albireo: the boy scout star chapter 5: binary stars and stellar masses
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Albireo: The Boy Scout star
Chapter 5: Binary stars and stellar masses
Kepler’s Three Laws of Planetary Motion
1.Planetary orbits are elliptical2.A planet sweeps out equal areas in equal times3.P2 = a3
M1
M2
r1
r2
CM
Two stars orbit their center of mass
M1
M2
a
Make one star the focus of an ellipse
Visual binary: not viewed face on
Centauri system (visual binary)
Spectroscopic binary
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
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a1
a2
M1
M2