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I.The Hertzprung-Russell (H-R) Diagram: Surface Temperature vs Luminosity Analogy: horsepower vs weight II.Where Stars plot in the H-R diagram Main Sequence:

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Presentation on theme: "I.The Hertzprung-Russell (H-R) Diagram: Surface Temperature vs Luminosity Analogy: horsepower vs weight II.Where Stars plot in the H-R diagram Main Sequence:"— Presentation transcript:

1 I.The Hertzprung-Russell (H-R) Diagram: Surface Temperature vs Luminosity Analogy: horsepower vs weight II.Where Stars plot in the H-R diagram Main Sequence: 90% of all stars Why? stars spend 90% of their lives fusing hydrogen Main sequence  Hydrogen fusion Giants, Supergiants, White Dwarfs III.Main Sequence Stars (cont.) Outline of Ch 11b: The H-R Diagram

2 III.Main Sequence Stars Stellar Masses and Densities along main sequence Mass-Luminosity Relation (L~M 3.5 ) Lifetime on Main Sequence (T MS ~ 1/M 2.5 ) Main sequence Thermostat IV. Star Clusters What is so special about Star Clusters? Open and Globular Clusters Ages of Clusters Outline of Ch 11b: The H-R Diagram (cont.)

3 Homework online due Mon.

4 I.Parallax and distance. II.Luminosity and brightness Apparent Brightness Absolute Brightness or Luminosity Inverse-Square Law III.Stellar Temperatures Color, Spectral lines, Spectral Classification:OBAFGKM IV.Stellar sizes (radius) V.Stellar masses: binary stars, Doppler effect Review of Chapter 11a

5 What is a Hertzsprung-Russell (H-R) Diagram?

6 Temperature Luminosity H-R diagram plots the luminosity vs. surface temperature of stars

7 Weight Horsepower Analogy with diagram that plots horsepower vs. weight of cars Race cars Sports cars Economy cars Most Cars

8 Hydrogen- fusion stars reside on the main sequence of the H-R diagram

9 Main Sequence: 90% of all stars Why? stars spend 90% of their lives fusing hydrogen Main sequence  Hydrogen fusion

10 Luminosity proportional to surface area x temperature: L= 4  R 2  T 4 If we can measure the luminosity and the temperature of a star we can tell how large its raduis is. Remember Stellar sizes (radius)

11 H-R Diagram: Radii of stars

12 Stars with low temperature and high luminosity must have ____ radius GIANTS SUPERGIANTS

13 Stars with low temperature and high luminosity must have a large radius: giants and supergiants GIANTS SUPERGIANTS

14 Stars with high temperature and low luminosity must have _____ radius

15 Stars with high temperature and low luminosity must have small radius: white dwarfs

16 Stellar Masses For main sequence stars, the larger the mass the higher the luminosity This mass- luminosity relation is valid only for the main sequence Mass- Luminosity Relation (L~M 3.5 )

17 Stellar Masses For main sequence stars, the larger the mass the higher the luminosity This mass- luminosity relation is valid only for the main sequence How do we know the masses of these stars?

18 Stellar Masses For main sequence stars, the larger the mass the higher the luminosity This mass- luminosity relation is valid only for the main sequence How do we know the masses of these stars? The study of binary stars

19 Stellar Densities Density = Mass/Volume V= 4/3(  R 3 )

20 Stellar Densities High Same as water Low

21 Stellar Densities M.S. same density as water Giants and Supergiants: same or lower density than air W.D. very dense

22

23 Lifetime on Main Sequence T MS ~ 1/M 2.5 M in solar masses T in units of Sun’s total lifetime on MS (10 billion years)

24 Temperature Luminosity H-R diagram depicts: Temperature Color, Spectral Type, Luminosity, and Radius of stars

25 Temperature Luminosity H-R diagram depicts: Temperature Color, Spectral Type, Luminosity, and Radius of stars (*Mass, *Lifespan, of MS stars only)

26 III.Main Sequence Stars Stellar Masses and Densities along main sequence Mass-Luminosity Relation (L~M 3.5 ) Lifetime on Main Sequence (T MS ~ 1/M 2.5 ) Main sequence Thermostat Outline of Ch 11b: The H-R Diagram (cont.)

27 Main Sequence Thermostat: In the Sun, and in all main sequence stars gravity is balanced by outward pressure due to the outflow of energy.

28 Temperature Luminosity Which star is the hottest?

29 Temperature Luminosity Which star is the hottest?

30 Temperature Luminosity Which star is the most luminous?

31 Temperature Luminosity Which star is the most luminous?

32 Temperature Luminosity Which star is a main-sequence star?

33 Temperature Luminosity Which star is a main-sequence star?

34 Temperature Luminosity Which star has the largest radius?

35 Temperature Luminosity Which star has the largest radius?

36 Temperature Luminosity Which star is most like our Sun?

37 Temperature Luminosity Which star is most like our Sun?

38 Temperature Luminosity Which of these stars will have changed the least 10 billion years from now?

39 Temperature Luminosity Which of these stars will have changed the least 10 billion years from now?

40 Temperature Luminosity Which of these stars can be no more than a few million years old?

41 Temperature Luminosity Which of these stars can be no more than a few million years old?

42 What have we learned? What is a Hertzsprung- Russell diagram? An H–R diagram plots stars according to their surface temperatures and luminosities.

43 Temperature Luminosity H-R diagram depicts: TemperatureCo lor, Spectral Type, Luminosity, and Radius of stars (*Mass, *Lifespan, [*Age], of MS stars only)

44 I.The Hertzprung-Russell (H-R) Diagram: Surface Temperature vs Luminosity Analogy: horsepower vs weight II.Where Stars plot in the H-R diagram Main Sequence: 90% of all stars Why? stars spend 90% of their lives fusing hydrogen Main sequence  Hydrogen fusion Giants, Supergiants, White Dwarfs III.Main Sequence Stars (cont.) Outline of Ch 11b: The H-R Diagram

45 III.Main Sequence Stars Stellar Masses and Densities along main sequence Mass-Luminosity Relation (L~M 3.5 ) Lifetime on Main Sequence (T MS ~ 1/M 2.5 ) Main sequence Thermostat Outline of Ch 11 part II: The H-R Diagram (cont.)

46 1.Which of the following correctly fills in the blank? A main-sequence star of spectral class B is _____ than a main-sequence star of spectral class G. 1. More massive 2. Hotter 3. Longer lived 4. More luminous The correct answer is A. 1 and 3 B. 2 and 3 C. 1, 2 and 4 D. 2, 3 and 4 E. 1, 2, 3 and 4

47 2. Which of the following correctly fills in the blank? If a star is on the main-sequence and one knows its temperature, then one can estimate its ____. 1. Spectral class 2. Mass 3. Luminosity 4. Density 5. Radial velocity The correct answer is A. 1, 2, 3, 4 and 5 B. 1 and 5 C. 2 only D. 1, 3 and 5 E. 1, 2, 3 and 4

48 3. Which of the following correctly fills in the blank? If a star of class O is on the main-sequence, that star must be ____. 1. Hotter than most stars 2. Very massive 3. Much denser than water 4. Very red 5. Not very old The correct answer is A. 2 and 3 B. 1, 2, 3 and 4 C. 1, 2, 3, 4 and 5 D. 1, 2 and 5 E. 4 and 5

49 4. Which of the following correctly fills in the blank? If a star of class M is on the main-sequence, that star must be ____. A. Very hot B. Very massive C. Very blue D. None of the other answers are correct

50 IV. Star Clusters: Confirmation of Stellar Evolution Open and Globular Clusters Ages of Clusters Outline of Ch 11b: The H-R Diagram (cont.)

51 1. What is special about star clusters? All stars formed at same time, so plotting clusters with different ages on H-R diagrams we can see how stars evolve This confirms our theories of stellar evolution without having to wait billions of years observing how a single star evolves Star Clusters : Confirmation of Stellar Evolution: 2. Two types of clusters: Open and Globular 3. Ages of Clusters

52 Open cluster: A few thousand loosely packed stars

53 Globular cluster: Up to a million stars in a dense ball bound together by gravity

54 Two types of star clusters Open clusters: young, contain up to several thousand stars and are found in the disk of the galaxy. Globular clusters: old, contain hundreds of thousands of stars, all closely packed together. They are found mainly in the halo of the galaxy.

55 Our Galaxy

56 Which part of our galaxy is older?

57 How do we measure the age of a star cluster?

58 Theoretical Evolution of a star cluster

59 Massive blue stars die first, followed by white, yellow, orange, and red stars

60 How do we know that this theoretical evolution is correct?

61 We plot observations of actual clusters on the H-R diagram

62 Young Stellar Cluster H-R Diagram of Young Stellar Cluster

63 Young Stellar Cluster H-R Diagram of Young Stellar Cluster How do we know this cluster is Young?

64 Old Stellar Cluster H-R Diagram of Old Stellar Cluster

65 Old Stellar Cluster H-R Diagram of Old Stellar Cluster How do we know this cluster is Old?

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

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

68 To determine accurate ages, we compare models of stellar evolution to the cluster data

69 Detailed modeling of the oldest globular clusters reveals that they are about 13 billion years old (The universe is about 13.7billion years old

70 What have we learned? How do we measure the age of a star cluster? Because all of a cluster’s stars we born at the same time, we can measure a cluster’s age by finding the main sequence turnoff point on an H–R diagram of its stars. The cluster’s age is equal to the hydrogen- burning lifetime of the hottest, most luminous stars that remain on the main sequence.

71 Question 1 If the brightest main sequence star in cluster 1 is a B star and the brightest main sequence star in cluster 2 is an M star. What can we say about the age of these two clusters?

72 Question 1 If the brightest main sequence star in cluster 1 is a B star and the brightest main sequence star in cluster 2 is an M star. What can we say about the age of these two clusters? A.Nothing, there is not enough information B.Cluster 1 is older than cluster 2 C.Cluster 2 is older than cluster 1 D.None of the answers are correct

73 Chapter 12. Star Stuff Part I Birth of Stars I. Birth of Stars from Interstellar Clouds Young stars near clouds of gas and dust Contraction and heating of clouds Hydrogen fusion stops collapse


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