Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...434..756m&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 434, no. 2, p. 756-765
Astronomy and Astrophysics
Astronomy
50
Calcium, Gamma Ray Spectra, Iron, Plasma Dynamics, Resonance Lines, Solar Flares, Sulfur, X Ray Astronomy, X Ray Spectra, Bragg Cells, Centroids, Doppler Effect, Satellite-Borne Instruments, Spectral Line Width, Spectrometers
Scientific paper
Using data from the Bragg Crystal Spectrometer (BCS) on the Yohkoh spacecraft, we have computed measures of the total intensity, centroid position, and line widths for the resonance lines of Fe XXV, Ca XIX, and S XV during the rise phase and after maximum for 190 solar flares. The difference between centroid positions early and late in each flare yields a measure of the line-of-sight velocity shift of the line centroids. Roughly 25% of the flares show evidence for spatial shifts of the emitting plasma during the flare. For all three resonance lines in those flares that show only Doppler shifts, we find a trend in the average value of the centroid shift with distance from Sun center suggesting radial mass motions with characteristic velocities of 76, 63, and 58 km/s in the resonance lines of Fe XXV, Ca XIX, and S XV, respectively. For each resonance line there is also a correlation between the rise-phase line widths and the centroid shift. For each resonance line we find no correlation between the centroid shift and the peak intensity, rise time, and total flare duration; and no correlation between the line width and the distance from Sun center, peak intensity, rise time, and total flare duration. Comparing data from the different BCS wavelength channels, we find that the centroid shift in each channel is correlated with the centroid shifts in the other channels. Similarly, the line width in each channel is correlated with the line width in the other channels.
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