1. Charles Hakes Fort Lewis College1

2. Charles Hakes Fort Lewis College2 Light Pollution Stellar Evolution

3. Charles Hakes Fort Lewis College3 Lab Notes Be sure you have started your “report” lab. Constellation presentations next week. Observatory field trips…

4. Charles Hakes Fort Lewis College4 Night Lights http://apod.nasa.gov/apod/ap101104.html

5. Charles Hakes Fort Lewis College5 Limiting Magnitude and Light Pollution

6. Charles Hakes Fort Lewis College6 Limiting Magnitude Limiting Magnitude is a measure of the dimmest star visible from a given location. Center of a big city: ~2.0 Suburbs: ~4.5 Downtown Durango: ~5.5 La Plata County (FLC observatory): ~6.5 Depends on observer experience Depends on local glare Depend on how dark adapted your eyes are. You should wait 20-30 minutes to measure this.

7. Charles Hakes Fort Lewis College7 Limiting Magnitude Use stars of known magnitude (e.g. Little Dipper)

8. Charles Hakes Fort Lewis College8 Limiting Magnitude Count the stars in a well-defined region Chose one of the predefined star regions that is overhead Count the number of stars visible within the region boundary Look up the number on the published tables to find the corresponding limiting magnitude

9. Charles Hakes Fort Lewis College9 Limiting Magnitude

10. Charles Hakes Fort Lewis College10 Limiting Magnitude Alpha-Epsilon-Beta Gem starsLM 11.2 22.4 33.2 43.9 54.3 65.0 75.1 85.3 95.6 105.7 115.9 126.1 136.2 146.3 156.4 166.5 186.6 206.7 226.9 237.0 257.2 307.5

11. Charles Hakes Fort Lewis College11 How many Stars Can You See? MagnitudeRangeCumulative Stars% Increase Seen -1-1.50 to -0.512- 0-0.50 to +0.498400% 1+0.50 to +1.4922275% 2+1.50 to +2.4993423% 3+2.50 to +3.49283304% 4+3.50 to +4.49893316% 5+4.50 to +5.492,822316% 6+5.50 to +6.498,768311% 7+6.50 to +7.4926,533303% 8+7.50 to +8.4977,627293% 9+8.50 to +9.49217,689280% 10+9.50 to +10.49626,883288% 11+10.50 to +11.491,823,573291% 12+11.50 to +12.495,304,685291% 13+12.50 to +13.4915,431,076291% 14+13.50 to +14.4944,888,260291% 15+14.50 to +15.49130,577,797291% 16+15.50 to +16.49379,844,556291% 17+16.50 to +17.491,104,949,615291% 18+17.50 to +18.493,214,245,496291% 19+18.50 to +19.499,350,086,162291% 20+19.50 to +20.4927,198,952,706291%

12. Charles Hakes Fort Lewis College12 How many Stars Can You See? Dark-adapted naked eye (1x7 binoculars) Can see to magnitude 6.5 -> ~10 4 stars Light gathering ability scales with area. Magnitude Increase = log 10 (Area increase) / 0.4 10x50 binoculars ~50x area -> +4.25 magnitudes 16” SCT ~64x area -> +4.5 magnitudes 10m Keck telescope ~625x area -> +7 magnitudes

13. Charles Hakes Fort Lewis College13 How many Stars Can You See? So for naked eye observing 10x50 binoculars 50x area +4.25 magnitudes (to 10.75) > 10 6 stars 16” SCT 64x area +4.5 magnitudes (to 15.25) > 10 8 stars 10m Keck telescope 625x area +7 magnitudes (to 22.75) > 10 11 stars

14. Charles Hakes Fort Lewis College14 Figure 10.6 Apparent Magnitude

15. Charles Hakes Fort Lewis College15 Light Pollution Generally not an issue in La Plata county. Durango has a dark sky ordinance, but only for new construction. Fort Lewis is making progress with outside light fixtures.

16. Charles Hakes Fort Lewis College16 Light Pollution Earth at Night Credit: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive

17. Charles Hakes Fort Lewis College17 Light Pollution From IDA Website: http://www.darksky.org/images/sat.html

18. Charles Hakes Fort Lewis College18 Light Pollution You Are Here Observatory

19. Charles Hakes Fort Lewis College19 Figure 10.15 Hipparcos H–R Diagram Plot the luminosity vs. temperature. This is called a Hertzsprung- Russell (H-R) diagram

20. Charles Hakes Fort Lewis College20 What fraction of the stars on an H-R diagram are on the main sequence A.0-50% B.50-70% C.70-80% D.>80%

21. Charles Hakes Fort Lewis College21 What fraction of the stars on an H-R diagram are on the main sequence A.0-50% B.50-70% C.70-80% D.>80%

22. Charles Hakes Fort Lewis College22 Distance Scale If you know brightness and distance, you can determine luminosity. Turn the problem around…

23. Charles Hakes Fort Lewis College23 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.

24. Charles Hakes Fort Lewis College24 Distance Scale Spectroscopic Parallax - the process of using stellar spectra to determine distances. Can use this distance scale out to several thousand parsecs.

25. Charles Hakes Fort Lewis College25 Figure 10.16 Stellar Distances

26. Charles Hakes Fort Lewis College26 Stellar Evolution

27. Charles Hakes Fort Lewis College27 Figure 11.16 Atomic Motions Low density clouds are too sparse for gravity. A perturbation could cause one region to start condensing.

28. Charles Hakes Fort Lewis College28 Figure 11.17 Cloud Fragmentation

29. Charles Hakes Fort Lewis College29 Figure 11.20 Interstellar Cloud Evolution

30. Charles Hakes Fort Lewis College30 l http://discovermagazine.com/2009/interact ive/star-formation-game/ http://discovermagazine.com/2009/interact ive/star-formation-game/ l google “star formation game”

31. Charles Hakes Fort Lewis College31 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.

32. Charles Hakes Fort Lewis College32 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

33. Charles Hakes Fort Lewis College33 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

34. Charles Hakes Fort Lewis College34 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

35. Charles Hakes Fort Lewis College35 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

36. Charles Hakes Fort Lewis College36 Figure 11.19 Protostar on the H–R Diagram

37. Charles Hakes Fort Lewis College37 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink.

38. Charles Hakes Fort Lewis College38 Figure 11.18 Orion Nebula, Up Close

39. Charles Hakes Fort Lewis College39 Figure 11.23 Protostars

40. Charles Hakes Fort Lewis College40 Figure 11.21 Newborn Star on the H–R Diagram

41. Charles Hakes Fort Lewis College41 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

42. Charles Hakes Fort Lewis College42 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

43. Charles Hakes Fort Lewis College43 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.

44. Charles Hakes Fort Lewis College44 Figure 10.21 Stellar Masses

45. Charles Hakes Fort Lewis College45 Figure 11.24 Prestellar Evolutionary Tracks

46. Charles Hakes Fort Lewis College46 Figure 11.25 Brown Dwarfs

47. Charles Hakes Fort Lewis College47 Figure 11.22 Protostellar Outflow

48. Charles Hakes Fort Lewis College48 Stellar Evolution

49. Charles Hakes Fort Lewis College49 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink.

50. Charles Hakes Fort Lewis College50 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Can have violent “winds” streaming outwards; often bipolar flow from poles; T-Tauri phase

51. Charles Hakes Fort Lewis College51 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Can have violent “winds” streaming outwards; often bipolar flow from poles; T-Tauri phase 6 - a newborn star Core temperature high enough to ignite nuclear fusion.

52. Charles Hakes Fort Lewis College52 Figure 11.21 Newborn Star on the H–R Diagram

53. Charles Hakes Fort Lewis College53 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

54. Charles Hakes Fort Lewis College54 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.

55. Charles Hakes Fort Lewis College55 Figure 10.21 Stellar Masses

56. Charles Hakes Fort Lewis College56 Figure 11.24 Prestellar Evolutionary Tracks

57. Charles Hakes Fort Lewis College57 Figure 12.1 Hydrostatic Equilibrium

58. Charles Hakes Fort Lewis College58 Figure 11.24 Prestellar Evolutionary Tracks The final location on the main sequence depends entirely on the size (mass) of the condensing cloud.

59. Charles Hakes Fort Lewis College59 Figure 11.25 Brown Dwarfs Not big enough to start fusion. Mass <~ 0.08 solar masses ~=80x mass of Jupiter. These are likely very numerous

60. Charles Hakes Fort Lewis College60 Stellar Evolution 7 - the star stays on the main sequence for most (~90%) of its lifetime.

61. Charles Hakes Fort Lewis College61 Figure 10.15 Hipparcos H–R Diagram

62. Charles Hakes Fort Lewis College62 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

63. Charles Hakes Fort Lewis College63 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

64. Charles Hakes Fort Lewis College64 Figure 10.21 Stellar Masses

65. Charles Hakes Fort Lewis College65 What forces a star like our Sun to evolve off the main sequence? A) It loses all its neutrinos, so fusion must cease. B) It completely runs out of hydrogen. C) It builds up a core of inert helium. D) It explodes as a violent nova. E) It expels a planetary nebula to cool off and release radiation.

66. Charles Hakes Fort Lewis College66 What forces a star like our Sun to evolve off the main sequence? A) It loses all its neutrinos, so fusion must cease. B) It completely runs out of hydrogen. C) It builds up a core of inert helium. D) It explodes as a violent nova. E) It expels a planetary nebula to cool off and release radiation.

67. Charles Hakes Fort Lewis College67 Figure 12.2 Solar Composition Change 7 - fusion of H to He occurs in the core until the H is used up.

68. Charles Hakes Fort Lewis College68 After hydrogen fusion stops in the core of a star, the core… A) expands and cools B) expands and heats C) contracts and cools D) contracts and heats

69. Charles Hakes Fort Lewis College69 After hydrogen fusion stops in the core of a star, the core… A) expands and cools B) expands and heats C) contracts and cools D) contracts and heats

70. Charles Hakes Fort Lewis College70 After hydrogen fusion stops in the core of a star, the star as a whole… A) expands B) contracts

71. Charles Hakes Fort Lewis College71 After hydrogen fusion stops in the core of a star, the star as a whole… A) expands B) contracts

72. Charles Hakes Fort Lewis College72 Figure 12.3 Hydrogen Shell Burning 7 - fusion of H to He occurs in the core until the H is used up. 8 - the He core begins to shrink (and heat!), while the H- burning region moves out into a shell

73. Charles Hakes Fort Lewis College73 Figure 12.4 Red Giant on the H–R Diagram 9 - the He core continues to shrink (just a few times bigger than Earth) and heat (to 10 8 K) Heat  pressure demo

74. Charles Hakes Fort Lewis College74 Figure 12.1 Hydrostatic Equilibrium

75. Charles Hakes Fort Lewis College75 Figure 12.5 Horizontal Branch 9 - the Helium flash is when the He in the core begins to fuse into carbon. This happens when the core is ~10 8 K. l Core expands and cools. l New equilibrium on the “horizontal branch.” 10 - New equilibrium on the “horizontal branch.”

76. Charles Hakes Fort Lewis College76 Figure 11.27b Globular Cluster l Note the “horizontal branch”

77. Charles Hakes Fort Lewis College77 Question l What happens when the He in the core is used up?

78. Charles Hakes Fort Lewis College78 Figure 12.6 Helium Shell Burning In the He shell burning stage, the star expands just like in the H shell burning stage

79. Charles Hakes Fort Lewis College79 Figure 12.7 Reascending the Giant Branch 11 - Helium shell burning begins. l Core shrinks and heats. l Exterior expands and cools.

80. Charles Hakes Fort Lewis College80 Figure 12.10 White Dwarf on H–R Diagram 12 - For 1 solar mass stars, that is all that will fuse. l (need 600 million K for the next reactions to occur.) l The outer shell gets “blown off” by the hot, dense, core. l Result is a planetary nebula around a white dwarf (13).

81. Charles Hakes Fort Lewis College81 Figure 12.9 Planetary Nebulae

82. Charles Hakes Fort Lewis College82 White Dwarf stage l Just the core of the star remains l Very small - about the size of Earth l Very dense - about half as massive as the sun. l Will eventually fade and become a black dwarf (stage 14).

83. Charles Hakes Fort Lewis College83 Figure 12.8 G-Type Star Evolution

84. Charles Hakes Fort Lewis College84 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?

85. Charles Hakes Fort Lewis College85 Earth Hour Saturday, March 27, 2010. 8:30 P.M. Turn off lights - save energy. http://www.myearthhour.org/

86. Charles Hakes Fort Lewis College86 How many Stars Can You See? But who uses naked eye observing any more? High quantum efficiency CCD cameras greatly extend the depth of a telescope. Image stacking lets you go even deeper. Depth scales linearly until star brightness is about the same as the background sky brightness. A dark sky on Earth is about magnitude 21/arcsec 2. For film, this would be about as deep as you could go. 16” SCT should reach magnitude 21.5 with a 5 minute exposure using SBIG full frame CCDs For deeper images, the signal only scales as the ~sqrt(time)