AST 450 Stellar Atmospheres

Credit Hours: 4
Prerequisite: PHY 407, PHY 408 and PHY 418, in the past or concurrently

Spectra of main sequence stars. Radiative transfer. The gray atmosphere. Opacities and non-gray model atmospheres. Theory of line formation and broadening: curve of growth analyses of stellar spectra.

syllabus

1. Background. What is a stellar atmosphere? Black body. Absolute magnitudes and luminosities of stars. Introduction of the basic quantities: specific intensity, K integral and radiation pressure, absorption coefficient and optical depth, emission coefficient and the source function, pure isotropic scattering, pure absorption, Einstein coefficients.
2. Radiative transfer. Kinetic equations. The equation of radiative transfer. Milne's equation. Eddington approximation. Solutions of equation of radiative transfer. Limb-darkening, emergent flux. The relativistic equation of radiative transfer.
3. Local thermodynamic equilibrium (LTE). Non-LTE effects. The Boltzmann excitation equation. The Saha ionization equation. Charge and particle conservation. The ionization equilibrium. The excitation equilibrium. Detailed conditions for LTE.
4. Opacity. The mechanisms of continuous absorption. The absorption in lines. Tables of opacities.
5. Theoretical models and observations. Continuum model atmosphere. Balmer jump. Late-type and early-type model atmospheres. Convection.
6. Atomic and molecular spectroscopy. Atomic energy levels. Fine structure. Spectral series of the Hydrogen Atom. Hydrogenlike ions. Stark effect and Zeeman effect. Diatomic molecules: vibrational and rotational levels, multiplets.
7. Line transfer problem and mechanisms of line broadening. Pure scattering lines. Pure absorption lines. Natural broadening, Doppler broadening and Voight profile. Collision broadening. Stark broadening. Center-to-limb variations. Curve of growth. Model atmosphere line calculations.
8. Moving atmospheres. Stellar winds in hot luminous stars. Flows with spherical symmetry. Free expansion of a supernova remnant. The Eddington limit.

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