The results of the NEA astrometric observations with the Pulkovo 40-cm telescope at the Assy-Turgen observatory

We present the results of astrometric observations of two near-Earth asteroids (2005 XY7 and 2007 UM12) performed in September-November 2023 with the 40-cm Pulkovo telescope in the Assy-Turgen observatory. Stellar and asteroid pixel coordinates were calculated by varying the photo center position, background, and flux values for the PSF (point spread function) based on the analysis of the stellar images. The stars within the 4-arcmin asteroid-centered ring were not involved in the astrometric calibration. These stars were used for the asteroid systematic correction calculation. As a result, the internal accuracy of asteroid positions was better than 0.1 arcsec. The estimation of the mean position and the apparent rate components were performed for each set of CCD frames. Finally, the typical accuracy of the coordinates reached values of 0.024 – 0.088 arcsec. In addition, the numerical integration of the asteroid motion was made by varying the components of the state vector and A2-parameter (Yarkovsky acceleration). The unexpected and statistically insignificant A2 value for the 2007 UM12 has been found. It can be explained by the low quality of the data related to the first approach of this asteroid to the Earth and/or the tidal effects that changed the rotational state of the asteroid. The value A2 = (8.1 ± 6.4) · 10−14 a.u. per day2 on the significance boundary has been calculated for 2005 XY7 asteroid. This value does not contradict well-known data for the same size asteroids.