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Chapter 5: Binary stars and stellar masses. Albireo: The Boy Scout star. Kepler’s Three Laws of Planetary Motion. Planetary orbits are elliptical A planet sweeps out equal areas in equal times P 2 = a 3. M 2. r 2. r 1. CM. M 1. Two stars orbit their center of mass. M 2. M 1. a.
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Chapter 5: Binary stars and stellar masses Albireo: The Boy Scout star
Kepler’s Three Laws of Planetary Motion Planetary orbits are elliptical A planet sweeps out equal areas in equal times P2 = a3
M2 r2 r1 CM M1 Two stars orbit their center of mass
M2 M1 a Make one star the focus of an ellipse
MASS-LUMINOSITY RELATION (for MAIN SEQUENCE STARS) L = M where [L] = L and [M] = M Approximately: M < 0.3 M = 1.8 0.3 M< M < 3 M = 3.5 M > 3 M = 2.8
OBSERVED APPROXIMATE FITS
M2 a2 a1 M1