1. What is a Hertzsprung-Russell Diagram?
MSU: Frontier
SOAR 9-15
Cecilia P. Popashki (sp?)

2. Note: stars do not uniformly fill the diagram!
An H-R diagram plots the luminosity (light-energy emitted/time) and temperature of stars
Luminosity
Note: stars do not uniformly fill the diagram!
Plot of luminosity vs. temp
IMAGES are NOT to scale
When a star dies, it goes from core burning (H) to shell burning which causes it to enter the Red giant phase
Temperature

3. burning stars reside on the main sequence of the H-R diagram
Normal hydrogen-
burning stars reside on the main sequence of the H-R diagram
Stars spend the majority of their life on the main sequence.
White dwarf- electron degeneracy is reached within the core of the red giant. Since it is reached before the temp was high enough to fuse heavier elements, it will not shrink any further and become “stable”

4. High-Mass Stars
Normal hydrogen-
burning stars reside on the main sequence of the H-R diagram
Low-Mass Stars

5. Large radius
Stars with low temperature and high luminosity must have large radius
Small radius

6. SUPERGIANTS
Stars with low temperature and high luminosity must have large radius
GIANTS

7. SUPERGIANTS
Stars with low temperature and high luminosity must have large radius
GIANTS
WHITE
DWARFS

8. H-R diagram depicts:
Temperature
Color
Spectral Type
Luminosity
Radius
Mass
Lifespan
Age
Luminosity
Temperature

9. C B
Which star is the hottest? D
Luminosity A
Temperature

10. C B
Which star is the hottest? A D
Luminosity A
Temperature

11. C B
Which star is the most luminous? D
Luminosity A
Temperature

12. C B
Which star is the most luminous? C D
Luminosity A
Temperature

13. C B
Which star is burning hydrogen in its core? D
Luminosity A
Temperature

14. C B
Which star is burning hydrogen in its core? (It’s a main sequence star) D
Luminosity D A
Temperature

15. C B
Which star has the largest radius? D
Luminosity A
Temperature

16. C B
Which star has the largest radius? C D
Luminosity A
Temperature

17. A
Which star is most like our Sun? D
Luminosity B C
Temperature

18. A
Which star is most like our Sun? D B
Luminosity B C
Temperature

19. A
Which of these stars will have changed the least 10 billion years from now? D
Luminosity B C
Temperature

20. A
Which of these stars will have changed the least 10 billion years from now? D
Luminosity B C C
Temperature

21. A
Which of these stars can be no more than 10 million years old? D
Luminosity B C
Temperature

22. A
Which of these stars can be no more than 10 million years old? D A
Luminosity B C
Temperature

23. How can we know this if stars live millions or billions of years?

24. Stars in a Star Cluster Born at the same time
All about the same distance
Same chemical composition
Because they formed from the same gas cloud

25. How do we measure the age of a star cluster?

26. Pleiades now has no stars with life expectancy less than around 100 million years
Main-sequence
turnoff

27. Main-sequence turnoff point of a cluster tells us its age

28. Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old
Age of universe… ish