Stellar Atmospheres Motivation Stellar Atmospheres Literature Dimitri Mihalas

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/node 20. html 1

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 2

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

Stellar Atmospheres: Motivation Hertzsprung Russell Diagram 100 R 4 1026 W 1 R L~R 2 T 4 eff =700000 Km 5800 K 0. 01 R 4

Stellar Atmospheres: Motivation Massive stars 5

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

Stellar Atmospheres: Motivation SN movie 7

Stellar Atmospheres: Motivation SN Ia 8

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 9

Stellar Atmospheres: Motivation SN Ia Kosmologie 10

Stellar Atmospheres: Motivation Uranium-Thorium clock 11

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 12

Stellar Atmospheres: Motivation Sonne 13

Stellar Atmospheres: Motivation Fraunhofer lines 14

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

Stellar Atmospheres: Motivation Spectrum formation 16

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

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

Stellar Atmospheres: Motivation The spectral types on the main sequence O B A F G K M A 7 F 3 O 5 O 7 F 8 B 4 B 6 A 1 G 2 G 5 A 8 G 8 A 9 19

Stellar Atmospheres: Motivation Die Spektraltypen der Hauptreihe O B A A 7 F 3 F G K M F 6 F 8 G 1 F 8 G 6 G 2 G 9 G 5 K 4 K 5 G 8 20

Stellar Atmospheres: Motivation Classification scheme M 9 L 3 L 5 L 8 21

Stellar Atmospheres: Motivation Classification scheme T dwarfs 22

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 23

Stellar Atmospheres: Motivation Optical telescopes Calar Alto (Spain) 3. 5 m telescope 24

Stellar Atmospheres: Motivation Optical telescopes ESO/VLT 25

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

Stellar Atmospheres: Motivation UV/optical telescopes HST 27

Stellar Atmospheres: Motivation X-ray telescopes XMM 28

Stellar Atmospheres: Motivation Gamma-ray telescopes INTEGRAL 29

Stellar Atmospheres: Motivation Infrared observatories JWST ISO 30

Stellar Atmospheres: Motivation Sub-mm telescopes 31

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 33

Stellar Atmospheres: Motivation PN – NGC 6751 - HST 34

Stellar Atmospheres: Motivation Planetary nebula spectrum 35

Stellar Atmospheres: Motivation ISM spectrum 36

Stellar Atmospheres: Motivation Quasar + IGM spectrum 37

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 38

Stellar Atmospheres: Motivation Eta Carinae - HST 39

Stellar Atmospheres: Motivation Stellar wind spectrum 40

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

Stellar Atmospheres: Motivation Stellar winds – P Cyg profiles 42

Stellar Atmospheres: Motivation Accretion disks 43

Stellar Atmospheres: Motivation AM CVn disk spectrum models 44

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

Stellar Atmospheres: Motivation Planetary atmospheres 46

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

Stellar Atmospheres: Motivation Zeeman effect 48

Stellar Atmospheres: Motivation Magnetic fields L optical spectrum of a white dwarf (PG 1658+440) with field strength of about 5 MG circular polarization position of line components 49

Stellar Atmospheres: Motivation Magnetic fields L optical spectrum White dwarf Grw+70 8247 B=300 MG Circular polarization position of line components 50

Stellar Atmospheres: Motivation Velocity fields ~ 0. 01Å distance / 1000 km Distance / 1000 km Solar disk Wavelength / Å time / min 52

Stellar Atmospheres: Motivation Flux Time dependent line profiles 55

Stellar Atmospheres: Motivation Doppler tomography 56

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 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 theoretician and, hence, to drive 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 thermodynamic equilibrium of the stellar interior into the empty blackness of space occurs. It is a region of extreme nonequilibrium states. 57

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 58