Dynamical fine structure of a quiescent filament

Physics

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Chromosphere, Doppler Effect, Solar Prominences, Spectrum Analysis, Velocity Distribution, H Alpha Line, Histograms, Mathematical Models, Statistical Analysis

Scientific paper

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, V1, and the intensity, I1, at the center of the H-alpha profile (+/- 0.256 A), versus the minimum intensity I0. We use a statistical model simulating a number nmax of threads (of optical thickness tau0 and source function S0), seen over the chromosphere. The threads j along the same line-of-sight i are identical except for the velocity upsilonj (gaussian distribution upsilon0, sigmaupsilon). We search for the best fit between the observed and simulated quantities: V1, sigma (V1), I1, sigma (I1), and the histogram of the I0 values over the field of view. A good fit is obtained with: (a) threads characterized by tau0 = 0.2, S0 = 0.06 (unit of the continuum at disk center), mean upward velocity upsilon0 = 1.7 km s-1 and gaussian-type velocity distribution sigmaupsilon = 3.5 km s-1. Other possible values of tau0 and sigmaupsilon 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 factor Fc is approximately 0.7. The results are discussed in connection with the values deduced from prominence observations.

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