Stability of a flux tube model for prominences

We discuss the stability of a flux tube model for quiescent solar prominences. The main result is that the configurations are stable only up to a critical width (defined as the extension of the central part of the flux tube with prominence matter at low temperatures) of about 1000 km to 3000 km. The dependence of the critical width on the prominence parameters height, temperature, density contrast, external magnetic field, external gas pressure and external temperature is analysed. The normal modes and eigenfrequencies obtained numerically cover the range of observational data for prominence oscillations.