Lectures to be published in the proceedings of the XIII Canary Islands Winter School of Astrophysics
astro-ph/0207500

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Abstract. The methods of abundance determinations in H II regions and planetary nebulae are described, with emphasis on the underlying assumptions and inherent problems. Recent results on abundances in Galactic H II regions and in Galactic and extragalactic Planetary Nebulae are reviewed.

Table of Contents

• 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