Light scattering of irregularly shaped dust grains applied to debris disks
Abstract
Several hundred nearby main sequence stars host debris disks, a type of circumstellar disk that contains μm- to mm-sized dust [1,2] generated by collisions and disruptions of protoplanets and/or planetesimals. We seek to determine the composition of the material within these extrasolar systems in order to better understand the planet formation process. As debris disks are typically too cold to produce key identifying silicate spectral features near 10 μm in TIR emission, understanding scattering properties in the VNIR is important for making compositional determinations. Many previous works have relied on Mie theory to calculate the scattering properties of particulates in a variety of astrophysical and planetary settings, including circumstellar disks [e.g. 3,4]. However, not all dust shapes are well-approximated by a sphere. Circumstellar dust grains are expected to take on complex, porous structures similar to dust from a wide variety of sources within our own solar system. For example, IDPs have a wide variety of shapes [5] and comet grains were shown by the Stardust mission to have diverse shapes and densities [6]. Irregularly-shaped particles produce a better match to the interstellar silicate extinction spectrum [7] and can be used to model photo-polarimetric data of comets [8,9]. We use the Zubko et al. implementation of the DDA method [10] to calculate the light-scattering properties of irregularly shaped agglomerated dust grains. In the DDA code, targets are generated by placing electric dipoles within a 3D lattice of points. Each dipole has a specified index of refraction m. The number of and spacing between the dipoles are constrained by the condition |m|kd < 1.0 [9,11], where d is the lattice spacing and k is the wavenumber. We compare modeled disk spectra of AU Mic using spherical grains with those modeled using agglomerated dust grains as well as with telescopic data. [1]Wyatt 2008 [2]Hughes, Duchene & Matthews 2018 [3]Kruegel and Siebenmorgen 1994 [4]Wolf and Voshchinnikov 2004 [5]Brownlee 1985 [6]Hörz et al. 2006 [7]Min et al. 2006 [8]Mukai & Mukai 1990 [9]Zubko et al. 2015 [10]Zubko et al. 2010 [11]Draine & Flatau 1994
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5011312A