stellar mass
Post on 06-Jan-2016
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Stellar Mass
Ursa Major
Alcor
Mizar
(Binary star)
Gravitational Orbits Animation
Binary star (system): two stars orbiting a commoncenter of mass (CM).
CM
1
2
r1 r2
1
2
2
1
r
r
M
M
r2 = 3 AU, r1 = 1 AU 3 AU 1
AU 3
M
M
2
1
Kepler’s laws apply here . . .
Yuk!
21
32
M M
a P
P: yearsa: AUM: Solar Masses
32
2 a m) G(M
4 P
a = r1 + r2 = 4 AU
Suppose: P = 8 yrs . . .
8
4
P
a M M
2
3
2
3
21 1 M
“Seeing” Binary Stars
1. Visual Binary: Two stars seen in telescopee.g., Mizar
Albireo
Sirius A & B
AB
Kruger 60
Distance = 13 ly
A
B
L M
A
B
0.01 L
0.0034 L
P = 44.6 yrsa = 9.5 AU
0.28 M
0.16 M
2. Spectroscopic Binary: Motion of starsdetected via Doppler shift of spectrum lines.
Mizar
Each star is itself binary!
Earth
* Doppler shift
* No Doppler shift
Spectroscopic Binary Animation
3. Eclipsing Binary: Stars mutually eclipseeach other.
Earth
* No eclipse
* Eclipse
Binary ‘light curve’B
righ
tnes
s
Time
½ orbit period
Eclipsing Binary Animation
Binary Statistics
* At least 50% of all stars reside in binaries.
* The sun is apparently a loner!
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