Oscillatory motions in intense flux tubes

Abstract

The intricate nature of oscillatory motions in intene flux tubes is examined and states in which the ratio of gas to magnetic pressure (Beta) is constant are considered. Results are presented for both polytropic and real atmospheres by means of linear analysis; in the latter case, a height-dependent radiation exchange time constant is used. For purposes of comparison with earlier studies, results for the adiabatic case are also given. These results indicate that states, characteristicaly stable in the adiabatic limit, can be driven overstable when heat exchange is included in the analysis. It was found that for solar stratification, oscillatory behavior occurs for Beta less than Betac, where Betac denotes a (tube) radius-dependent critical value. A bifurcation at Beta = Betac was also found owing to overstability into two purely unstable modes. The height dependence of the eigenvectors is discussed along with the sensitivity of the results on boundary conditions. Observational consequences of the study are also noted.