1. Stellar Clusters Homework Problems Chapter 13
Review Questions: 1-3, 9-11
Review Problems: 1, 2, 7
Web Inquiries: 1, 4

2. H-R Diagram An H-R diagram reveals three significant features. L/Lsun
The Main Sequence
core hydrogen fusion
Red Giants
hydrogen shell source
(core helium fusion)
White Dwarfs
carbon-oxygen core leftovers
This is a snapshot in the life of many,
unrelated stars.
L/Lsun
O B A F G K M

3. H-R Diagram Other areas of the H-R diagram are
sparsely populated either because
stars just don’t exist with those
specific combinations of
luminosity and
temperature, or because the
stars evolve so quickly and
spend so little time in that area
that the probability of seeing
stars located there is very low.
(Example: “Hertzsprung Gap”)
L/Lsun
O B A F G K M

4. Clusters Formation
Stars from the same formation epoch (same “birthday”)
Same Age
Similar Chemical Composition
Same Distance from the Earth

5. Stellar Clusters OPEN Cluster GLOBULAR Cluster Bright Hot, Young stars
Thousands of stars
Loose Associations
GLOBULAR Cluster
Fainter
Cooler, Older stars
Hundreds of Thousands of stars
Tightly Bound Systems

6. Double Cluster
OPEN Cluster
Very few evolved
stars.

7. Globular Cluster
Many evolved stars.

8. Cluster HR Diagrams H-R diagrams revealing a variety of ages among
clusters.
Who is the youngest?
Who is the oldest?

9. Young Cluster

10. Young Cluster HR Diagram

11. Cluster Evolution

12. Combined Cluster H-R diagrams

13. Hyades

14. M44 Cluster

15. M41 Cluster

16. M2001 Cluster

17. Globular Cluster M5

18. Main Sequence Turnoff Since stellar evolution is highly dependent
upon the mass of a star,
the turn-off point
of a clusters
main-sequence
is a measure of the
clusters age.

19. Horizontal Giant Branch

20. Pulsating Variable Stars

21. Instability Strip

22. The Pulsating Stars

23. Cepheid Pulsation Sequence

24. Pulsating Variables Light curves for two different Cepheid
variables showing
the periodic changes
in brightness.

25. Cepheids

26. Cepheid Pulsation
The interplay
of Radius
and Temperature.
L = 4pR2sT4

27. Period - Luminosity Relation

28. Cepheid Period - Luminosity
Observe apparent magnitude (m)
Observe Period of pulsation (P)
Utilize P-L relation to infer absolute magnitude (M)
Use distance modulus to
obtain distance:
m-M = 5 log D - 5

29. SMC and LMC
The Milky Ways two irregular satellite galaxies.

30. Distance Determinations

31. Distance Indicators