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Astronomy Problems 561: 02-15-11 HR Diagram part II
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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
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L = 4πR 2 σT 4 For a given radius, we Can sketch lines of L vs T on the HR diagram Red Dwarfs
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Luminosity Classes: Higher density gas > broader absorption lines in spectrum Higher density gas in stars atmosphere > smaller star > smaller luminosity for a given temp. L = 4πR 2 σT 4
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Lecture 8 Part 2 Masses of Stars; Binary Star Systems
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How do you weigh a star?
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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
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Binary Stars Between 50% and 67% of all stars are in multiple star systems Proxima Centauri....... Orbits Alpha Centauri A and B
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Keplers third law: M A + M B = a 3 /P 2 a AB a = average separation of stars in astronomical units P = period of orbit in years M A + M B = total mass in terms of solar mass
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rara r b AB r a :r b = M A : M B
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I: Visual Binaries Rigel
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I: Visual Binaries Mizar
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II: Spectroscopic Binaries
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III: Eclipsing Binaries
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Mass-Luminosity Relation for the Main Sequence: L = M 3.5
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+5 0 -5 -10 +10 +15 Absolute Magnitude
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