Dynamical fine structure of a quiescent filament |
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Authors: | N Mein P Mein J E Wiik |
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Institution: | (1) Observatoire de Paris, DASOP, URA326, 92195 Meudon Principal Cedex, France;(2) Present address: Space Department-Sc. ESA, Noordwijk, The Netherlands |
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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. |
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Keywords: | |
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