Abstract
We present a physical interpretation for the locations of the sources of radio emission in IM Pegasi (IM Peg, HR 8703), the guide star for the NASA/Stanford relativity mission Gravity Probe B. This emission is seen in each of our 35 epochs of 8.4-GHz VLBI observations taken from 1997 to 2005. We found that the mean position of the radio emission is at or near the projected center of the primary to within about 27% of its radius, identifying this active star as the radio emitter. The positions of the radio brightness peaks are scattered across the disk of the primary and slightly beyond, preferentially along an axis with position angle, p.a. = (-38 +- 8) deg, which is closely aligned with the sky projections of the orbit normal (p.a. = -49.5 +- 8.6 deg) and the expected spin axis of the primary. Comparison with simulations suggests that brightness peaks are 3.6 (+0.4,-0.7) times more likely to occur (per unit surface area) near the pole regions of the primary (|latitude| >= 70 deg) than near the equator (|latitude| <= 20 deg), and to also occur close to the surface with ~2/3 of them at altitudes not higher than 25% of the radius of the primary.
Highlights
IM Pegasi (IM Peg; HR 8703; HD 216489; FK5 3829) is the radio-bright binary star which served as the guide star for the Gravity Probe B (GP-B) mission, the space-borne relativity experiment developed by NASA and Stanford University to test two predictions of general relativity
We focus on the orbit
The Mean Location of the Source of the Radio Emission In Paper V, we show that the residuals of our nine-parameter astrometric fit to set (3) of the 35 positions of IM Peg scatter about a well-determined orbit on the sky
Summary
IM Pegasi (IM Peg; HR 8703; HD 216489; FK5 3829) is the radio-bright binary star which served as the guide star for the Gravity Probe B (GP-B) mission, the space-borne relativity experiment developed by NASA and Stanford University to test two predictions of general relativity. In the related case of the close binary in the Algol system, Lestrade et al (1993) were able, with astrometric VLBI from four epochs, to identify the cooler K subgiant star, and not its B dwarf companion or the intermediary region, as the likely source of the radio emission. Until now, no such identification has been made for any RS CVn system.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
