Theory for thermal pulses of nuclear shell-burning is advanced to include the case of finite amplitude. The aims are to predict the progress of thermal pulse quantitatively and to obtain the peak values of the temperature and nuclear energy generation rate without making detailed numerical computation of stellar structure. In order to attain them the physical processes involved in the progress of the pulse are clarified using the concepts of the flatness of the shell source, which destabilizes nuclear burning, and the effect of radiation pressure, which stabilizes it. It is shown that the progress of the pulse can be predicted quantitatively when the pressure and the gravitational potential of the burning shell are specified for the onset stage of the pulse. The pulse height is determined mainly by the initial pressure; the higher initial pressure results in the higher pulse. Mass dependence is also obtained by approximating the gravitational potential by that of white dwarfs. The initial pressure is the quantity which is determined in the course of evolution preceding the pulse. The theory is shown to give a satisfactory agreement with numerical computations for a wide variety of the preceding evolutions, i.e., both for the cases of the core in red giant stars and of the accreting white dwarfs. Key words: Helium shell-flash; Intermediate mass star; Thermal pulse; White dwarf.
Publications of the Astronomical Society of Japan
- Pub Date: