Modeling Composite and Fluffy Grains: Angular Scattering Functions

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Session 14 -- Interstellar Dust and Extinction
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[14.06] Modeling Composite and Fluffy Grains: Angular Scattering Functions

M. J. Wolff, S. J. Gibson (Space Astronomy Lab, University of Wisconsin)

Hapke and his collaborators (1993) reveal the potential for using polarimetry (specifically the Stokes' Q parameter) as a diagnostic of dust grain/planetary regolith composition. They present laboratory data which demonstrates that Q depends only on Fresnel reflection from the particle surface over the phase angle range of 30 to 70 degrees. In this work, we attempt to reproduce these results in the Mie regime (the laboratory data were made in the regime of geometrical optics) through theoretical means. We present finite element computations of the angular scattering field (intensity and polarization) for porous and ``rough'' spheres. We extend the methodology outlined by Wolff et al. (1994) for use with the Discrete-Dipole Approximation (as implemented in B. Draine's DDSCAT). Our computations were made on the Cray C90 at Pittsburgh Supercomputing Center (PSC/NSF grant AST920002P).

Hapke, B. 1993, Theory of Reflectance and Emittance Spectroscopy, Cambridge U. Press, Chapter 14.

Wolff, M. J., Clayton, G. C., Martin, P. G., \& Schulte-Ladbeck, R. E. 1994, ApJ 423, in press.

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