1. Stellar Evolution
In post-Main-Sequence evolution, what you see on the surface is not a good indicator of what is happening deep in the interior

2. Core contraction occurs, core smaller and hotter
Core contraction occurs, core smaller and hotter. Star “ascends the Giant Branch”
Question: Why don’t
The Helium nuclei
Begin to fuse?

3. In low mass PMS stars, the “Helium Flash” occurs
In low mass PMS stars, the “Helium Flash” occurs. Nuclear reactions involving Helium – Carbon. Also called the “Triple Alpha Process”
3He C

4. At time of the Helium Flash, a star evolves to the right on the HR diagram, at near constant luminosity

5. Helium Flash converts Helium core to Carbon, Oxygen
Stellar evolution making chemical structure of the star more and more complicated

6. As star evolves further, it develops a Helium-burning shell
All the action is deep in the tiny core of the star

7. As Helium shell burning stars, the star moves onto the “Asymptotic Giant Branch”

8. The Helium shell-burning is unstable and sends thermal pulses through the star, throwing off the outer layers of the star into space. As the outer layers are peeled back, it reveals the extremely hot, ultraviolet-emitting carbon and oxygen core which ionizes the stellar wind

9. Hot core photoionizes the surrounding stellar wind or ejecta.
Resulting object is a Planetary Nebula, like M57

10. An incredible yarn, but all the pieces are there in the night sky
Red Giants
Horizontal Branch Giants
Asymptotic Giant Branch Stars
Mira Variables
Planetary Nebulae
White Dwarf Stars