) in the outer penumbra, in agreement with penumbral MHD models. Title: Spectroscopy of Solar Prominences Simultaneously From Space and Ground Authors: Stellmacher, G.; Wiehr, E.; Dammasch, I. E. Bibcode: 2003SoPh..217..133S Altcode: 2013arXiv1303.1126S 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 Å and Caii 8542 Å yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Caii 8542 Å and Hei 10830 Å were taken, their widths yielding 8000 K <Tkin<9000 K and 3<vnth<8 km s−1. The integrated line intensities show a distinct relation E(Hei) versus E(Caii) for each prominence (`branching'). The intensity ratio of the helium triplet components is used for a simple estimate of the optical thickness, which is τ<1.0 for the fainter prominence but reaches up to τ=2.0 for the brighter one. The τ0 values allow us to deduce the source function from the central line intensities and thus a mean excitation temperature Texmean=3750 K, which determines the relative populations of the helium 3S and 3P 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 Oiv, Sv, Nv, Ov, 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 singly-ionized 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 Feix/x171 Å 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 Tkin from the ground-based spectra. The level populations along the line of sight follow for 5 lekle a smooth Boltzmann distribution with Tex>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. Title: Solar prominence polarimetry Authors: Wiehr, E.; Bianda, M. Bibcode: 2003A&A...404L..25W Altcode: We measure the resonance polarization in solar prominences in Hα , Hβ and HeD3. A two-dimensional set-up with narrow-band filter, polarization analyzer and CCD camera is used to take prominence images in polarized light at high spatial resolution. Placed on a coudé telescope's hour axis, the observations near the equinoxia are free from purely instrumental polarization. Above the 0.1% noise limit, the Balmer lines do not show a polarization in contrast to the HeD3 line. Here, we determine the complete polarization profile after exchange of filter and CCD with the spectrograph, keeping the polarization analyzer fixed. In most prominences the Stokes-U and -Q profiles are not similar to Stokes-I: occasionally the blue and the red components of the emission are equal or even show a reverse ratio. This fits calculations for magnetic field strengths of the order of 50 Gauß being markedly stronger than commonly assumed. Title: High spatial resolution solar polarimetry with interference filters Authors: Wiehr, E.; Bianda, M. Bibcode: 2003A&A...398..739W Altcode: A new type of two-dimensional polarimeter is used to measure the center-to-limb variation of the scattering induced polarization in a narrow continuum window up to the extreme limb. The polarimeter is set on the Tenerife Gregory Coudé telescope's hour axis, where the two folding flat mirrors cancel their polarizing effects for zero solar declination at the equinox. The short CCD exposure of only 5 ms allows high spatial resolution images in polarized light. A beam switching technique together with an integration parallel to the solar limb over 20\arcsec, yields a high polarimetric accuracy with an rms noise of 2*E-4. Our results for a continuum window at 4506-4508 Å agree with model calculations down to limb distances of 0\farcs32 (i.e. cos vartheta < 0.025). Title: Continuum limb polarization at high spatial resolution Authors: Bianda, M.; Wiehr, E. Bibcode: 2003AN....324..323B Altcode: No abstract at ADS Title: GREGOR - optical design considerations Authors: Soltau, D.; Berkefeld, Th.; von der Lühe, O.; Hofmann, A.; Schmidt, W.; Volkmer, R.; Wiehr, E. Bibcode: 2003AN....324..292S Altcode: After many years of successful work the Gregory Coudé Telescope (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is the result of design considerations which to a wide extent are based on new technologies. Special aspects of the design are presented, including measures to compensate for optical aberrations caused by instrumental and atmospheric effects (Adaptive Optics). First light is expected for the end of 2004. Title: From the Gregory-Coudé Telescope to GREGOR: a development from past to future. Summary of workshop held in Göttingen, July 24-26, 2002 Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D. Bibcode: 2003AN....324..283K Altcode: No abstract at ADS Title: Automatic guiding of solar Gregory telescopes Authors: Küveler, G.; Wiehr, E.; Bianda, M. Bibcode: 2003AN....324..308K Altcode: No abstract at ADS Title: Spectroscopy of solar prominences from space and ground Authors: Dammasch, I. E.; Stellmacher, G.; Wiehr, E. Bibcode: 2003AN....324..338D Altcode: 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 Å and Ca II at 8542 Å show no significant spatial variation of their pressure-sensitive emission ratio. Slit spectra of the Ca II 8542 Å and He i 10830 Å lines obtained at the Gregory-Coudé telescope yield 8000 K < T_kin < 9000 K and 3 km/s < V_n-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. Title: Removing instrument and dome from the GCT building Authors: Duensing, U.; Harke, R.; König, D.; Wiehr, E. Bibcode: 2003AN....324..317D Altcode: No abstract at ADS Title: From the first Gregory-Coudé Telescope to Gregor Authors: Wiehr, E. Bibcode: 2003AN....324..285W Altcode: The historic development of the Göttingen Gregory-Coudé Telescope is sketched. The use of a Gregory system for a solar telescope was driven by the severe disadvantages of an existing Cassegrain solar telescope. The possibility of placing a (water-cooled) field-stop at the prime-focus diminishes heat stress as well as straylight on the mirrors behind the field-stop. The measured aureole intensity of the first solar Gregory telescope, installed 1959 near Locarno, classifies that instrument as a `quasi coronograph' and makes it particularly suitable for straylight-sensitive observations. The coudé mounting with two folding flat mirrors (`German type') assures small and daily constant instrumental polarization. This was compensated in a first step with a co-rotating tilted glass-plate and a modified Bowen compensator fixed to the hour axis. In a later step, a half-wave plate between both folding flat mirrors simulates the polarimetric situation of zero-declination. The Gregory-Coudé Telescope was then particularly suitable for polarimetry; it operated 25 years near Locarno and finally 15 years on Tenerife. Title: Two-dimensional polarimetry in solar prominences at high spatial resolution Authors: Wiehr, Eberhard Bibcode: 2002ESASP.505...33W Altcode: 2002solm.conf...33W; 2002IAUCo.188...33W Two-dimensional images of solar prominences in polarized light are obtained at the evacuated Gregory-Coudé telescope on Tenerife. A linear polarization analyzer with CCD camera is placed on the telescope's hour axis. Prominence emission lines are selected by narrow filters of a few Angstrom widths. This set-up allows short exposure times of a few milliseconds yielding spatially very high resolved two-dimensional prominence images in the polarized light. The particular Coudé mounting assures a daily constant instrumental polarization. For zero solar declination near the equinoxia, where the two folding flat mirrors are oriented perpendicular to each other, this polarization largely vanishes. We applied our method to prominence emissions of H-alpha, H-beta and He-D3. The Balmer lines show no linear polarization in excess of the 3×10-4 noise level. For He-D3 we find a linear polarization of a few percent; its relation to the prominence fine-structure is discussed. Title: Two-dimensional distribution of oscillations in a quiescent solar prominence Authors: Terradas, J.; Molowny-Horas, R.; Wiehr, E.; Balthasar, H.; Oliver, R.; Ballester, J. L. Bibcode: 2002A&A...393..637T Altcode: Using time series of two-dimensional Dopplergrams, a temporal and spatial analysis of oscillations in a quiescent prominence has been performed. The presence of an outstanding oscillatory signal in the acquired data has allowed us to study the two-dimensional distribution of wave motions and, in particular, to detect the location of wave generation and the anisotropic propagation of perturbations from that place. Moreover, a strong damping of oscillations has been observed, with damping times between two and three times the wave period. The direction of propagation, wavelength and phase speed, together with the damping time and wave period, have been quantified and their spatial arrangement has been analysed. Thanks to the goodness of the observational data, the image alignment procedure applied during the data reduction stage and the analysis tools employed, it has been possible to carry out a novel and far-reaching observational study of prominence oscillations. The five movies are available at http://www.edpsciences.org Title: GREGOR, a 1.5 m Gregory-type telescope for solar observation Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Soltau, W. Schmidt D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2002NCimC..25..689K Altcode: No abstract at ADS Title: Post-focus instrumentation for GREGOR Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.; Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2001AN....322..361K Altcode: GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR. Title: Spatial offsets between lines and continuum in limb faculae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2001SoPh..202..259S Altcode: High-spatial-resolution spectra of limb faculae show spatial displacements of line cores relative to the adjacent continuum at cos θ<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. Title: A New Algorithm for Pattern Recognition and its Application to Granulation and Limb Faculae Authors: Bovelet, B.; Wiehr, E. Bibcode: 2001SoPh..201...13B Altcode: We have developed a new pattern-recognition algorithm based on multiple intensity clips which assures an optimal adaptation to the solar structure under study. The shapes found at higher clip levels are repeatedly extended to lower levels, thus filling more and more of the observed intensity contours. Additionally, at each intensity threshold new shapes, exceeding the level, are integrated. The number and height of the levels can be optimized making this `multiple level tracking' algorithm (MLT) superior to commonly used Fourier-based recognition techniques (FBR). The capability of MLT is demonstrated by application to the intensity structure of solar granulation near the disk center, both speckle reconstructed and not. Comparisons with Doppler maps prove its reliability. The granular pattern recognized by MLT differs essentially from that obtained with FBR. Elongated `snake-like' granules do not occur with MLT and, consequently, the perimeter-area distribution exhibits only a marginal `second branch' of higher fractal dimension, which dramatically diminishes the better the MLT pattern matches the granular structure. The final distribution obtained with optimized parameters has a single fractal dimension near 1.1, making the question of a `critical size', a `second branch', and the often discussed dimension of 4/3; highly questionable. This result is equally obtained from application of MLT to the corresponding Doppler velocity map of granular up-flows. In contrast, the pattern of down-flows contains some elongated `snake-like' structures with higher fractal dimension. We also use the new algorithm to recognize speckle-reconstructed limb faculae, which MLT separates from their granular surroundings, and compare both, granules and faculae, using large statistical samples. The facular grains near cosθ=57° exhibit a slightly different ellipticity than the (geometrically foreshortened) adjacent granules. However, small facular grains are more round than small granules and larger grains are more similar to granules. Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.; Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D. Bibcode: 2001AGM....18.P223K Altcode: GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar atmosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the Observatorio del Teide on Tenerife. We describe the optical design and the focal plane instrumentation. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying processes. GREGOR will also serve as a test bed for next generation solar telescopes. Title: Magnetic field strength and inclination in the penumbral fine-structure Authors: Wiehr, E. Bibcode: 2000SoPh..197..227W Altcode: 2012arXiv1210.2870W The uncertainty about a possible correlation between magnetic field strength, inclination, and the continuum intensity of sunspot penumbral fine-structure has been removed from detailed analysis of a spatially very well-resolved spectrum: the darker, long penumbral lanes host a 10% stronger and ≤ 30° flatter magnetic field as compared to the field in bright penumbral locations. This finding is not only based on the high spatial resolution but also on the use of a spectral line, here Fe 6842.7 Å, obtaining its essential contribution from those deep layers where the penumbral structure is seen, i.e. the continuum intensity level. The almost perfect correlation establishes that the penumbral structure is formed by the two magnetic components mainly differing by the field inclination. The different results from other Zeeman lines, as, e.g., Fe 6302.5 Å, indicate a different field structure above the white-light penumbral layers. Title: Two-dimensional photometric analysis of emission lines in quiescent prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 2000SoPh..196..357S Altcode: 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. Title: Applying speckle masking to spectra Authors: Sütterlin, P.; Wiehr, E. Bibcode: 2000SoPh..194...35S Altcode: We have applied the technique of speckle masking to spectra. The observation of elongated solar structures avoids the problem of missing information in one-dimensional spectra. Image motion perpendicular to the slit was diminished by a one-dimensional image stabilization system. The remaining influence of the Earth's atmosphere was removed by a modified speckle-masking algorithm, adapted to the single spatial dimension occurring in the spectra. The reconstructed spectra achieve the diffraction limit of the telescope and the spectrograph. Title: Two-dimensional Mapping of Emission Ratios in Quiescent Prominences Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1999ESASP.448..435W Altcode: 1999ESPM....9..435W; 1999mfsp.conf..435W No abstract at ADS Title: Continuum photometry of solar white-light faculae Authors: Sütterlin, P.; Wiehr, E.; Stellmacher, G. Bibcode: 1999SoPh..189...57S Altcode: 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. Title: Mass Motions and Magnetic Fields in Penumbrae Authors: Wiehr, E. Bibcode: 1999ASPC..184...86W Altcode: Results from sunspot penumbral spectra of photospheric lines are discussed under the particular aspect of the structuring of magnetic fields and of the Evershed effect. Since the pioneering papers in the mid-sixties, a variety of observations were made at increasing spatial resolution. These establish spatially altering steeper and flatter penumbral flux-tubes. The Evershed effect seems to be located in the flatter field structure which has weaker field strengths. No clear relation is found between the spatial structure of the continuum intensity and that of the magnetic field and of the Evershed effect. This even holds for speckle reconstructued spectra which achieve a spatial resolution of 0.2 arcsec. The relation to the line-core intensities is closer; possibly since these originate from similar layers as those where field and flow are measured. Title: Protuberanzen - glühendes Plasma in der Magnet-Falle. Authors: Wiehr, E. Bibcode: 1999S&WSp...4...50W Altcode: No abstract at ADS Title: Prominence Doppler oscillations. Authors: Molowny-Horas, R.; Wiehr, E.; Balthasar, H.; Oliver, R.; Ballester, J. L. Bibcode: 1999joso.proc..126M Altcode: Longitudinal velocity maps have been constructed from time series of Hβ filtergrams, obtained at three positions along the emission line profile. Several examples of velocity perturbations with a periodic behaviour have been found at different spatial locations in the prominence. Periods have been determined to vary approximately between 28 and 95 minutes. The presence of damping (and in one case, of excitation) in those oscillatory motions is discussed. Title: Automatic guiding of the primary image of solar Gregory telescopes Authors: Küveler, G.; Wiehr, E.; Thomas, D.; Harzer, M.; Bianda, M.; Epple, A.; Sütterlin, P.; Weisshaar, E. Bibcode: 1998SoPh..182..247K Altcode: The primary image reflected from the field stop of solar Gregory telescopes is used for automatic guiding. This new system avoids temporal varying influences from the bending of the telescope tube by the main mirror's gravity and from offsets between the telescope and a separate guiding refractor. The required stiffness of the guider mechanics and the small areas of the sensors demand small f numbers for the guider optics, which cause problems with the image quality and with heat. Problems also arise from the pinhole in the telescope's field stop which is imaged as a dark dot on the sensor. Pointing errors introduced by the telescope affect shifts of the solar image on the sensor. These are numerically determined by Fourier methods which are found to be less sensitive to noise than profile centering methods. Several types of guiders are tested, the final equipment, now installed at the Gregory telescopes at Tenerife and at Locarno, is described. Title: Temperature mapping of sunspots and pores from speckle reconstructed three colour photometry Authors: Suetterlin, P.; Wiehr, E. Bibcode: 1998A&A...336..367S Altcode: The two-dimensional temperature distribution in a highly structured sunspot and in two small umbrae is determined from a three-colour photometry in narrow spectral continua. Disturbing influences from the earth's atmosphere are removed by speckle masking techniques, yielding a spatial resolution limited by the telescope's aperture. The corresponding colour temperatures are consistent over a range of more than 2000 K, although the numerical correction introduced by the reconstruction differs largely for the three colours. Part of the scatter in the temperature relation disappears when convoluting the final images with artificial PSFs that compensate for the different, colour dependent spatial resolution. The remaining spread in the scatter plots does not reflect noise, but is related to local variations of the temperature difference between the continuum emitting layers. This is most obvious for a small umbra which yields `branches' in the scatter plots the `bluer' of which corresponding to the limb-side umbral border. Here, the `hot rim' of a Wilson depressed umbra becomes visible. The temperature map of the large spot shows that the bright umbral dots do not reach the temperature of the non-spot surroundings. Instead, they exceed the 2000 K cooler umbral temperature minimum by 900-1300 K. The filamentary structure of the surrounding penumbra has spatial temperature fluctuations of typically 700 K, a value which fits earlier observed contrasts. However, the mean temperatures of 5650 K in the dark and 6250 K in the bright penumbral fine structures exceed former findings. Exceptionally bright penumbral grains are 250 K hotter than the mean solar surface and thus exceed even brightest granules. Title: The hot prominence periphery in EUV lines Authors: de Boer, C. R.; Stellmacher, G.; Wiehr, E. Bibcode: 1998A&A...334..280D Altcode: Two sets of He I and metallic lines were observed with the EUV spectrograph SUMER in a quiescent prominence. H, He, and Ca II lines were observed simultaneously with both German telescopes on Tenerife. The visible lines from elements with different atomic weights yield thermal and non-thermal broadening parameters of 7500 <= Tkin <= 8000 K and 2.5 <xi <5.0 km/s for the cool prominence body. The EUV lines, however, show line widths which correspond to much higher temperatures and non-thermal velocities. If the calculated formation temperature for every individual ion is assumed, the observed line widths require non-thermal velocities of 14 - 25 km/s. The narrowest reduced widths of the EUV He I 584 and He I 537 lines are 3.1 and 2.9 times broader than those of the visible He D_3 and He 3888 lines. If this is due to optical depth effects in the EUV lines, one obtains tau_0 (584) ~ 8*10(3) and tau_0 (537) ~ 2*10(3) , respectively. The emission ratios of the Ca II-to-Balmer lines vary little inside the prominence, indicating a largely constant gas pressure. The ratios of the visual He-to-Balmer lines as well as those of the EUV He-to-metallic lines show a significant branching between peripheral and central prominence regions. The total emissions in the main prominence body amount to 13, 0.3, and 4 [Watt/ (m(2*) ster)] for the 584, 537, and D_3 lines, respectively. The observed emission ratio E(He 584)/E(He 537)= 45 agrees with model calculations whereas their total emissions are about 37 times higher than calculated. The observed ratio E(He D_3)/ E(He 584)~0.3 is about 15 times smaller than model predictions. The observations indicate that the emissions of different ions originate from individual (isothermal) threads with different temperatures between 10(4) and 10(5) K. Title: 3-Color Photometry of a Sunspot Using Speckle Masking Techniques Authors: Sütterlin, P.; Wiehr, E. Bibcode: 1998ASPC..155...44S Altcode: 1998sasp.conf...44S No abstract at ADS Title: Prominence Emissions with SUMER and Optical Telescopes Authors: Wiehr, E.; Stellmacher, G.; de Boer, C. R.; Sütterlin, P. Bibcode: 1998ASPC..155..331W Altcode: 1998sasp.conf..331W No abstract at ADS Title: Prominence Emission Lines Observed with SUMER and Two Ground-Based Telescopes Authors: de Boer, C. R.; Stellmacher, G.; Wiehr, E. Bibcode: 1998ASPC..150..196D Altcode: 1998npsp.conf..196D; 1998IAUCo.167..196D No abstract at ADS Title: Three colour photometry of solar limb faculae. Authors: de Boer, C. R.; Stellmacher, G.; Wiehr, E. Bibcode: 1997A&A...324.1179D Altcode: The contrasts of limb faculae at various heliocentric angles are observed in three continuum windows largely free of absorption lines. Observations with interference filters show a contrast decrease with wavelength which is not found when using an `UBF' to select the shortest continuum window. Limb faculae in speckle-reconstructed images yield contrasts being typically 1.2 times higher than those deduced from the `best images' of the corresponding bursts. The fit of the wavelength dependence (`colour index') to a black-body law is significantly better for the contrasts deduced from the reconstructed images than for the contrasts from the best images. The uncorrected contrasts yield a mean facular temperature excess of 200-300K; those from the reconstructed images yield about 470 K. The center-to-limb variation is found to be much smaller than the fluctuations between individual faculae. Title: Problems in measuring prominence oscillations. Authors: Suetterlin, P.; Wiehr, E.; Bianda, M.; Kueveler, G. Bibcode: 1997A&A...321..921S Altcode: Time variations of Doppler shifts of the Ca^+^ 8542Å emission in quiescent solar prominences have been measured. A new type of 'limb guider' assures a highly constant distance of the spectrograph slit from the solar limb and furthermore removes low frequency image motion in the direction perpendicular to the slit. Remaining image motion along the slit is usually removed by a correlation of subsequent spectra. This procedure, however, cannot be applied globally to the whole spatial height in the spectra if individual structures exhibit lateral motions along the slit or even decay or arise during the observation. We therefore correlate defined individual emission maxima from successive spectra. The finally obtained power spectra show oscillations with a variety of periods at restricted locations. The data favour the known general presence of periods near 20 and 60-min, however they give only slight indication for `typical' periods near 3 and 5 min. Title: The Depth Dependence of Penumbral Absolute Velocities Authors: Balthasar, H.; Schmidt, W.; Wiehr, E. Bibcode: 1997SoPh..171..331B Altcode: Penumbral line-core shifts at different heights are determined from the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two adjacent water vapor lines for an absolute wavelength scale. The large granular blue shift of 0.6 km s-1 for the faint Fe 5435 line from deep layers yields for the centre-side penumbra absolute velocities up to 3 km s-1. This value is much larger than velocities deduced from the bisectors of the line wings of Ni 5436 and Fe 5434, thus supporting the concern against an interpretation of the line asymmetries in term of a velocity gradient with depth. Title: The helium singlet-to-triplet line ratio in solar prominences. Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1997A&A...319..669S Altcode: The emissions of the He singlet line at 6678Å and the He triplet line at 4471Å are simultaneously observed in three solar prominences. For two of them, the line pairs He-D_3_/Hbeta_ and Ca^+^8662/Hbeta_ were also observed. Comparisons with model calculations show that the emission line ratios require low densities (n_H_=~3.10^10^cm^-3^), low gas pressures (P_g_=~0.02dyn/cm^2^), and large physical slab widths. The relative He-to-H number density cannot be much lower than y=0.1. Title: Three colour photometry of a sunspot using speckle masking techniques. Authors: Sütterlin, P.; Wiehr, E. Bibcode: 1997AGAb...13...10S Altcode: No abstract at ADS Title: The Sharp Boundary of Magnetic Field and Flow in Sunspot Penumbrae Authors: Wiehr, E. Bibcode: 1997ASPC..118..175W Altcode: 1997fasp.conf..175W The line asymmetry, characteristic signature of the Evershed effect, ends abruptly at the outer sunspot border defined by the ends of the dark penumbral structures. This is most impressively demonstrated by the absence of line asymmetries at the center-side of sunspots close enough to the limb that the Wilson effect makes that penumbra invisible. It supports the idea that the line asymmetries are produced by a superposition of Doppler-shifted profiles from the dark, and less shifted profiles from the bright penumbral structures. Title: Emission Lines in a Quiescent Prominence Observed with the SUMER, VTT, a nd Gregory Telescopes Authors: Wiehr, E.; de Boer, C. R.; Stellmacher, G.; Sutterlin, P. Bibcode: 1997ASPC..118..294W Altcode: 1997fasp.conf..294W A number of emission lines have been observed in a quiescent prominence with the two German telescopes on Tenerife and with SUMER. The Gregory telescope monitored simultaneously the lines H_8 3889, He 3888, Ca(+\:) 8498, the VTT simultaneously the lines H_β, He-D_3, Ca(+\:) 8542, and H_α slit jaw pictures on 1024 x 1024 CCDs. At the same time, SUMER monitored successively three combinations of EUV lines containing He 584, He 537 in the second, and Ar, N(+) , C, C(++) , O, O(+) , O(++) , S(++) , S(+++) lines in the first order. Two dimensional images in the various EUV lines establish the anti-relation between temperature and Balmer brightness. Title: The structure of sunspot penumbrae. Authors: Wiehr, E. Bibcode: 1996NAWG.1996..193W Altcode: At sufficiently large heliocentric angles θ ≥ 65° where the line-of-sight is almost parallel to the penumbral filaments, the line asymmetry of the Evershed effect shows up as a distinct "kink" in the line wings. It can be explained by a superposition of a main component from the bright penumbral structures containing a very small gasflow and a line satellite from the dark structures containing a gasflow of 5.2 km s-1 at 250 km and 7.7 km s-1 at 550 km height. This flow is just strong enough to yield a Doppler shift of the line satellite slightly larger than the line halfwidths. Any inclination of the line-of-sight with respect to the structures reduces the distance of the satellite. The kink is therefore absent in limb-side penumbrae and in spots at smaller viewing angles. In such cases, the superposition produces a "smooth" asymmetry without a kink, but with an additional line core shift of maximally 0.8 km s-1. Title: A search for formation-height oscillations in umbrae. Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wiehr, E.; Woehl, H. Bibcode: 1996A&A...310..328B Altcode: The formation heights of spectral lines and continua in sunspots can be determined by measuring the apparent distance of the spot relative to the nearby solar limb. In order to confirm the existence of oscillatory variations of such limb distances and to exclude possible influences of differential image motion between the spot and the nearby limb, we have obtained time series observations of the lines Ca^+^ 8542, Mg b, and the non-magnetic line Fe 5576 simultaneously on two telescopes. No indication is found for periodic fluctuations of the spot's apparent limb distance. Only one of the seven time series shows a significant 40 min period of the line core but not of the continuum in the data from both telescopes. This variation of the line formation height, however, may be attributed to parallel guiding corrections of a spatially inhomogenous umbral chromosphere. The other time series show different periods for the two telescopes, which must be caused by unrelated guiding corrections. Title: The spatial structure of the Evershed effect. Authors: Wiehr, E. Bibcode: 1996A&A...309L...4W Altcode: The line asymmetry from the Evershed effect disappears beyond the boundary of the white-light penumbra over a horizontal distance of less than 500km. Immediately beyond the ends of the dark penumbral continuum structures, the lines NiI5435.9 (g=0.5) and FeI5434.5 (g=O; formed about 300km higher) simultaneously lose their asymmetry. The spatial distance of maximally 500km is too short for a "disappearence with height" as suggested by models of a penumbral "canopy". Instead, the data favour a rather flat orientation of the dark structures with an abrupt disappearance. It is suggested that this location marks the sharp threshold of the equipartition between kinetic and magnetic energy density at the outer penumbral border. Title: Branching of the helium-to-Balmer emission ratio in solar prominence structures. Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1995A&A...299..921S Altcode: The Halpha_, Hbeta_, and He D_3_ emission lines are simultaneously observed with high spatial resolution at the VTT on Tenerife. It is found that the emission ratios He D_3_/ Hbeta_ and He D_3_/Halpha_ show typical mean values for each individual prominence. This branching is related to the mean kinetic temperature and to the structuring of each prominence. Whereas the Balmer excitation is almost uniformly distributed throughout prominences, the He excitation is enhanced in structured prominences of low Balmer brightness or outer parts of unstructured bright prominences, where exciting and ionizing EUV radiation can freely penetrate. In these regions the He ionization may exceed that of hydrogen. The atmospheric prominence parameters are not yet sufficiently known to allow a reliable determination of the solar Helium abundance. Title: The origin of the Evershed asymmetry. Authors: Wiehr, E. Bibcode: 1995A&A...298L..17W Altcode: The line asymmetry of the Evershed effect shows up as a distinct "line kink" if observed along the penumbral filaments, i.e. in center-side penumbrae of spots at θ>=65deg. The kink can be explained by a superposition of a main component from the bright penumbral structures with a line satellite from the dark structures shifted by >=5km/s. The gas flow shows a gradient of 0.8km/s per 100km height. The flow is just strong enough to yield a maximum Doppler shift of the line satellite slightly larger than the line halfwidths. Any inclination of the line-of-sight with respect to the structures reduces the distance of the satellite. The kink is therefore absent in limb-side penumbrae and in spots at smaller viewing angles. In such cases, the superposition produces a "smooth" asymmetry without a kink and a line core shift of up to 0.8km/s. Larger core shifts occasionally observed indicate additional motions in the bright structures of the order of the proper motions of bright penumbral grains. This picture removes the contradictions in explaning the asymmetry and the core-shift of different lines in terms of velocity gradients. Title: Erforschung von Sonnenprotuberanzen. Authors: Wiehr, E. Bibcode: 1995S&W....34..442W Altcode: No abstract at ADS Title: Sunspot limb distance variations measured simultaneously with two telescopes. Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E. Bibcode: 1995AGAb...11..142B Altcode: No abstract at ADS Title: The Hα and Hβ emissions in solar prominence structures. Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1994A&A...290..655S Altcode: High precision photometry of the Halpha_ and Hbeta_ emissions is performed from spectra of four spatially high resolved quiescent prominences. The data are compared with recent observations and calculations. It is found that for faint emissions the observed Balmer decrement D=E_tot_(Halpha_)/E_tot_(Hbeta_) significantly exceeds the limiting value D=10.0 calculated for slab models. In contrast to former observations, the spatially and spectrally high resolved emission profiles do not require a hot and a cool component for an optimal fit. The deduced source functions do not yield a common value for different prominences, but show an individual mean for each prominence with a tendency for an increase with the optical thickness of Halpha_. Optically thick Halpha_ emissions with central absorptions are spatially related with narrow Hbeta_ emissions and hence with small kinetic temperatures. The narrow Hbeta_ emissions exist over a large range of optical thickness and show equal macroscopic shifts for individual emission features favouring a picture of closely tied bundles of threads. Title: The Evershed effect in penumbral fine structures. I. Height dependence of velocity fluctuations. Authors: Degenhardt, D.; Wiehr, E. Bibcode: 1994A&A...287..620D Altcode: A number of spectral lines with negligible Zeeman splitting have been used for a spectroscopic observation of sunspot penumbrae at different slit positions and heliocentric angles: Fe I 5576 simultaneously with Si I 6145, and, separately, Fe I 5434 and Ni I 5435 simultaneously with Ni I 4912. The formation levels of cores and wings at 20% depression were determined from contribution functions to the line depression. The spatial fluctuations of the continua, the residual line intensities, and the Doppler shifts of cores and wings are separated from a mean penumbral variation. A power spectrum analysis shows that the typical spatial scale of both the velocity and the intensity fluctuations increases with height. The rms velocity fluctuations decrease with height, resembling the known granular behaviour. The coincidence of a coarser spatial intensity and velocity structure and smaller velocities at higher levels favour an explanation by a height dependent filling. Title: The Evershed effect in penumbral fine structures II. Spatial correlation analysis. Authors: Wiehr, E.; Degenhardt, D. Bibcode: 1994A&A...287..625W Altcode: Spatially high resolved spectra of sunspot penumbrae were taken simultaneously in a number of lines with negligible Zeeman splitting. The formation layers of the different lines span the entire height of the penumbral photosphere. The intensity and velocity fluctuations from these different levels were subject to a spatial coherence and phase analysis which yields the following results: a) Spectra with a spatial resolution of at least 0.5 arcsec are necessary to detect a perfect correlation between dark penumbral structures and wing shifts of lines emerging from deep layers near the continuum level. b) This correlation rapidly decreases towards higher levels in the penumbra; it almost disappears near the temperature minimum. c) The correlation increases when the velocity fluctuations are compared with intensity fluctuations of the corresponding residual intensities of the line cores rather than with the continuum intensity emerging from much deeper layers. d) The line asymmetry ends abruptly with the penumbral continuum depression thus suggesting an interpretation of a causal relation with the penumbral fine structure. e) If Doppler shifts occasionally occur outside the white light penumbral border, the corresponding line profiles are symmetric and do not show a significant dependence on the formation height. Title: The height variation of sunspot umbral dots. Authors: Wiehr, E. Bibcode: 1994A&A...287L...1W Altcode: The visibility of sunspot umbral dots is measured in different spectral lines that are insensitive to Zeeman splitting. At the formation height of the Fe 5576 line core, the dot to inter-dot brightness ratio amounts to about 30% of that at the conlinuum level. It further drops to less than 15% at the formalion height of the Fe 5576 line core, that is expected to correspond to the temperature minimum. A contrast of 50% occurs at about 130 km height where the inner wings of Fe 5576 ({DELTA}λ=45mA) and the outer wings of Fe 5434 ({DELTA}λ=75mA) are formed. Simultaneously observed Ni and Si lines from very deep layers show the same brightness excess as the adjacent continuum. Neither systematic Doppler shifts nor line asymmeties are found in umbral dots with respect to their inter-dot neighbourhood. Title: Dependence of the He/H_8_ emission ratio on brightness, temperature, and structuring of prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1994A&A...286..302S Altcode: 2012arXiv1211.3636S The line pair He 3888 and H_8_ 3889 has been observed simultaneously with the Ca^+^8498 line in a number of quiescent prominences. The He/H_8_ emission ratio R is found to cover defined parts of a general anti-correlation with the total H_8_ emission, depending on the kinetic temperature, T_kin_, of the individual prominence: High H_8_ brightness is related to small R and Tkin values and preferably occurs in prominences with less significant fine-structure. Title: Temporal and spatial variation of physical parameters in a quiescent prominence. Authors: Balthasar, H.; Wiehr, E. Bibcode: 1994A&A...286..639B Altcode: The emission lines He 3889 A, H_8_ and Ca^+^IR_3_ are observed simultaneously in a prominence over a total of 4 hours. The time variations of the He 3889 / H_8_ emission ratio R, the thermal and the non-thermal line broadenings T_kin_ and ξ, respectively, are compared with those of the Doppler shift, v_D_, for 10 spatial locations along the slit. The time-averaged spatial variations along the slit show an increase of R, T_kin_, and ξ with height related to a decrease of the H_8_ emission, E_tot_(H_8_), in agreement with other authors. The short-time fluctuations show that quasi-oscillations, known from Doppler shifts, also exist for other physical parameters. The long-term variations over the total of 4 hours indicate a smooth increase of R, T_kin_, and ξ at the upper parts of the prominence, resembling the known spatial behaviour of these parameters at prominence edges. Also the well known anti-correlation of the emission ratio R and the E_tot_(H_8_) occurs in the long-term behaviour. We suggest that the decrease of E_tot_(H_8_) parallel with the increase of R might be related to a dissolution of the prominence yielding a smaller density of fine-structures. Title: Das Sonnenobservatorium im Tessin. Authors: Wiehr, E.; Bianda, M. Bibcode: 1994S&W....33..108W Altcode: No abstract at ADS Title: The Fe I 10265 Å line as an excellent tool for magnetic field measurements Authors: Schmidt, W.; Balthasar, H.; Wiehr, E. Bibcode: 1994ASIC..433...49S Altcode: No abstract at ADS Title: Time saeries of the penumbral Evershed effect. Authors: Schleicher, H.; Wiehr, E.; Balthasar, H.; Wöhl, H. Bibcode: 1994AGAb...10..113S Altcode: No abstract at ADS Title: Magnetic field strengths in umbral dots Authors: Wiehr, E.; Degenhardt, D. Bibcode: 1993A&A...278..584W Altcode: Stokes-V and I spectra of sunspot structures have been observed simultaneously in the lines Fe 6843 and Ca 6103 originating from layers which differ by more than 350 km. The Fe line is totally split thus allowing to deduce the field strength from the Stokes-I and V profiles. Both splitting values yield a field strength reduction up to 20% in brighter (peripheral) dots at the umbral border. This reduction is not seen in the higher layer where the Ca line originates. The faint (central) dots do not exhibit a field strength difference with respect to their darker surroundings. Using the ratio of pi to sigma depressions of the totally split Fe 6843 line as a measure for the field inclination, the field lines are found to be essentially flatter in a light bridge than in its neighborhood. Flatter fields are also found in some of the peripheral dots. The Doppler shifts of the Fe and of the Ca line deviate significantly from each other but do not show a relation to the umbral structures. Title: Doppler oscillations in solar prominences simultaneously observed with two telescopes. Discovery of a 30 S oscillation Authors: Balthasar, H.; Wiehr, E.; Schleicher, H.; Wohl, H. Bibcode: 1993A&A...277..635B Altcode: Time series of Doppler shifts are observed simultaneously with two telescopes in order to separate actual solar velocities from influences of image motion or unperfect guiding. Several maxima of the power contours occur only in the data set from one of the two telescopes and may thus originate from non-solar sources. Considering only those power maxima which are observed with both telescopes we establish the solar origin of periods near 20 and 12 min, which may be identified with `hybrid fast modes' from model calculations. For one prominence a significant period of 30 5 is detected which theory predicts as a wave guided by the prominence fine-structures. Our prominence oscillations are restricted to spatially small areas of a few arc see diameter. Title: Gasströmung im Magnetfeld von Sonnenflecken-Penumbren. Authors: Wiehr, E. Bibcode: 1993S&W....32..174W Altcode: No abstract at ADS Title: Influence of non-thermal broadening on the He 3889/H8 emission ratio in prominence fine-structures Authors: Stellmacher, G.; Wiehr, E.; Grupe, D. Bibcode: 1992A&A...265..781S Altcode: The neighboring emission lines H8 and He near 3889 A were observed in a quiescent prominence at high spatial resolution. The systematic increase of the He/H8 emission ratio R towards the edges of the prominence is found to be largely cospatial with a corresponding behavior of the nonthermal line-broadening parameter Xi while the thermal broadening does not increase. The good relation between R and Xi also exists in the fine-structures. This is explained by broadening of the absorption coefficient increasing the efficiency of the exciting UV radiation preferably for the (heavier) helium. Interpretation of the nonthermal broadening parameter in terms of a velocity dispersion may favor the influence of waves. Title: Spatial structure of the Evershed effect Authors: Wiehr, E.; Degenhardt, D. Bibcode: 1992A&A...259..313W Altcode: Spectra of a sunspot penumbra at 27 deg are taken in four adjacent slit positions at exceptionally good seeing conditions, yielding smallest continuum structures of 0.35 arcsec width. The Doppler shifts of line-core and line-wings of the nonmagnetic line Fe I 7090.4 are cospatial, but their amplitudes are unrelated. The amount of line asymmetry is thus not related to the corresponding line-core shift. A good correlation with the continuum occurs only in spectra achieving highest spatial resolution. A slightly less resolved spectrum does not show a similar correlation, thus explaining the missing relation in former observations. The amplitudes of shift and asymmetry are not related to those of the continuum intensity. The lack of any amplitude relation in spite of an almost perfect spatial correlation among shift, asymmetry, and continuum might be explained by the different angles-of-view through fine structures aligned along flux tubes of individual inclination angles recently observed. In addition, actual penumbral structures being essentially smaller than 250 km as deduced from white light pictures might yield different influences of spatial smearing on continuum, line shift, and line asymmetry. Title: Time series of Doppler velocities in prominences. Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E. Bibcode: 1992AGAb....7..151B Altcode: No abstract at ADS Title: Fluctuation of wing strengths as diagnostic tool for the structure of granulation. Authors: Nolte, U.; Kneer, F.; Wiehr, E. Bibcode: 1992AGAb....7..150N Altcode: No abstract at ADS Title: Spatial variation of the magnetic field inclination in a sunspot penumbra Authors: Degenhardt, D.; Wiehr, E. Bibcode: 1991A&A...252..821D Altcode: Stokes-V-spectra from a sunspot penumbra show significant spatial fluctuations. Due to its deep formation layer, the Fe 6842.7 used is totally split (B = 2200 Gs) showing field fluctuations of the order of 10 percent. The spatial variations of the Stokes-V spectra are strongly affected by telescopic phase retardation thus allowing only a rough estimate of the inclination angle. Its fluctuation to the solar surface is spatially related to the field-strength fluctuation in the sense that steeper fields are stronger. Doppler shifts of the Stokes-V give slight indication for upward motions at locations of steeper field inclination. A relation with the continuum-intensity fluctuation is only found in the center-side penumbra, possibly due to the steeper angle-of-view. The absence of a similar correlation in the limb-side spectra agrees with earlier findings that field strength and Evershed effect are not related to penumbral fine-structures. Title: Modelling the moustache phenomenon in network regions Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1991A&A...251..675S Altcode: The intensity enhancement in the inner line wings (moustache) of Mgb1 5183 and Fe 5434.5 A observed in Ca(+) K bright points outside active regions is found to result from a superposition of a hot component (representing the magnetic structure) surrounded by a cool (intergranular) region. The I + V and I - V profiles of the magnetically sensitive line Fe 6302.5, observed strictly simultaneously with Mgb1, are equally well modeled by the same procedure (which in an earlier paper had successfully been used to explain the gap effect of Zeeman insensitive lines in plages). The Mgb1 moustaches are cospatial with the simultaneously observed Fe 6302.5 gaps. Their equal spatial extent indicates equal width of the temperature and the magnetic structures of the Ca(+) K region. Title: Geometric line elevation in solar limb faculae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1991A&A...248..227S Altcode: Spectra of markedly visible white light faculae near the solar limb are used to determine the geometric displacement, Delta-h, of line cores with respect to their adjacent continuum. The observed Delta-h are plotted as a function of the excitation potential and, respectively, equivalent width of the different lines. Comparison with calculated Delta-h from a photospheric LTE model shows that the observed facula values significantly exceed the photospheric ones. Title: Stokes-V in an active prominence Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1991A&A...247..379W Altcode: Stokes-V spectra of the Ca(+)8542 emission were taken with a CCD in an active prominence showing extremely high line-of-sight velocities up to 25 km/s. The spatial resolution allows detecting prominence fine-structures as small as 1.1 arcsec. Exact field strengths were determined from the measured steepness of the individual emission line flanks. Values between 75 and 180 Gs are obtained. No indication is found for a dependence of the field strength on the spatial resolution or on the line-of-sight velocity, nor on the emission brightness. Title: Samples of recent high resolution solar observations at Tenerife Authors: Wiehr, E.; Mattig, W. Bibcode: 1991AdSpR..11e.199W Altcode: 1991AdSpR..11..199W The new German telescopes in Izan~a (Tenerife) are now fully operational. The first spectroscopic observations demonstrate the outstanding quality of the site. Examples of the first scientific results are given. They are focused on the fine structure of the granulation, small fluxtubes and faculae, the Evershed-effect in sunspots and magnetic field strengths in prominences. Title: Oscillations of Evershed velocities and asymmetries Authors: Balthasar, H.; Wiehr, E. Bibcode: 1990A&A...237..243B Altcode: Four sunspots at different heliocentric angles have been observed to study the oscillatory behavior of line asymmetries and velocities due to the Evershed effect. For two spots the power maxima of the line core velocities and of the line asymmetries are spatially anticorrelated. The central part of the penumbra as intersected by the spectrograph slit is the location of a velocity power maximum for the one spot, however, of an asymmetry power maximum for the other spot. In contrast, for two other spots several local power maxima are spatially coincident for the line asymmetry and the line core velocity. These variable spatial relations of line core velocities and line asymmetries support the idea that the Evershed effect may be a result of the superposition of penumbral fine structures affected by the underlying oscillating layers. Title: Intensity correlations in granular spectra Authors: Balthasar, H.; Grosser, H.; Schroeter, C.; Wiehr, E. Bibcode: 1990A&A...235..437B Altcode: Spectra of high spatial resolution were taken at the Gregory-Coude Telescope on Tenerife to investigate the relation between the line core intensities and the adjacent continuum for selected iron lines. Anti-correlations of these two quantities are found for the four lines with low excitation potential Fe5079, Fe5434, Fe5501, and Fe5506 which are known to show a limb effect although they have no blue shift at the disk center. An anti-correlation is also found for the line with high excitation potential, Fe5074, which shows a very small limb effect. This result is compatible with a granular intensity pattern which reverses in high layers, as suggested by numerical simulations of the granulation. Title: Magnetic field, relative Doppler shift and temperature for an inhomogeneous model of sunspot umbrae Authors: Pahlke, K. -D.; Wiehr, E. Bibcode: 1990A&A...228..246P Altcode: From spatially unresolved umbral Stokes-V spectra, magnetic field strength, relative Doppler shift and temperature of a hot and a cool umbral component are investigated. The observed Stokes-V profiles are compared to numerically superposed Stokes-V profiles calculated with various intrinsic model atmospheres and magnetic field parameters and filling factors. An optimal fit is obtained if the temperature of the hot component lies between that of the undisturbed photosphere and 500 K less, whereas the cool component is found to be 350 K hotter than typical models for darkest umbrae suggest. The hot component covers 5 percent of the umbral area observed; this value seems to vary from spot to spot. The magnetic field strength in the hot component is found to be about 20 percent lower than that in the cool component; the magnetic field in both components decreases with height by 2 Gs/km. Title: Doppler Velocity Oscillations in Quiescent Prominences Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1990LNP...363..255W Altcode: 1990IAUCo.117..255W; 1990doqp.coll..255W No abstract at ADS Title: Observations of Magnetic Features with the German Solar Telescopes at the Observatorio-Del / Tenerife Authors: Kneer, F.; Soltau, D.; Wiehr, E. Bibcode: 1990IAUS..142..113K Altcode: No abstract at ADS Title: Velocity and magnetic field fluctuations in penumbral fine-structures Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1989A&A...225..528W Altcode: Spatially very highly resolved spectra of sunspot penumbrae show that the Evershed effect is not spatially related to the continuum intensity fluctuations. The line asymmetry and the core shift (both a signature of the Evershed effect) show fluctuations at a larger horizontal scale than the continuum and a trend for an anticorrelation, in the sense that locations with smaller asymmetry trend to show larger shifts. The Zeeman broadening also shows variations at a larger spatial scale than the continuum. There is no indication for field enhancements in dark continuum streaks, some spots even show a certain trend for enhanced field strengths in bright streaks. The absence of a general relation to continuum streaks might be explained by the finding that the continuum structures in the spectrum are almost invisible at the formation height of the Fe 5576-A line, where a coarser spatial structure of a few arcsec width occurs. Title: Compensation of image motion and discrimination of blurring for spectroscopy Authors: Wiehr, E.; Pahlke, K. -D.; Koch, A. Bibcode: 1989hsrs.conf..100W Altcode: No abstract at ADS Title: Combination of a 256 x 256 pixel matrix detector and an image intensifier Authors: Balthasar, H.; Wiehr, E. Bibcode: 1989hsrs.conf..345B Altcode: No abstract at ADS Title: The decrease of penumbral velocity and magnetic field at the outer sunspot boundary Authors: Wiehr, E.; Balthasar, H. Bibcode: 1989A&A...208..303W Altcode: Numerical simulation of atmospheric and instrumental smearing indicates that velocity and magnetic field disappear at the outer spot border within a length of maximally 1650 km and 2200 km, respectively. Accepting the (known) inclination of 84 deg, the corresponding height ranges of 165 and 220 km, respectively, are not compatible with the picture of a disappearance of both fields due to a kind of 'optical dilution' with height. Indication is given for a disappearance of the fields beyond an iso-tau discontinuity. Title: The Gregory-Coudé- Telescope at the Observatorio Del Teide Tenerife Authors: Kneer, F.; Wiehr, E. Bibcode: 1989ASIC..263...13K Altcode: 1989ssg..conf...13K No abstract at ADS Title: Doppler Velocity Oscillations in Quiescent Prominences Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1989HvaOB..13..131W Altcode: No abstract at ADS Title: Plasma oscillations inside small fluxtubes. Authors: Wiehr, E.; Lustig, G. Bibcode: 1989sasf.confP.349W Altcode: 1988sasf.conf..349W; 1989IAUCo.104P.349W Periodic Doppler motions inside small fluxtubes are determined from the zero-crossing point of the circular Zeeman polarization profile (Stokes-V = 0). The gas fully participates on the known solar 5 min oscillations without affecting amplitude or frequency. Averaging the oscillations, the gas is at rest in an absolute solar scale. Discrepancies with formerly observed redshifts are explained by the systematic westward displacement of the magnetic structure relative to the Ca+K bright point used for guiding. Title: Oscillations in presence of local magnetic fields. Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G. Bibcode: 1988ESASP.286..269W Altcode: 1988ssls.rept..269W Oscillatory Doppler shifts in sunspots and in small fluxtubes are observed using either the intensity profile of lines with negligible magnetic splitting or the circular Zeeman profile (Stokes-V inversion point) of lines with strong Zeeman splitting. Sunspot umbrae show local 5 min oscillations of reduced amplitude as compared to the neighbouring photosphere. Occasionally the authors find 5 min oscillations of opposite phase at both outer penumbral borders. This could be interpreted as tilting and bobbing of the spot as a whole on the oscillating solar surface. In contrast to these larger scale sunspot fluxtubes the gas in the small fluxtubes of a few hundred km diameter seems to fully participate in the photospheric oscillations without any interaction with the magnetic field. Prominence magnetic fields show sometimes a reaction to the photospheric 5 min and to the chromospheric 3 min oscillations, in addition several other periods are found. Indication is found for eigenmodes of Alfvén waves. Title: Periodic and quasiperiodic Doppler velocity variations in solar prominences along one spatial direction Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988A&A...204..286B Altcode: Temporal variations of the Doppler displacement of the Hα-emission line were measured in four quiescent prominences in autumn 1986 at the recently installed Gregory telescope on Tenerife. As detector, a 100×100 pixel diode array was used. The length of the time series was up to seven hours. The slit was oriented parallel to the solar limb in the first case and perpendicular in the others. In November 1987 another prominence was observed with a 256×256 pixel camera simultaneously in Ca+H and Hɛ over five hours. In this case, the slit was oriented parallel to the solar limb. The result for the two lines are in good agreement. The authors earlier result of periods near one hour is confirmed. Short periods near five and three minutes are found in some parts of the prominences. They might be interpreted as a reaction of the prominence on the photospheric and chromospheric oscillations. For the time series of more than five hours indications of eigenmodes of the prominences are found. Title: Spectroscopic analysis of prominence emissions Authors: Bendlin, C.; Wiehr, E.; Stellmacher, G. Bibcode: 1988A&A...197..274B Altcode: Prominence spectra of fairly high spatial resolution of 3arcsec to 4arcsec are analysed. The total optical thickness of the Ca+K emission is determined from the self-absorption factor, using the true upper level population obtained from the Ca+8542 emission. Turbulence values determined from the widths of optically thin lines show fair agreement with microturbulence values obtained from the emission relation of the optically thick Ca+H and K lines. Variations of the emission ratio E8542/E&beta; in prominences may be related to different gas pressures. Title: Spectroscopy of the solar photosphere with high spatial resolution Authors: Wiehr, E.; Kneer, F. Bibcode: 1988A&A...195..310W Altcode: A high-resolution spectrogram from the solar photosphere obtained with the recently installed Gregory-Coude telescope at the Canary Islands is analyzed. Continuum intensity fluctuations are seen at scales down to 0.53 arcsec, which demonstrates the high spatial resolution. Peak velocities reach 1.5 km/s, while rms velocities range from 350 to 490 m/s. It is found that, for deeply-formed spectral lines, shifts are well correlated with continuum intensity fluctuations at scales between 1.5 and 6 arcsec. Title: Spectrophotometric analysis of small sunspots Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1988A&A...191..149S Altcode: High resolution spectra of two small sunspots were obtained with the Gregory Vacuum Telescope at Izaña (Tenerife) on 1986 Oct. 8 and 9. The two lines Fe+ 6149 and Li7 6707 (doublet) were chosen for their very different behaviour in umbra atmospheres. Detailed shape analysis shows that cold spot models (Teff ≅ 4000K) cannot explain the present observations; a higher Teff ≅ 4600K has to be assumed. The influence of parasitic light produced by penumbral blurring and the contribution of dots is discussed. Title: Velocity variations of prominences. Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988AGAb....1R..12B Altcode: No abstract at ADS Title: Oscillations in Sunspot Umbra Penumbra and the Surrounding Photosphere Authors: Balthasar, H.; Fangmeier, E.; Kuveler, G.; Wiehr, E. Bibcode: 1988IAUS..123..183B Altcode: Doppler shifts of the nonsplit line Fe I 7090 Å have been measured simultaneously in the sunspot umbra, penumbra and the photosphere using a 100×100 diode array. The power in the range 2.5 - 4.5 mHz is found to decrease from the photosphere towards the umbra. Besides the minimum at the center of the umbra, further power minima occur at the transition region between umbra and penumbra. No significant power is found in the range 5.0 - 6.0 mHz. Title: The Gregory-Coudé-Telescope in the Observatorio del Teide, Izaña. Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D. Bibcode: 1988AGAb....1...46K Altcode: No abstract at ADS Title: Oscillatory motions of the Hα-emission line in quiescent prominences. Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G. Bibcode: 1988dssp.conf...63B Altcode: Temporal variations of the Doppler displacement of the Hα-emission were measured in 4 prominences (September 28 through October 5, 1986) at the recently installed Gregory telescope at Tenerife, using a 100×100 pixel diode array. Long periods near one hour confirm former results. The amplitude of these long periods vary with height and also in the direction parallel to the limb. Short periods near 5 minutes and near 3 minutes are found which might be interpreted as perturbations by the photospheric and chromospheric oscillations. Title: Oscillations of sunspots in the Stokes-V-inversion point. Authors: Balthasar, H.; Wiehr, E. Bibcode: 1988AGAb....1Q..12B Altcode: No abstract at ADS Title: Spectroscopic analysis of prominence emissions. Authors: Wiehr, E.; Bendlin, C.; Stellmacher, G. Bibcode: 1988dssp.conf...67W Altcode: Spatially well resolved prominence spectra of Ca+ and H lines are used to determine (1) optical thickness of Ca+K from the self-absorption factor, taking the true upper level population from Ca+8542; (2) turbulence values from the emission relations of the thick Ca+H and K lines yielding results similar to those from the widths of optically thin lines; (3) gas pressure from the emission ratio Ca+8542/Hβ. Title: The gradient of the small-scale velocity fluctuation in the solar atmosphere Authors: Nesis, A.; Fleig, K. H.; Mattig, W.; Wiehr, E. Bibcode: 1987A&A...182L...5N Altcode: The vertical small-scale velocity gradient in the photosphere is determined using spectrograms of high spatial resolution obtained with the Gregory-Coude telescope in Izana on August 1, 1986. The measured Doppler shifts along the spectrograph slits are analyzed using spatial Fourier analysis. The height dependence of the size of the velocity fluctuations measured at Doppler velocity is examined. It is observed that both the amplitude of the smallest velocity structures and the integrated rms small-scale velocity decrease with height in the photosphere. The derived rms small-scale velocity values are compared with the data of Canfield (1976) and Nesis (1985), and good correlation is observed. Title: The gradient of the small-scale velocity fluctuation in the solar atmosphere Authors: Nesis, A.; Mattig, W.; Fleig, K. H.; Wiehr, E. Bibcode: 1987BAAS...19..942N Altcode: No abstract at ADS Title: A comparison of the oscillations in sunspot umbrae, penumbrae, and the surrounding photosphere Authors: Balthasar, H.; Wiehr, E.; Kueveler, G. Bibcode: 1987SoPh..112...37B Altcode: Time series of the nonsplit FeI 7090 Å line have been observed in several sunspots with a 100 x 100 diode array corresponding to 48 arc sec times 1.39 Å. The spatial behaviour of Doppler motions along one fixed slit position has been studied as a function of time. Former results are confirmed, that the power in the five minute range decreases from the photosphere to the umbra, where, however, values still well above the noise level are measured. Regarding the penumbra, the power tends to exhibit a maximum at locations where the line-of-sight component of a radial horizontal field should be maximal. This indicates that the direction of the oscillatory velocities might be influenced by the magnetic field or the Evershed flow. No significant power is found in the 3 min range. An exception might be seen in a small patch at the limb of the umbra of one spot. Title: Shifts of the Circular Zeeman Profile in Small Solar Fluxtubes Authors: Wiehr, E. Bibcode: 1987LNP...291...54W Altcode: 1987csss....5...54W No abstract at ADS Title: Spectroscopic Analysis of Prominence Emissions Authors: Wiehr, E.; Bendlin, C.; Stellmacher, G. Bibcode: 1987dssp.work...67W Altcode: 1987ASSL..150...67W No abstract at ADS Title: Needs and Limits of Magnetic and Velocity Field Measurements with Sub-Arcsecond Resolution Authors: Wiehr, E. Bibcode: 1987rfsm.conf...93W Altcode: It is possible to deduce information about magnetic and velocity fine structures far below one arcsec even with a relatively small instrument. The author discusses methods of observation of fine structures of sunspots and solar faculae. Title: Construction of the German Solar Telescopes at Observatorio del Teide/Tenerife: The Gregory-Coude Telescope Authors: Kneer, F.; Schmidt, W.; Wiehr, E.; Wittmann, A. D. Bibcode: 1987MitAG..68..181K Altcode: No abstract at ADS Title: Present and Future Facilities for the Vacuum Gregory Coudé Telescope at Izaña Authors: Wiehr, E. Bibcode: 1987rfsm.conf..354W Altcode: The whole instrumentation had been operated at the Locarno station until August 1984 when it was dismantled for a transfer to the Izaña site at Tenerife. In the course of that re-installation the telescope had been completely overhauled. Instrument description, adjustment and optical tests are given. Title: Oscillatory Motions of the H Emission Line in Quiescent Prominences Authors: Balthasar, H.; Wiehr, E. Bibcode: 1987dssp.work...63B Altcode: 1987ASSL..150...63B No abstract at ADS Title: Modelling active region fine structures from observations. Authors: Wiehr, E. Bibcode: 1987PAICz..66...29W Altcode: 1987eram....1...29W Problems, methods and results are discussed to model fine structures of sunspots, plages and prominences from observed data. Two component models or other indirect methods are used to deduce model atmosphere, magnetic and velocity field within these fine structures. Title: High Resolution Spectroscopy of Sunspot Penumbrae Authors: Wiehr, E.; Knölker, M.; Grosser, H.; Stellmacher, G. Bibcode: 1987rfsm.conf..162W Altcode: The spatial variation of velocity- and magnetic field within penumbral finestructures is investigated from two very highly resolved spectra. Title: Evidence for quasi-periodic Doppler motions in solar prominences Authors: Balthasar, H.; Knoelker, M.; Wiehr, E.; Stellmacher, G. Bibcode: 1986A&A...163..343B Altcode: Observations of Doppler displacements in solar prominences have been performed using the Hα emission line. Evidence is found for the existence of quasi-periodic line-of-sight velocities in the range of 2.5 - 4.7 mHz. Former findings of long time variations near one hour are confirmed. Possible influences by misguiding and by image motion can be excluded. Scattered light from the solar aureola cannot produce the observed amplitudes. Title: Geschwindigkeits-Oszillationen in solaren Magnetfeld-Gebieten. Authors: Wiehr, E. Bibcode: 1986S&W....25..316W Altcode: Solar activity observed in the H-alpha and Ca(+) K lines are analyzed. Zeeman profiles are studied in order to evaluate the velocity oscillations in the magnetic field; 5-minute oscillations were detected. The penumbra and umbra intensities and a power spectrum reveal the presence of oscillations in the center of sunspots. The possibility of oscillations in the fields of prominences is investigated. Spectra displaying the magnetic-field oscillations are provided. Title: The sharp decrease of Evershed effect and magnetic field at the outer sunspot border Authors: Wiehr, E.; Knoelker, M.; Grosser, H.; Stellmacher, G. Bibcode: 1986A&A...155..402W Altcode: Spatially high-resolved spectra of a small split line (g = 0.5) in four sunspots at different heliographic angles show that the combined effect of line core velocities and line asymmetries (defined as Evershed effect) is strongly limited to the sunspot area defined by the continuum intensity step. Occasionally observed 'adjoining velocity maxima' just outside the sunspot edges are not related to line asymmetries, thus indicating a different origin than that of the classical Evershed effect. A similar concentration of the very spot area is found for the magnetic line broadening of two large split lines. Both results indicate that magnetic field and velocity field are sharply restricted to the visible sunspot, the often observed smooth discontinuity of both quantities are thus considered to be due to seeing. Title: Oszillationen in Sonnenflecken-Umbren, -penumbren und der benachbarten Photosphäre Authors: Balthasar, H.; Fangmeier, E.; Küveler, G.; Wiehr, E. Bibcode: 1986MitAG..65..155B Altcode: No abstract at ADS Title: Asymmetric Stokes-V Profiles in Plages and Enhanced Network Regions Authors: Wiehr, E. Bibcode: 1986ssmf.conf...77W Altcode: No abstract at ADS Title: Stokes-spectro-polarimetry with a two-dimensional diode array. Authors: Scholiers, W.; Wiehr, E. Bibcode: 1985SoPh...99..349S Altcode: A new apparatus is described which measures the Stokes profiles by means of a two-dimensional 100 × 100 detector array. On-line data processing allows the immediate visualization of the profiles corresponding to several spectral lines observed simultaneously along one spatial direction on the solar disk. An improved method for the accurate compensation of the telescopic birefringence with a Bowen compensator is realized. Three different methods for the investigation of fluxtube properties are discussed, based on the analysis of V profiles and illustrated by first measurements with the apparatus. Two characteristics of V profiles; excess polarization and zero crossing wavelength of the V profile show strong spatial variations in plages and network indicating different dynamical conditions for individual fluxtubes. Title: Observation of Stokes-V Profiles Authors: Wiehr, E. Bibcode: 1985tphr.conf..176W Altcode: No abstract at ADS Title: Spatial and temporal variation of circular Zeeman profiles in isolated solar Ca(+) K structures Authors: Wiehr, E. Bibcode: 1985A&A...149..217W Altcode: Simultaneous wavelength scans (Delta lambda = 1 A; Delta t = 10 s) of the circular Zeeman profile, Stokes-V, and of the intensity profile, Stokes-I, are performed in isolated Ca(+) K features near solar disc center for the large split line Fe 8468.4 (g = 2.5; chi-ex = 2.2 eV; W(lambda) = 128 mA). It is found that the V-profiles are always redshifted with respect to the I-profiles indicating a downdraft equal to or less than 2 km/s inside the flux-tube with respect to its non-magnetic surroundings. Both this redshift as well as the known asymmetry of the V-profiles is found to vary largely between the 12 structures observed. Repeated lambda-scans in one selected Ca(+) K feature show large time variation of asymmetry and redshift of the V-profile in the sense of a decrease of both quantities within a few minutes. This might be a first hint for the existence of a convective instability. Simultaneous Doppler measurements of the line flanks (I-profile) and of the inversion point V = 0 show that the V-profile participates on the photospheric 5 min oscillation. Title: Die deutschen Sonnenteleskope des Observatorio del Teide auf Teneriffa. Authors: Schröter, E. H.; Wiehr, E. Bibcode: 1985S&W....24..319S Altcode: No abstract at ADS Title: Evershed Effect and Magnetic Field in Penumbral Finestructures Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1985LNP...233..198W Altcode: 1985hrsp.proc..198W A highly resolved penumbra spectrum obtained from the Locarno telescope on July 4, 1982 is studied. It is observed that line core shifts are predominant in dark spectrum streaks and line asymmetries in bright spectrum streaks. The relationship between line widths and continuum brightness is investigated. A continuous dependence of these line parameters on the continuum brightness is detected; decreasing continuum brightness results in increasing line widths. Explanations for this increase are discussed. The effect of line widths/brightness variations on magnetic field fluctuations in penumbral fine structures is examined. Title: Observation of Stokes V profiles. Authors: Wiehr, E. Bibcode: 1985MPARp.212..176W Altcode: No abstract at ADS Title: The German solar telescopes at the observatorio del Teide Authors: Schroeter, E. H.; Soltau, D.; Wiehr, E. Bibcode: 1985VA.....28..519S Altcode: This article gives a survey of the German solar telescope installations which are going to be operational in 1985 (Gregory Coudé Telescope) and in 1986 (Vacuum Tower Telescope) respectively. Title: Influence of Umbral Dots on Sunspot Models Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1985LNP...233..254W Altcode: 1985hrsp.proc..254W A photoelectric investigation was conducted of umbrae of different brightness in three clean continuum windows at 4365 + or - 1/8, 6305 + or - 1/4, and 8089 + or - 1/2. These were conducted simultaneously in the 13th, 9th and 7th order of the f = 10 m echelle grating spectrograph. It was found that the presence of umbral dots could not account for observed differences in umbral brightness. In effect, it is proposed that the dots represent a less important additive for umbrae of different temperatures. Title: Velocity and asymmetry mapping of sunspots Authors: Kueveler, G.; Wiehr, E. Bibcode: 1985A&A...142..205K Altcode: Using the two-dimensional diode array system at the Locarno solar observatory, velocity and asymmetry maps of several sunspots were measured in the photospheric nonsplit 4.2-V line Fe 7090.4. It is found that the velocity and asymmetry contours of individual spots correspond very well. The Evershed velocity field taken from Doppler displacements of the very line core does not show any discontinuity at the penumbra borders. Velocity maxima are usually found very close to the outer spot border. The largest horizontal velocities are obtained at smallest heliocentric angles observed (25 deg), thus indicating a very steep velocity increase with depth. From time series of identical sunspots a slow temporal development of the Evershed field is seen, indicating a time delay with respect to the development of the visible spot structure. The vertical upflow needed to feed the observed horizontal flux is estimated to be of the order of 20-100 m/s. Title: Measurements of vector fields with a diode array. Authors: Wiehr, E. J.; Scholiers, W. Bibcode: 1985NASCP2374..153W Altcode: A polarimeter has been designed for high spatial and spectral resolution. It consists of a quarter-wave plate alternately operating in two positions for Stokes-V measurements; and, resp., an additional quarter-wave plate for Stokes-U and -Q measurements. At the spectrum plane a 100×100 pixel Reticon is used as receiver. The spatial range covers 75 arcsec, the spectral window of about 1.8 Å allows the simultaneous observation of neighbouring lines. Title: Time-dependence of umbral oscillations Authors: Soltau, D.; Wiehr, E. Bibcode: 1984A&A...141..159S Altcode: Doppler shifts of the magnetically insensitive line Fe 7090.4 are observed in two sunspot umbrae on three days over time intervals up to 8.5 h. The temporal power spectra show a large variety of periods whose pattern reoccurs periodically. Neither the 300 s nor the 180 s periods are preferred umbral modes. Conspicuous power near 0.8 m Hz closely corresponds to the known 20 min time scale of umbral dots. A 240 s period from the revolution of the telescope's RA drive screw indicates the occasional existence of a structured umbral velocity field; its relation to intensity structures, e.g. the dots, is seen from the 240 s power peak in the simultaneously recorded continuum intensity. Title: The gas pressure in solar prominences Authors: Hellwig, J.; Wiehr, E.; Stellmacher, G. Bibcode: 1984A&A...140..449H Altcode: Attention is given to the results of new measurements of the emission relation of Ca(+)8542 and H-beta, which indicate that the emission ratio E(Ca/+/8542)/E(H-beta), at about 0.16, is significantly lower than the value of about 0.3 obtained by Landsman et al. (1977). The presently undertaken comparison of these results with those of the Heasley and Milkey (1978) model indicates that a much higher value of the gas pressure, approximately 0.1 dyn/sq cm, must be assumed in order to match the observed lower ratio. Title: The influence of penumbral fine structures on line profiles Authors: Wiehr, E.; Koch, A.; Knoelker, M.; Kueveler, G.; Stellmacher, G. Bibcode: 1984A&A...140..352W Altcode: An experimental investigation of the effect of penumbral fine structure on the line profiles of Ti 5222.7 A and Fe(+) 5264.8 is presented. The highly resolved penumbral spectrum was observed with the evacuated Locarno telescope of the Goettingen observatory. It is shown that the highly excited Fe(+) line has a strong correlation in its line symmetry to bright spectrum streaks. Line core shift was correlated with dark spectrum streaks. The Doppler shift of the Be(+) line increased by 1.2 km/s, and that of the Ti line by 0.7 km/s for a continuum brightness decrease of 20 percent. On the basis of the observational data, it is concluded that the two-component model of sunspot penumbrae is unlikely. It is suggested that Evershed asymmetry originates mainly from a mixture of fine structure. Title: Oscillations of the Hα Emission in Solar Prominences Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H. Bibcode: 1984SoPh...94..285W Altcode: The time dependence of Doppler shift and line-center intensity is simultaneously observed for the Hα emission of three solar prominences, each one during about two hours. Doppler oscillations with periods near one hour and amplitudes between 1 and 2 km s−1 are conspicuously visible in the recordings of all three prominences. Fourier analysis yields periods of 50, 60, and 64 min, as well as slight indications of short periods near 3 and 5 min. No oscillations are found in the line-center brightness. Title: Umbral Oscillations Measured in the Stokes-V Inversion Point Authors: Balthasar, H.; Wiehr, E. Bibcode: 1984SoPh...94...99B Altcode: The inversion point of the circular Zeeman polarization profile (V-Stokes) parameter is used to observe umbral Doppler oscillations free from disturbing influences of parasitic light. In a second step, purely umbral lines are used to avoid remaining influences from the V-profile of the (oscillating) penumbra. Among a total of nine sunspot umbrae, three exhibit oscillations within the various 1.5 to 2.5 hr samples. The periods differ significantly from 300 s, vary with time, and occur within time intervals of high tranquility thus explaining the lack of oscillations in the remaining sunspots. Title: Geschwindigkeitskartierung von Sonnenflecken Authors: Küveler, G.; Wiehr, E. Bibcode: 1984MitAG..62..189K Altcode: No abstract at ADS Title: Oszillationen in Flecken-Umbren Authors: Soltau, D.; Balthasar, H.; Koch, A.; Küveler, G.; Wiehr, E. Bibcode: 1983MitAG..60..225S Altcode: No abstract at ADS Title: Bericht und Programm Authors: Wiehr, E. Bibcode: 1983MitAG..60..213W Altcode: No abstract at ADS Title: Magnetfeld, Intensität und Strömung in Penumbra-Feinstrukturen Authors: Stellmacher, G.; Wiehr, E.; Knölker, M. Bibcode: 1982MitAG..55...68S Altcode: No abstract at ADS Title: Line profiles and magnetic field in penumbral fine structures Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1981A&A...103..211S Altcode: Spectra at high spatial resolution are taken in a sunspot penumbra at disc center. The magnetic low sensitive lines Fe (+) 5264.8 (g equals 0.1) and Ti 5222.7 (g equals 0) as well as the large split line Fe 6302.3 are analyzed by comparison with model calculations. No systematic fluctuations of the magnetic field strength and inclination are found in the bright and dark spectral streaks, b and d. It is shown that this result is still compatible with actual field fluctuations of less than or equal to 1,000 G between the individual penumbral bright and dark regions, BR and DR. The observed fluctuations of the central intensity of the two oppositely temperature sensitive Fe(+) and Ti lines are essentially smaller than expected from the continuum fluctuations. The DR model requires a larger macro turbulence parameter than the BR model in agreement with a spatially low resolved Evershed flow in the DR. Title: On the branching in the emission relations of Ca+ in prominences Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1981SoPh...71..299S Altcode: 2012arXiv1211.3641S Spatially well resolved prominence spectra of the three lines Ca+ K, Hβ, and Ca+ 8542 are analysed. It is confirmed that the branching in the emission relations of Ca+ versus Hβ correlates with the magnitude of non-thermal (turbulent) broadening. Title: Umbral Models with Enhanced Continuum Opacity Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1981A&A....95..229S Altcode: Umbral models based on the assumption of an additional continuum opacity (Zwaan, 1974; Kollatschny et al., 1979: M4) are compared with model M3 by Stellmacher and Wiehr (1975) which is based on the standard continuum opacity.

The strong Fe 4063.6 lime is observed in several sunspot umbrae. An upper limit of parasitic light is estimated on the basis of vanishing Fe+ limes in umbrae. It is shown that the wings of the so corrected Fe 4063.6 line cannot be reproduced by model M3. The recent model M4 requires an opacity enhancement q4063 = 2.5 ± 0.2; Zwaan's model needs q4063 = 2.7. The relative umbral intensity at λλ4063 is obtained to 0.026 Iphot using model M4 with q4063 = 2.5. Assuming line haze as origin for qλ the true continuum would amount to 0.065 Iphot. Measurements of umbral continuum contrasts near the peaks of the opacity curve q(λ) suggested by Gaur et al. (1979) do not show the marked contrast depressions predicted and are thus at variance with the idea that the additional opacity arises from electronic transitions of CN, CaB, MgH and TiO molecules. Title: Measurement of solar disc polarization in a number of Fraunhofer lines and their adjacent continuum. III - Comparison with independent measurements and with calculations Authors: Wiehr, E. Bibcode: 1981A&A....95...54W Altcode: High-sensitivity measurements of resonance line polarization in the Sr(+) 4078, Sr 4607, Ba(+) 4554, Na D2, Mg b, Fe 4063 and Cr 4275 lines of the solar disk are presented in an attempt to resolve discrepancies between previous measurements (Wiehr, 1975, 1978) and the data of Stenflo et al. (1980). The present observations were made with the Locarno polarimeter improved by the insertion of a new KDP crystal having double transmission and double modulation amplitude to increase spectral resolution. The F3 4063.6 line is found to show resonance polarization, whereas Cr 4274.8 requires further observations to establish the possible presence of polarization. The present results for Ba(+) 4554 and Sr 4607 agree with both sets of previous results, however an excess polarization is observed in the blue wing rather than the red for Sr(+) 4087, in agreement with Wiehr (1975); the double reversal found by Stenflo et al. in the Na D2 core has also not been observed. Finally, the center-to-limb variation of the polarization maximum in the blue wings of Ca 4227 and Na D2 given by Wiehr (1975) are shown to yield different damping parameters when fitted to the calculations of Auer et al. (1980) than those deduced from the data of Stenflo et al. Title: Zusatz-Opazität für Sonnenflecken und späte Sterne Authors: Wiehr, E.; Kollatschny, W.; Stellmacher, G. Bibcode: 1981MitAG..52..162W Altcode: No abstract at ADS Title: Solar observations at the Göttingen University Observatory Authors: Wiehr, E.; Wittmann, A.; Wöhl, H. Bibcode: 1980SoPh...68..207W Altcode: No abstract at ADS Title: Erratum - Evidence for a Lower Limit of Solar Magnetic Field Strengths Authors: Wiehr, E. Bibcode: 1980A&A....91..377W Altcode: No abstract at ADS Title: The infrared Ca/+/ lines in sunspot umbrae Authors: Kollatschny, W.; Wiehr, E.; Stellmacher, G.; Falipou, M. A. Bibcode: 1980A&A....86..245K Altcode: 2012arXiv1210.3336K We present an empirical working model for sunspot umbrae which equally describes observed continuum intensities and line profiles. The wings of the infrared Ca II lines depend sensitively on the temperature gradient at -0.6 < log(tau-0.5) < +0.3 but not essentially on the absolute value of T. These lines are observed to remain almost unchanged from photosphere to umbra and are thus insensitive to parasitic light. It is also shown that the infrared K I 7699 line is suitable for umbral spectroscopy since it is not seriously blended, its continuum is well defined and it is less influenced by parasitic light as compared to lines in the visible spectrum, due to the smaller umbral contrast. Calculations show that the umbral gradient dT/d(tau), required to fit the Ca II triplet lines, strongly conflicts with the observed profiles of K I 7699, NaD2 and Fe I 5434 (g=0), even when assuming vanishing Fe II lines for a maximum correction of parasitic light. It is shown that this discrepancy from the different line profiles may be removed by adopting an opacity enhancement as introduced by Zwaan (1974) from a discussion of continuum contrasts alone. The finally proposed umbral working model is very close to a scaled model of the quiet sun with T(eff)= 4000 K thus resembling a M0 rather than a K5 stellar atmosphere Title: Die Temperatur-Schichtung in Sonnenflecken. Authors: Wiehr, E. Bibcode: 1980S&W....19..172W Altcode: Various mechanisms to explain the lower temperature of sunspots in relation to their surroundings are considered. The investigation of the physical characteristics of sunspots is significant for other aspects of solar research, as in the determination of the frequency of easily ionized elements (e.g., Li, Be, B, and Cs). The recent development of methods that permit the measurement of individual linear profiles in the umbra of the sunspots is examined, along with the falsification of spectra through stray light interference from the surroundings. The use of an additional absorber effective at lower temperatures of the umbra is discussed. Title: The influence of spatial resolution on the Ca/+/K line width and shift in a quiescent prominence Authors: Engvold, O.; Wiehr, E.; Wittmann, A. Bibcode: 1980A&A....85..326E Altcode: A series of 17 spectrograms of the Ca+ K line in a large quiescent prominence are investigated for the effects of spatial smearing due to seeing. It is found that the full width at half- maximum (FWHM) decreases from 0.190 Å to 0.125 Å when the spatial resolution increases from 15" to about 2". High spatial resolution also facilitates the detection of large line shifts Δλ. The narrowest line profiles - which are detected in the case of high spatial resolution and large shift - yield FWHMmin ≍ 0.090 Å, which exceeds the pure thermal broadening width by a factor of 2-3. The most probable value of the resolved macroscopic velocity is found to be 23 km s-1. This velocity corresponds to an equipartition magnetic field strength of about 3.8 G. Title: Line shifts and asymmetries in sunspot penumbrae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1980A&A....82..157S Altcode: The paper considers the line shifts and asymmetries in sunspot penumbrae. Spatially unresolved spectra show decreasing shifts of line cores and increasing symmetries with height; it is shown that a decomposition of the asymmetric profiles into a main component and a satellite yields contradictory results when considering the depth dependence and the center-to-limb variation of different lines. Line profiles from the bright and dark spectral streaks are analyzed, showing that line widths, residual intensities, and asymmetries increase with increasing line shift. Finally, an attempt is made to simulate the bright and dark line profiles by simple superposition of intrinsic profiles from the bright and dark penumbral regions calculated with the corresponding models given by Kjeldseth-Moe and Maltby (1974). Title: Reconstruction of the Locarno Telescope before shifting to the Canary Islands site Authors: Wiehr, E.; Wöhl, H. Bibcode: 1980fsoo.conf...63W Altcode: No abstract at ADS Title: A common model for solar filigree and faculae. Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1979A&A....75..263S Altcode: A disk-center filigree model for facular plages is examined by using photographic spectra of solar lines with a reasonably small Zeeman splitting. The results fully confirm previously reported line weakenings as well as a previously observed decrease in the line weakenings toward the limb. It is found that the highly excited lines of Fe II at 5264 A, Ti II at 4568 A, and Si I at 6145 A exhibit line strengthenings for most limb faculae but that the absolute intensities of the line cores are always higher than those of the neighboring photosphere. Photoelectric measurements of the wavelength dependence of the contrast in true continuum windows and in facular spectra obtained at various heliocentric angles reveal that the contrast decreases with wavelength, as reported earlier. Title: Evidence for a lower limit of solar magnetic field strengths. Authors: Wiehr, E. Bibcode: 1979A&A....73L..19W Altcode: Magnetograph observations of the solar quiet network at the disk center with a 4-arcsec aperture are reported. The results obtained for 37 Ca II K features indicate a lower limit of 20 G for the solar magnetic fields. A lower limit of 2.4 x 10 to the 18th Mx is placed on the magnetic flux. A true diameter of 390 to 550 km is estimated for the smallest flux tubes, and a field threshold of 200 G is determined for pores. The results are compared with previous observations. Title: Ein Modell für solare Filigrees und Fackeln Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1979MitAG..45..149W Altcode: Previous measurements of magnetically nonsplit lines are extended to slightly magnetically split lines to gather data on low ionization lines of Fe(+), Ti(+), and Si. Attention is given to Schmahl's model in determining the rest-intensity effect, as well as to correlations between solar filigrees and faculae. Title: Reconstruction of the Locarno telescope before shifting to the Canary Islands site. Authors: Wiehr, E.; Wöhl, H. Bibcode: 1979MmArc.106...63W Altcode: No abstract at ADS Title: A Unique Magnetic Field Range for Nonspot Solar Magnetic Regions Authors: Wiehr, E. Bibcode: 1978A&A....69..279W Altcode: Summary. The `line-ratio method' for simultaneous Zeeman polarization in different lines (Stenflo, 1973) has been modified: A) By using the 3 temperature-insensitive Fe-lines at 6302.5, 6336.8 and 6408.0 A, with constant exit slits. B) By measuring Fe 6173.3 simultaneously with 3 different exit slits. Difficulties in the data reduction found for Case A are less important for Case B. Both methods yield true field strengths 1500< rue <2200 Gauss equally for Ca + K bright points, H -faculae, pores in plages and pores in spot groups; assuming `rectangular field shapes'. A simple evaluation of the `integrated' true diameters gives (t)true [km] 65 (Happ [Gs]) , indicating that apparent field strengths are almost a measure of diameter rather than of field strengths of the magnetic regions. The different features observed are characterized by different diameters rather than different Htrue Double polarity features do not show a different behaviour as compared to single polarity features. No indication is found for quantization offluxes or diameters. Simultaneous measurements of the central intensity of Ca+ 8498 and the circular polarization in Fe 8514 show for a considerable part of the magnetic regions (i. e. 11 among 32) westward displacements of the magnetic field relative to the Ca+ feature. This might indicate field inclinations caused by faster rotation of the deeper layers. Key words: small scale - field strengths - field diameters - field inclination - field displacement Title: Measurement of solar disk polarization in a number of Fraunhofer lines and their adjacent continuum. II: Improved data, new line measurements. Authors: Wiehr, E. Bibcode: 1978A&A....67..257W Altcode: Summary. The measuring accuracy of 2 t0- achieved in Paper I has been increased to 5 10- by investigating a number of instrumental effects which are described. The observations of Paper I were verified under these conditions with the result that the -dependence of the continuum polarization is actually flatter than given in Paper I; and that the line polarization of NaD2 and Ba+ 4554 has to be corrected. Furthermore, line polarization has been detected in the resonance lines of neutral Ba and Sr at 5535 and 4608, respectively. A number of lines do not show resonance polarization in contradiction with theoretical predictions. Key words: solar disc polarization - resonance polarization Title: Magnetfeld-Feinstrukturen auf der Sonne. Authors: Wiehr, E. Bibcode: 1978S&W....17..162W Altcode: Current investigations of fine structure of the magnetic field on the sun are reviewed. Mention is made of two remarkable discoveries: (1) the observation of filigrees in the H-alpha wing by Dunn (1973), and (2) the discovery by Stenflo (1973) of small regions of less than 100-km diameter with magnetic field strengths of around 2000 gauss. The principles of three-slot magnetography are reviewed. Title: Zur Existenz einer unteren Grenze solarer Magnetfelder Authors: Wiehr, E. Bibcode: 1978MitAG..43..134W Altcode: Certain problems regarding the determination of the actual field intensities with the aid of simultaneous Zeeman polarimetry in three lines can be overcome by using a procedure based on Zeeman polarimetry in a single line with three slits of differing widths. The results obtained with this procedure confirm results reported by Stenflo (1973). The results obtained by three independent methods show that even very weak solar fields lie in reality near the 2000 Gauss region. No significant differences could be observed between quiet and active networks, and facula and sunspot pores. Title: Reconstruction of the Locarno Telescope before shifting to the Canary Islands site Authors: Wiehr, E.; Wöhl, H. Bibcode: 1978fsoo.conf...63W Altcode: No abstract at ADS Title: Das Sonnen-Observatorium der DFG bei Locarno. Authors: Spindler, R.; Wiehr, E. Bibcode: 1978S&W....17..117S Altcode: No abstract at ADS Title: Zum Problem der Evershedströmungen in Penumbra-Feinstrukturen Authors: Wiehr, E.; Stellmacher, G.; Soltau, D. Bibcode: 1977MitAG..42..117W Altcode: The use of a two-flow model in the interpretation of the solar Evershed flows reported by Schroeter (1965) leads to contradictions with respect to recent measurements regarding the flow characteristics in the penumbra fine structures. Stellmacher and Wiehr (1971) have found in an analysis of line asymmetries based on such a model that the line main component must be related to slow-flowing bright penumbra structures. The line satellite, on the other hand, must be related to fast-flowing dark penumbra structures. A series of nonsplitting lines in two long-term individual spots were recorded in connection with a more detailed investigation of this model concept. The asymmetrical penumbral line profiles were decomposed with the aid of a computer calculation into a main component and a satellite. The significance of the results is discussed. It is found that the observational phenomena can be very well reconciled with a depth-dependent flow concept for the penumbra proposed by Maltby (1964). Title: Limb polarization in spectral lines and the continuum. Authors: Wiehr, E. Bibcode: 1977ROLun..12...89W Altcode: No abstract at ADS Title: Some comments on the measurement of small scale strong magnetic fields on the sun. Authors: Wiehr, E. Bibcode: 1977IAUS...62..251W Altcode: No abstract at ADS Title: Erratum; The Deep Layers of Sunspot Umbrae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1976A&A....47..479S Altcode: No abstract at ADS Title: Messung von Magnetfeldern mit Durchmessern unterhalb des Seeing-Scheibchens Authors: Wiehr, E. Bibcode: 1976MitAG..40..163W Altcode: No abstract at ADS Title: Ein empirisches Modell für die tiefen Umbra-Schichten Authors: Wiehr, E.; Stellmacher, G.; Schleicher, H. Bibcode: 1976MitAG..38..217W Altcode: No abstract at ADS Title: The deep layers of sunspot umbrae. Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1975A&A....45...69S Altcode: 2012arXiv1210.4393S We model the deepest observable layers of dark sunspot umbral atmospheres in terms of an empirical model which equally describes observed near infrared continuum intensities and line profiles. We use the umbral continuum intensity at 1.67 nm and the three C I lines at 1,6888, 1,7449 and 1,7456 nm to model the deep layers near the minimum of H- absorption. We find that a radiative equilibrium stratification yields the best compromise between continuum and C I line observations. We determine the effective temperature from the umbral and photospheric flux ratio by down-scaling the monochromatic photospheric flux with the umbral contrast for each frequency. The thus obtained monochromatic umbral flux and the photospheric one are integratied over the whole frequency range, yielding the ratio of total umbral and photospheric flux, which gives 3560 K < T_eff < 3780 K. We assume for our model M3 T_eff=3750 K and fit M3 to the theoretical model by Meyer et al. (1974). Comparison of the model's 'nabla' gradient with the adiabatic one shows that umbral convection, if existing at all, can only occur at considerably deeper layers than in the photosphere. Title: Zum Problem des Kontinuum-Kontrastes solarer Fackeln Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1975MitAG..36..148W Altcode: No abstract at ADS Title: Measurement of solar disc polarization in a number of Fraunhofer lines and their adjacent continuum. Authors: Wiehr, E. Bibcode: 1975A&A....38..303W Altcode: Summary. The linear polarization in the absorption lines Sr+ 4077, Ca 4227, Ba+ 4554, Mgb1,2,3 and NaD1,2, including their adjacent continua, is measured at a limb distance of 5 arcsec. In addition, the polarization of the violet wings of Ca 4227 and NaD2 as well as that of the continua close to these two lines is measured as function of the heliocentric angle . Key words: solar disc polarization resonance polarizati on Title: On the Solar Magnetic `Monopole' Authors: Stix, M.; Wiehr, E. Bibcode: 1974SoPh...37..493S Altcode: A superposed epoch analysis shows that the Sun's spurious magnetic monopole varies like the solar declination. This indicates that the monopole is caused by instrumental effects. Title: On Polarimetry in Solar Active Regions. VII: A New Zeeman Polarimeter and its Advantages as Compared to Other Designs Authors: Wiehr, E. Bibcode: 1974SoPh...35..351W Altcode: A new modulation procedure for Zeeman polarimeters is described and tested. The azimuth rotation by means of two steady λ/4-plates, combined with the common EOLM, has several advantages as compared to `two-EOLM-polarimeters'. The new polarimeter operates with two λ/4-plates which are alternately passed through the beam in front of the EOLM by means of an electro-mechanical chopper. The exact time of the λ/4-plate change is monitored by a photoelectric sensor. The obtained signals drive a number of relays by use of an intervening bistable electronic device. These relays allow to cut-off the erroneous Doppler signal mode and they furthermore distribute the U and Q signals into the corresponding lock-in amplifiers. As a first application of the new polarimeter, the linear polarization is measured in a sunspot penumbra. The telescope was first compensated for instrumental linear polarization down to ≲ 5 × 10-4 by means of a tilted glass plate and well as for phase retardation down to ≲ 1° by means of a Bowen compensator. Title: On Polarimetry in Solar Active Regions. VI: Experimental Compensation of Telescopic Phase Retardation: Influences on Zeeman Polarimetry Authors: Wiehr, E.; Rossbach, M. Bibcode: 1974SoPh...35..343W Altcode: Phase retardation caused by the Grégory-Coudé telescope at Locarno is determined empirically and compared with calculations. Good agreement is found for a proper retardation angle Δ = 16° for each of the two plane mirrors in the telescope. Title: Zur Eliminierung teleskopischer Einflüsse auf Polarimetrie Authors: Wiehr, E. Bibcode: 1974MitAG..35..209W Altcode: No abstract at ADS Title: A Facula Model and its Application to Facula Fine Structures Authors: Wiehr, E.; Stellmacher, G. Bibcode: 1974IAUS...56..179W Altcode: No abstract at ADS Title: Observed Facula Line Profiles and Contrasts, Comparison with Models Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1973A&A....29...13S Altcode: Summary. Profiles of magnetically insensitive lines are measured together with contrasts in real continuum windows for solar facula regions at different positions on the disc with a spatial resolution of about 3". The contrast measurements earlier observations (Fig. 1); the line profiles show the "rest-intensity effect" (discussed in a previous paper) to decrease towards the limb (Fig. 2). Calculations with a number of reasonable facula models indicate that a homogeneous LTE model fails to represent simultaneously the observed contrasts and line profiles, without further assumptions. Key words: facula models Title: Observatino of an Instability in a "Quiescent" Prominence Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1973A&A....24..321S Altcode: 2012arXiv1210.6779S Summary. A cavity-like instability has been observed in a"quiescent" prominence. -yaw pictures (Fig. 1) are shown together with Ca+ 8542 spectra (Fig. 2) taken with an image intensifier. The instability propagates almost with the phase velocity of MHD compres sive waves. A violation of the lateral stability criterion in the Kippenhahn- model is indicated, producing a material outflow along the lines of force. Key words: prominences - magnetic instability Title: Protuberanzen-Spektroskopie hoher Auflösung mit Hilfe des Bildverstärkers Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1973MitAG..32..166S Altcode: No abstract at ADS Title: A Working Model for Sunspot Umbrae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1972A&A....19..293S Altcode: Comparison of magnetically non-split line profiles with the predictions of several umbra models (Stell macher and Wiehr, 1970) resulted in the selection of three "best umbra models", those by Zwaan, Henoux and Stellmacher-Wiehr. These models have now been tested by the much stronger criterion of the center-to-limb variation (CLV) of the non-split line Fe 5434.5 and the Na D-lines. The Stellmacher-Wiehr model best represents these observations. This model is thus able to simultaneously represent the observations of wavelength dependence and CLV of umbra continuum contrasts, the profiles of non-split lines including their CLV, and the Na D-lines. This model is proposed as a "working model" for reductions of umbra observations. Key words: umbra of line proflles in umbrae Title: On Polarimetry in Solar Active Regions. V. The Magnetic Field before and after a Flare Authors: Wiehr, E. Bibcode: 1972SoPh...24..129W Altcode: High resolved magnetograms (≈ 3″) were obtained 3 hrs before and 1 hr after a 1b flare, respectively, the only bright flare reported for that active region. Careful comparison between both magnetograms shows that the line-of-sight component of the active region magnetic field remains constant. In particular there is no simplification of the rather complicated field structure in connection with the flare. Magnetic flux and field gradients also do not show any variation above the 3″ scale. Essential changes, however, were observed after 19 hrs without flare activity. This indicates that evolutionary field changes predominate over `flare related' variations. Title: Zeeman Splitting in Some Bright Prominences Authors: Wiehr, E. Bibcode: 1972A&A....18...79W Altcode: The Zeeman splitting of the Mg b2, Na D2 and Ca+ 8M2 lines in several bright prominences has been determined photographically with A/4 plate and Wollaston prism. Application of an image intensffier allowed exposure times of the order of a few seconds in spite of high spectral resolution of about 3.5- 10 . The resulting field strengths do not exceed significantly the error limits of 150 Gauss in agreement with previous polarimetric measurements. The recently reported strong prominence magnetic fields of H 1500 Gauss measured photographically with low resolution and without image intensffier have not been observed. Key words: prominence magnetic fields Title: The Influence of the Sunspot Model on the Li-Abundance Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1971SoPh...21...96S Altcode: The dependence of the Li-abundance on the equivalent width of the Li-resonance doublet at λ 6708 Å 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 ɛLi = 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 ɛLi = 1.1±0.05 (in the log ɛH = 12.0 scale). Title: On Polarimetry in Solar Active Regions. IV: Influence of Telescopic Phase Retardation Authors: Wiehr, E. Bibcode: 1971SoPh...18..226W Altcode: Phase retardation originating in a telescope is measured by means of polarizer and analyzer. The amount of this retardation depends only on the declination δ of the telescope. The retardation axes rotate with the Coudé image. Title: Magnetically Non-Split Lines in Faculae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1971SoPh...18..220S Altcode: 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. Title: Magnetically Non Split Lines in Penumbrae Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1971SoPh...17...21S Altcode: Line asymmetries of five magnetically insensitive lines in penumbrae are investigated in detail. Title: On the Circular Polarization in Active Regions Authors: Wiehr, E. Bibcode: 1971IAUS...43..235W Altcode: No abstract at ADS Title: Difficulties in the Simultaneous Measurement of all Stokes Parameters Authors: Wiehr, E. Bibcode: 1971IAUS...43...89W Altcode: No abstract at ADS Title: On Polarimetry in Solar Active Regions. III: Circular Polarization in Different Lines; Development of Magnetic Fields. Authors: Wiehr, E. Bibcode: 1970SoPh...15..148W Altcode: Measurements of the circular polarization V in different lines show that the deduced magnetic field strength and flux are systematically influenced by variations of the line absorption coefficient from photosphere to spot and faculae. Title: Magnetically Non Split Lines in Sunspots Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1970A&A.....7..432S Altcode: Three magnetically non split lines are measured photographically in sunspot umbrae and penumbrae by means of & "spot contrast discriminator", which is described and tested. The origin of parasitic light is investigated in detail, its upper limit is determined by means of a non split Fe+ line being absent in umbrae. These observational data are compared with calculations for six umbra models and one penumbra model. Concerning the wavelength dependence and the center-to-limb variation of the continuum contrast, the umbra models "Zwaan preliminary", "Wittmann.Schr6ter" and " " are in accordance with the observations. Concerning the proffles of the three non split lines, the models "Zwaan preliminary" and " " show a fairly good agreement, which is improved by slight alteration of Henoux's temperature stratffication in the outer layers (T0 < 1). From the unchanged non split line Fe A 4065.4 the best agreement between observed and calculated umbral proffles is obtained with a microturbulent velocity 1 km/s being of the same order as the photospheric value from recent works. The good agreement between measured and calculated umbral proffles indicates that inhomogenities are less important for umbrae than for the photosphere. Title: On Polarimetry in Solar Active Regions. II: Selection of Lines; Interpretation of Polarimetric Data Authors: Wiehr, E. Bibcode: 1970SoPh...11..399W Altcode: The usefulness of magnetically sensitive iron lines Fe λ5250.2, 6173.3 and 6302.3 for solar polarimetry is investigated. The line-to-continuum absorption coefficient η0 for Fe λ5250.2 depends strongly on temperature variations. Thus a photospheric calibration of polarimeter signals cannot be used for the different parts of an active region. This is also true for the Doppler calibration of `longitudinal magnetographs'. Title: Messung von Magnetfeldern auf der Sonne. Authors: Wiehr, E. Bibcode: 1970S&W.....9...65W Altcode: No abstract at ADS Title: Erratum: On polarimetry in solar active regions. I. The new Locarno polarimeter; observing procedures. [Sol. Phys., Vol. 9, p. 225 - 234 (1969)]. Authors: Wiehr, E. Bibcode: 1970SoPh...11..172W Altcode: No abstract at ADS Title: On Polarimetry in Solar Active Regions. I: The New Locarno Polarimeter Observing Procedures Authors: Wiehr, E. Bibcode: 1969SoPh....9..225W Altcode: The miscentering by the Doppler compensator of the Locarno polarimeter is investigated in detail. It is shown that the linear polarization is strongly falsified by this effect which also occurs at the Crimean and Izmiran polarimeters. Title: Indium, Rubidium, and Caesium in Sunspots Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1969ApL.....3...91S Altcode: No abstract at ADS Title: Instrumentelle und technische Neuerungen der Sonnenstation Locarno Authors: Schröter, E. H.; Wiehr, E. Bibcode: 1968MitAG..25..187S Altcode: No abstract at ADS Title: On Lithium in Sunspots Authors: Wiehr, E.; Stellmacher, G.; Schröter, E. H. Bibcode: 1968ApL.....1..181W Altcode: No abstract at ADS Title: Die Häufigkeiten einiger leichter Elemente abgeleitet aus Fleckenspektren Authors: Stellmacher, G.; Wiehr, E. Bibcode: 1968MitAG..25Q.199S Altcode: No abstract at ADS Title: Zur Eichung von Magnetographensignalen Authors: Wiehr, E. Bibcode: 1968MitAG..25..188W Altcode: No abstract at ADS Title: Problems in the Interpretation of Polarization Measurements in Active Regions Authors: Wiehr, Eberhard Bibcode: 1968IAUS...35..259W Altcode: No abstract at ADS