Astrometric Observations of NEA 1998 HH49 Using the Daocheng 50 cm Telescope

This study details an astrometric observation campaign of the Near-Earth Asteroid 1998 HH49,conducted with the aim of refining our understanding of its physical characteristics.Utilizing the 50 cm telescope located at the Wumingshan Mountain in Daocheng,Sichuan,images were obtained over four nights,from 2023 October 19 to October 22.These observations were processed using Astrometrica software,facilitating the precise determination of the asteroid's position.The observational results were compared with the ephemerides from three distinct sources to verify accuracy:the Jet Propulsion Laboratory(JPL)Horizons System,the Institut de Mécanique Céleste et de Calcul deséphémérides(IMCCE)Miriade,and the Near-Earth Objects Dynamic Site(NEODyS-2).When compared with the JPL ephemeris,a mean observed-minus-calculated(O-C)result of 0.″07 in the R.A.direction and-0.″35 in the decl.direction was yielded.Furthermore,the comparison with the IMCCE ephemeris yielded mean O-C results of 0.″08 in the R.A.direction and-0.″06 in the decl.direction.The comparison with the NEODyS-2 ephemeris yielded the mean O-C results of 0.″06 in R.A.and-0.″49 in decl.direction.The study's findings demonstrate a general consistency between the observed data and the ephemeris predictions,with minor discrepancies observed across the data sets.Notably,both the JPL and NEODyS-2 ephemerides show that the residuals in the decl.direction exceed those in the R.A.direction.The disparities may result from atmospheric differential color refraction,ephemeris discrepancies,observational errors,and other factors.Additionally,it is worth noting that further investigation is required due to the potential influence of additional factors.Overall,the Daocheng 50 cm Telescope exhibits the ability to conduct high-precision positional measurements.

CCD astrometric observations of 2017 VR12, Camillo and Midas

We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, 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 M′ecanique C′eleste et de Calcul des ′Eph′em′erides(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.