Sacred Astrometry

Minimum credit line: Image courtesy of NRAO/AUI and Jerusha Lederman, York University(for details, see Image Use Policy).

About this Image

IM Pegasi (HR 8703) is an active binary star system located approximately 100 parsecs or 300 light years from Earth. It serves as the guide star for the NASA / Stanford Gravity Probe B Mission (GP-B) which will be testing the warping and twisting of spacetime around Earth predicted by Einstein's theory of general relativity. An artist's conception of what IM Pegasi may look like is shown at the top right corner of the image. To the left, a false colour radio intensity image displays regions of high radio brightness. The leftmost image displays the corresponding radio contours as detected by a world-wide network of telescopes consisting of NRAO's telescopes including NRAO's Very Large Array (shown in foreground), others from the DSN and EVN through the technique of Very Long Baseline Interferometry (VLBI.) The motion of IM Pegasi on the sky is determined relative to three extragalactic reference sources. Shown in a geometric formation in the lower left are images of the three extragalactic reference sources displayed in false colour. Clockwise from bottom, these sources are: 3C454.3, 2252+172,and 2250+194. Using these sources together enables tracking of IM Pegasi's motion over several years. This accurate tracking is crucial for the success of the Gravity Probe B Mission.

Investigator(s):  Ratner, M.I. and Bartel, N.

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Technical Data

    Telescope VLBA 
    Date of Observation 1999-09-18 
    Type of Observation Continuum Observations 
    Band X 
    Wavelength 3.6 cm 
    Frequency 8.4 GHz 
    Center of Image RA: 22:53:2.27, Dec: 16:50:28.31 (J2000)  
    Field of View 0.0000 x 0.0000 degrees  
    Technical Caption This poster contains images for the GP-B guide star, IM Pegasi (HR 8703), and GP-B's extragalactic reference sources. The star is shown both in contours amd false colour. The geometric formation of reference sources features the false colour images of (clockwise from bottom)3C454.3, 2252+172, and 2250+194. All images were produced from an 8.4GHz (3.6cm) observing session for the Gravity Probe B guide star, IM Pegasi (HR 8703), and the three extragalactic reference sources on 18/19 September 1999. The images were produced using a global array of telescopes including the ten VLBA antennas, the phased VLA, the 100-m Effelsberg antenna, and the three 70-m NASA/JPL DSN antennas. The observations were made by M.I. Ratner, D.E. Lebach, I.I. Shapiro, N. Bartel, R.R. Ransom, M.F. Bietenholz, J.I. Lederman, and J.-F. Lestrade.  

  • Astronomical database entries for HR8703
    • Query NED for images of HR8703
    • Query SIMBAD for more HR8703 data


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