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Abstract:
It is noted that linear adiabatic perturbations of a differentially rotating, axisymmetric, perfect fluid stellar model have normal modes described by a quadratic problem. The paper studies the problem and the associated time evolution equation. It is shown that in the Hilbert space H-prime, whose norm is square-integration weighted by A, the operators (A to the -1st power)(B) and (A to the -1st power)(C) are anti-selfadjoint and selfadjoint, respectively, when restricted to vectors belonging to a particular but arbitrary axial harmonic. Bounds are found on the spectrum of normal modes and it is shown that any initial data in the domain of C leads to a solution whose growth rate is limited by the spectrum and which can be expressed in a certain weak sense as a linear superposition of the normal modes.
