Dynamical fine structure of a quiescent filament
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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.
KeywordsSolar Phys Optical Thickness Source Function Disk Center Upward Velocity
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