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Published online by Cambridge University Press: 14 August 2015
While the physics of some processes which are going in planetary nebulae grows to be one of the most elaborated parts of theoretical astrophysics, the origin of these objects is enigmatic. Ten years ago Shklovsky (1956) made a supposition that the formation of planetary nebulae occurs at the last evolutionary stage of a red giant as a result of the violation of mechanical equilibrium in the envelope of the star. In connection with this the possibility of the separation of an envelope of a red giant under the influence of a shock wave which moves with the velocity of the order of 100 km/sec was considered by Kaplan and Klimishin in 1959. Later on numerical calculations of the motion of a weak shock wave in the envelope of a red giant, were made which showed the basic possibility of formation of a planetary nebula with a mass of the order of 0·5 M⊙ and an initial velocity about 95 km/sec (Sakashita and Tanaka, 1962). The ballistic character of the mechanism of the formation of the planetary nebulae has been recently discussed also by Abell and Goldreich (1966).