The Guiding Light: Vri/uvby & Tio Photometry Of The Chromospherically Active & Spotted Binary System Im Peg - The Guide-star For The Gravity Probe-b Mission

Details The Guiding Light: Vri/uvby & Tio Photometry Of The Chromospherically Active & Spotted Binary System Im Peg - The Guide-star For The Gravity Probe-b Mission The Guiding Light: Vri/uvby & Tio Photometry Of The Chromospherically Active & Spotted Binary System Im Peg - The Guide-star For The Gravity Probe-b Mission

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.6004z&link_type=abstract

American Astronomical Society, AAS Meeting #211, #60.04; Bulletin of the American Astronomical Society, Vol. 39, p.844

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We report on the starspot and chromospheric properties of IM Pegasi - the guide star of the Gravity Probe B (GP-B) satellite. GP-B's mission is to measure two predicted consequences of General Relativity - frame-dragging and geodetic effects, via its extremely precise onboard gyroscopes. IM Peg was selected as the mission's guide star as it is not only bright enough to be seen with GP-B's onboard optical telescope but it is also a bright radio source. Thus, ground-based radio telescope observations can easily and accurately correct for IM Peg's motions in space. However, IM Peg is a chomospherically active binary system with a luminous K2 III primary star showing rotationally modulated (Prot 24.5 days) light variations from starspots. The starspots can cause problems as GP-B can erroneously interpret a change in starspot coverage (and corresponding shifts in the light center) as the star's movement. This apparent shift can also be exacerbated by possible changes in the light-center of the binary system arising from changes in the light balance with the fainter dK component. Since 2000 we have carried out multi-band high-precision photoelectric photometry of IM Peg to determine its activity and starspot coverage. Our photometry uses Strömgren uvby filters, VRCIC filters and TiO (719/755 nm ) narrow-band filter sets. Measurements were made relative to neaby comparsion & check stars using a robotic 0.8-m telescope (located in AZ) and 0.25-m telescope (located in PA). The TiO- and multi-band continuum photometry constrains the starspot areas, temperatures and distributions. The photometry is being modeled to determine the effects of changing starspot areas and distributions on the light center of the binary. The results of our analysis and possible impacts on the GP-B Mission will be discussed.
This research is supported by NSF/RUI Grants AST- 0507536 and AST- 0507542 which we gratefully acknowledge.

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