ON DENSITY-WAVE THEORY OF GALACTIC SPIRALS .1. SPIRAL STRUCTURE AS A NORMAL MODE OF OSCILLATION

[[abstract]]An exact formulation of the linearized problem, including appropriate boundary conditions, is developed to explore whether extensive galactic density waves of spiral form are permissible normal modes of oscillation for a stellar disk. An “anti-spiral theorem,” of the type reported previously by Lynden-Bell and Ostriker for neutral modes in a gaseous disk, holds here with limited validity─namely, whenever the effects of stellar resonances can be ignored.[[fileno]]2010118010134[[department]]物理