VLBI Imaging and Astrometry of the Gravity Probe B Guide Star HR 8703

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VLBI Imaging and Astrometry of the Gravity Probe
BGuide Star HR 8703
Ryan Ransom, Norbert Bartel, Michael
Bietenholz York University
Michael Ratner, Daniel Lebach, Irwin
Shapiro Harvard-Smithsonian Center for
Astrophysics

• Jean-Francois Lestrade
• Observatoire de Paris/DEMIRM

June 12, 2003
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Outline

• Gravity Probe B Mission
• VLBI Observations
• Astrometric Results
• Light Curves and Images
• Summary

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GRAVITY PROBE B
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Global VLBI Array
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Phase-Reference Mapping
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See Poster
J. Lederman et al.
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Flux-Density History at 8.4 GHz
1997 Jan 16
2002 Nov 20
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97 Jan 16
02 Nov 20
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97 Jan 16
?µa 0.17 mas ?µd 0.17 mas ?p 0.13
mas
02 Nov 20
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a1 0.9 0.2 mas
O 40 15
i 80 10
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K2 III
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Summary

• 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.