An Astrometric Experiments on the 2.4m Telescope of the Yunnan Observatory

Geometric distortions (GDs) are important in high-precision astrometry. In this paper, we report some experiments to analyze the effect of GD on the positional measurement of the Phoebe (the ninth satellite of the Saturn). The approach recently proposed by us in Reference1 has been used to process our observed data to correct for the GDs. In total, 212 frames of CCD images were taken by the YFOSC (Yunnan Faint Object Spectrograph and Camera) attached to the 2.4m telescope of the Yunnan Observatory during February 18-19, 2012. Specifically, 96 of these frames are for the open cluster NGC 2324 and the other 116 are for the Phoebe. Our data reduction shows that the precision of the positional measurement of the Phoebe is significantly improved with GDs corrected. The mean GD residuals (observed minus computed) are 0.23 arcsec and -0.17 arcsec in right ascension and declination, respectively, with the standard deviation in each direction about 0.03 arcsec.