We presented 60 astrometric positions of Phoebe taken in 1995, 1996 and 1997 with CCD. The use of USNO-A2.0 catalogue stars to materialize the local frame on the CCD field, enabled us, for the first time, to make the astrometric calibration for a natural satellite position without using a secondary catalog.
Comparing the positions here obtained with the orbit calculated by Jacobson, the O-C residuals are alike to the best observations of Phoebe. The unusually large residuals for the observations taken near the periapsis suggest that the fit of the orbit is not good in this position. However, some new observations of Phoebe near the periapsis must be made to confirm this suggestion.
Acknowledgements
The authors wish to thank the CNPq-Brazil for partial support of this work. C.H. Veiga would like to thank State of Rio de Janeiro Science Foundation - FAPERJ for providing computational facilities for this project.
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