Download Basic Properties of Stars D • Composition L

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slides are
on the web
Basic Properties of Stars
• Composition
• Mass
• Diameter = D
• Measure temperature T from
spectrum.
Emitted energy
per unit surface area 
• Luminosity = L
[Fig. 5.10]
5000o
T = 15,000K
[fig 4.8]5800K
3000K
310K
4000o
3000o
Wavelength 
 Energy
•
Total energy emitted per unit surface area = E =  T 4
•
Total energy from whole star:
L = E x (surface area) = ( T 4) x (D2)
Measure L and T, solve for D
The Hertzprung-Russell (H-R) Diagram [11.2]
• Representative sample
of stars.
• Plot Luminosity vs.
Surface Temperature.
• Most stars fall along
“main sequence”.
M ai
nS
eq u
en c
e
• Any theory about how
stars work has to
explain this.
Hot
Cool
[see Fig. 11.10]
1
The H-R
H-R Diagram
Diagram (with
with Sizes
The
sizes)
Larg
er D
i a.
106
Luminosity

104
[Fig. 11.10]
102
Con
stan
t Dia
me t
100
er
10-2
10-4
25,000
L = ( T4 ) x (D2)
10,000
5,000
Temperature
3,000
Diameter!
Here’s what we observe about stars.
The Mass-Luminosity
Relation
The H-R Diagram
Hot
Higher (Luminosity, Temperature, Diameter)
(O)
mass
stars
Cool
(M)
stars
Lower
mass
Main sequence is
a mass sequence
Hot
Cool
2
What is inside the Sun?
energy
generation
(cumulative)
Measure
•
•
•
•
Infer
Luminosity
Mass
Diameter
Chemical
composition
(from our knowledge of Physics)
0
1
• Internal
structure
16 million deg K
H
temperature
composition
density
4He
160 x water
What is inside other stars?
3He
Measure
•
•
•
•
Calculate
11 atmospheres
2.5x10
Luminosity
Mass
Surface
mass
temperature
(cumulative)
Chemical
composition
0
1
radiation
Infer
Diameter
pressure
convection
• Internal
Energy structure
transport
from
Luminosity and
Temperature
radius
0
1
0
1
Here’s what we observe about stars.
The Mass-Luminosity
Relation
The H-R Diagram
Hot
Higher (Luminosity, Temperature, Diameter)
(O)
mass
stars
Cool
(M)
stars
Lower
mass
Main sequence is
a mass sequence
MAIN SEQUENCE:
Stars convert H into He in their cores.
3
H
composition
4He
3He
Models of Sun show:
Burning of H in center has
already changed the
composition a lot!
Eventually, H burns outward in a shell
•
•
•
•
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
Luminosity 
 Red
giant.
H  He burning
core
Diameter
Inert H
 Temperature
4
Eventually, H burns outward in a shell
•
•
•
•
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
Luminosity 
 Red
giant.
Inert He core
HHe burning
shell
Inert H
Diameter
 Temperature
Eventually, H burns outward in a shell
•
•
•
•
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
Luminosity 
 Red
giant.
Inert He core
HHe burning
shell
Inert H
Diameter
 Temperature
5
Eventually, H burns outward in a shell
•
•
•
•
Heat source moves closer to surface.
Layers below surface swell up.
Star becomes larger
Surface becomes cooler
Luminosity 
 Red
giant.
Inert He core
HHe burning
shell
Inert H
Diameter
 Temperature
6