天体测量技术及应用研究组知识库

We have observed three near-Earth objects (NEOs), 2017VR12, Camillo andMidas, during 2018. The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights. Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory (JPL) Horizons System and Institut de Mecanique Celeste et de Calcul des Ephemerides (IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means (O - C) of right ascension and declination are -0.090''' and -0.623 '' respectively based on the published JPL ephemeris, but the corresponding means (O - C) are 3.122 '' and -0.636 '' based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors. (1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy. (2) The poor timing system may introduce systematic errors, especially in the high speed direction. (3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling method. For Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.