A Theory of Hydrogen Shell Flashes on Accreting White Dwarfs - Part Two - the Stable Shell Burning and the Recurrence Period of Shell Flashes

Details A Theory of Hydrogen Shell Flashes on Accreting White Dwarfs - Part Two - the Stable Shell Burning and the Recurrence Period of Shell Flashes A Theory of Hydrogen Shell Flashes on Accreting White Dwarfs - Part Two - the Stable Shell Burning and the Recurrence Period of Shell Flashes

Jun 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...257..767f&link_type=abstract

Astrophysical Journal, Vol.257, P. 767, 1982

Astronomy and Astrophysics

Astrophysics

153

Scientific paper

By means of analytical solutions of the envelope, thermal properties of hydrogen shell burnings on accreting white dwarfs are studied and a general picture for their progress is presented which is described by two parameters, the accretion the mass of the white dwarf. On a white dwarf, the thermal behavior of gas in the burning shell depends on the configuration of the envelope, which gives birth to two distinct types of stable configurations in thermal equilibrium, a high and a low state. In the high state, the nuclear shell burning makes up for the energy loss from the surface. There exists the lower limit to the envelope mass for this state. The nuclear burning rate lies in a narrow range of about a factor of 2.5, irrespective of the mass of the white dwarf, while the range itself varies greatly with the latter. In the low state, the nuclear burning is extinct, and yet the compressional heating by accreted gas balances with the cooling through the diffusion of heat. Therefore, the structure depends on the accretion rate. Thermal instability of nuclear burning sets the upper limit to the envelope mass of this state.
The shell flash is a phenomenon associated with the transition from the low to the high state driven by nuclear burning. This transition is a result of the increase in the envelope mass by the accretion. After the first shell flash, the shell burning settles into a steady state in the high state, if the amount of hydrogen supplied by accretion is as great as the hydrogen consumed by the nuclear burning. For the accretion rate higher than this range, the shell burning also remains stable, but the envelope expands with the increase in its mass. If the accretion rate is lower, the shell burning is extinguished by the consumption of nuclear fuel, and a transition from the high to the low state is caused. Thereafter, the white dwarf experiences recurrent hydrogen shell-flashes. From the stability of the low state, their recurrence period is estimated. It is possibly as short as a year for a very massive white dwarf, while longer than ten thousand years for a less massive one. The recurrent shell flashes are stronger for lower accretion rates and/or for more massive white dwarfs.

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