INTRODUCTION
BASIC PHYSICS OF PHOTOIONIZED NEBULAE
- Ionization and recombination
- Global ionization budget
The ionization structure
Heating and cooling
Line intensities
BASICS OF ABUNDANCE DETERMINATIONS IN IONIZED
NEBULAE
- Empirical methods
- Direct methods
Strong line or statistical methods
Model fitting
- Philosophy of model fitting
Photoionization codes
MAIN PROBLEMS AND UNCERTAINTIES IN ABUNDANCE
DETERMINATIONS
- Atomic data
- Ionization, recombination and charge
exchange
Transition probabilities, collision
strengths and effective recombination coefficients
Stellar atmospheres
Reddening correction
Aperture correction, nebular geometry and density
inhomogeneities
Spatial temperature variations
- Temperature gradients
Small scale temperature variations
The optical recombination lines mystery
The role of internal dust
- Evidence for the presence of dust in
the ionized regions
Heavy element depletion
The effect of dust on the ionization
structure
The effect of dust obscuration on the
emission line spectrum
The effects of grains on heating and
cooling of the gas
The specific case of the helium abundance
determination
OBSERVATIONAL RESULTS ON ABUNDANCES IN H II
REGIONS OF THE MILKY WAY
- The Orion nebula: a benchmark
Abundance patterns in the solar vicinity and the
solar abundance discrepancy
Abundance gradients in the Galaxy from H II
regions
The Galactic center
Nebulae around evolved massive stars
OBSERVATIONAL RESULTS ON ABUNDANCES IN PLANETARY
NEBULAE
- NGC 7027 and IC 418: two test cases
What do PN abundances tell us?
PNe as probes of the chemical evolution of
galaxies
- The universal Ne/H versus O/H
relation
Abundance gradients from PNe in the
Milky Way
PNe in the Galactic bulge
PNe in the Galactic halo
PNe probe the histories of nearby galaxies
PNe probe the nucleosynthesis in their progenitor
stars
- Global abundance ratios
Abundance inhomogeneities
REFERENCES
