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The discrete-dipole approximation and its application to interstellar graphite grains
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1988
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The discrete dipole approximation (DDA) is a flexible method for computing radiation scattering by particles of arbitrary shape, now extended to include radiative reaction and possible dielectric tensor anisotropy. The authors present formulas for extinction, absorption, scattering, and polarization cross sections, establish two validity criteria for the DDA, and apply it to compute these cross sections for both spherical and nonspherical graphite grains of three geometries. A conjugate‑gradient algorithm efficiently and robustly solves the scattering problem for absorptive and dielectric grain materials, and the results indicate that small graphite grains with aspect ratios near unity can reproduce the interstellar 2175 Å extinction feature. Published in The Astrophysical Journal (Oct 1988), DOI 10.1086/166795.
view Abstract Citations (996) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Discrete-Dipole Approximation and Its Application to Interstellar Graphite Grains Draine, B. T. Abstract The discrete dipole approximation (DDA), a flexible method for computing scattering of radiation by particles of arbitrary shape, is extended to incorporate the effects of radiative reaction and to allow for possible anisotropy of the dielectric tensor of the material. Formulas are given for the evaluation of extinction, absorption, scattering, and polarization cross sections. A simple numerical algorithm based on the method of conjugate gradients is found to provide an efficient and robust method for obtaining accurate solutions to the scattering problem. The method works well for absorptive, as well as dielectric, grain materials. Two validity criteria for the DDA are presented. The DDA is then used to compute extinction cross sections for spherical graphite grains and to calculate extinction cross sections for nonspherical graphite grains with three different geometries. It is concluded that the interstellar 2175 A extinction feature could be produced by small graphite grains which should have aspect ratios not far from unity. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/166795 Bibcode: 1988ApJ...333..848D Keywords: Computational Astrophysics; Cosmic Dust; Discrete Functions; Graphite; Interstellar Space; Absorption Cross Sections; Grain Size; Polarization (Waves); Radiative Transfer; Scattering Cross Sections; Astrophysics; INTERSTELLAR: GRAINS; POLARIZATION; RADIATIVE TRANSFER full text sources ADS |