Other
Scientific paper
Sep 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jkas...40...67c&link_type=abstract
Journal of the Korean Astronomical Society, vol. 40, no. 3, pp. 67-82
Other
4
Sun: Atmospheric Motions, Sun: Chromosphere, Sun: Filaments, Sun: Magnetic Fields, Sun: Prominences
Scientific paper
The basic building block of solar filaments/prominences is thin threads of cool plasma. We have studied the spectral properties of velocity threads, clusters of thinner density threads moving together, by analyzing a sequence of Hα images of a quiescent filament. The images were taken at Big Bear Solar Observatory with the Lyot filter being successively tuned to wavelengths of -0.6, -0.3, 0.0, +0.3, and +0.6 Å from the centerline. The spectra of contrast constructed from the image data at each spatial point were analyzed using cloud models with a single velocity component, or three velocity components. As a result, we have identified a couple of velocity threads that are characterized by a narrow Doppler width ( Δ λ_D=0.27 Å), a moderate value of optical thickness at the Hα absorption peak (τ_0 = 0.3), and a spatial width (FWHM) of about 1 arcsec.
It has also been inferred that there exist 4--6 velocity threads along the line of sight at each spatial resolution element inside the filament. In about half of the threads, matter moves fast with a line-of-sight speed of 15±3 km/s, but in the other half it is either at rest or slowly moving with a line-of-sight velocity of 0±3 km/s. It is found that a statistical balance approximately holds between the numbers of blue-shifted threads and red-shifted threads, and any imbalance between the two numbers is responsible for the non-zero line-of-sight velocity determined using a single-component model fit. Our results support the existence not only of high speed counter-streaming flows, but also of a significant amount of cool matter either being at rest or moving slowly inside the filament.
Chae Jongchul
Park Hyung-Min
Park Young-Deuk
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