Stellar atmospheres: an overview M = 2x10 33 g 50 M o R = 7x10 10 cm 20 R o L = 4x10 33 erg/s 10 6 L o 10 4 (PN) 10 6 (HII) 10 12 (QSO) L o ∆R = 200 km ~ 3x10 ‐4 R o 0.1 R o n = 10 15 cm ‐3 10 14 cm ‐3 T = 6000 K 40,000 K ∆R = 1000 km/1 R o 100 R o 10 5 R o 0.1 (PN) 10 (HII) 1,000 (QSO) pc n = 10 12 /10 6 cm ‐3 10 11 …10 8 cm ‐3 T = 20,000/2x10 6 K 40,000…15,000 K Core Photosphere Envelope Chromosphere/Corona
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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
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