Polarimetry of main belt asteroids: impact of surface mineralogy
Authors: Belskaya Irina , Berdyugin Andrej , Krugly Yurij , Sergeyev Alexey , Shevchenko Vasilij , Slyusarev Ivan , Berdyugina Svetlana , Kagitani Masato , Sakanoi Takeshi 
Published: July 2024

Polarimetric observations provide valuable information on surface properties of asteroids that complements other remote techniques. Measurements of the dependence of the linear polarization degree of asteroids on phase angle and wavelength revealed many interesting observational features. It was shown that asteroids of the same composition type tend to cluster on the plot of polarimetric parameters characterizing negative polarization branch (e.g. [1,2]). This suggests that the relationship between polarization minimum and inversion angle may be primarily related to surface composition rather than to significant changes in surface texture from a dust free surface to very fine-grained regolith as was considered in the early work [3].This work is a continuation of our work aimed at characterizing the surface composition of &#160;X/M type asteroids using polarimetry as a complimentary technique to spectral and radar data [4]. We present new observations of 14 main-belt asteroids from the list of asteroids classified as M-type or X-complex asteroids with moderate surface albedo ranging from 0.1 to 0.35. Observations were carried out in 2022-2024 at the remotely controlled Tohoku 0.6 m telescope at Haleakala Observatory, Hawaii, simultaneously in BVR filters. The main aim of our observations was to reliable determine the depth of polarization minimum Pmin and the inversion angle. With our new observations and literature data, the polarimetric parameters were obtained for all M-type asteroids with diameters greater than 50 km. Moreover, thanks to the Calern Asteroid Polarimetric Survey [5] the number of other types main belt asteroids studied by means of polarimetry has increased considerably, reaching the majority of large main-belt asteroids (D>50 km). We analyzed all available polarimetric data and searched for possible correlations of polarimetric parameters characterizing the negative polarization branch with various parameters obtained from observations by other techniques in order to explore the potential of polarimetry to retrieve surface mineralogy. &#160;Acknowledgment. Ukrainian team is supported by the National Research Foundation of Ukraine (grant N 2020.02/0371 &#8220;Metallic asteroids: search for parent bodies of iron meteorites, sources of extraterrestrial resources&#8221;).References[1] Penttil&#228;, A., Lumme, K., Hadamcik, E., and Levasseur-Regourd, A.-C. 2005, Astron. Astrophys., 432, 1081[2] Belskaya, I. N., Fornasier, S., Tozzi, G. P., et al. 2017, Icarus, 284, 30[3] &#160;Dollfus, A., Wolff, M., Geake, J. E., Lupishko, D. F., and Dougherty, L. M. 1989. In Asteroids II (R. P. Binzel et al., eds.), pp. 594&#8211;616, Univ. of Arizona, Tucson[4] Belskaya, I.; Berdyugin, A.; Krugly, Yu et al. 2022. Astron. Astroph, 663, id.A146[5] Bendjoya, Ph., Cellino, A., Rivet, J.-P., Devog&#232;le, M., Bagnulo, S., Abe, L., Vernet, D., Gil-Hutton, R., Veneziani, A. 2022, Astron. Astroph., 665, id.A