Red Giants of Population II. II.

In continuation of the work described in Paper I of this series, a sequence of 70 core models has been constructed for a red giant of population II, covering the helium flash. This phenomenon occurs when helium-burning starts in the contracting core. Because of the high degeneracy in the core, the new energy source causes heating, not an expansion. The rise of the temperature accelerates the helium-burning, and thus a thermal runaway occurs, which terminates only when the core becomes non-degenerate. Subsequent helium-burning causes rapid expansion and cooling. At the peak of the helium flash the temperature reaches over 300 million degrees. The rate of energy liberation at this peak corresponds to about 1012 solar luminosities. Practically none of this energy penetrates the thermal blanket of the non-degenerate outer layers of the helium core. The evolution at the peak is so fast that the time interval between successive numerical models had to be reduced to as low as 2 seconds.