Opacity of fluffy dust aggregates

Akimasa Kataoka, Satoshi Okuzumi, Hidekazu Tanaka, Hideko Nomura

研究成果: Article査読

91 被引用数 (Scopus)

抄録

Context. Dust grains coagulate to form dust aggregates in protoplanetary disks. Their porosity can be extremely high in the disks. Although disk emission may come from fluffy dust aggregates, the emission has been modeled with compact grains. Aims. We aim to reveal the mass opacity of fluffy aggregates from infrared to millimeter wavelengths with the filling factor ranging from 1 down to 10-4. Methods. We use Mie calculations with an effective medium theory. The monomers are assumed to be 0.1 μm sized grains, which is much shorter than the wavelengths that we focus on. Results. We find that the absorption mass opacity of fluffy aggregates is characterized by the product a × f, where a is the dust radius and f is the filling factor, except for the interference structure. The scattering mass opacity is also characterized by af at short wavelengths while it is higher in more fluffy aggregates at long wavelengths. We also derive the analytic formula of the mass opacity and find that it reproduces the Mie calculations. We also calculate the expected difference of the emission between compact and fluffy aggregates in protoplanetary disks with a simple dust growth and drift model. We find that compact grains and fluffy aggregates can be distinguished by the radial distribution of the opacity index β. The previous observation of the radial distribution of β is consistent with the fluffy case, but more observations are required to distinguish between fluffy or compact. In addition, we find that the scattered light would be another way to distinguish between compact grains and fluffy aggregates.

本文言語English
論文番号A42
ジャーナルAstronomy and Astrophysics
568
DOI
出版ステータスPublished - 2014 8月
外部発表はい

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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