Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21534905g&link_type=abstract
American Astronomical Society, AAS Meeting #215, #349.05; Bulletin of the American Astronomical Society, Vol. 42, p.531
Astronomy and Astrophysics
Astronomy
Scientific paper
When a planet with radius Rp transits in front of its parent star with radius R*, the flux of the star decreases by a fractional amount r2=(Rp/R*)2, while the stellar photocenter shifts by r2 theta*, where theta* is the angular radius of the star. For the nearest transiting planet systems, this shift is of order microarcseconds, and should be detectable by future space-based precision astrometric satellites, such as the Space Interferometry Mission Lite. I explore the phenomenology of this effect, and estimate its detectability using SIM Lite for known transiting systems. Measurement of the astrometric shift during transit yields the angular radius of the star, which when combined with the stellar density determined from the photometric light curve, and the stellar parallax, yields a direct measurement the radius and mass of the star. This astrometric shift also allows one to determine the (three-dimensional) direction of the planet orbit normal, which can be used to confirm or constrain polarized reflected light measurements, determine the inclination of the transiting planet orbit relative to more distant planetary or stellar companions, and remove degeneracies in systems with multiple transiting planets. For nearby eclipsing binaries, the astrometric signal during eclipse should be larger than that for planets, although it will also be more complicated to interpret due to the contaminating effects of the light from the secondary.
This work was performed for the Jet Propulsion Laboratory, California Institute of Technology, sponsored by the National Aeronautics and Space Administration.
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