Author name code: deboer ADS astronomy entries on 2022-09-14 =author:"De Boer, C.R." ------------------------------------------------------------------------ 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: 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: Dynamics of Solar Fine Structure: Observation with High Spatial Resolution Authors: Al, N.; Bendlin, C.; de Boer, C. R.; Denker, C.; Kneer, F.; Schmitt, D.; Volkmer, R.; Wilken, V. Bibcode: 1998ASPC..154..553A Altcode: 1998csss...10..553A The Sun is an ideal object for studying non-magnetic and magnetic processes in cool stars. Here, we focus on fine structures of a few 100 km in the solar atmosphere. Granular overshoot, motions and waves of magnetic elements in the quiet Sun and in plages, etc., all affect the atmospheric structure from the bottom of the photosphere up to the corona and the solar wind. Observations with high spatial resolution are required to reveal the dynamic behaviour and to understand the underlying physical processes. During the past five years, speckle methods have become an excellent tool to obtain images of solar fine structure with diffraction-limited resolution. We demonstrate by some examples how one can gain new insights from speckle interferometry. Likewise, spectroscopy of solar fine structure is also making rapid progress towards high spatial resolution. Our two-dimensional, narrow-band spectrometer (Delta\lambda = 20-30 mAA ), working with a scanning Fabry-Perot interferometer, proves very powerful in several aspects. We present some results obtained in Na D_2 from the quiet solar chromosphere. Using suitable observing techniques together with image restoration, we aim at achieving diffraction-limited resolution also for narrow-band spectroscopy. Title: Speckle measurements of the centre-to-limb variation of the solar granulation. Authors: Wilken, V.; de Boer, C. R.; Denker, C.; Kneer, F. Bibcode: 1997A&A...325..819W Altcode: The Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife was used to perform speckle observations of photospheric granulation from disc centre to limb at λ=550+/-5nm. Images were reconstructed with the spectral ratio technique (von der Luehe 1984) and the speckle masking method (Weigelt 1977, Optics Comm. 21, 55, Weigelt & Wirnitzer 1983, Optics Letters 8, 389, Lohmann et al. 1983, Applied Optics 22, 4028). The granular rms contrast relative to the local average intensity decreases monotonically from 13.5+/-1.0% at disc centre to 8-9% at cosθ=0.1. The granular images as well as the power spectra of the intensity fluctuations show a fading of the coarse granular pattern towards the limb while smaller structures become more pronounced off the disc centre. We identify these as the bright worm-like structures appearing sometimes at the granular borders (de Boer et al. 1992A&A...257L...4D). This finding supports the result from simulations of granular dynamics by Steffen et al. (1994, Shocks in the solar photosphere and their spectroscopic signature. In: Schuessler M., Schmidt W. (eds.) Solar Magnetic Fields, Cambridge Univ. Press, p. 298). There the bright structures are locations of low pressure between the centres of granules and intergranular spaces with penetration of hot gas into the lower photosphere. 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: 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: Noise filtering in solar speckle masking reconstructions. Authors: de Boer, C. R. Bibcode: 1996A&AS..120..195D Altcode: A new method of obtaining a sensitive noise filter for solar speckle masking reconstructions is presented below. This filter separates the true image information from noise most reliably. Its efficiency is demonstrated by some representative examples considering observed and artificial image data which were generated in a computer. The latter set of data also suffered realistic degradations by the influence of seeing and noise taken from suitable observations. Title: Untersuchung von Feinstrukturen der Sonne. Authors: Denker, C.; de Boer, C. R.; Volkmer, R. Bibcode: 1996S&W....35..184D Altcode: Fine structures are elements in the solar photosphere with sizes smaller than 1 arcsec. The observation of such structures requires exquisite instrumentation and reduction methods. In this article two methods are represented: image reconstruction by means of speckle-interferometry and two-dimensional spectro-polarimetry. Title: Empirical speckle transfer function measurements from partial eclipse observations of the Sun. Authors: de Boer, C. R. Bibcode: 1995A&AS..114..387D Altcode: Empirical speckle transfer functions are derived from time series obtained during the partial eclipse on May 10, 1994, using the lunar limb as a reference structure. These functions are compared with theoretical transfer functions usually applied to solar data. Moreover, the observations are suitable for testing the spectral ratio method which is often used to estimate the seeing-dependent Fried parameter r_0_. The results indicate that the spectral ratio method overestimates the Fried parameter. The empirical speckle transfer functions exhibit a steeper decrease at spatial frequencies above the seeing-cutoff where speckle methods restore the usually lost image structures. This steeper decrease was taken into account for correcting the theoretical transfer functions. Applications of these new speckle transfer functions to solar data are presented. In comparison with previous reconstructions based on theoretical transfer functions, the sharpness of the reconstructed pictures is significantly increased. Besides, the contrast of solar structures can be estimated more reliably. Title: Speckle masking imaging of the moustache phenomenon. Authors: Denker, C.; de Boer, C. R.; Volkmer, R.; Kneer, F. Bibcode: 1995A&A...296..567D Altcode: We present high spatial resolution observations of a sunspot near the solar disc centre obtained with the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife). Our investigation aims at a better comprehension of umbral and penumbral fine structures. The speckle masking image reconstruction technique was applied to narrow-band filtergrams taken in the red wing of Hα. The reconstructed images reveal small-scale structures close to the telescopic diffraction limit of 0.19". Especially, the moustache phenomenon - the intensity enhancement in the inner wings of strong chromospheric absorbtion lines - is clearly discernible. The moustaches are concentrated at the outer border of the penumbra and in its neighbourhood. There, they appear at locations coinciding with the intergranular lanes. The moustaches are not circular in shape. Instead they show sharp intensity peaks surrounded by bright areas with frayed borders. Due to the high spatial resolution achieved in the restored filtergrams and the correction for the speckle transfer function, we find much higher intensities than in previous investigations concerning the moustache phenomenon. The peak intensities are sometimes larger than 1.7 times the intensity of the granular background, i.e. the line profiles in the inner wing of Hα exhibit emission features. Attempts to restore narrow-band filtergrams with speckle interferometry are relatively new. In this paper it is shown that the speckle masking technique is capable to reconstruct images with a low signal-to-noise ratio taken within a passband of 0.05nm. Title: Speckle observations of solar granulation Authors: de Boer, C. R.; Kneer, F. Bibcode: 1994IAUS..158..398D Altcode: No abstract at ADS Title: Speckle-Interferometrie und ihre Anwendungen auf die Sonnenbeobachtung Authors: de Boer, C. R. Bibcode: 1993PhDT.......155D Altcode: No abstract at ADS Title: Speckle observations of abnormal solar granulation Authors: de Boer, C. R.; Kneer, F. Bibcode: 1992A&A...264L..24D Altcode: We present observations of solar granulation obtained with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Speckle methods were applied to restore images of abnormal granulation in the vicinity of a sunspot near disk center. These reconstructions show nests and chains of bright 'points', whose diameters and spatial distances are close to the diffraction limit of the telescope (about 0.2 arcsec). The 'points' are not always circular in shape but also elongated. If these features are identified with the footpoints of small-scale magnetic fluxtubes, their fast temporal evolution within one or two minutes and their horizontal motion with velocities up to 2 - 3 km/sec will influence the understanding of fluxtube dynamics. Title: Speckle observations of solar granulation. Authors: de Boer, C. R.; Kneer, F.; Nesis, A. Bibcode: 1992A&A...257L...4D Altcode: We present observations of solar granulation in a plage region near disc center obtained with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Speckle methods were employed for data acquisition and data reduction. The images show small-scale structures of the size near the telescopic diffraction limit of 0.2 arcsec. We call attention to bright lanes at the borders between granules and intergranular areas. Conceivably, they are the intensity signature of strong upflows at the border of granules or of shocks in supersonic convection which are predicted by computer simulations of the granular phenomenon.