1. Charles Hakes Fort Lewis College1

2. Charles Hakes Fort Lewis College2

3. Charles Hakes Fort Lewis College3 Outline Remove extra folder debris Magnitudes and Distance H-R diagrams Stellar Evolution

4. Charles Hakes Fort Lewis College4 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) Does not change with distance At 10pc, Apparent magnitude= Absolute magnitude

5. Charles Hakes Fort Lewis College5 Chapter 10 Star Temperatures (Colors)

6. Charles Hakes Fort Lewis College6 Figure 10.7 Star Colors – Orion (20°) and the Milky Way Center (2 ’ )

7. Charles Hakes Fort Lewis College7 Which star would be the hottest? A) A B) B C) G D) M E) O

8. Charles Hakes Fort Lewis College8 Which star would be the hottest? A) A B) B C) G D) M E) O

9. Charles Hakes Fort Lewis College9 Star Spectral Classification New order is: O, B, A, F, G, K,M. Remember the order... Oh, Be A Fine Girl/(Guy) Kiss Me

10. Charles Hakes Fort Lewis College10 Chapter 10 HR Diagrams

11. Charles Hakes Fort Lewis College11 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. Charles Hakes Fort Lewis College12 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

13. Charles Hakes Fort Lewis College13 Figure 10.12 H–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!

14. Charles Hakes Fort Lewis College14 Figure 10.15 Hipparcos H–R Diagram Plot many stars and notice that 90% fall on the “main sequence”. Add radius lines, and now have luminosity temperature radius

15. Charles Hakes Fort Lewis College15 Figure 10.14 H–R Diagram of 100 Brightest Stars Most very bright stars are also distant

16. Charles Hakes Fort Lewis College16 Figure 10.13 H–R Diagram of Nearby Stars Most close stars are very dim Best estimate now is that 80% of stars are red dwarfs

17. Charles Hakes Fort Lewis College17 Chapter 10 Star Sizes

18. Charles Hakes Fort Lewis College18 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  radius 2 x T 4 (  means proportional to)

19. Charles Hakes Fort Lewis College19 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  r 2  T 4 (= means equal)

20. Charles Hakes Fort Lewis College20 Star Sizes Can directly measure the radius on very few stars. (~dozen) Can calculate the radius if you know the luminosity and the temperature.

21. Charles Hakes Fort Lewis College21 Figure 10.11 Stellar Sizes Giants - radius between 10x and 100x solar Supergiants - larger (up to 1000x) Dwarf - radius comparable to or smaller than the sun.

22. Charles Hakes Fort Lewis College22 Figure 10.15 Hipparcos H–R Diagram Plot the luminosity vs. temperature. This is called a Hertzsprung- Russell (H-R) diagram

23. Charles Hakes Fort Lewis College23 Review What fraction of the stars on an H-R diagram are on the main sequence. Enter numbers 1-9 for 10%-90%

24. Charles Hakes Fort Lewis College24 Discussion What fraction of the stars on an H-R diagram are on the main sequence. Enter numbers 1-9 for 10%-90%

25. Charles Hakes Fort Lewis College25 Distance Scale If you know brightness and distance, you can determine luminosity. Turn the problem around…

26. Charles Hakes Fort Lewis College26 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.

27. Charles Hakes Fort Lewis College27 Distance Scale Spectroscopic Parallax - the process of using stellar spectra to determine distances. Can use this distance scale out to several thousand parsecs.

28. Charles Hakes Fort Lewis College28 Figure 10.16 Stellar Distances

29. Charles Hakes Fort Lewis College29 Stellar Evolution

30. Charles Hakes Fort Lewis College30 Figure 11.16 Atomic Motions Low density clouds are too sparse for gravity. A perturbation could cause one region to start condensing.

31. Charles Hakes Fort Lewis College31 Figure 11.17 Cloud Fragmentation

32. Charles Hakes Fort Lewis College32 Figure 11.20 Interstellar Cloud Evolution

33. Charles Hakes Fort Lewis College33 l http://discovermagazine.com/2009/interact ive/star-formation-game/ http://discovermagazine.com/2009/interact ive/star-formation-game/

34. Charles Hakes Fort Lewis College34 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.

35. Charles Hakes Fort Lewis College35 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

36. Charles Hakes Fort Lewis College36 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

37. Charles Hakes Fort Lewis College37 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. Charles Hakes Fort Lewis College38 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

39. Charles Hakes Fort Lewis College39 Figure 11.19 Protostar on the H–R Diagram

40. Charles Hakes Fort Lewis College40 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink.

41. Charles Hakes Fort Lewis College41 Figure 11.18 Orion Nebula, Up Close

42. Charles Hakes Fort Lewis College42 Figure 11.23 Protostars

43. Charles Hakes Fort Lewis College43 Figure 11.21 Newborn Star on the H–R Diagram

44. Charles Hakes Fort Lewis College44 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. Charles Hakes Fort Lewis College45 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

46. Charles Hakes Fort Lewis College46 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.

47. Charles Hakes Fort Lewis College47 Figure 10.21 Stellar Masses

48. Charles Hakes Fort Lewis College48 Figure 11.24 Prestellar Evolutionary Tracks

49. Charles Hakes Fort Lewis College49 Figure 11.25 Brown Dwarfs

50. Charles Hakes Fort Lewis College50 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?