Adiabatic Pulsations and Convective Instability of Gaseous Masses--III

Abstract

The non-radial adiabatic pulsations of a homogeneous gas sphere pervaded by a weak magnetic field which vanishes on the boundary is investigated on the basis of the third-order virial equations. It is shown that Prendergast's magnetic field partially removes the degeneracy in the frequency spectrum. It increases the acoustic and Kelvin frequencies belonging, respectively, to the spherical harmonics l = 1 and l = 3. Convective instability associated with the harmonics l = 1 can be suppressed only if the adiabatic exponent is sufficiently large. In the limiting case of a fluid sphere, the system is thoroughly stable. As for the compressible configuration, the magnetic field increases the Kelvin frequencies and allows purely hydromagnetic modes with periods much larger than those associated with the Kelvin modes.