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The Umov effect for single irregularly shaped particles with sizes comparable with wavelength

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Title: The Umov effect for single irregularly shaped particles with sizes comparable with wavelength
Authors: Zubko, Evgenij Browse this author
Videen, Gorden Browse this author
Shkuratov, Yuriy Browse this author
Muinonen, Karri Browse this author
Yamamoto, Tetsuo Browse this author
Keywords: Polarimetry
Comets, dust
Issue Date: Mar-2011
Publisher: Elsevier
Journal Title: Icarus
Volume: 212
Issue: 1
Start Page: 403
End Page: 415
Publisher DOI: 10.1016/j.icarus.2010.12.012
Abstract: The Umov effect manifests itself as an inverse correlation between the linear polarization maximum of an object's scattered light P_[max] and its geometric albedo A. This effect is observed for the Moon, Mercury and Mars, and there are data suggesting this effect is valid for asteroids. The Umov effect is due to the contribution of interparticle multiple scattering that increases albedo and decreases polarization. We here study if the Umov effect can be extended to the case of single irregularly shaped particles with sizes comparable with the wavelength. This, in particular, is important for cometary dust polarimetry. We show the Umov effect being valid for weakly absorbing irregular particles (Im(m) ≤ 0.02) almost through the entire range of size parameters x considered. Highly absorbing particles (Im(m) > 0.02) follow the Umov effect only if x exceeds 14. In the case of weakly absorbing particles, the inverse correlation is essentially non-linear, which is caused by the contribution of particles with small x. However, averaging over many different types of irregularly shaped particles could make it significantly more linear. The size averaging does not change qualitatively the diagram log(P_[max])-log(A) for weakly absorbing particles. For single irregular particles whose sizes are comparable with wavelength, there is no reliable correlation between the slope of the polarization curve h near the inversion phase angle and geometric albedo A. Using the extended Umov law, we estimate the geometric albedo of dust particles forming cometary circumnuclear haloes A = 0.1 - 0.2, which is a few times larger than the average geometric albedo over the entire comae. Note that, using the obtained values for A of cometary particles, one can derive their number density in circumnuclear haloes from photometric observations.
Type: article (author version)
URI: http://hdl.handle.net/2115/45038
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 山本 哲生

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