Preliminarily Astrometric Observations of NEO Apophis

The Near-Earth Asteroid Apophis is a potentially hazardous asteroid (PHA), thus it is crucial to develop high precision astrometry that can provide basic data for the accurate calculation of its orbit.The original CCD frames were taken by the YFOSC (the Yunnan Faint Object Spectrograph and Camera) attached to the 2.4m telescope at Yunnan Observatories during February 4-7, 2013.After we used the astrometry image reduction software "Astrometrica" to process the CCD frames, 76 observational positions of Apophis were obtained.When compared with JPL and IMCCE ephemerides, the absolute mean difference between our results and that of JPL is less than 0.1 arcsec in both right ascension and declination.This is consistent with what is expected.