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

Stellar Atmospheres: Motivation 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

Stellar Atmospheres: Motivation 3 Magnetic fields in white dwarfs and neutron stars Shift of spectral lines with increasing field strength

Stellar Atmospheres: Motivation 4 Hertzsprung Russell Diagram L~R 2 T 4 eff 100 R  1 R  =700000Km 0.01 R  W 5800K

Stellar Atmospheres: Motivation 5 Massive stars

Stellar Atmospheres: Motivation 6 Chemical evolution of the Galaxy Carretta et al. 2002, AJ 124, 481

Stellar Atmospheres: Motivation 7 SN movie

Stellar Atmospheres: Motivation 8 SN Ia

Stellar Atmospheres: Motivation 9 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 10 SN Ia Kosmologie  

Stellar Atmospheres: Motivation 11 Uranium-Thorium clock

Stellar Atmospheres: Motivation 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

Stellar Atmospheres: Motivation 13 Sonne

Stellar Atmospheres: Motivation 14 Fraunhofer lines

Stellar Atmospheres: Motivation 15 Spectrum - schematically Intensity Wavelength / nm

Stellar Atmospheres: Motivation 16 Spectrum formation

Stellar Atmospheres: Motivation 17 Formation of absorption lines Interior outer boundary observer continuum line center continuum stellar atmosphereintensity

Stellar Atmospheres: Motivation 18 Line formation / stellar spectral types spectral line temperature structure interior flux wavelength temperature depth / km

Stellar Atmospheres: Motivation 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

Stellar Atmospheres: Motivation 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

Stellar Atmospheres: Motivation 21 Classification scheme M9 L3 L5 L8

Stellar Atmospheres: Motivation 22 Classification scheme T dwarfs

Stellar Atmospheres: Motivation 23 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 24 Optical telescopes Calar Alto (Spain) 3.5m telescope

Stellar Atmospheres: Motivation 25 Optical telescopes ESO/VLT

Stellar Atmospheres: Motivation 26 Why is it important? UV / EUV observations flux wavelength / Å

Stellar Atmospheres: Motivation 27 UV/optical telescopes HST

Stellar Atmospheres: Motivation 28 X-ray telescopes XMM

Stellar Atmospheres: Motivation 29 Gamma-ray telescopes INTEGRAL

Stellar Atmospheres: Motivation 30 Infrared observatories ISO JWST

Stellar Atmospheres: Motivation 31 Sub-mm telescopes

Stellar Atmospheres: Motivation 32 Radio telescopes 100m dish at Effelsberg

Stellar Atmospheres: Motivation 33 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 34 PN – NGC HST

Stellar Atmospheres: Motivation 35 Planetary nebula spectrum

Stellar Atmospheres: Motivation 36 ISM spectrum

Stellar Atmospheres: Motivation 37 Quasar + IGM spectrum

Stellar Atmospheres: Motivation 38 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 39 Eta Carinae - HST

Stellar Atmospheres: Motivation 40 Stellar wind spectrum

Stellar Atmospheres: Motivation 41 Formation of wind spectrum (P Cygni line profiles)

Stellar Atmospheres: Motivation 42 Stellar winds – P Cyg profiles

Stellar Atmospheres: Motivation 43 Accretion disks

Stellar Atmospheres: Motivation 44 AM CVn disk spectrum models

Stellar Atmospheres: Motivation 45 Temperature structure of an accretion disk Distance from star [km] Height [km]

Stellar Atmospheres: Motivation 46 Planetary atmospheres

Stellar Atmospheres: Motivation 47 Quantitative spectral analyses – what can we learn? Shape of line profile: Temperature FilmFilm Density FilmFilm Abundance FilmFilm Rotation Turbulence Magnetic field Line position: Chemical composition Velocities Redshift Temporal variation: Companion Surface structure Spots Pulsation

Stellar Atmospheres: Motivation 48 Zeeman effect

Stellar Atmospheres: Motivation 49 Magnetic fields L l optical spectrum circular polarization position of line components spectrum of a white dwarf (PG ) with field strength of about 5 MG

Stellar Atmospheres: Motivation 50 Magnetic fields L White dwarf Grw B=300MG optical spectrum Circular polarization position of line components

Stellar Atmospheres: Motivation 51 Extrasolar planets

Stellar Atmospheres: Motivation 52 Velocity fields Wavelength / Å Distance / 1000 km ~ 0.01Å Solar disk time / min distance / 1000km

Stellar Atmospheres: Motivation 53 Non-radial pulsation modes

Stellar Atmospheres: Motivation 54 Time resolved spectroscopy

Stellar Atmospheres: Motivation 55 Time dependent line profiles Time Flux

Stellar Atmospheres: Motivation 56 Doppler tomography

Stellar Atmospheres: Motivation 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,m v ) of the observer into the HRD (L,T eff ) 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.

Stellar Atmospheres: Motivation 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