6 – Hertzsprung-Russell
Diagram
Hertzsprung
Russell
2
The Plan
•
Are all stars the same?
•
Why are some hotter and others cooler?
•
What about luminosity?
•
These and other issues are resolved by the
Hertzsprung-Russell Diagram
– Main Sequence
– Luminosity Function
– MS stars sit on the HR diagram 10
9
yr
– Giants move over periods of 10
5
yr
– White dwarf move over 10
10
yr
3
Sun
Degenerate gas
pressure
Homogeneous
Inhomogeneous
M < 0.08Mo
will not burn H
M>50Mo
will be
unstable
O
B
A
F
G
K
M
HR Diagram
4
re: HR Diagram
•
The range in Luminosity, 10
8
:1!
(It’s even up
to 10
14
:1 if you count the brown dwarfs!!)
– Max 10,000 L
Sun
O5 stars
– Min
0.0001 L
Sun
M5 stars
•
What is the range in Temperature, 15:1
– Max 40,000K
– Min 2,500K
•
What are R
max
and R
min
?
• L
α
R
2
x T
4
=> R
α
L
1/2
T
-2
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5
Stellar Statistics
•
Of known stars:
• 90% are MS stars
• 10% are White Dwarfs
• 1% are Giants
•
Of the main sequence stars
80% are M stars.

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- Spring '09
- HOUCK,J
- Globular cluster, Star cluster
-
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