Volume 568, August 2014
|Number of page(s)||15|
|Section||Planets and planetary systems|
|Published online||11 August 2014|
Opacity of fluffy dust aggregates
1 Department of Astronomical Science, School of Physical Sciences, Graduate University for Advanced Studies (Sokendai)Mitaka, 181-8588 Tokyo Japan
2 National Astronomical Observatory of Japan, Mitaka, 181-8588 Tokyo, Japan
3 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, 152-8551 Tokyo, Japan
4 Institute of Low Temperature Science, Hokkaido University, Kita, 060-0819 Sapporo, Japan
Received: 5 December 2013
Accepted: 12 June 2014
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.
Key words: planets and satellites: formation / protoplanetary disks
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.