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Line Spectra
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
Composition
H lines
CaI line
CaII lines
Fe I lines
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
 Temperature (relative strength of lines)
Strengths of Spectral Lines
Line Strength
Atoms become ionized
Less energy to
stimulate transitions
Temperature
Strengths of Spectral Lines
Line Strength
Ionized
Helium
Hydrogen
Ionized Calcium
Ionized
Iron
Helium
50,000
25,000
Titanium
Oxide
10,000
8000
6000
Temperature (K)
5000
4000
3000
Astronomical Computers
Annie Jump Cannon
Henrietta Leavitt
Harvard College Observatory
Spectral Classification
 First
scheme based on complexity of
the spectrum (A - Q)
 Cannon reordered them by temperature
around 1901.
O B A F G K M
Spectral Classification
 Oh,
Be A Fine Girl (Guy) Kiss Me
 Only Boys Accepting Feminism Get
Kissed Meaningfully
A5
O
B
A
F
K7
G
35,000 K
K
M
3,000 K
Sun(G2)
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
 Temperature (relative strength of lines)
 Radial Velocity (Doppler Effect)
Doppler Effect
Christian
Doppler
Doppler Shift Gives Radial
Velocity
True Velocity
Radial Velocity
Tangential
Velocity
Radar
Doppler Shift Gives Radial
Velocity
True Velocity
Radial Velocity
Tangential
Velocity
Telescope
Compare these spectra.
Spectrum of Hydrogen in Lab
Spectrum a Star
What do these spectra tell us about the star?
Doppler Effect
 Blue
shift means approaching
 Red shift means receding
Red & Blue shifts denote motion - not color
 Size
of the shift gives speed
 Gives Radial velocity
No information on tangential velocity
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
 Temperature (relative strength of lines)
 Radial Velocity (Doppler Effect)
 Rotation Rate (Doppler Broadening)
Stellar Rotation
This limb
produces
blue shift
This limb
produces red
shift
Doppler Broadening
Spectra
Tracings
Slow rotation
Rapid rotation
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
 Temperature (relative strength of lines)
 Radial Velocity (Doppler Effect)
 Rotation Rate (Doppler Broadening)
 Radius (Pressure Broadening)
Pressure Broadening
Low Pressure
Moderate Pressure
Atomic
View
Spectrum
Pressure Broadening
 In
stars gravity is the “piston”
M
F 2
R
High pressure  High gravity  Small Star
Low pressure  Low gravity  Large Star
Pressure Broadening
A3
Supergiant
A3
Giant
A3
Dwarf
From the Study of Spectral
Lines We can Know...
 Composition
(which lines occur)
 Temperature (relative strength of lines)
 Radial Velocity (Doppler Effect)
 Rotation Rate (Doppler Broadening)
 Radius (Pressure Broadening)
 Magnetic Field (Zeeman Effect)
Zeeman Effect
Spectrum
Prism
Light
N
S
Without Field
With Field
Pieter
Zeeman
End of Line Spectra