THE MODES OF OSCILLATION OF A PROMINENCE .2. THE SLAB WITH TRANSVERSE MAGNETIC-FIELD

We investigate theoretically the possible magnetoacoustic modes of oscillation in a prominence that may arise solely due to a weak transverse magnetic field component. The prominence is modelled as an infinitely long plasma slab embedded in a uniform magnetic field that threads the prominence transversely and is anchored to rigid walls on either side of the prominence. The effect of gravity is ignored. Particularly interesting in this study is the appearance of magnetosonic modes that are analogous to the fundamental mode of vibration of a stretched string loaded with a heavy point mass at its centre. These modes may correspond to some of the long-period (1 h) oscillations in a quiescent prominence. Intermediate periodicities, in the range 8-10 min, may be due to an acoustic-type mode in the prominence slab.