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  • 1
    Electronic Resource
    Electronic Resource
    Relation between cool and hot post-flare loops of 26 June 1992 derived from optical and X-ray (SXT-Yohkoh) observations (1995)
    Springer
    Solar physics 156 (1995), S. 337-361 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have analyzed the physical conditions of the plasma in post-flare loops with special emphasis on dynamics and energy transport using SXT-data (hot plasma) and optical ground-based data from Pic du Midi, Wrocław, and Ondřejov (cool plasma). By combining the Hα observations with the SXT images we can understand the relationship between cool and hot plasmas, the process of cooling post-flare loops and the mechanism which maintains the long duration of these loops. Using recent results of NLTE modeling of prominence-like plasmas, we derive the emission measure of cool Hα loops and this gives us a realistic estimate of the electron density (2.2 × 1010 cm−3). Then, by comparing this emission measure with that of hot loops derived from SXT data, we are able to estimate the ratio between electron densities in hot and cool loops taking into account the effect of geometrical filling factors. This leads to the electron density in hot loops 7 × 109 cm−3. We also derive the temperature of hot X-ray loops (≃ 5.5 × 106 K), which, together with the electron density, provides the initial values for solving the time-dependent energy balance equation. We obtain the cooling times which are compared to a typical growth-time of the whole loop system (∼ 2000 s). In the legs of cool Hα loops, we observe an excess of the emission measure which we attribute to the effect of Doppler brightening (due to large downflow velocities).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00670231
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamical fine structure of a quiescent filament (1994)
    Springer
    Solar physics 151 (1994), S. 75-89 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A quiescent filament was observed near the center of the disk (N5, W5) with the MSDP spectrograph of the 50 cm refractor of the Pic-du-Midi Observatory on June 17, 1986. We focus our study on the statistical moments of the Dopplershift,V 1, and the intensity,I 1, at the center of a chord of the Hα profile (±0.256 Å), versus the minimum intensityI 0. We use a statistical model simulating a numbern max of threads (of optical thicknessτ 0 and source functionS 0), seen over the chromosphere. The threadsj along the same line-of-sighti are identical except for the velocityv j (gaussian distributionv 0,σ v). We search for the best fit between the observed and simulated quantities:V 1,σ (V 1),I 1,σ(I 1), and the histogram of theI 0 values over the field of view. A good fit is obtained with: (a) threads characterized byτ 0 = 0.2,S 0 = 0.06 (unit of the continuum at disk center), mean upward velocityv 0 = 1.7 km s−1 and gaussian-type velocity distributionσ v = 3.5 km s−1. Other possible values ofτ 0 andσ v are discussed; (b) underlying chromosphere deduced from observed quiet Sun (outside the filament) by modifying the chromospheric velocities: additional mean upward velocity 0.7 km s−1, standard deviation reduced by a factorF c ∼ 0.7. The results are discussed in connection with the values deduced from prominence observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654083
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  • 3
    Electronic Resource
    Electronic Resource
    Post-flare loops of 26 June 1992 (1996)
    Springer
    Solar physics 166 (1996), S. 89-106 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Post-flare loops were observed on June 26, 1992 in the Hα line with the Multichannel Subtractive Double-Pass spectrograph (MSDP) on Pic-du-Midi and with the Swedish telescope on La Palma. The highly dynamic loops are inhomogeneous (blobs). The cool loops were observed 10–12 hours after the X 3.9 class flare which had a maximum on June 25 at 20∶11 UT. From 2D images obtained with the MSDP on June 26 we derive Hα intensities and Doppler velocities of the loop plasma. Using a geometrical reconstruction technique we show that these loops are mainly perpendicular to the solar surface and have the shape of a dipole magnetic configuration. We derive the bulk-flow velocities along the loop as a function of height using the Doppler velocities and the results from the loop reconstruction. Where the Doppler velocities are too small, we derive the bulk-flow velocities from the displacements of the falling blobs. We discuss existing deviations from free-fall velocity in the lower parts of the loops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179357
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  • 4
    Electronic Resource
    Electronic Resource
    Eruptive prominence and associated CME observed with SUMER, CDS and LASCO (SOHO) (1997)
    Springer
    Solar physics 175 (1997), S. 411-436 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of an eruptive prominence were obtained on 1 May 1996, with the SUMER and CDS instruments aboard SOHO during the preparatory phase of the Joint Observing Programme JOP12. A coronal mass ejection observed with LASCO is associated temporally and spatially with this prominence. The main objective of JOP12 is to study the dynamics of prominences and the prominence–corona interface. By analysing the spectra of Oiv and Siiv lines observed with SUMER and the spectra of 15 lines with CDS, Doppler shifts, temperatures and electron densities (ratio of Oiv 1401 to 1399Å) were derived in different structures of the prominence. The eruptive part of the prominence consists of a bubble (plasmoid) of material already at transition region temperatures with red shifts up to 100 km s-1 and an electron density of the order of 1010cm-3. The whole prominence was very active. It developed both a large helical loop and several smaller loops consisting of twisted threads or multiple ropes. These may be studied in the SUMER movie (movie 2). The profiles of the SUMER lines show a large dispersion of velocities (±50 km s-1) and the ratio of the Oiv lines indicates a large dispersion in electron density (3 x 109cm-3 to 3x 1011cm-3). The CME observed by LASCO left the corona some tens of minutes before the prominence erupted. This is evidence that the prominence eruptions are probably the result of the removal of the restraining coronal magnetic fields which are in part responsible for the original stability of the prominence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004925024794
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  • 5
    Electronic Resource
    Electronic Resource
    Physical properties of the quiescent prominence of 5 June 1996, from Hα observations (1998)
    Springer
    Solar physics 183 (1998), S. 323-338 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Multichannel Subtractive Double Pass spectrograph (MSDP) is designed to observe line profiles in a 2D field of view with a good spatial and temporal resolution. In order to deal with this unique opportunity, we introduce a new method for fitting the hydrogen Hα line formed in prominences and deriving various plasma parameters from line profile observations. A quiescent prominence was observed on 5 June 1996, at the Pic du Midi during an international campaign between 09:30 UT and 11:00 UT with the MSDP spectrograph operating in Hα at the Turret Dome. Using the new fitting method, we show that the temperature, column density of hydrogen atoms and microturbulent velocity of the prominence are respectively about 8500 K, 1.4×1012 cm−2, and 10 to 20 km s−1. The electron density of the prominence is about 1.8×1010 cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005060613653
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  • 6
    Electronic Resource
    Electronic Resource
    Hierarchy of spatial scales in UV prominences (1994)
    Springer
    Space science reviews 70 (1994), S. 175-180 
    Details
    ISSN: 1572-9672
    Keywords: Sun ; Prominences ; UV radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ultraviolet spectra of a quiescent prominence observed with theHigh Resolution Telescope and Spectrograph (HRTS) are analyzed. Different techniques lead to greatly different spatial scales for the prominence structures. The UV spectra show strong variations in intensity and Doppler shift on scales larger than 1700 km. Spectroscopic diagnostics employing line intensity ratios indicate the existence of scales between 400 m to some hundred kilometers. We attempt to interpret various aspects of the prominence intensities and velocities with a multiple thread model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00777863
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  • 7
    Electronic Resource
    Electronic Resource
    Coronal environment of quiescent prominences (1994)
    Springer
    Solar physics 149 (1994), S. 51-62 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract With thespectro-coronagraph and themultichannel subtractive double pass spectrograph (MSDP) at the Pic du Midi Observatory two quiescent prominences were observed simultaneously. From the spectro-coronagraph observations 2D maps of Hei λ 10830 Å, Fexiii λ 10798 and 10747 Å line intensities were obtained. In addition, we obtained 2D maps of the ratioR of the two iron lines. This ratio is used as a diagnostic for determining the density of the hot coronal plasma surrounding prominences. We found that the electron density is higher at the location of the prominences than in the corona, whereas small regions (∼40″) of lower electron density are unevenly distributed around the prominences indicating that the surrounding corona is highly inhomogeneous. The density of the cavity is reduced by a factor 1.5 compared to the density of the prominence environment (∼5 × 108 cm−3). We discuss the existence of cavities around these prominences according to the orientation of their axes relative to the line of sight and according to the velocity field inside the prominences. Constraints on models for prominence formation are derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00645177
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