SIMBAD references

298 CCD observations during the year 2013 have been reduced to derive the precise positions of near-Earth asteroid (99942) Apophis. The observations were made by the 2.4-m telescope at Yunnan Observatory over 10 nights. The position and proper motion errors of the reference stars in the USNO CCD Astrograph Catalogue 4 (UCAC4) star catalogue are corrected by using the newest correction table provided by Farnocchia et al. The geometric distortion of the field of view is also derived from the unbiased star positions in UCAC4 and removed. The theoretical position of Apophis was retrieved from the Jet Propulsion Laboratory Horizons system. Our results show that the mean O-Cs (observed minus computed) are 0.016 and 0.034 arcsec in right ascension and declination, respectively. The dispersions of our observations are estimated at 0.041 and 0.045 arcsec in right ascension and declination, respectively.