Download presentation

Presentation is loading. Please wait.

Published byTaylor Dobson Modified over 3 years ago

1
**Umov effect for single-scattering agglomerate particles**

E. Zubko,1,2 G. Videen,3 Yu. Shkuratov,2 K. Muinonen,1,4 and T. Yamamoto5 1 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 May 8, 2012

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

3
**log(Pmax) linearly depends on log(A)**

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

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

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

7
**Models for Cometary Dust Particles**

sparse agglomerate agglomerated debris pocked spheres ρ = 0.169 ρ = 0.236 ρ = 0.336

8
**Input Parameters for Simulation**

We study 21 (!) various refractive indices m: 1.2+0i i i i 1.4+0i i i i i 1.5+0i i i i i i i i i 1.7+0i i i Size 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)**

– i 2.2 0.036 i i i 0.063 i 3.4 0.079 i i 3.1 0.067 1.4+0i 2.9 0.066 i 2.6 0.048 i 2.4 0.046 i i 2.3 0.044 i i 1.0 0.021 1.7+0i 3.6 0.081 i i 1.8 0.034 1.5+0i 3.2 0.070 i i 0.054 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
**Application to innermost coma in 26P/Grigg-Skjellerup –**

2.1 0.224 i i 1.2 0.114 1.4+0i i i i i i i 1.7+0i 2.4 0.238 i i 1.5+0i 1.1 0.216 i i Inner coma 0.231

16
Summary 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.

Similar presentations

OK

Lunar Regolith in the Laboratory Spectropolarimetry on Apollo Moon Dust W E Martin, J H Hough Centre for Astrophysics Research Centre for Atmospheric.

Lunar Regolith in the Laboratory Spectropolarimetry on Apollo Moon Dust W E Martin, J H Hough Centre for Astrophysics Research Centre for Atmospheric.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on self awareness activities Ppt on morbid obesity and anaesthesia Ppt on bond length of hbr Ppt on online banking Ppt on distrust of science Ppt on regional trade agreements in asia Ppt on waxes biology Ppt on condition based maintenance dod Ppt on conservation of wildlife and natural vegetation in california Ppt on business life cycle