Radiative damping of quiescent prominence oscillations

Observations of quiescent prominence oscillations point out their finite li fetime, which suggests the presence of time damping. Recent analysis of gro und-based observations of prominence oscillations (Molowny-Horas et al. 199 9) has revealed for the first time the temporal damping of velocity perturb ations at different spatial locations within a quiescent prominence. Althou gh the damping of wave motions can be explained using a variety of mechanis ms, here we have adopted a very simple one, namely a radiative loss term ba sed on Newton's law of cooling with constant relaxation time (tau (R)), 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 shor t damping times, which indicates that these oscillations are heavily damped , whereas fast modes are practically unaffected by this radiative dissipati on and have very long damping times. Moreover, for a range of values of the radiative relaxation time the fundamental slow mode attains very large val ues of the period because of the destabilising effect of gravity. On the ot her hand, three-dimensional dispersion diagrams (i.e. plots of the real and imaginary parts of the frequency versus the wavenumber) are used to invest igate the coupling between slow and fast modes. It turns out that far from adiabatic and isothermal conditions, the radiation mechanism can effectivel y decouple the two magnetoacoustic modes.