THERMAL-INSTABILITY AND PULSATIONS OF THE FLAME FRONT IN WHITE-DWARFS

It is shown that the thermonuclear flame front in white dwarfs is unstable against one-dimensional thermal instability which leads to the pulsating regime of flame propagation. The efficiency of the instability increases for the flame propagating in the layers of lower density in comparison with the flame in the central part of the white dwarf. The instability is also more efficient for the flame supported by oxygen thermonuclear reactions in comparison with the flame supported by carbon reactions. This is because the reaction time in the flame becomes more sensitive to the temperature variation with the decrease of initial density and with the decrease of initial carbon fraction of the fuel. The average velocity of the flame front propagating in the pulsating regime is smaller than the velocity of a steady flame. The flame velocity is reduced as a result of pulsations by 3% for the flames supported by carbon reactions and by 25% for the flames supported by oxygen reactions.