Download Starlight (conclusion)

Starlight (conclusion)
Apply Wien’s law and Kirchoff’s Laws to deduce
Properties of stars
Kirchoff’s First Law + Wien’s Law
• Hot, opaque objects produce
continuous spectrum
• The hotter the object, the bluer it is
• Wien’s Law lmax = 2.9E-03/T
• The hotter an object, the brighter it is
Demo
Kirchoff’s First Law + Wien’s
Law
Kirchoff’s 2nd Law: Emission
Line Spectra
Wavelengths of emission lines unique
“fingerprint” of element
Kirchoff’s Third Law:
Absorption Spectra
See Figure 16.6
Starlight…application of
spectroscopy to stars
• Continuous spectrum gives surface
temperature (Wien’s Law)
• Spectral lines give chemical
composition, temperature (also), speed
of rotation (How?) and other properties
• Examples of stellar spectra (Figure
16.11)…what can we say?
Spectral classes of stars:
O,B,A,F,G,K,M
What can you say about the temperatures of these stars?
Examples of stellar
spectra
Question: apply Wien’s
Law to the O5 star. What
Can you say about its
Temperature (relative to the
Sun?)
With information provided by
spectroscopy, we can search for
correlations between stellar
properties
What the data
show: the
HertzsprungRussell Diagram
Highest quality
data from the
Hipparchos
spacecraft
The Hertzsprung-Russell Diagram and
the Types of Stars
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See Figure 16.19
Types of stars, important terms
Main Sequence
Giants
Supergiants
White dwarfs
What does it all mean?
The Hertzsprung-Russell Diagram
Understanding the Main Sequence
(stars like the Sun)
• A statistical argument (no physics)
• Physical argument 1: what holds stars
up?
• Physical argument 2: what powers the
stars (where do they get their energy
supply?)
The nature of the Main Sequence #1:
the MS as a Cambus Stop
Many more people seen on the sidewalk near a
Cambus stop than a random point
The Main Sequence is a long-lived phase of
stellar evolution. Stars spend a much longer
time here than in other parts of the HR
diagram