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Composition and radiative properties of grains in molecular clouds and accretion disksWe define a model of the compositon and abundances of grains and gases in molecular cloud cores and accretion disks around young stars by employing a wide range of astronomical data and theory, the composition of primitive bodies in the solar system, and solar elemental abundances. In the coldest portions of these objects, we propose that the major grain species include olivine (Fe, Mg, 2SiO4), orthopyroxene (Fe, Mg, SiO3), volatile and refractory organics, water ice, troilite (FeS), and metallic iron. This compositional model differs from almost all previous models of the interstellar medium (ISM) by having organics as the major condensed C species, rather than graphite; by including troilite as a major grain species; and by specifying the mineralogical composition of the condensed silicates. Using a combination of laboratory measurements of optical constants and asymptotic theory, we derive values of the real and imaginary indices of refraction of these grain species over a wavelength range that runs from the vacuum ultraviolet (UV) to the radio domain. The above information on grain properties is used to estimate the Rosseland mean opacity of the grains and their monochromatic opacity.
Document ID
19950035523
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Pollack, James B.
(NASA Ames Research Center Moffet Field, CA, United States)
Hollenbach, David
(NASA Ames Research Center Moffet Field, CA, United States)
Beckwith, Steven
(Max-Planck-Institut fuer Astronomie Heidelberg, Germany)
Simonelli, Damon P.
(Cornell Univ. Ithaca, NY, United States)
Roush, Ted
(NASA Ames Research Center Moffet Field, CA, United States)
Fong, Wesley
(Synernet, Fremont, CA United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 421
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A67122
Distribution Limits
Public
Copyright
Other

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