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J. Piironen, K. Muinonen (Observatory, Univ. of Helsinki)
Circular and linear polarimetric observations of selected asteroids were carried out at the Nordic Optical Telescope in 1997/98. Analysis of the data shows the usual negative linear polarization branch seen for the regoliths. Circular polarization is expected to depend on the metallicity of the surface material and steepness of the asteroid's shape. Thus we observed some objects across wider time ranges to look for lightcurve--like behaviour. We noticed possible variation of polarization with rotational phase for 43 Ariadne, 22 Kalliope and 25 Phocaea. This work clearly shows the need of further efforts in this field of research with VLT--sized telescopes. The main emphasis could be on large--phase--angle observations of preferably M--type near--Earth objects. Also highly elongated objects would be ideal for circular polarimetric observations.