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Session 107 - Radio Astronomy and VLBI Instruments.
Display session, Thursday, January 16
The Gravity Probe B (GP-B) mission is being developed by NASA and Stanford University to test two unverified predictions of general relativity through measurements of the precessions of gyroscopes placed in low-Earth orbit. For the measurement-accuracy goals of the mission to be met, the proper motion of a ``guide star,'' whose position provides a reference against which the precessions are measured, must be determined in an extragalactic reference frame with a standard error less than 0.5 mas/yr. Very-long-baseline interferometry (VLBI) is the only technique currently available that is capable of measuring, in a few years time, the proper motions of stars at this level of accuracy. To minimize the uncertainty in the VLBI-determined position of the to-be-selected guide star, one must examine the structure of radio emissions of candidate stars and their corresponding extragalactic reference sources. This paper reports on our progress in mapping the GP-B guide star candidate HR~5110 and its reference sources J1328+363, J1334+371, and J1340+379, and the candidate HR~1099 and its reference sources J0331+022 and J0339-017 (CTA26). We discuss the source structures revealed in our maps and model fits and their likely effects on the accuracy of the proper motions that can be determined for these stars.
Program listing for Thursday