VLBI Imaging and Astrometry of the Gravity Probe B
Guide Star HR 8703
Jean-Francois LestradeObservatoire de Paris/DEMIRM
Ryan Ransom, Norbert Bartel, Michael BietenholzYork University
Michael Ratner, Daniel Lebach, Irwin ShapiroHarvard-Smithsonian Center for Astrophysics
June 12, 2003
OutlineOutline
• Gravity Probe B Mission
• VLBI Observations
• Astrometric Results
• Light Curves and Images
• Summary
GRAVITY PROBE B
GOAL: Measure precessions with standard error < 0.5 mas/yr
ASTROMETRY: Measure proper motion with standard error 0.15 mas/yr
~1%
SummarySummary• A very precise measurement of the proper motion of
HR 8703 has been made based on 23 VLBI observations.
• The orbit of the primary K giant star has been detected.
• Motion of the centroid of the radio emission has been detected on hour time scales and likely represents the rapid flow of energetic electrons along closed magnetic field lines attached to the giant star.
• Double-lobe radio source structures have been observed and may be a signature of emission from the north and south poles of the giant star.