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Outline. Remove extra folder debris Magnitudes and Distance H-R diagrams Stellar Evolution. Magnitudes. Apparent Magnitude how bright it looks depends on distance brightness depends on distance 2 Absolute Magnitude Only depends on Luminosity (how much energy is being produced)

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  1. 1

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  3. Outline • Remove extra folder debris • Magnitudes and Distance • H-R diagrams • Stellar Evolution 3

  4. Magnitudes • Apparent Magnitude • how bright it looks • depends on distance • brightness depends on distance2 • Absolute Magnitude • Only depends on Luminosity (how much energy is being produced) • Does not change with distance • At 10pc, Apparent magnitude= Absolute magnitude 4

  5. Chapter 10 Star Temperatures (Colors) 5

  6. Figure 10.7Star Colors – Orion (20°) and the Milky Way Center (2’) 6

  7. Which star would be the hottest? A) A B) B C) G D) M E) O 7

  8. Which star would be the hottest? A) A B) B C) G D) M E) O 8

  9. Star Spectral Classification • New order is: O, B, A, F, G, K ,M. • Remember the order... • Oh, Be AFine Girl/(Guy) Kiss Me 9

  10. Chapter 10 HR Diagrams 10

  11. On the H-R diagram, red supergiants like Betelguese lie: A) top right B) top left C) about the middle D) lower left E) on the coolest portion of the main sequence 11

  12. On the H-R diagram, red supergiants like Betelguese lie: A) top right B) top left C) about the middle D) lower left E) on the coolest portion of the main sequence 12

  13. Figure 10.12H–R Diagram of Well-Known Stars • Plot the luminosity vs. temperature. • This is called a Hertzsprung-Russell (H-R) diagram • Need to plot more stars! 13

  14. Figure 10.15Hipparcos H–R Diagram • Plot many stars and notice that 90% fall on the “main sequence”. • Add radius lines, and now have • luminosity • temperature • radius 14

  15. Figure 10.14H–R Diagram of 100 Brightest Stars • Most very bright stars are also distant 15

  16. Figure 10.13H–R Diagram of Nearby Stars • Most close stars are very dim • Best estimate now is that 80% of stars are red dwarfs 16

  17. Chapter 10 Star Sizes 17

  18. Star Sizes • The luminosity of a star depends on the stars diameter as well as its temperature. • When radius is combined with Stefan’s Law: luminosity  radius2 x T4 ( means proportional to) 18

  19. Star Sizes • The luminosity of a star depends on the stars diameter as well as its temperature. • When surface area is combined with Stefan’s Law: luminosity = 4r2T4 (= means equal) 19

  20. Star Sizes • Can directly measure the radius on very few stars. (~dozen) • Can calculate the radius if you know the luminosity and the temperature. 20

  21. Figure 10.11Stellar Sizes • Giants - radius between 10x and 100x solar • Supergiants - larger (up to 1000x) • Dwarf - radius comparable to or smaller than the sun. 21

  22. Figure 10.15Hipparcos H–R Diagram • Plot the luminosity vs. temperature. • This is called a Hertzsprung-Russell (H-R) diagram 22

  23. Review • What fraction of the stars on an H-R diagram are on the main sequence. • Enter numbers 1-9 for 10%-90% 23

  24. Discussion • What fraction of the stars on an H-R diagram are on the main sequence. • Enter numbers 1-9 for 10%-90% 24

  25. Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… 25

  26. Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… • If a star is on the main sequence, then we know its luminosity. So • If you know brightness and luminosity, you can determine a star’s distance. 26

  27. Distance Scale • Spectroscopic Parallax - the process of using stellar spectra to determine distances. • Can use this distance scale out to several thousand parsecs. 27

  28. Figure 10.16Stellar Distances 28

  29. Stellar Evolution 29

  30. Figure 11.16Atomic Motions • Low density clouds are too sparse for gravity. • A perturbation could cause one region to start condensing. 30

  31. Figure 11.17Cloud Fragmentation 31

  32. Figure 11.20Interstellar Cloud Evolution 32

  33. http://discovermagazine.com/2009/interactive/star-formation-game/http://discovermagazine.com/2009/interactive/star-formation-game/ 33

  34. H-R diagram review • The H-R diagram shows luminosity vs. temperature. • It is also useful for describing how stars change during their lifetime even though “time” is not on either axis. • How to do this may not be obvious. • Exercise - Get in groups of ~four and get out a blank piece of paper. 34

  35. Group Exercise • As a group, create a diagram with “financial income” on the vertical axis, and “weight” on the horizontal axis. • Use this graph to describe the past and future of a fictitious person (or a group member). • Label significant events, for example • birth • college • retirement • death 35

  36. Stellar Evolution 1 - interstellar cloud - vast (10s of parsecs) 2(and 3) - a cloud fragment may contain 1-2 solar masses and has contracted to about the size of the solar system 4 - a protostar • center ~1,000,000 K • Too cool for fusion, but hot enough to see. (photosphere ~3000 K) • radius ~100x Solar 36

  37. How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter 37

  38. How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter 38

  39. Figure 11.19Protostar on the H–R Diagram 39

  40. Figure 11.21Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. 40

  41. Figure 11.18Orion Nebula, Up Close 41

  42. Figure 11.23Protostars 42

  43. Figure 11.21Newborn Star on the H–R Diagram 43

  44. Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years 44

  45. Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years 45

  46. Stellar Lifetimes • Proportional to mass • Inversely proportional to luminosity • Big stars are MUCH more luminous, so they use their fuel MUCH faster. • The distribution of star types is representative of how long stars spend during that portion of their life. • Example - snapshots of people. 46

  47. Figure 10.21Stellar Masses 47

  48. Figure 11.24Prestellar Evolutionary Tracks 48

  49. Figure 11.25Brown Dwarfs 49

  50. Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? 50

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