Astron. Astrophys. 363, 1155-1165 (2000)

Statistical study of polarization of light scattered by rough grains

I. The method with preliminary results

K. Chamaillard and J.-P.J. Lafon

Observatoire de Meudon, DASGAL, 92195 Meudon, France

Received 18 November 1999 / Accepted 19 July 2000

Abstract

In order to quantify the effects of shape of grains on their optical properties, we use a new statistical approach to study the effects of roughness on the degree of linear polarization.

In this approach, we compute the degree of linear polarization of light scattered by a rough grain. The roughness is obtained by a random depletion of the surface of an homogeneous sphere. The analysis of the results is achieved through a specific statistical method: the probability density function of the linear polarization is estimated by a Gaussian kernel method. This method allows the characterization of effects specifically due to the roughness.

The grain is described by the Discrete Dipole Approximation (DDA) (Draine 1988). We present the preliminary results for a spherical grain of water ice with radius which is comparable to the incident wavelength where water ice is non-absorbing.

The effect of grains roughness on polarization can be distinguished from the effects of volume in several different ways. The shape of the density function of the polarization is found to be non-symmetrical to the mean value of and non-unimodal for several scattering angles. We compare the mean value of the linear polarization deduced from the probability density function to the value obtained from a mass equivalent sphere and from the core sphere. We present the effects of roughness for various scattering angles.

Key words: polarization scattering ISM: dust, extinction stars: circumstellar matter

Send offprint requests to: K. Chamaillard

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Contents

• 1. Introduction
• 2. Previous works and description of the new approach
  • 2.1. Review of the problem and previous works on roughness
  • 2.2. Description of the statistical approach
• 3. Numerical method
  • 3.1. Numerical modeling and accuracy of the model DDA
  • 3.2. Generation of the grain roughness
• 4. Results and discussion
• 5. Conclusions and perspective
• Appendices
  • A: The Gaussian kernel method
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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