Improved precise positions of Apophis in 2013: recalibration based on <i>Gaia</i> DR3 and differential colour refraction correction

ABSTRACT The near-Earth asteroid (99942) Apophis is recognized as potentially hazardous and will pass Earth at a close-approach distance in 2029. High-precision astrometry of Apophis is essential for refining its orbital parameters. In our previous study, we published 298 CCD observations of Apophis during the year 2013, with a precision of about 0.04 arcsec in either right ascension or declination. However, the differential colour refraction (DCR) effect was not addressed for observations when using the Johnson-B or no filters. Additionally, we now have the opportunity to utilize the high-accuracy Gaia DR3 catalogue. These considerations motivated us to reanalyse our previous data based on Gaia DR3 and DCR correction. Furthermore, we discuss the trailing problem evident in the Apophis images. We found that the modified moment centering method can effectively handle slightly trailed images. After re-reduction, the mean (O–C)s (observed minus computed) are more consistent over several nights, and the precision improves from 0.040 to 0.023 arcsec in right ascension and from 0.043 to 0.025 arcsec in declination, respectively. We believe that these improved precise positions of Apophis will be very useful for refining its orbital parameters.