stellar atmospheres: an overview - institute for … · stellar atmospheres: an overview m = 2x1033...
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Stellar atmospheres: an overview
M = 2x1033 g 50 Mo
R = 7x1010 cm 20 RoL = 4x1033 erg/s 106 Lo 104 (PN) 106 (HII) 1012 (QSO) Lo
∆R = 200 km ~ 3x10‐4 Ro 0.1 Ron = 1015 cm‐3 1014 cm‐3
T = 6000 K 40,000 K
∆R = 1000 km/1 Ro 100 Ro 105 Ro 0.1 (PN) 10 (HII) 1,000 (QSO) pcn = 1012/106 cm‐3 1011…108 cm‐3
T = 20,000/2x106 K 40,000…15,000 K
Core
Photosphere
Envelope Chromosphere/Corona
Spectral Analysis
Plasma phyics: diagnostics, line broadeningAtomic physics + quantum mechanics: light-matter interaction (micro)Thermodynamics: TE, LTE, non-LTEHydrodynamics: atmospheric structure, velocity fieldsRadiative transfer (macro)
Stellar properties: mass, radius, luminosity, temperature, chemical composition
Galactic structureStellar and galactic evolutionDistance scale
Spectral Analysis
Observed spectrum Synthetic spectrumcomparison
Theory of stellar atmospheres
•Geometry•Hydrodynamics•Thermodynamics•Radiative transfer•Atomic physics
ModelNumerical solution of theoretical
Equations
L, R, M, chemical composition
AWAP 05/19/05
complex atomic models
Non-Local Thermodynamic
Equilibrium (NLTE)
Kinetic equationsTransport TheoryThermodynamics
Quantum Mechanics
Photons11 TdV , 22 TdV ,
r
T
NLTE a non local problem!
Rate EquationsRate Equations
AWAP 05/19/05
NLTENLTE ModelsModels require atomic data atomic data forlines, collisions, ionization, recombination
Essential for occupation numbers, line blocking, line forceAccurate atomic models have been includedAccurate atomic models have been included
26 elements149 ionization stages5,000 levels ( + 100,000 )20,000 diel. rec. transitions4 106 b-b line transitions
Auger-ionization
recently improved models are based onrecently improved models are based on SuperstructureSuperstructureEisner et al., 1974, CPC 8,270
Rate EquationsRate Equations
Examples of models
HD 93129A (Milky Way)
O3 Iaf+
Taresch, Kudritzkiet al. 1997, A&A, 321, 531
consistent treatment of expanding atmospheres along withspectrum synthesis techniquesspectrum synthesis techniques allow the determination of
stellar parameters, wind parameters, andstellar parameters, wind parameters, and abundancesabundancesPauldrach, 2003, Reviews in Modern Astronomy, Vol. 16
AzV 232 (SMC)O7 Iaf+
Crowther et al. 2002, ApJ, 579, 774
non-LTE atmospheres with windsplus stellar evolution models
Synthetic spectra of galxies at high zas a function of Z, IMF, SFR
Population synthesis of highPopulation synthesis of high--z galaxiesz galaxies
Galaxy spectra
Stellar spectra
Stellar Population
Initial Mass Function
Star Formation History MetallicityStellar Evolution
Spectral diagnostics of high-z starburstsStarburst models - fully synthetic spectra based on model atmospheres
Rom
e 200
5
Rix, Pettini, Leitherer, Bresolin, Kudritzki, Steidel, 2004, ApJ 615, 98
Spectral diagnostics of high-z starburstsRo
me 2
005
cB58 @ z=2.7
fully synthetic spectravs. observationRix, Pettini, Leitherer,Bresolin, Kudritzki, Steidel2004, ApJ 615, 98
Starburst99 population synthesis models
+
UV stellar libraries at ~solar and ~0.25 solar (LMC,
SMC) abundance
NGC 5253
Leitherer et al. 2001, ApJ, 550, 724
OutlineIntroduction: Modern astronomy and the power of quantitative spectroscopy Basic assumptions for “classic” stellar atmospheres: geometry, hydrostatic equilibrium, conservation of momentum-mass-energy, LTE (Planck, Maxwell)Radiative transfer: definitions, opacity, emissivity, optical depth, exact and approximate solutions, moments of intensity, Lambda operator, diffusion (Eddington) approximation, limb darkening, grey atmosphere, solar modelsEnergy transport: Radiative equilibrium and convection, grey atmospheres,numerical solutions for model atmospheresAtomic radiation processes: Einstein coefficients, line broadening, continuous processes and scattering (Thomson, Rayleigh)Excitation and ionization (Boltzmann, Saha), partition functionExample: Stellar spectral typesNon-LTE: basic concept and examples2-level atom, formation of spectral lines, curves growthRecombination theory in stellar envelopes and gaseous nebulaeStellar winds: introduction to line transfer with velocity fields and radiation driven winds
ReadingsMihalas, D., “Stellar Atmospheres”, 2nd ed., Freeman & Co., San Francisco, 1978Gray, D.F., “The Observation and Analysis of Stellar Photospheres”, 2nd ed., Cambridge University Press, Cambridge, 1992Rutten, R.J., “Radiative Transfer in Stellar Atmospheres”, 7th ed., 2000 (http://www.astro.uu.nl/~rutten/tmr/)Rybicki, G.B. & Lightman, A., “Radiative Processes in Astrophysics”, New York, Wiley, 1979Osterbrock, D.E., “Astrophysics of Gaseous Nebulae and Active Galactic Nuclei”, University Science Books, Mill Valley, 1989our notes