The evolution of a 1 M⊙ population I model star of initial composition (Z, Y) = (0.015, 0.275), begun in Volume 1 (Section 11.1) and carried there to the ignition of helium on the red giant branch, is continued in this chapter through four distinct helium- and hydrogen-burning phases. In Section 17.1, evolution is followed from the off-center ignition of helium at the tip of the red giant branch through a series of helium shell flashes which lift electron degeneracy in shells successively closer to the center of the hydrogenexhausted core.

Once helium burning reaches the center, shell flashes of this sort no longer occur. As described in Section 17.2, the model metamorphoses into a horizontal branch star, converting helium quiescently into carbon and oxygen at the base of a convective core which grows in mass, while hydrogen burning continues to convert hydrogen quiescently into helium in a shell outside of the core. Once helium is exhausted at the center, the model continues to burn helium quiescently in a shell. The helium exhausted core contracts until electrons in the core become degenerate, converting the core into a hot white dwarf composed of carbon and oxygen. The envelope of the model expands to giant dimensions, the strength of the hydrogen-burning shell at the base of the envelope declines significantly, and the surface luminosity is provided primarily by a helium-burning shell which increases in strength as the model climbs upward in the HR diagram.