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Paper: Progress in VLBI Stellar Astrometry for the NASA/Stanford Relativity Mission (Gravity Probe B)
Volume: 144, Radio Emission from Galactic and Extragalactic Compact Sources, IAU Colloquium 164
Page: 385
Authors: Ratner, M. I.; Lebach, D. E.; Shapiro, I. I.; Bartel, N.; Bietenholz, M. F.; Ransom, R. R.; Lestrade, J.-F.
Abstract: The NASA/Stanford Relativity Mission (Gravity Probe B) is to test the unverified ``frame-dragging'' prediction of general relativity through measurements of the precessions of orbiting gyroscopes. For mission accuracy goals to be met, the proper motion of a ``guide star,'' whose position will be used as an inertial reference, must be determined in an extragalactic reference frame with a standard error less than 0.5 mas/yr. We discuss our VLBI observations of the current guide-star candidates (radio stars HR 1099, HR 5110, and HR 8703) and our techniques for obtaining differential astrometric positions with the needed accuracy.
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