Lab 09

1. Astronomy 105 Laboratory Lab 09

2. Lab Quiz 09

3. Last week we used the “Main-sequence Fitting” technique to find the • distance to the Pleiades star cluster. • size of the Pleiades star cluster. • mass of the Pleiades star cluster. • age of the Pleiades stars cluster.

4. All the stars within a given cluster are assumed to have the same ______. • spectral class • distance • color • luminosity class

5. If you were to leave the Earth and travel 4 AUs from the Sun, how would the sun’s brightness change? • 1/2 as bright • 1/4 as bright • 1/8 as bright • 1/16 as bright • 1/32 as bright

6. What two stellar properties are plotted on a color-magnitude diagram? • absolute magnitude and spectral class • absolute magnitude and color • apparent magnitude and color • apparent magnitude and distance

7. Color is a measure of a star’s _____. • temperature • size • brightness • luminosity

8. The “turn-off point” on the color-magnitude diagram of a star cluster can be used to find the cluster’s • temperature • distance • age • apparent magnitude

9. Lab 09 Ages and Distances to Clusters

10. Stellar Main-sequence Lifetime • Stellar Birth • Massive stars form quickly • Low mass stars form slowly • Main-sequence Stars • Fuse hydrogen in their cores • High mass stars • consume hydrogen at a furious rate • high luminosities • short lifetimes • Low mass stars • consume hydrogen at a low rate • low luminosities • long lifetimes • Giant Stars • Core hydrogen exhausted

11. Main-Sequence Lifetimes

12. Stars in a Cluster • Stars in a Cluster • Common Properties • Distance • Age • Chemical composition • Different Properties • Spectral Types (temperature) • Luminosity Class (size)

13. Star clusters help us test models of stellar evolution because they contain stars of same age but at different life stages Massive blue stars die first, followed by white, yellow, orange, and red stars

14. Pleiades - Open Cluster Distance - 380 ly Age - 100 million years B6 stars -- 100 million yrs. MS lifetime age of cluster = lifetime of stars at main-sequence turnoff point

15. M3 - Globular Cluster distance - 32,000 ly age - 10 billion years old standard main-sequence G stars -- 10 billion yrs. MS lifetime age of cluster = lifetime of stars at main-sequence turnoff point

17. Interstellar Dust • Reddens Light (makes stars appear cooler) • Dims Light (makes stars appear further away)

18. Important: Do not write or mark on the Cluster Handout

19. M45

20. D.M. = 5.7

21. M45 5.7

22. Distance = 130 pc D.M. = 5.7 M45 5.7 130

23. Color Excess = + 0.05

24. 5.55 391 0.15 0.05 M45 5.7 130 120

25. Color of Turn-off Point = - 0.01

26. 5.55 391 0.15 0.05 -0.01 M45 5.7 130 120

27. Age = 1 X 108 years Color of Turn-off Point = - 0.01 5.55 420 0.15 0.05 -0.01 M45 5.7 130 129 1x108

28. 5.55 391 0.15 0.05 -0.01 M45 5.7 130 120 1x108

29. The End