Precise CCD positions of Phoebe in 2011–2014

Abstract

346 new CCD observations during the years 2011–2014 have been reduced to derive the precise positions of Phoebe, the ninth satellite of Saturn. The observations were made by the 2.4 m telescope at Yunnan Observatory over nine nights. Due to the use of a focal-reducer on the telescope, its significant geometric distortion is solved for and removed for each CCD field of view. The positions of Phoebe are measured with respect to the stars in UCAC2 catalogue. The theoretical position of Phoebe was retrieved from the Institute de Méchanique Céleste et de Calcul des Éphémérides ephemeris which includes the latest theory PH12 by Desmars et al., while the position of Saturn was obtained from the Jet Propulsion Laboratory ephemeris DE431. Our results show that the mean O−Cs (observed minus computed) are −0.02 and −0.07 arcsec in right ascension and declination, respectively. The dispersions of our observations are estimated at about 0.04 arcsec in each direction.