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Polarimetry of main belt asteroids: Wavelength dependence |
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| Authors: | Irina N Belskaya Anny-Chantal Levasseur-Regourd Yuriy S Efimov Edith Hadamcik |
| Institution: | a Astronomical Institute of Kharkiv National University, Sumska str. 35, Kharkiv 61022, Ukraine b UPMC Univ. Paris 06, UMR 7620, Aéronomie CNRS-IPSL, BP 3, 91371 Verrières, France c INAF - Osservatorio Astronomico di Torino, Via Osservatorio, 20, 10025 Pino Torinese, Italy d SRI Crimean Astrophysical Observatory, Nauchny, Crimea 98409, Ukraine e Lab. Fizeau, Université de Nice Sophia Antipolis, Observatoire de la Côte d'Azur, CNRS 06108, Nice cedex 2, France |
| Abstract: | New UBVRI polarimetric observations of ten asteroids, including space mission targets 1 Ceres and 21 Lutetia, are presented. These observations were obtained with the 1.25-m telescope of the Crimean Astrophysical Observatory and have been used to study the wavelength dependence of polarization for a sample of asteroids belonging to the M and low albedo classes. A more general analysis including also a larger data set of UBVRI polarimetric observations available in the literature for more than 50 main belt asteroids belonging to different taxonomic classes shows that the variation of the polarization degree Pr as a function of wavelength is generally well described by a linear trend. It typically does not exceed 0.2% in the studied spectral range 0.37-0.83 microns and tends to increase for increasing phase angle. Asteroids belonging to the S and M classes are found to exhibit a deeper negative branch and smaller positive polarization for increasing wavelength (negative sign of the slope of ΔPr/Δλ). Since the objects belonging to these classes are known to exhibit reddish reflectance spectra, the observed wavelength behavior of negative polarization contradicts the well-known inverse correlation of Pmin and albedo. Low albedo asteroids show larger dispersion of spectral slopes, but the overall trend is characterized by a shallower negative branch and a larger positive polarization for increasing wavelength (positive sign of the slope of ΔPr/Δλ). A few exceptions from this general trend are discussed. The observed variety in the wavelength dependence of asteroid polarization seems to be mainly attributed to surface composition. |
| Keywords: | Asteroids surfaces Polarimetry |
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