Polarimetric Monitoring of Primitive Asteroids near Perihelion in Order to Detect Their Sublimation-Dust Activity

UBVR polarimetric observations of 12 main-belt mostly primitive asteroids located near perihelion heliocentric distances were carried out from December 2022 to April 2023 with Zeiss-2000 telescope at the Terskol Peak observatory. The purpose of the monitoring program was to search for changes in the polarimetric parameters of the asteroids caused by possible sublimation-dust activity, as a result of which the formation of rarefied dust exospheres of asteroids is possible. The objects of the program were asteroids: (1) Ceres, (53) Kalypso, (117) Lomia, (164) Eva, (214) Ashera, (324) Bamberga, (419) Aurelia, (505) Cava, (554) Peraga, (654) Zelinda, (704) Interamnia, (1021) Flammario. Polarimetric observations of asteroids (117) Lomia, (164) Eva and (505) Kava were made for the first time, the remaining asteroids were observed earlier. Only for two asteroids (1) Ceres and (704) Interamnia, according to spectrophotometric observations, temporal spectrophotometric variability was noted earlier. Analysis of temporal changes in the degree of polarization of asteroids and comparison of the results of observations with the data available in the literature showed that the stability of the observed degree of polarization is comparable with measurement errors of similar to(0.02-0.1)% for asteroids of different brightness. Thus, during the observation period, no noticeable polarization signs of temporary sublimation-dust activity of the observed asteroids were detected. Additionally, it is shown that the currently existing variants of the spectral taxonomy of asteroids, based on spectrophotometric data and albedo, demonstrate a significant scattering of the selected classes when compared with their polarimetric phase dependencies. The asteroid (554) Peraga has been confirmed to have a negative degree of polarization at angles less than the inversion angle. Measurements of the polarization of the asteroid (1) Ceres in a wide range of wavelengths did not confirm the previously suspected change in the angle of the polarization plane with the wavelength.