To appear in "Carnegie Observatories Astrophysics Series, Vol. 4: Origin and Distribution of the Elements", ed. A. McWilliam and M. Rauch (Cambridge: Cambridge Univ. Press) (2004)
astro-ph/0312592

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Abstract. In the interstellar medium of the Milky Way, certain elements - e.g., Mg, Si, Al, Ca, Ti, Fe - reside predominantly in interstellar dust grains. These grains absorb, scatter, and emit electromagnetic radiation, heat the interstellar medium by photoelectric emission, play a role in the ionization balance of the gas, and catalyze the formation of molecules, particularly H₂. I review the state of our knowledge of the composition and sizes of interstellar grains, including what we can learn from spectral features, luminescence, scattering, infrared emission, and observed gas-phase depletions. The total grain volume in dust models which reproduce interstellar extinction is significantly greater than estimated from observed depletions.

Dust grains might reduce the gas-phase D/H ratio, providing an alternative mechanism to explain observed variations in the gas-phase D/H ratio in the local interstellar medium. Transport in dust grains could cause elemental abundances in newly-formed stars to differ from interstellar abundances.

Table of Contents

• INTRODUCTION
• PRESOLAR GRAINS IN METEORITES ARE NONREPRESENTATIVE
• INTERSTELLAR REDDENING
• SPECTROSCOPY OF DUST IN EXTINCTION AND EMISSION
• PAH Emission Features
• 2175Å Feature: Graphitic C
• 10 and 18 µm Silicate Features
• 3.4 µm C-H Stretch: Aliphatic Hydrocarbons
• Diffuse Interstellar Bands
• Extended Red Emission
• X-Ray Absorption Edges
• INFRARED EMISSION SPECTRUM OF INTERSTELLAR DUST
• DUST GRAIN SIZE DISTRIBUTION
• DUST ABUNDANCES VS. DEPLETION PATTERNS
• TIME SCALE FOR DEPLETION
• LOCAL VARIATIONS IN D/H: DOES DUST PLAY A ROLE?
• TRANSPORT OF ELEMENTS IN DUST GRAINS
• Anisotropic Starlight
• Star-Forming Regions
• ION RECOMBINATION ON DUST GRAINS
• SUMMARY
• REFERENCES