Stellar Atmospheres: Motivation 1 Stellar Atmospheres: Literature Dimitri Mihalas –Stellar Atmospheres, W.H. Freeman, San Francisco Albrecht Unsöld –Physik.
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Stellar Atmospheres: Motivation
1
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
Stellar Atmospheres: Motivation
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Why physics of stellar atmospheres?
Physics
Stellar atmospheres as laboratories
Plasma-, atomic-, and molecular physics, hydrodynamics, thermodynamics
Basic research
Technical application
Astronomy
Spectral analysis of stars
Structure and evolution of stars
Galaxy evolution
Evolution of the Universe
Stellar Atmospheres: Motivation
3
Magnetic fields in white dwarfs and neutron stars
Shift of spectral lines with increasing field strength
Stellar Atmospheres: Motivation
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Hertzsprung Russell Diagram
L~R2 T4eff
100 R
1 R
=700000Km
0.01 R
4 1026 W
5800K
Stellar Atmospheres: Motivation
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Massive stars
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Chemical evolution of the Galaxy
Carretta et al. 2002, AJ 124, 481
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SN movie
Stellar Atmospheres: Motivation
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SN Ia
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SN Ia cosmology
M,
0 , 1
0.5, 0.5
1 , 0
1.5, -.5
0 , 0
1 , 0
2 , 0
Redshift z
Stellar Atmospheres: Motivation
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SN Ia Kosmologie
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Uranium-Thorium clock
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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
Stellar Atmospheres: Motivation
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Sonne
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Fraunhofer lines
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Spectrum - schematicallyIn
ten
sit
y
Wavelength / nm
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Spectrum formation
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Formation of absorption lines
Interior outerboundary
observer
continuum
line center
continuum
stellar atmosphere intensity
Stellar Atmospheres: Motivation
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Line formation / stellar spectral types
spectral line temperature structure
interior
f
lux
wavelength
temp
erature
depth / km
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The spectral types on the main sequence
O B A F G K M
O5
B4
O7
B6
A1
A5
A8
A9
F8
G2
G5
G8
A7
F3
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Die Spektraltypen der Hauptreihe
O B A F G K M F6
F8
G2
G5
G8
A7
F3
G6
G9
K4
K5
F8
G1
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Classification scheme
M9
L3
L5
L8
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Classification scheme
T dwarfs
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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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Optical telescopes
Calar Alto (Spain)3.5m telescope
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Optical telescopes
ESO/VLT
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Why is it important?
UV / EUV observations
flux
flux
wavelength / Å
wavelength / Å
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UV/optical telescopes
HST
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X-ray telescopes
XMM
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Gamma-ray telescopes
INTEGRAL
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Infrared observatories
ISO
JWST
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Sub-mm telescopes
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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
Stellar Atmospheres: Motivation
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PN – NGC6751 - HST
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Planetary nebula spectrum
Stellar Atmospheres: Motivation
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ISM spectrum
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Quasar + IGM spectrum
Stellar Atmospheres: Motivation
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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
Stellar Atmospheres: Motivation
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Eta Carinae - HST
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Stellar wind spectrum
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Formation of wind spectrum (P Cygni line profiles)
Stellar Atmospheres: Motivation
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Stellar winds – P Cyg profiles
Stellar Atmospheres: Motivation
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Accretion disks
Stellar Atmospheres: Motivation
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AM CVn disk spectrum
models
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Temperature structure of an accretion disk
Distance from star [km]
He
igh
t [k
m]
Stellar Atmospheres: Motivation
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Planetary atmospheres
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Quantitative spectral analyses – what can we learn?
Shape of line profile:Temperature Film
Density Film
Abundance Film
Rotation
Turbulence
Magnetic field
Line position:Chemical composition
Velocities
Redshift
Temporal variation:Companion
Surface structure
Spots
Pulsation
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Zeeman effect
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Magnetic fieldsL
l
optical spectrum
circular polarization
position of line components
spectrum of a white dwarf (PG 1658+440) with fieldstrength of about 5 MG
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Magnetic fieldsL
White dwarf Grw+70 8247B=300MG
optical spectrum
Circular polarization
positionof line components
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Velocity fields
Wavelength / Å
Dis
tan
ce /
10
00 k
m
~ 0.01Å
Solar disk
time / min
dist
ance
/ 1
000k
m
Stellar Atmospheres: Motivation
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Time dependent line profilesT
ime
Flu
x
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Doppler tomography
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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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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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