1. Factors affecting Fusion Rate Density –Since protons are closer together, the mean free path between collisions will be smaller Temperature –At higher temperatures a larger proportion of protons are moving fast enough to overcome the Coulomb Barrier –Faster protons take less time to cover the distance between collisions

2. The Effect of Mass Higher mass condensing into the star means –More hydrogen fuel to fuse –Higher pressure leading to higher density and temperature in the centre of the core –Much higher nuclear energy generation rates –So higher mass stars have much higher luminosities e.g. a 10 Solar Mass Star generates 10,000 times more luminosity than the Sun

3. Star Formation

4. Mass –Luminosity

5. Main Sequence Masses

6. Lifetime High mass stars have more hydrogen to fuse BUT They fuse this hydrogen much faster SO They run out sooner

7. Mass-Lifetime

8. Main Sequence Lifetimes

9. Cluster Formation Red green and yellow dots represent post main sequence stars

10. Clusters

11. 1 Solar Mass Evolution

12. Approach to Main sequence Core is always contracting and heating up, in vertical track heat is transported by convection so the increase in core temperature doesn’t show on the photosphere

13. Approach with time scales

14. Approach for different Masses

15. Vertical & Horizontal tracks

16. Protostar Tracks Protostars are always getting smaller and hotter Vertical Track <> Convective envelope –Convection requires larger temperature difference between the core and the photosphere –Although the core is getting hotter, the temperature of the photosphere stay relatively constant –Luminosity falls because the star is shrinking Horizontal Track <> Radiative Envelope –Radiation results in smaller temperature difference between the core and the photosphere –Photosphere temperature rises but contraction results in luminosity staying nearly constant

17. MS Structure

18. 1 Solar Mass Evolution 5.Vertical track 6.Horizontal trrack 7.Main Sequence 8.Red Giant Branch 9.Helium Flash 10.Horizontal Branch 11.Asymptotic Giant Branch 12.Planetary Nebula 13.White Dwarf 14.Brown Dwarf

19. Core Degeneracy Heat energy goes into nuclei but density is controlled by the electrons

20. Degenerate Gas If you push the electrons closer together, the energy levels all get farther apart, in a non degenerate gas some electrons will jump to lower energy levels

21. Evolution to Red Giant

22. Red Giant

23. 1 Solar Mass Evolution

24. Helium Flash Ash dumped from shell raises core Temp to 100 Million K, Helium to Carbon Fusion Degenerate gas has no safety valve, He fusion proceeds explosively Most of the energy goes into making the core expand, lifting degeneracy

25. In a non-degenerate core… 1.More reactions Higher Temp 2.Higher TempHigher Pressure 3.Higher PressureExpansion 4.ExpansionLower Temp 5.Lower TempLess Reactions –In a degenerate core step 2 doesn’t happen because heat energy goes to lifting the degeneracy rather than raising the pressure Safety Valve ?

26. Helium to Carbon Fusion

27. Core and Shell Fusion

28. Post Main Sequence HR

29. Asymptotic Giants

30. Descent to White Dwarf

31. Cooling Embers

32. Mass-Radius for Degenerate Stars

33. Mass-Radius for White Dwarfs

34. Multiple Shell Burning

35. Iron catastrophe

36. Timescales to Supernova

37. Heavy element synthesis

38. Cosmic Abundance

39. Open Cluster

40. Globular Cluster

41. Cluster HR Diagram

42. Cluster Turn-off