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Published online by Cambridge University Press: 14 August 2015
The particle resonance in a galaxy is of special interest because, according to the recent theory of Lynden-Bell and Kalnajs (1972), it provides the excitation of the density waves. In particular it is of interest to know if the density wave reaches the particle resonance, because the dispersion relation derived by Lin and Shu (1966) has a forbidden region if the parameter where (with α0 the surface density and κ the epicyclic frequency), is larger than one. If Q= 1, Lin and Shu find two waves going through the resonance but the amplitude tends to infinity there.