APERTURE POLARIMETRY AND PHOTOMETRY OF COMET HALE–BOPP


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Abstract

We present results of polarimetric and photometric observations of bright comet C/1995 O1 (Hale–Bopp)) obtained at the 0.7 m telescope of Kharkov University Observatory from June 18, 1996 to April 24, 1997. The IHW and HB comet filters were used. The C2and C3production rates for Hale–Bopp are more than one order of magnitude larger and the dust production rates are more than two orders of magnitude larger than the Halley ones at comparable distances. Hence, Hale–Bopp was one of the most dusty comets. The average UC-BC and BC-RC colours of the dust were -0.02 and 0.13 mag, respectively. The polarization of comet Hale–Bopp at small phase angles of 4.8–13.0° was in good agreement with the date for comet P1/Halley at the same phase angles in spite of the fact that the heliocentric distances of comments differed nearly twice. However, at intermediate phase angles of 34–49° the polarization of comet Hale–Bopp was significantly larger than the polarization of the other dusty comets. It is the first case of such a large difference found in the continuum polarization of comets. The wavelength dependence of polarization for Hale–Bopp was steeper than for other dusty comets. The observed degree of polarization for the anti-sunward side of the coma was permanently higher than that for the sunward shell side. The polarization phase dependence of Hale–Bopp is discussed and compared with the polarization curves for other dusty comets. The peculiar polarimetric properties of comet Hale–Bopp are most likely caused by an over-abundance of small or/and absorbing dust particles in the coma.

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