Abstract
Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i λ10830 Å line.
The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.
The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.
The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures.
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Zhang, Y., Engvold, O. & Keil, S.L. Structure and oscillations in quiescent filaments from observations in He i λ10830 å. Sol Phys 132, 63–80 (1991). https://doi.org/10.1007/BF00159130
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DOI: https://doi.org/10.1007/BF00159130