The Photocenter Shift Phenomenon in Positional Observations of Active Asteroids (6478) Gault and (248370) 2005 QN173/433Р

Active asteroids are the Main-Belt asteroids that manifest physical signs of cometary activity, such as the presence of coma and tails and significant changes in brightness. This raises the question of whether these bodies require a more sophisticated approach to specifying the orbital parameters as compared to ordinary asteroids. In this work, we performed a series of improvements in the orbital parameters of active asteroids (6478) Gault and (248370) 2005 QN173/433P both with taking into account nongravitational accelerations (NGAs), which is common for comets, and without this procedure. For time intervals coinciding with the periods of activity of the considered asteroids, we have found statistically significant systematic deviations in the residuals (O–C) between the observed and calculated values in the positional observations of these bodies. Our results show that taking into account the nongravitational acceleration according to the Marsden model does not improve the representation of the observations. We also considered the possibility of the photocenter shift (PS) presence in the positional observations, i.e., the offset between the center-of-light and the center-of-mass. The obtained PS for asteroids (6478) and (248370) are directed away from the Sun with the values of 985 ± 54 and 1145 ± 119 km respectively, which is close to the sizes of the Hill spheres of the bodies. Taking into account the PS effect, one can eliminate the systematic deviations in the residuals for asteroid (248370) and significantly reduce them for asteroid (6478).