In close binary systems consisting of a normal star and a white dwarf, a rapid mass transfer commences when the normal star evolves to fill its Roche lobe. Evolution of the accreting white dwarf is studied all the way from the initial stages of accretion in which assumed is the accretion rate close to the critical rate for the initial radius of the white dwarf. The following sequence of events is found to take place. As soon as the accretion commences, the white dwarf becomes highly luminous due to the rapid release of the gravitational energy. Inner layers of the accreted hydrogen-rich envelope are compressed by further accumulation of matter. A relatively small mass of the accreted matter is enough to ignite the hydrogen shell-burning. The resultant shell flash is relatively weak. During the decaying phase, much mass is accreted, which is not compressed into the star but accumulates simply layer by layer. The stellar radius increases and the white dwarf looks like a supergiant star. Further evolution and its dependence on the accretion rate are also discussed.
Publications of the Astronomical Society of Japan
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