CCD astrometric observations of Phoebe in 2005-2008

Abstract

Astrometric observations of Phoebe, the faint ninth satellite of Saturn, with a visual magnitude of 16.5, were performed during four successive oppositions in 2005, 2006, 2007 and 2008. A total of 1173 new observed positions of Phoebe, representing more than 50 per cent of the observational data now available, were obtained during 30 nights of observation involving six missions and three telescopes. A comparison of our observed positions with the JPL Phoebe ephemeris shows the high quality of our observations, which have an accuracy of about 100 mas. Moreover, our observations appear to be consistent with this ephemeris within only about 50 mas.

Updated Phoebe’s orbit

“…This is a quite good result for such a small satellite orbiting rather far from Saturn, and necessarily with reference to absolute positions, when inner satellites with reference to relative intersatellite positions can be expected to be more accurate, as they are less affected by possible systematic errors of star catalogues. However, the improvement in star catalogues, such as UCAC2 used by some recent authors like Qiao et al (2006, 2011), has limited the effect of these possible systematic errors in the recent past. The use of this latest accurate catalogue has also contributed to present here a more reliable updated orbit of Phoebe.…”

“…Table 7 shows that the two recent observational sets made by Qiao et al (2006) and Qiao et al (2011) at the Sheshan Station are the most accurate. These two sets, respectively, contain 101 observations made in 2003 and 1173 observations made in the period 2005–08.…”

“…Moreover, we have collected 1388 new observations of Phoebe made after 2007 in nine different observatories (see Table 1). Among these new observations, we especially mention the 1173 CCD observations made over the period 2005–08 by Qiao et al (2011) at the Sheshan Station, as these form the largest observational set, and we will also show later in this work that it is also the most accurate set we have used here. All the new sources of observations that we have used for determining the new orbit of Phoebe are listed in Table 1.…”

“…For providing a quantitative comparison of the updated Phoebe orbit with the earlier orbits by Shen et al (2005) and Emelyanov (2007), and with the JPL ephemeris, we have compared a brand new set of 22 CCD observations of Phoebe, made in 2010 January 17 by Qiao et al (2011), with these four different orbits. We have chosen these new observations because they had not been previously used by any author, including us, to update the orbit of Phoebe.…”

The GEO satellites and space debris optical angle measuring system

“…For the above equations, the constant term (c, f ) are on behalf of the optical center of the celestial coordinates (A, D) , and the linear term represents the space scale along the X and Y directions [6].…”