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1 Introduction

Phoebe is the most distant known satellite of Saturn. Its distance from the planet is larger than 12 million kilometers which gives an elongation larger than 34'. Its eccentricity is about 0.16 and its visual magnitude is larger than 16.

After its discovery in 1898 by E.C. Pickering (1899), there were more than four hundred astrometric observations of this satellite, made in 42 observational sets (Jacobson 1998b). These sets are not well distributed in time. In particular, from 1982 on there are available 66 ground observations, made at USNO and at McDonald. From these, only 21 had been made with CCD. When compared with Jacobson's orbit, a quarter of all observations have residuals with $\sigma$ smaller than 0 $\hbox{$.\!\!^{\prime\prime}$ }$5, and almost all recent observations are included in this group.

In this paper we present a set of 60 CCD new positions of Phoebe, from observations carried out in 1995, 1996 and 1997. The observations and measurements are presented in Sect. 2. In Sect. 3 we present an astrometric calibration procedure using the USNO-A2.0 Catalog and in Sect. 4 the observations and the theoretical positions given by Jacobson (1998a) and Bec-Borsenberger & Rocher (1982) are compared. The conclusion is presented in the last section.


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Up: CCD observations of Phoebe,

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