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Published online by Cambridge University Press: 12 April 2016
According to modern conceptions the cause of nova outbursts is a thermal runaway (TR) taking place in the deep layers of the accreted envelope of a white dwarf (WD), component of a close binary system. The theory of TR was considered by many authors and, especially, has been developed in detail by Starrfield et al. (1974, 1984). It has been shown that when the pressure at some level in the envelope reaches a critical value Pcr, the thermonuclear reactions of the “hot” CNO cycle become very fast, and after a time interval of several tenths seconds the temperature at this level rises to (2 ÷ 3)× 108 K. If the CNO abundances are high enough, the total outburst energy may exceed 1047 ergs. As a consequence of TR, a considerable fraction of the envelope mass (20% ÷ 50%) must be torn off by shock waves. As suggested by Starrfield et al. (1974), the remaining matter forms an extended atmosphere (R ≃ 1011 cm) and the star transforms itself into a supergiant having a luminosity L* ≲ Ledd during several months.