1. Announcements Exam Grades Wednesday March 31 Angel Grade update Friday April 2 Star Assignment 6, due Wednesday March 31 ÜDo Angel quiz,

2. Objectives Plot an Hertzsprung-Russell Diagram Locate the regions of giant, main sequence and white dwarf stars. Describe the relations between surface temperature, luminosity, mass and size for these types of stars. Describe the evolutionary state of the 16 brightest northern-hemisphere stars.

3. What should we do with our information? Luminosities Surface Temperatures Masses

4. Number of Stars vs Luminosity LOWHIGHLuminosity 1 1000.010.0001

5. Stellar Masses

6. What should we do with our information? Luminosities Surface Temperatures Masses Look for Relationships

7. No Relationship

8. Luminosity - Mass Relation L~M 3.5

9. HR Diagram: Luminosity vs. Surface Temperature

10. Luminosity - Temperature Relation: Hertzsprung- Russell Diagram Luminosity ->

11. Temperature Luminosity Recall: Hotter -> Brighter Hotter -> Bluer Bigger -> Brighter Then cool + Luminous -> Large

12. Temperature Luminosity Recall: Hotter -> Brighter Hotter -> Bluer Bigger -> Brighter Then small Luminosity + Hot -> small

13. Stellar Size, Mass & HR Diagram

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

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

16. Low-Mass Stars High-Mass Stars Most Low Mass stars have Small Luminosity Most Large Mass stars have Large Luminosity

17. Regions of the H-R Diagram

18. Activity Answer the questions on your scantron sheet

19. Temperature Luminosity 1. Which star is the hottest? A B C D

20. Temperature Luminosity 1. Which star is the hottest? A B C A D

21. Temperature Luminosity 2. Which star is the most luminous? A B C D

22. Temperature Luminosity 2. Which star is the most luminous? A B C DC

23. Temperature Luminosity 3. Which star is a main- sequence star? A B C D

24. Temperature Luminosity 3. Which star is a main- sequence star? A B C D D

25. Temperature Luminosity 4. Which star has the largest radius? A B C D

26. Temperature Luminosity 4. Which star has the largest radius? A B C D C

27. Temperature Luminosity 5. Which star is most like our Sun? A B C D

28. Temperature Luminosity 5. Which star is most like our Sun? A B C D B

29. HOTCOOL BRIGHT FAINT HR Diagram

30. Astronomy Place Questions 6. Spica is a Main Sequence star, having a surface temperature of 26,000K. In order for a star with a surface temperature of only 6,000K to have the same Luminosity as Spica, its radius must be? Luminosity = 4  R 2  T 4 If T ~ 4 x smaller, then R ~ 4 2 x larger = 16x

31. 7. The rate of fusion (number of He nuclei produced per second) in the core of the star Vega (a main-sequence star with a temperature of about 10,000K is roughly? L vega = 60 L sun, so rate of energy generation = rate of energy loss is 60 x larger than Sun’s

32. 8. A star having the same radius as the Sun, but a surface temperature 5 times higher than the Sun, would have a luminosity? L ~ T 4 5 4 = 625

33. 9. A main-sequence star that is twice as massive as the Sun will have a Luminosity? L ~ M 3. 5 2 3 = 8, 2 4 = 16, so 2 3.5 in between

34. Lifetime on the Main Sequence How long will it be before MS stars run out of fuel? i.e. Hydrogen? How much fuel is there? M How fast is it consumed? L  M 3.5 How long before it is used up? M/L = M/M 3.5 = M -2.5

35. Main Sequence Lifetimes

36. Lifetime on the Main Sequence O & B Dwarfs burn fuel like a bus! M Dwarfs burn fuel like a compact car! Our Sun will last 10 10 years on the Main Sequence MS Lifetime  = 10 10 yrs / M 2.5

37. Stars occur alone

38. or in clusters

39. another type of cluster

40. Star Clusters Stars approximately the SAME AGE Stars approximately the SAME DISTANCE

41. Cluster HR Diagrams Same Distance Same Age

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

43. Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old

44. Cluster Ages

45. Activity Answer the questions on your scantron sheet

46. Temperature Luminosity 6. Which of these stars will have changed the least 10 billion years from now? A B C D

47. Temperature Luminosity 6. Which of these stars will have changed the least 10 billion years from now? A B C D C

48. Temperature Luminosity 7. Which of these stars can be no more than 10 million years old? A B C D

49. Temperature Luminosity 7. Which of these stars can be no more than 10 million years old? A B C D A

50. A stars properties depend mostly on 1. Mass 2. Age

51. NEXT TIME Evolution of Stars READ chapter 17