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Participant 5 (P5)
==================

Dr. V.P. Tishkovets - Astronomical Observatory, Kharkov University, UA

Dr. N.N. Kiselev - Astronomical Observatory, Kharkov University, UA

P.V. Litvinov - 26 years old; Astronomical Observatory, Kharkov
University, UA

S.A. Beletsky - 28 years old; Astronomical Observatory, Kharkov
University, UA

The head of the team, Dr. Tishkovets, and Mr. Litvinov made many investigations
of light scattering by clusters of particles - analogues of interplanetary dust
grains. Dr. Kiselev is a high-level expert in polarimetry and world known
observer of comets, asteroids, and stars. Mr. Beletsky is one of the authors of
the IRIS - a special astronomical information system. The recent works of the
team members on the subject of the project are as follows:

Task 1 (Light scattering theory)

Asymptotic formulas for the extinction and absorption cross sections for
randomly oriented multiple-sphere clusters were obtained by Tishkovets &
Litvinov ("Coefficient of light extinction by randomly oriented clusters of
spherical particles in the double scattering approximation." Opt. Spectrosc.,
v. 81, 319, 1996) and Litvinov & Tishkovets ("Light absorption coefficients for
randomly oriented clusters of spherical particles in the double-scattering
approximation." Opt. Spectrosc., v. 86, 87, 1999).

A new mechanism of coherent effects in backscattering by closely packed
particles was discovered and discussed in detail by Tishkovets, Shkuratov, and
Litvinov ("Comparison of collective effects at scattering by randomly oriented
clusters of spherical particles." J. Quant. Spectrosc. Rad. Transfer, v. 61,
767, 1999). It was shown that in the case of randomly oriented clusters the
enhancement backscattering of light and negative linear polarization occurred
at nearly zero phase angles. Both phenomena are typical of interplanetary
and cometary dust.

Task 2 (Light scattering experiments)

Properties of the negative polarization of light scattered by different samples
at small phase angles were studied experimentally and a comparative analysis of
different theoretical models of this phenomenon was made by Shkuratov,
Muinonen, Tishkovets et al. ("A critical review of theoretical models for the
negative polarization of light scattered by atmosphereless Solar system bodies."
Earth, Moon & Planets, v. 6, 201, 1994).

Task 3 (Electronic database)

An universal information system IRIS was developed in the Astronomical
Observatory of the Kharkov University (all documentation on the system is freely
accessible via the Internet - http://members.xoom.com/cyteg). The system
includes the IRIS-integrator, WisA-subsystem and editor Head-Edit. The
IRIS-integrator creates, sorts, filters and makes processing of graphic data
files by making use of a special computer language Bastis. The WisA-subsystem
serves for visualization and analysis of the data. The editor Head-Edit allows
users to edit information connected with data and convert all files into FITS
and other formats. All components of the IRIS are supplied by user-friendly
Windows-like graphic interfaces with rich service functions.

The experience gained during the work on the IRIS system will be used in the
development of the Database of Optical Properties and in particular its
library of the optical properties (see above 3.1.4.1).

Task 4 (Polarized radiation transfer)

A model of collective effects in light polarization by systems of randomly
oriented clusters of spherical particles has been proposed. In this model the
interference of scattered waves by different scatterers is taken into account
(Tishkovets & Litvinov, "Electromagnetic scattering by a system of chaotically
oriented clusters of spherical particles." Radiophys. Electronics, v. 3, 57,
1998).

Task 5 (Astrophysical applications)

Observations of a number of dusty comets in a wide range of the phase angles and
wavelengths were fulfilled and processed by Kiselev and his co-workers
(Chernova, Jockers, and Kiselev "Imaging photometry and color of comet
Shoemaker-Levy 9." Icarus, v. 121, 38, 1996; Kolokolova, Jockers, Chernova, and
Kiselev "Properties of cometary dust from color and polarization." Icarus,
v. 126, 351, 1997; Kiselev & Velichko "Polarimetry and photometry of comet
C/1996 B2 Hyakutake." Icarus, v. 133, 286, 1998; Kiselev "Some problems of
cometary polarimetry: a review." Astron. Vestn., v. 33, 181, 1999).

The properties of cometary dust were studied using the inverse problem solution
by Kolokolova, Jockers, Chernova, and Kiselev ("Properties of cometary dust
from color and polarization." Icarus, v. 126, 351, 1997).

The oppositional effects in brightness and polarization observed for cometary
and interplanetary dust have been discussed by Tishkovets & Litvinov
("Opposition effects in scattering of light by regolith-like media." Astron.
Vestn., v. 33, 186, 1999). They found that the properties of the fields near
scatterers played an important role in originating the effects.

P5 team:

5.1. Shkuratov Yu.G., Muinonen K., ..., Tishkovets V.P. et al. (1994)
A critical review of theoretical models for the negative polarization of
light scattered by atmosphereless Solar system bodies.
Earth, Moon & Planets, v. 6, 201-246.

5.2. Tishkovets V.P., Litvinov P.V. (1996)
Coefficient of light extinction by randomly oriented clusters of spherical
particles in the double scattering approximation.
Optics & Spectroscopy, v. 81, 319-322.

5.3. Chernova G., Jockers K., Kiselev N. (1996)
Imaging photometry and color of comet Shoemaker-Levy 9.
Icarus, v. 121, 38-45.

5.4. Kolokolova L., Jockers K., Chernova G., Kiselev N. (1997)
Properties of cometary dust from color and polarization.
Icarus, v. 126, 351-361.

5.5. Tishkovets V.P., Litvinov P.V. (1998)
Electromagnetic scattering by a system of chaotically oriented clusters of
spherical particles.
Radiophysics & Electronics, v. 3, 57-61.

5.6. Kiselev N.N., Velichko F.P. (1998)
Polarimetry and photometry of comet C/1996 B2 Hyakutake.
Icarus, v. 133, 286-292.

5.7. Kiselev N.N. (1999)
Some problems of cometary polarimetry: a review.
Astronomicheskii Vestnik, v. 33, 181-185.

5.8. Tishkovets V.P., Litvinov P.V. (1999)
Opposition effects in scattering of light by regolith-like media.
Astronomicheskii Vestnik, v. 33, 186-192.

5.9. Litvinov P.V., Tishkovets V.P. (1999)
Light absorption coefficients for randomly oriented clusters of spherical
particles in the double-scattering approximation.
Optics & Spectroscopy, v. 86, 87-90.

5.10.Tishkovets V.P., Shkuratov Yu.G., Litvinov P.V. (1999)
Comparison of collective effects at scattering by randomly oriented
clusters of spherical particles.
Journal of Quantitative Spectroscopy & Radiative Transfer, v. 61, 767-773.