Astron. Astrophys. 323, 566-584 (1997)

A unified model of interstellar dust

Aigen Li and J. Mayo Greenberg

Laboratory Astrophysics, University of Leiden, Postbus 9504, 2300 RA Leiden, The Netherlands (agli@strw.LeidenUniv.nl; mayo@rulhl1.LeidenUniv.nl)

Received 12 October 1996 / Accepted 10 January 1997

Abstract

We have simultaneously modeled both the interstellar extinction and polarization (both linear and circular) on the basis of a trimodal dust model: large silicate core-organic refractory mantle dust particles; very small carbonaceous particles responsible for the hump extinction; and PAH's responsible for the FUV extinction. The core-mantle particles which are the exclusive contributor to the interstellar polarization and the dominant contributor to the visual and NIR extinction are modeled as finite cylinders with a Gaussian size distribution in terms of perfect spinning alignment. Results for models using infinite cylinders are presented for comparison. Our model results are in good agreement with such observational constraints as the average interstellar extinction curve, the polarization law, the ratio of visual polarization to extinction , the scattering properties (albedos), the excess NIR polarization over the extrapolation of the Serkowski law. The constraint imposed on other dust models (e.g., the silicate/graphite model, the composite dust model) leads to either a too low value (the silicate/graphite model) or instability of particle structure (the composite dust model). The cosmic abundance constraints, in particular the evidence for lower oxygen abundance in the interstellar medium than in the solar system and the possible interstellar ratios, are discussed extensively. Considering the uncertainties in the interstellar "cosmic" abundances, the ratio and the interstellar non-dust elemental abundances, although our model requires a bit more carbon than the reference abundance, it is within the limit of an acceptable range and is a significant improvement over other models. All the other major reference abundance (cosmic - non-dust) constraints on are well satisfied.

Key words: ISM: dust, extinction polarization scattering ISM: abundances ultraviolet: ISM infrared: ISM: continuum

Send offprint requests to: J.M. Greenberg

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Contents

• 1. Introduction
• 2. Dust composition
• 3. Optical constants
  • 3.1. Silicates
  • 3.2. Organic refractory
  • 3.3. Hump particles and FUV particles
• 4. Model calculation description
• 5. Interstellar polarization
  • 5.1. Model results for the infinite cylinder
  • 5.2. Model results for the finite cylinder
• 6. Interstellar extinction
• 7. The polarization to extinction ratio
• 8. Albedo
• 9. Cosmic abundance constraint
  • 9.1. Dust-gas correlation
  • 9.2. Cosmic abundance
  • 9.3. Cosmic abundance constraint
• 10. Summary
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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