AST 551 Diffuse Matter in Space

Credit Hours: 4
Prerequisite: permission of instructor

Physical state of gas and dust. Heating and cooling mechanisms. Grain and molecular formation. Gas dynamics, ionization fronts, supernova explosions.

syllabus

1. Overview. Mass; spatial distribution; coupling with stars; energy densities; abundances; dust; phases.
2. Basick. Kinetic equilibrium; thermalization; Coulomb collisions; stopping times; ion-neutral collisions; neutral-neutral collisions; thermodynamic equilibrium; Saha equation; detailed balance; departure coefficient; equation of radiative transfer; Einstein A and B coefficients; absorption; stimulated emission; absorption coefficient; equivalent width and curve of growth.
3. Radio observations. 21 cm line; spin temperature; column density; circular polarization by Zeeman splitting; free-free emission and adsorption; continuum spectrum of HII regions; Faraday rotation; dispersion and scintillation.
4. Lines. Collisional excitation; collision strength; two-level systems with and without radiation; examples; temperature and density diagnostics; excitation by recombination; free-bound continuum; two-photon continuum; optical pumping; photon pumping of molecular hydrogen; electronic, vibrational and rotational energy levels in molecular hydrogen.
5. HII regions. HI lines; ionization of hydrogen; HII regions; Strömgren sphere; recombination; Milne relationship; ionization fraction in HII regions; transition to neutral gas; heating and UV hardening; effect of dust; ionization of helium; temperature.
6. Heating and cooling.
7. Heating by photoionization; photoelectric heating; cooling processes: recombination, free-free collisional excitation; ionization potentials; forbidden lines; cosmic-ray ionization; photionization of metals; photo-electric ejection from grains; [C II] and [O I] lines; thermal stability and the two-phase model of the ISM; cooling function at high temperatures; cooling time; coronal gas.
8. Molecular clouds. Rotational states of diatomic molecules; optical depth; chemistry; formation of molecules; formation of molecular hydrogen; heating and cooling; photodissociation regions; grains.
9. Fluid dynamics. Fluid equations; MHD; flux-freezing; magnetic stresses; MHD waves; shock waves; jump conditions isothermal shocks; MHD jump conditions; J-, C- and C*- shocks; Parker instability, instability in C-type shocks.
10. Star formation. Critical mass-flux ratio; magnetic flux problem; outflows; centrifugal acceleration; disk winds: "X-cellerator" model.
11. Supernova remnants. Sedov-Taylor solution; effect of clouds, snowplow models.

Go to Astronomy Course Listing