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

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ABUNDANCE DETERMINATIONS IN H II REGIONS AND PLANETARY NEBULAE

Grazyna Stasinska


Observatoire de Paris-Meudon, 5, place Jules Janssen, 92195 Meudon cedex, France


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

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