Radiative damping of quiescent prominence oscillations

Abstract

Observations of quiescent prominence oscillations point out their finite lifetime, which suggests the presence of time damping. Recent analysis of ground-based observations of prominence oscillations (Molowny-Horas et al. [CITE]) has revealed for the first time the temporal damping of velocity perturbations at different spatial locations within a quiescent prominence. Although the damping of wave motions can be explained using a variety of mechanisms, here we have adopted a very simple one, namely a radiative loss term based on Newton's law of cooling with constant relaxation time (), to analyse the influence of this type of radiative dissipation on the modes of oscillation of Kippenhahn-Schluter and Menzel quiescent prominence models. Among other results, it is shown that slow modes are characterised by short damping times, which indicates that these oscillations are heavily damped, whereas fast modes are practically unaffected by this radiative dissipation and have very long damping times. Moreover, for a range of values of the radiative relaxation time the fundamental slow mode attains very large values of the period because of the destabilising effect of gravity. On the other hand, three-dimensional dispersion diagrams (i.e. plots of the real and imaginary parts of the frequency versus the wavenumber) are used to investigate the coupling between slow and fast modes. It turns out that far from adiabatic and isothermal conditions, the radiation mechanism can effectively decouple the two magnetoacoustic modes.