Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011a%26a...528a..96k&link_type=abstract
Astronomy & Astrophysics, Volume 528, id.A96
Astronomy and Astrophysics
Astrophysics
5
Dust, Extinction, Methods: Miscellaneous
Scientific paper
Context. Observations of cold condensed clouds in the interstellar medium show an enhancement in the dust emissivity at long wavelengths. Model calculations with the discrete-dipole approximation (DDA) can explain this enhancement with the coagulation of dust particles into aggregates. Aims: We study the nature of grain-grain contacts and their effects on the aggregate optical properties. Methods: We use DDA and the T-matrix method (TMM) to calculate the absorption properties of aggregate dust grains and analyse where and why the enhancement in the emissivity occurs. Results: We find that the absorption coefficient changes with material composition and with the contact area between monomers. A larger contact area, with DDA, compared to a zero-point contact with TMM, results in an enhancement of the absorption coefficient for wavelengths where the considered material has a large value n (the real part of the refractive index). Conclusions: DDA seems to be the most realistic way of taking into account "real" inter-particle contact effects in aggregate particles.
Appendix is only available in electronic form at http://www.aanda.org
Guillet V.
Jones Allan
Köhler Manuel
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