Main Sequence  Red Giant

1. Giant Stages – Low Mass Stars Main Sequence  Red Giant • At the center, Hydrogen is gone – there is only Helium “ash” • As more Helium accumulates, gravity pulls the core together – it shrinks and heats up • Hydrogen continues to burn in a layer around the center • High temperature – it burns fast • Luminosity rises • This dumps lots of heat into the outer layer • It expands and cools • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf

2. Main Sequence  Red Giant • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Main Sequence Red Giant Hydrogen Helium

3. Red Giant • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Double Shell-Burning Core Helium-Burning • Star moves up and right on H-R diagram

4. Red Giant • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • The star is incredibly bright and incredibly large • Goodbye Mercury • It is using up fuel faster than ever • It evolves fast • 200 Myr for Sun • The core keeps getting more massive, more compressed, and hotter • It accelerates faster and faster

5. An Aside: Some Nomenclature Issues • Astronomers use different names for the same thing • My old tests, and occasional diagrams, use alternate names: New Names:Old Names: Core Helium-Burning Horizontal Branch Double Shell-Burning Asymptotic Branch Massive Star Supernova Type II Supernova White Dwarf Supernova Type I Supernova

6. More Nuclear Physics • There are other processes besides Hydrogen burning • At 100 million K, three Heliums can join to make carbon plus a little energy • 3He  C + Energy • With a little higher temperature,they can add one more to makeoxygen • C + He  O + Energy • These processes produce farless energy than hydrogen burning

7. Red Giant  Core Helium Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • At 100 million K, the helium core in a red giant star ignites • Suddenly for light stars (< 3 MSun) • Gradually for heavy stars (> 3 MSun) • New heat source in core • It expands and cools • Hydrogen, still burning in a shell, burns more slowly now • Less heat going into hydrogen envelope • Hydrogen envelope shrinks and heats up • Star moves down and left on H-R diagram

8. Red Giant  Core Helium Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Red Giant Core Helium- Burning Hydrogen Helium Carbon/Oxygen

9. Core Helium Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Double Shell-Burning Core Helium-Burning • Star gets hotter and dimmer

10. Core Helium  Double Shell Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • The star is burning Helium to Oxygen and Carbon • It doesn’t produce much energy – Helium gets used up fast • Eventually, Helium is completely used up and we have a Carbon/Oxygen core left • 50 Myr for the Sun • The star enters Double Shell-Burning

11. Double Shell Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • The Core consists of Carbon/Oxygen ash • It grows more massive over time • Heat is leaking out of it • It gets smaller and hotter • Helium and Hydrogen burning accelerate • Lots of energy dumped in outer layers • Star gets big, cool, and luminous • Bye bye Venus and maybe Earth • Star gets brighter than ever • Up and to the right again on H-R diagram

12. Core Helium-  Double-Shell Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Core Helium- Burning Double Shell- Burning Hydrogen Helium Carbon/Oxygen

13. Double Shell Burning • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Double Shell-Burning Core Helium-Burning • Star moves up and right on H-R diagram

14. Giant Stages – Mass dependance • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • For stars from 0.5 to 3 MSun, it is qualitatively the same • Heavy stars do everything faster • For heavier stars, some details are different • Higher temperature and lower density • Core isn’t so compact • No dramatic increase in luminosity • Motion on the H-R diagram is mostly horizontal • Stars get bigger and cooler, not brighter

15. Giant Stages – Mass dependance • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf

16. Giant Stages – Mass Dependence • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Core Helium-Burning

17. Giant Stages – Mass Dependence • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf Core Helium Burning Double Shell-Burning

18. Mass Loss • Molecular Cloud • Protostar • Main Sequence • Red Giant • Core Helium-Burning • Double Shell-Burning • Planetary Nebula • White Dwarf • During Red Giant and especially Double Shell-Burning stage, star is huge and luminous • Gravity is weak at the surface • Dust particles form on surface • These absorb light very efficiently • Light pressure begins pushing surface away • Like solar wind, but much stronger • Star begins to quickly lose substantial mass • The inside is hardly affected, for a while • Hydrogen  Helium  Carbon/Oxygen