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)
For a PDF version of the article, click
For a PDF version of the article, click here.
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.
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