Abstract
During the MEDOC Campaign 4, on October 1999, observations of a solar active region filament were carried out by the SUMER/SoHO spectrometer. A time sequence of this filament has been obtained with a duration of 7 h 30 min and with a temporal resolution of 30 s. The Fourier analysis of the line-of-sight Doppler velocities measured in the 584.33 ÅHeI line allows us to detect oscillations in several ranges of periodicities (short periods: less than 5 min, intermediate periods: 6-20 min, and long periods: greater than 40 min). From a theoretical point of view, we consider the possible modes of oscillations of an active region filament. Following Joarder & Roberts (1993), we treat the filament as a plasma slab embedded in a uniform magnetic field inclined at an angle $\phi$ to the long axis of the slab. Solving the dispersion equations for Alfvén waves and magnetoacoustic waves, primary and secondary mode frequencies appear to be non-equidistant. For the comparison between the observed and calculated frequencies, we outline an identification method of the oscillation modes in the observed filament. This identification provides a diagnostic of the filament: the angle between the magnetic field and the long axis of the slab is estimated to be 18°, and the magnetic field strength B (G) is proportional to the square root of the density in the slab.
Original language | English |
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Pages (from-to) | 292-301 |
Journal | Astronomy & Astrophysics |
Volume | 376 |
Issue number | 1 |
DOIs | |
Publication status | Published - Sept 2001 |
Keywords
- Sun: filaments
- Sun: oscillations
- MHD
- waves