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S. Loiseau, A.F. Boden, S. C. Unwin, M. Shao (JPL, Caltech)
The Space Interferometry Mission (SIM) is a space-based interferometric observatory primarily dedicated to high-precision astrometric measurements. Unlike the European astrometric satellite Hipparcos, SIM will operate in various astrometric modes: grid mode, wide-angle mode, and narrow-angle mode. Each of these modes has a well defined purpose. We give here the results of extensive simulations for the wide-angle mode, showing the subtleties of relative astrometry -- as opposed to global astrometry. The results are mainly presented as variations of the final astrometric accuracy with respect to mission parameters such as number of observations per star, number of reference stars, mission length, measurement noise, and precision of the reference frame. We also revisit the idea of the rigidity equation, linking the mission accuracy to the single measurement accuracy and show how to derive optimal observing scenarios for SIM. We will briefly present the method we are currently implementing for the narrow-angle simulations, showing how SIM could detect invisible companions and which portion of phase-space could be reachable. Quantitative as well as qualitative results are given and emphasis is put on the distinction between precision and accuracy, as in any astrometric study.
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The author(s) of this abstract have provided an email address for comments about the abstract: mailto:loiseau@huey.jpl.nasa.gov