Nikolai Kiselev

Photometric and Polarimetric Opposition Phenomena Exhibited by Solar System Bodies

Ground-based and spacecraft observations of atmosphere less solar system bodies (planets, satellites, planetary rings, and asteroids) and cometary and interplanetary dust particles have provided a wealth of new photometric and polarimetric data over a wide range of phase angles and wavelengths. This chapter reviews the progress in the study of the photometric and polarimetric phase effects observed near opposition. We also present the results of recent polarimetric observations of the Galilean satellites of Jupiter, Iapetus, and the asteroid 64 Angelina at very small phase angles. Analyses of the available data allow us to determine the parameters of the brightness and polarization opposition effects and investigate correlations between them. The results obtained may form the observational basis for detailed theoretical modeling and interpretation of the phase effects.

Polarimetry of Comets: Progress and Problems

In this chapter we review the history and progress in the study of scattered light from comets using polarimetry along with its significance for understanding the nature of comets. We present observed characteristics of linear and circular polarized light and their angular, spectral, spatial and temporal dependencies. We discuss the main problems of taxonomy of comets based on direct observations of the scattered light. It is shown that at least a part of gas-rich comets has a low polarization at large phase angles and blue color mainly due to a low spectral and spatial resolution of the measurements. The existence of the two taxonomical classes of comets is still an open question.

Comparative Study Of The Dust Polarimetric Properties In Split And Normal Comets

Our polarimetric database contains six comets, C/1975 V1 (West), 16P/Brooks 2,C/1988 A1 (Liller), D/1996 Q1 (Tabur), C/1999 S4 (LINEAR), and C/2001 A2(LINEAR), which can be related to the group of split comets. Comets West, S4(LINEAR) and A2 (LINEAR) were observed during splitting. We compare thepolarimetric measurements of the dust particles in these comets, sometimes togetherwith available photometric and colorimetric data, with those in normal comets. Weconclude that there is no significant evidence for differences of polarization betweentidally split comets (e.g., Brooks 2), dissipating comets (e.g., Tabur), non-tidally splitcomets (e.g., West) and normal comets. The total disintegration of Comet S4 (LINEAR), however, did produce significant changes in the observed properties of dust.

Polarimetric and Photometric Observations of Split Comet C/2001 A2 (LINEAR)

We present the results of polarimetric and photometric observations of split Comet C/2001 A2 (LINEAR), which were obtained at the 70-cm telescope of the Astronomical Observatory of Kharkiv National University between 30 June and 31 July 2001. The brightest fragment of the comet, nucleus B, was observed. Eight narrowband cometary filters in the continuum and in emission bands and a wideband red filter have been used. The comet was observed through apertures of 88, 33, and 19 arcsec. Polarization phase curves were obtained for the continuum and for the first time, for NH2(0, 7, 0) emission. The degree of polarization of the light scattered by the dust decreases with the increase of aperture size. An important temporal variation of the polarization with a rotation of the polarization plane was observed at two phase angles (26.5° and 36.2°). Molecular column densities and production rates of CN, C2, C3, and NH2 species are calculated in the framework of the Haser model. A comparative analysis of the temporal variations of the visual magnitudes, gas and dust production rates, dust color and polarization are presented.

Disk-Integrated Polarimetry of Mercury in 2000–2002

The orbital and rotation characteristics of Mercury lead to distinctly different solar irradiation intensities (photons, solar wind and cosmic rays) and radiative heating of the Mercury hemispheres with central meridians 0°, 180° on the one hand and 90°, 270° on the other. These differences allow us to hypothesize that the intensity of Mercury regolith maturation may depend noticeably on the planetocentric longitude, which would result in a corresponding variation of optical properties over the surface. The purpose of this study is to explore the variation of polarization over the Mercury surface. Polarimetric observations of Mercury were carried out during its three apparitions in 2000–2002 with a 70-cm reflector (Cassegrain configuration, f/16) and a single-channel photoelectric polarimeter. The polarization phase curve of Mercury obtained in the phase-angle interval of 39.1° → 135.5° shows measurements that approximate a curve with a maximal polarization difference ΔP = 1%, which is about one order of magnitude larger than the measurement accuracy. The dependence of differences between measured and approximated polarization ΔP on the planetocentric longitude of the center of the illuminated part of the visible disk revealed polarization variations with amplitude of approximately 1.5% over the range of observed planetocentric longitudes 265° → 330°. In order to obtain such variations in the whole interval of longitudes and to clarify their nature, the authors intend to carry out new observations of Mercury during its nearest apparitions.