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Chapter 14

Chapter 14. Variable Stars The Milky Way. Outline. Variable Stars The Milky Way Dark Matter Review Questions. Lab Notes. “ Extra ” group labs due Today. Star/constellation ID lab. Telescope lab? Observatory Field Trip(s) Wednesday (?) Thursday (?) with sign up.

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Chapter 14

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  1. 1

  2. Chapter 14 Variable Stars The Milky Way 2

  3. Outline • Variable Stars • The Milky Way • Dark Matter • Review Questions 3

  4. Lab Notes • “Extra” group labs due Today. • Star/constellation ID lab. • Telescope lab? • Observatory Field Trip(s) • Wednesday (?) Thursday (?) with sign up. • Dress very warmly - temperature drops fast! 4

  5. For waves, their velocity is the product of: A) frequency times wavelength B) period times energy C) frequency times period D) amplitude times wavelength E) amplitude times frequency 5

  6. For waves, their velocity is the product of: A) frequency times wavelength B) period times energy C) frequency times period D) amplitude times wavelength E) amplitude times frequency 6

  7. Which of these does not exist? A) a six solar mass black hole B) a million solar mass black hole C) a 3.8 solar mass neutron star D) a .06 solar mass brown dwarf E) a 1.3 solar mass white dwarf 7

  8. Which of these does not exist? A) a six solar mass black hole B) a million solar mass black hole C) a 3.8 solar mass neutron star D) a .06 solar mass brown dwarf E) a 1.3 solar mass white dwarf 8

  9. Variable Star Observations • Some stars appear to change in brightness in a very regular way. 9

  10. Figure 14.4cVariable Stars - Cepheid example 10

  11. Figure 14.4abVariable Stars • RR Lyrae light curve • Cepheid light curve 11

  12. Variable Star Observations • RR Lyrae and Cepheid variables are types of variable stars. The brightness varies in a very regular way • The stars can be recognized and identified by observing the light variations • http://cfa-www.harvard.edu/~jhartman/M3_movies.html 12

  13. Figure 14.5Variable Stars on the H–R Diagram • Once identified, the luminosity (absolute magnitude) is known. 13

  14. Figure 14.6Period–Luminosity Plot 14

  15. Variable Star Observations • Globular clusters contain many RR Lyrae variables, so their distances can be determined. 15

  16. Figure 14.8Globular Cluster Distribution • The center of the Milky Way can be estimated by observing the center of all globular clusters. • Diameter of this halo is ~30 kpc (kilo-parsecs) 16

  17. Figure 14.9Stellar Populations in our Galaxy 17

  18. Variable Star Observations • Cepheid variables are so bright that they can be seen in neighboring galaxies. • We can therefore determine the distances to those galaxies. 18

  19. Figure 14.7Variable Stars on Distance Ladder • Greater distances can be determined than typically available through spectroscopic parallax, because these variables are so bright. 19

  20. You observe two Cepheid variable stars. Star A has a period of 10 days. Star B has a period of 30 days. Which is more luminous? A) A B) B C) they are the same D) not enough information 20

  21. You observe two Cepheid variable stars. Star A has a period of 10 days. Star B has a period of 30 days. Which is more luminous? A) A B) B C) they are the same D) not enough information 21

  22. You observe Cepheid stars in two different galaxies (A and B). They have the same apparent brightness.Star in galaxy A has a period of 10 days. Star in galaxy B has a period of 30 days. Which galaxy is closer? A) A B) B C) they are the same distance D) not enough information 22

  23. You observe Cepheid stars in two different galaxies (A and B). They have the same apparent brightness.Star in galaxy A has a period of 10 days. Star in galaxy B has a period of 30 days. Which galaxy is closer? A) A B) B C) they are the same distance D) not enough information 23

  24. Mapping the Milky Way 24

  25. Chapter 14Spiral Galaxy - NGC 4603 25

  26. Chapter 14Spiral Galaxy - 7331 26

  27. Figure 14.1Galactic Plane 27

  28. Figure 14.2a Spiral Galaxies - The Andromeda galaxy is the Milky Way’s big sister. Distance ~800kpc 28

  29. Figure 14.2bcSpiral Galaxies • A view of spiral galaxies from face-on and edge-on. 29

  30. Figure 14.3Herschel’s Galaxy Model • early attempt to map the galaxy by simply counting stars in a given direction. 30

  31. Mapping the Milky Way • Radio observations can determine much of the structure and rotation rates. 31

  32. Figure 14.10Observations of the Galactic Disk 32

  33. Mapping the Milky Way • Radio observations can determine much of the structure and rotation rates. • Orderly rotation in the plane. • Random orbits in the halo. 33

  34. Figure 14.12Stellar Orbits in Our Galaxy 34

  35. Figure 14.13Milky Way Formation • Recall solar system formation. • Halo objects formed before the gas and dust fell to a plane. 35

  36. Mass of the Milky Way • Recall Newton’s modification to Kepler’s third law: 36

  37. Figure 14.18Galaxy Rotation Curve 37

  38. Mass of the Milky Way • There is apparently more mass than can be seen. • Unseen mass out to ~50 kpc. • Recall radius of observable Milky Way is ~15 kpc. • Dark Matter • Can detect gravitational effects • Cannot detect any other way. 38

  39. Dark Matter • Is not atomic or molecular clouds - we would detect those using spectroscopy. • Could be brown dwarfs or white dwarfs - very difficult to see. • MACHOs - MAssive Compact Halo Objects • Could be exotic subatomic particles • WIMPs - Weakly Interacting Massive Particles 39

  40. Figure 14.19Gravitational Lensing 40

  41. Review Questions 41

  42. A star has an apparent magnitude of +1.0 and an absolute magnitude of +1.0. If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase 42

  43. A star has an apparent magnitude of +1.0 and an absolute magnitude of +1.0. If the distance between Earth and the star increases, the apparent magnitude would _____, and the absolute magnitude would _____. A) increase; decrease B) decrease; increase C) increase; not change D) decrease; not change E) not change; increase 43

  44. Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed. 44

  45. Using spectroscopic parallax, you find a star’s distance to be 76 parsecs. You now find out that the star isn’t a main sequence star, but is a red giant. Your distance estimate is A) too large B) too small C) fine - no significant change in estimate is needed. 45

  46. A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) +18.0 C) -8.0 D) -2.0 E) +3.0 46

  47. A star has apparent magnitude of +8.0 before it goes nova and increases its luminosity by 10,000 times. Its apparent magnitude after it goes nova is. A) +8.0 B) +18.0 C) -8.0 D) -2.0 E) +3.0 47

  48. Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon. 48

  49. Which is correct? 1 - The new moon rises at noon. 2 - The first quarter moon rises at noon. 3 - The full moon rises at noon. 4 - The third quarter moon rises at noon. 49

  50. In Paris, France (50 degrees north latitude), what is the longest day of the year? 1: March 21 2: June 21 3: September 21 4: December 21 50

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