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D. E. Lebach, M. I. Ratner, I. I. Shapiro (CfA), N. Bartel, M. F. Bietenholz, R. R. Ransom (York U.), J. F. Lestrade (Obs. de Meudon)
VLBI continuum observations at 3.6~cm of the RS Canum Venaticorum binary star IM~Pegasi (HR~8703) on 1997~January 16--17 and 18--19, made in support of the NASA-Stanford Relativity Gyroscope Experiment (Gravity Probe B), revealed ~1~mas motions of its radio centroid over time periods as short as ~1~h. These motions, which we deduced from phase-delay measurements using a Kalman-filter estimator, coincided temporally with changes in the star's flux density measured with the VLA. Phase-referenced maps of the stellar radio emission show motions consistent with those found with the Kalman-filter estimator. We present our estimates of source motion as a function of time during our observations, and discuss the corresponding evolution of the structure seen in our phase-referenced maps. We also discuss what we may learn from additional VLBI observations of the star, which we continue to make at the rate of ~4 per year.
The author(s) of this abstract have provided an email address for comments about the abstract: dlebach@cfa.harvard.edu