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X. Pan, S. Unwin (JPL)
The Space Interferometry Mission (SIM) can provide unprecedented accuracy of 4 \muas in astrometry. One of the key issues is to determine the baseline vector to high precision in inertial space. Two guide interferometers on SIM are used for that purpose. So it is critical to have bright guide stars with accurate known positions.
The important issues discussed here include criteria of guide star selection and choices of suitable guide stars. A statistical analysis of guide stars is presented in details. Distribution of guide stars and precision of positions are summarized. In particular, the problems with objects of multiple components are presented. Error estimations with guide stars are discussed.
This work is supported under contract with the National Aeronautics and Space Administration.