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Astron. Astrophys. 321, 921-926 (1997)

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6. Discussion

The deduced periods refer to a highly accurate spatial location of the prominence, both perpendicular and parallel to the spectrograph slit. The data establish a general existence of periods near one hour and near 20 min, but not near 12 min. A certain 'grouping' of periods near 3.5, 4.1, 5.3, 8.2, and 9.4 min is only slightly indicated, in agreement with Wiehr et al. (1989) who find the 3 and 5 min periods only occasionally. The majority of periods show a large variation between different prominences and within one prominence. The oscillations often last only a few periods and have spatial extents of a few arcsec (see Fig. 3).

This is not surprising when considering that essential parameters determining the oscillation, such as magnetic field, density and geometry, exhibit significant variations in space as well as with time (see e.g. Balthasar & Wiehr 1994). In addition, evolutionary changes and drifts of prominence structures may simulate quasi-oscillatory motions. A comparison with theory may thus only be allowed for highly stable prominences.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998