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Astronomy Problems 561: 02-15-11 HR Diagram part II

Astronomy Problems 561: 02-15-11 HR Diagram part II. HR Diagram for nearest 16,000 stars:. Most stars lie along the “Main Sequence” Simple relationship between temperature and luminosity

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Astronomy Problems 561: 02-15-11 HR Diagram part II

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  1. Astronomy Problems 561: 02-15-11HR Diagram part II

  2. HR Diagram for nearest 16,000 stars: • Most stars lie along the “Main Sequence” • Simple relationship between temperature and luminosity • Stars spend most of their lives converting hydrogen to helium, and this is what occurs when the star is on the main sequence

  3. L = 4πR2σT4 For a given radius, we Can sketch lines of L vs T on the HR diagram Red Dwarfs

  4. Luminosity Classes: Higher density gas > broader absorption lines in spectrum Higher density gas in star’s atmosphere > smaller star > smaller luminosity for a given temp. L = 4πR2σT4

  5. Lecture 8 Part 2Masses of Stars; Binary Star Systems

  6. How do you weigh a star?

  7. Orbital Motion: An object in orbit around another object is in continual free-fall How fast you orbit an object depends on your mass and how far out you are orbiting Therefore we need to look at binary stars systems

  8. Binary Stars Between 50% and 67% of all stars are in multiple star systems Proxima Centauri.... ... Orbits Alpha Centauri A and B

  9. Kepler’s third law: MA + MB = a3/P2 A B a = average separation of stars in astronomical units P = period of orbit in years MA + MB = total mass in terms of solar mass a

  10. ra:r b = MA : MB ra r b A B

  11. I: Visual Binaries Rigel

  12. I: Visual Binaries Mizar

  13. II: Spectroscopic Binaries

  14. III: Eclipsing Binaries

  15. Mass-Luminosity Relation for the Main Sequence: L = M3.5

  16. -10 -5 0 Absolute Magnitude +5 +10 +15

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