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Umov effect for single-scattering agglomerate particles E. Zubko, 1,2 G. Videen, 3 Yu. Shkuratov, 2 K. Muinonen, 1,4 and T. Yamamoto 5 May 8, 2012 1 Department.

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Presentation on theme: "Umov effect for single-scattering agglomerate particles E. Zubko, 1,2 G. Videen, 3 Yu. Shkuratov, 2 K. Muinonen, 1,4 and T. Yamamoto 5 May 8, 2012 1 Department."— Presentation transcript:

1 Umov effect for single-scattering agglomerate particles E. Zubko, 1,2 G. Videen, 3 Yu. Shkuratov, 2 K. Muinonen, 1,4 and T. Yamamoto 5 May 8, Department of Physics, University of Helsinki, Finland 2 Institute of Astronomy, Kharkov National University, Ukraine 3 Army Research Laboratory AMSRL-CI-EM, USA 4 Finnish Geodetic Institute, Finland 5 Institute of Low Temperature Science, Hokkaido University, Japan

2 Polarimetry of Comets Circumstances of polarimetric observations Dependence of polarization in comets on phase angle

3 The brighter powder, the lower its linear polarization N. Umov ( ) N. Umov, Phys. Zeits. 6, (1905) In , the qualitative law was quantified: log( P max ) linearly depends on log( A ) Origin of the phenomenon – depolarization due to multiple scattering in regolith Umov Effect

4 Shkuratov & Opanasenko, Icarus 99, (1992) Umov Effect

5 Geometric albedo A for single particles: A =( S 11 (0) )/( k 2 G ) Here, S 11 (0) is the Mueller matrix element at back- scattering, k – wavenumber, and G – the geometric cross-section of the particle. Umov Effect for Single-Scattering Particles As was found in Zubko et al. (2011, Icarus, 212, 403– 415), the Umov effect holds also for single- scattering particles with size comparable to wavelength. Therefore, it can be applied to comets.

6 Basic idea: Gains: (1) arbitrary shape and internal structure (2) simplicity in preparation of sample particles Method: Discrete Dipole Approximation (DDA) Numerical Simulation of Light Scattering

7 sparse agglomerate agglomerated debris pocked spheres Models for Cometary Dust Particles ρ = ρ = ρ = 0.336

8 We study 21 (!) various refractive indices m : Input Parameters for Simulation i i i i i i i i i i i i i i i i i i i i i Size parameter x = 2 r/ ( r – radius of circumscribing sphere and – wavelength) is varied from 1 throughout 26 – 40 (depending on m ).

9 (1) Over particle shapes: For each pair of x and m, we consider minimum 500 particle shapes. (2) Over particle size: Size distribution is considered to be a power law r –a. The power index a is varied from 1 to 4. Note: this range is well consistent with in situ study of Comet 1P/Halley: 1.5 a 3.4 (Mazets et al., 1986) Averaging of light-scattering characteristics

10 Application to whole Comet C/1996 B2 (Hyakutake)

11

12 maAmaA i –– i i –– i –– i i i –– i i i i i –– i i –– i i i –– i i i –– i Whole comets 0.050

13 Application to innermost coma in 26P/Grigg-Skjellerup McBride et al., MNRAS 289, (1997)

14 Application to innermost coma in 26P/Grigg-Skjellerup

15 maAmaA i –– i –– i –– i –– i –– i i –– i i –– i –– i –– i –– i –– i –– i –– i i –– i –– i i –– i –– Inner coma Application to innermost coma in 26P/Grigg-Skjellerup

16 Using the Umov effect, one can estimate albedo of single-scattering dust particles. When this technique is applied to whole Comet C/1996 B2 (Hyakutake), it yields the geometric albedo in the range A =0.034–0.079, that is well consistent with the expected value of A =0.05. For the innermost coma studied by Giotto in 26P/Grigg-Skjellerup, the Umov effect reveals dramatically higher geometric albedo A =0.23. Summary


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