DAMPING OF FILAMENT THREAD OSCILLATIONS: EFFECT OF THE SLOW CONTINUUM

Transverse oscillations of small amplitude are commonly seen in high-resolution observations of filament threads, i.e., the fine structures of solar filaments/prominences, and are typically damped in a few periods. Kink wave modes supported by the thread body offer a consistent explanation of these observed oscillations. Among the proposed mechanisms to explain the kink mode damping, resonant absorption in the Alfven continuum seems to be the most efficient as it produces damping times of about three periods. However, for a nonzero-beta plasma and typical prominence conditions, the kink mode is also resonantly coupled to slow (or cusp) continuum modes, which could further reduce the damping time. In this Letter, we explore for the first time both analytically and numerically the effect of the slow continuum on the damping of transverse thread oscillations. The thread model is composed of a homogeneous and straight cylindrical plasma, an inhomogeneous transitional layer, and the homogeneous coronal plasma. We find that the damping of the kink mode due to the slow resonance is much less efficient than that due to the Alfven resonance.