With the spontaneous compression of a completely ionized gas, its absorption coefficient decreases and stellar matter begins to intensively lose energy, as a result of which the matter cools. When an incompletely ionized gas is spontaneously compressed, its absorption coefficient increases, while the opacity increases. In this layer of the star, ionization begins to occur, and energy is accumulated in it. The first process ensures the stability of the star. The second process underlies self-oscillatory phenomena in Cepheids.
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