CCD astrometric observations of Phoebe in 2003–2004

¹ National Time Service Center, Chinese Academy of Sciences, PO Box 18, Lintong, 710600 Shaanxi, PR China e-mail: rcqiao@ntsc.ac.cn
² United Laboratory for Optical Astrometry, Chinese Academy of Sciences, PR China
³ Shanghai Astronomical Observatory (SHAO), Chinese Academy of Sciences, 200030 Shanghai, PR China
⁴ Observatoire Aquitain des Sciences de l'Univers, UMR 5804 Laboratoire d'Astrodynamique, d'Astrophysique et d'Aéronomie de Bordeaux (L3AB), 2 rue de l'Observatoire, 33270 Floirac, France

Received: 20 December 2005
Accepted: 2 March 2006

Abstract

In 2003–2004, we obtained 115 new observations of Phoebe, the 9th Saturnian faint satellite (visual magnitude of about 16.5). We used a large CCD detector ( pixels) mounted on the 1.56 m astrometric reflector at the Sheshan Station, near Shanghai. In our reduction, an up-to-date catalogue of stars, UCAC2 (Zacharias et al. 2004), was chosen to ensure a proper astrometric calibration. A comparison of our observations to three recently available, high quality ephemerides, including the JPL SAT185 by Jacobson (2004b), has shown that most of our observed positions of Phoebe present an accuracy of some tens of mas, which appears to be a very high level for such a faint satellite.