Annu. Rev. Astron. Astrophys. 1997. 35: 503-556
Copyright © 1997 by . All rights reserved

Reprinted with kind permission from , 4139 El Camino Way, Palo Alto, California, USA

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ABUNDANCE RATIOS AND GALACTIC CHEMICAL EVOLUTION

Andrew McWilliam


Carnegie Observatories, Room 33, 813 Santa Barbara Street, Pasadena, California 91101; e-mail: andy@marmite.ociw.edu


Abstract. The metallicity of stars in the Galaxy ranges from [Fe/H] = -4 to +0.5 dex, and the solar iron abundance is epsilon(Fe) = 7.51 ± 0.01 dex. The average values of [Fe/H] in the solar neighborhood, the halo, and Galactic bulge are -0.2, -1.6, and -0.2 dex respectively.

Detailed abundance analysis reveals that the Galactic disk, halo, and bulge exhibit unique abundance patterns of O, Mg, Si, Ca, and Ti and neutron-capture elements. These signatures show that environment plays an important role in chemical evolution and that supernovae come in many flavors with a range of element yields.

The 300-fold dispersion in heavy element abundances of the most metal-poor stars suggests incomplete mixing of ejecta from individual supernova, with vastly different yields, in clouds of ~ 106 Modot.

The composition of Orion association stars indicates that star-forming regions are significantly self-enriched on time scales of 80 million years. The rapid self-enrichment and inhomogeneous chemical evolution models are required to match observed abundance trends and the dispersion in the age-metallicity relation.


Key words: abundances, chemical composition, the Galaxy, nucleosynthesis, stars


Table of Contents

INTRODUCTION

THE SOLAR IRON ABUNDANCE

SUPER METAL-RICH STARS

OBSERVED METALLICITY DISTRIBUTION FUNCTION
The Disk
The Halo
The Bulge

AGE-METALLICITY RELATION

ABUNDANCE TRENDS WITH METALLICITY
Alpha Elements
Disk Alpha Elements
Bulge Alpha Elements
Halo Alpha Elements

SOME LIGHT ELEMENTS
Carbon
Aluminum and Sodium

HEAVY ELEMENTS
Disk and Bulge Heavy Elements
Halo Heavy Elements

IRON-PEAK ELEMENTS

FINAL THOUGHTS

REFERENCES

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