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S. C. Unwin (JPL/Caltech), J. H. Catanzarite (IPAC/Caltech)
The Space Interferometry Mission (SIM) requires an all-sky reference grid of unprecedented accuracy in order to perform parallax and proper motion measurements on science targets. SIM will cover the sky in a series of overlapping `tiles', each 15 deg in diameter, with an average of 6 stars per tile. In total, the grid will comprise approximately 1300 metal-poor K-giant stars at R magnitude 12. The challenge, prior to SIM launch in 2009, is to develop a catalog for which the uncertainty in the position of each star due to `astrophysical noise' is no more than 4 microarcseconds. To achieve this, we plan to screen candidate stars using precision radial velocities, for binary companions which would perturb the astrometric positions. We will also eliminate variable stars for which surface activity, or unseen long-period companions would cause shifts (the so-called variability-induced movers). Simulations show that for reasonable assumptions about companion statistics, RV filtering should yield a high confidence that the grid will perform adequately. In this talk we will also briefly cover how SIM operates, and how the grid will be observed during the mission.
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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.