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Stellar Atmospheres: Motivation
Stellar Atmospheres: Literature
•
Dimitri Mihalas
– Stellar Atmospheres, W.H. Freeman, San Francisco
•
Albrecht Unsöld
– Physik der Sternatmosphären, Springer Verlag (in German)
•
Rob Rutten
– Lecture Notes Radiative Transfer in Stellar Atmospheres
http://www.fys.ruu.nl/~rutten/node20.html
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Stellar Atmospheres: Motivation
Why physics of stellar atmospheres?
Physics
Astronomy
Stellar atmospheres as
laboratories
Spectral analysis of stars
Plasma-, atomic-, and molecular
physics, hydrodynamics,
thermodynamics
Structure and evolution of stars
Basic research
Technical application
Galaxy evolution
Evolution of the Universe
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Stellar Atmospheres: Motivation
Magnetic fields in white dwarfs and neutron stars
Shift of spectral lines with
increasing field strength
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Stellar Atmospheres: Motivation
Hertzsprung Russell Diagram
100 R 
4 1026 W
1R
L~R2 T4eff
=700000Km
0.01 R 
5800K
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Stellar Atmospheres: Motivation
Massive stars
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Stellar Atmospheres: Motivation
Chemical evolution of the
Galaxy
Carretta et al.
2002, AJ 124, 481
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Stellar Atmospheres: Motivation
SN movie
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Stellar Atmospheres: Motivation
SN Ia
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Stellar Atmospheres: Motivation
SN Ia cosmology
M, 
0 ,1
0.5, 0.5
1 ,0
1.5, -.5
Redshift z
0
,0
1
,0
2
,0
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Stellar Atmospheres: Motivation

SN Ia Kosmologie
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Stellar Atmospheres: Motivation
Uranium-Thorium
clock
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Stellar Atmospheres: Motivation
Stellar atmosphere – definition
• From outside visible, observable layers of the star
• Layers from which radiation can escape into space
– Dimension
• Not stellar interior (optically thick)
• No nebula, ISM, IGM, etc. (optically thin)
• But: chromospheres, coronae, stellar winds, accretion
disks and planetary atmospheres are closely related topics
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Stellar Atmospheres: Motivation
Sonne
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Stellar Atmospheres: Motivation
Fraunhofer lines
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Stellar Atmospheres: Motivation
Intensity
Spectrum - schematically
Wavelength / nm
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Stellar Atmospheres: Motivation
Spectrum formation
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Stellar Atmospheres: Motivation
Formation of absorption lines
Interior
outer
boundary
observer
continuum
line center
continuum
stellar atmosphere
intensity
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Stellar Atmospheres: Motivation
Line formation / stellar spectral types
spectral line
temperature
structure
flux
temperature
depth / km
wavelength
interior
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Stellar Atmospheres: Motivation
The spectral types on the main sequence
O
B
A
F
G
K
M
A7
F3
O5
O7
F8
B4
B6
A1
G2
G5
A5
A8
G8
A9
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Stellar Atmospheres: Motivation
Die Spektraltypen der Hauptreihe
O
B
A
A7
F3
F
G
K
M
F6
F8
G1
F8
G6
G2
G9
G5
K4
K5
G8
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Stellar Atmospheres: Motivation
Classification scheme
M9
L3
L5
L8
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Stellar Atmospheres: Motivation
Classification scheme
T dwarfs
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Stellar Atmospheres: Motivation
Stellar atmosphere – definition
• From outside visible, observable layers of the star
• Layers from which radiation can escape into space
– Dimension
• Not stellar interior (optically thick)
• No nebula, ISM, IGM, etc. (optically thin)
• But: chromospheres, coronae, stellar winds, accretion
disks and planetary atmospheres are closely related topics
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Stellar Atmospheres: Motivation
Optical telescopes
Calar Alto (Spain)
3.5m telescope
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Stellar Atmospheres: Motivation
Optical telescopes
ESO/VLT
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Stellar Atmospheres: Motivation
UV / EUV observations
flux
Why is it important?
flux
wavelength / Å
wavelength / Å
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Stellar Atmospheres: Motivation
UV/optical
telescopes
HST
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Stellar Atmospheres: Motivation
X-ray telescopes
XMM
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Stellar Atmospheres: Motivation
Gamma-ray telescopes
INTEGRAL
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Stellar Atmospheres: Motivation
Infrared observatories
JWST
ISO
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Stellar Atmospheres: Motivation
Sub-mm telescopes
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Stellar Atmospheres: Motivation
Stellar atmosphere – definition
• From outside visible, observable layers of the star
• Layers from which radiation can escape into space
– Dimension
• Not stellar interior (optically thick)
• No nebula, ISM, IGM, etc. (optically thin)
• But: chromospheres, coronae, stellar winds, accretion
disks and planetary atmospheres are closely related topics
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Stellar Atmospheres: Motivation
PN – NGC6751 - HST
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Stellar Atmospheres: Motivation
Planetary nebula spectrum
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Stellar Atmospheres: Motivation
ISM spectrum
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Stellar Atmospheres: Motivation
Quasar + IGM spectrum
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Stellar Atmospheres: Motivation
Stellar atmosphere – definition
• From outside visible, observable layers of the star
• Layers from which radiation can escape into space
– Dimension
• Not stellar interior (optically thick)
• No nebula, ISM, IGM, etc. (optically thin)
• But: chromospheres, coronae, stellar winds, accretion
disks and planetary atmospheres are closely related topics
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Stellar Atmospheres: Motivation
Eta Carinae - HST
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Stellar Atmospheres: Motivation
Stellar wind spectrum
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Stellar Atmospheres: Motivation
Formation of wind spectrum (P Cygni line profiles)
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Stellar Atmospheres: Motivation
Stellar winds – P Cyg profiles
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Stellar Atmospheres: Motivation
Accretion disks
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Stellar Atmospheres: Motivation
AM CVn disk spectrum
models
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Stellar Atmospheres: Motivation
Height [km]
Temperature structure of an accretion disk
Distance from star [km]
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Stellar Atmospheres: Motivation
Planetary atmospheres
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Stellar Atmospheres: Motivation
Quantitative spectral analyses – what can we learn?
Shape of line profile:
Temperature
Density
Abundance
Rotation
Turbulence
Magnetic field
Film
Film
Film
Temporal variation:
Companion
Surface structure
Spots
Pulsation
Line position:
Chemical composition
Velocities
Redshift
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Stellar Atmospheres: Motivation
Zeeman effect
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Stellar Atmospheres: Motivation
Magnetic fields
L
optical spectrum
l
spectrum of a white dwarf
(PG 1658+440) with field
strength of about 5 MG
circular polarization
position
of line
components
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Stellar Atmospheres: Motivation
Magnetic fields
L
optical spectrum
White dwarf Grw+70 8247
B=300MG
Circular polarization
position
of line
components
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Stellar Atmospheres: Motivation
Velocity fields
~ 0.01Å
distance / 1000km
Distance / 1000 km
Solar disk
Wavelength / Å
time / min
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Stellar Atmospheres: Motivation
Flux
Time
Time dependent line profiles
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Stellar Atmospheres: Motivation
Doppler tomography
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Stellar Atmospheres: Motivation
Summary – stellar atmospheres theory
The atmosphere of a star contains less than one billionth of its total mass, so, why
do we care at all?
• The atmosphere of a star is that what we can see, measure, and analyze.
• The stellar atmosphere is therefore the source of information in order to put a
star from the color-magnitude diagram (e.g. B-V,mv) of the observer into the
HRD (L,Teff) of the theoretician and, hence, to drive the theory of stellar
evolution.
• Atmosphere analyses reveal element abundances and show us results of
cosmo-chemistry, starting from the earliest moments of the formation of the
Universe.
• Hence, working with stellar atmospheres enables a test for big-bang theory.
• Stars are the building blocks of galaxies. Our understanding of the most
distant (hence most early emerged) galaxies, which cannot be resolved in
single stars, is not possible without knowledge of processes in atmospheres of
single stars.
• Work on stellar atmospheres is a big challenge. The atmosphere is that region,
where the transition between the thermodynamic equilibrium of the stellar
interior into the empty blackness of space occurs. It is a region of extreme
non-equilibrium states.
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Stellar Atmospheres: Motivation
Summary – stellar atmospheres theory
Important source of information for many disciplines in
astrophysics
– research for pure knowledge, contribution to our culture
– ambivalent applications (e.g. nuclear weapons)
Application of diverse disciplines
– physics
– numerical methods
Still a very active field of research, many unsolved problems
– e.g. dynamical processes
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