Stellar Atmospheres: Motivation 1 Stellar Atmospheres: Literature Dimitri Mihalas –Stellar...

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


2

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


3

Magnetic fields in white dwarfs and neutron stars

Shift of spectral lines with increasing field strength


4

Hertzsprung Russell Diagram

L~R2 T4eff

100 R

1 R

=700000Km

0.01 R

4 1026 W

5800K


5

Massive stars


6

Chemical evolution of the Galaxy

Carretta et al. 2002, AJ 124, 481


7

SN movie


8

SN Ia


9

SN Ia cosmology

M,

0 , 1

0.5, 0.5

1 , 0

1.5, -.5

0 , 0

1 , 0

2 , 0

Redshift z


10

SN Ia Kosmologie


11

Uranium-Thorium clock


12

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


13

Sonne


14

Fraunhofer lines


15

Spectrum - schematicallyIn

ten

sit

y

Wavelength / nm


16

Spectrum formation


17

Formation of absorption lines

Interior outerboundary

observer

continuum

line center

continuum

stellar atmosphere intensity


18

Line formation / stellar spectral types

spectral line temperature structure

interior

f

lux

wavelength

temp

erature

depth / km


19

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


20

Die Spektraltypen der Hauptreihe

O B A F G K M F6

F8

G2

G5

G8

A7

F3

G6

G9

K4

K5

F8

G1


21

Classification scheme

M9

L3

L5

L8


22

Classification scheme

T dwarfs


23



– Dimension




24

Optical telescopes

Calar Alto (Spain)3.5m telescope


25

Optical telescopes

ESO/VLT


26

Why is it important?

UV / EUV observations

flux

flux

wavelength / Å

wavelength / Å


27

UV/optical telescopes

HST


28

X-ray telescopes

XMM


29

Gamma-ray telescopes

INTEGRAL


30

Infrared observatories

ISO

JWST


31

Sub-mm telescopes


33



– Dimension




34

PN – NGC6751 - HST


35

Planetary nebula spectrum


36

ISM spectrum


37

Quasar + IGM spectrum


38



– Dimension




39

Eta Carinae - HST


40

Stellar wind spectrum


41

Formation of wind spectrum (P Cygni line profiles)


42

Stellar winds – P Cyg profiles


43

Accretion disks


44

AM CVn disk spectrum

models


45

Temperature structure of an accretion disk

Distance from star [km]

He

igh

t [k

m]


46

Planetary atmospheres


47

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


48

Zeeman effect


49

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


50

Magnetic fieldsL

White dwarf Grw+70 8247B=300MG

optical spectrum

Circular polarization

positionof line components


52

Velocity fields

Wavelength / Å

Dis

tan

ce /

10

00 k

m

~ 0.01Å

Solar disk

time / min

dist

ance

/ 1

000k

m


55

Time dependent line profilesT

ime

Flu

x


56

Doppler tomography


57

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.


58

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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Stellar Atmospheres: Motivation 1 Stellar Atmospheres: Literature Dimitri Mihalas –Stellar...

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