Presentation on theme: "Umov effect for single-scattering agglomerate particles"— Presentation transcript:
1 Umov effect for single-scattering agglomerate particles E. Zubko,1,2 G. Videen,3 Yu. Shkuratov,2K. Muinonen,1,4 and T. Yamamoto51 Department of Physics, University of Helsinki, Finland2 Institute of Astronomy, Kharkov National University, Ukraine3 Army Research Laboratory AMSRL-CI-EM, USA4 Finnish Geodetic Institute, Finland5 Institute of Low Temperature Science, Hokkaido University, JapanMay 8, 2012
2 Polarimetry of CometsDependence of polarization in comets on phase angleCircumstances of polarimetric observations
3 log(Pmax) linearly depends on log(A) Umov EffectThe brighter powder, the lower its linear polarizationN. Umov, Phys. Zeits. 6, (1905)Origin of the phenomenon – depolarization due to multiple scattering in regolithN. Umov ( )In , the qualitative law was quantified:log(Pmax) linearly depends on log(A)
5 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.Geometric albedo A for single particles:A=(S11(0))/(k2G)Here, S11(0) is the Mueller matrix element at back- scattering, k – wavenumber, and G – the geometric cross-section of the particle.
6 Numerical Simulation of Light Scattering Method: Discrete Dipole Approximation (DDA)Basic idea:Gains: (1) arbitrary shape and internal structure (2) simplicity in preparation of sample particles
8 Input Parameters for Simulation We study 21 (!) various refractive indices m:1.2+0i i i i1.4+0i i i i i1.5+0i i i ii i i i i1.7+0i i iSize parameter x=2r/ (r – radius of circumscribing sphere and – wavelength) is varied from 1 throughout 26 – 40 (depending on m).
9 Averaging of light-scattering characteristics (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: 1.5a3.4 (Mazets et al., 1986)
10 Application to whole Comet C/1996 B2 (Hyakutake)
11 Application to whole Comet C/1996 B2 (Hyakutake)
12 Application to whole Comet C/1996 B2 (Hyakutake) –i2.20.036iii0.063i3.40.079ii3.10.0671.4+0i2.90.066i2.60.048i2.40.046ii2.30.044ii1.00.0211.7+0i3.60.081ii1.80.0341.5+0i3.20.070ii0.054Whole comets0.050
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 Application to innermost coma in 26P/Grigg-Skjellerup – 2.10.224ii1.20.1141.4+0iiiiiii1.7+0i2.40.238ii1.5+0i1.10.216iiInner coma0.231
16 SummaryUsing 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.