New CCD astrometric observations of the five major uranian satellites using Gaia DR1 in 2014–2016

Abstract

710 CCD frames, observed by 1–m telescope at Yunnan Observatory over 15 nights, have been reduced to derive new precise positions of the five Uranian major satellites (Ariel, Umbriel, Titania, Oberon and Miranda). In the pixel positional measurement of the faint satellites near Uranus, a halo removal procedure similar to that of Veiga et al. (Veiga and Vieira Martins, 1995) was carried out. After that we adopted a two-dimensional symmetric Gaussian model with as high as a third order polynomial to deliver the pixel positions of the concerned satellites. Lastly, the positions of satellites were measured with reference stars from Gaia DR1. The theoretical positions of Uranian satellites were retrieved from the Jet Propulsion Laboratory (JPL) Horizons System that includes the satellite ephemeris ura111, while the position of Uranus was from DE431. We also compared our observations with different satellite ephemerides from the Institut de Mcanique Cleste et de Calcul des phmrides (IMCCE). When Gaia DR1 is used for the reference star catalogue and meanwhile satellites ephemeris is obtained from JPL, our results show that the absolute values of the mean (O-C) (observed minus computed) residuals are not greater than 0.020 arcsec in both right ascension and declination for the five satellites. The positional precision is better than 0.030 arcsec for the four greatest Uranian satellites and 0.050 arcsec for Miranda in each direction.