- Observations
- Planetary Nebulae, Seyfert Galaxies
- Ionization Equilibrium
- , Rate Equations, Photoionization, Collisional Ionization, Radiative Recombination
- Photoionization Equilibrium
- Photoionization
- Line Diagnostics
- Line Diagnostics, Collisional (De)Excitation, Line Diagnostics: Density, Line Diagnostics: Temperature, Line Diagnostics: Mass
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