For tightly wrapped density waves, a general criterion for their amplification due to non-adiabatic processes in gas is derived. The criterion is expressed in terms of the work integral known as the Carnot cycle, and is similar to that used in stellar pulsation. The estimation by this criterion of damping of density waves by their induced shocks is a generalization of that by Roberts and Shu (1972) in the sense that the effect of the angular momentum flux which arises from the fluid flow at the edges of a given annulus is taken into account in this criterion. It is shown that the non-adiabatic acceleration of clouds' random motion, which occurs behind the galactic shock, seems to be able to amplify the wave against the damping due to the shock. Key words: Density waves; Galactic shocks; Non-adiabatic processes; Overstability.
Publications of the Astronomical Society of Japan
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