**Syllabus**

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AST 383C

Stellar Atmospheres

Fall 2016

TuTh 12:30 - 2:00 RLM 15.216B; Unique No. 47610

LEVEL:

**Hubeny & Mihalas, The Theory of Stellar Atmospheres 2015**

Böhm-Vitense, Introduction to Stellar Astrophysics: Volume 2

Gray, Observations and Analysis of Stellar Photospheres

Rybicki and Lightman, Radiative Processes in Astrophysics

SYLLABUS

- Summary of Observational Data: Motivations for studying stars. Spectral
and luminosity classification. Relation of theory and observation. An
approach to Flat stars:
*accretion disks*. - Elements of Radiative Transfer Theory: Definitions. Emission, absorption, and scattering. Equation of transfer, radiative equilibrium.
- Gray Atmospheres: Milne's equation. Two-stream and Eddington approximations. Emergent flux and limb darkening.
- Local Thermodynamic equilibrium (LTE): Elements of statistical mechanics. Perfect gases and the Saha equation. Conditions for LTE. Depression of the adiabatic gradient in a partial ionization zone.
- Non-LTE: Rate: Rate equations. Radiative and collisional rates; departure coefficients. Calculation of Einstein coefficients and collision cross-sections.
- Continuum Opacity: Opacity sources in high-, intermediate-, and low-temperature stellar atmospheres.
- LTE Continuum model Atmospheres: Basic equations. Numerical solution of transfer equation: Lambda-iteration; Kurucz's and Feautrier's methods. Temperature-correction procedures.
- Results and Comparison With Observations: Absolute energy distributions. The Balmer jump. Sample model atmosphere calculation. Flux distributions for sample model stars. Effect of absorption edges on atmospheric structure, line-blanketing, molecule formation.
- Line Spectra: Line absorption profiles. Natural broadening and the Lorentz profile. Doppler broadening and the Voigt profile. Collisional broadening. Stark broadening, Inglis Teller formula.
- Line Transfer Problem.: Line transfer equation: pure scattering lines and pure absorption lines. Center-to-limb variations. Schuster mechanisms. Curve of growth and abundance determinations. Model atmosphere line calculations. Line blanketing theory, LTE line formation.
- Experimental Astrophysics: Line broadening and continuum lowering. New empirically validated approaches.
- Convective Energy Transport: Partial ionization zones. Mixing Length Theory. Simple phenomenological models. But what about the kinetic energy of turbulence? Modern approaches through 3D simulations.

22 August 2015

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