Protostars and Planets VI, Heidelberg, July 15-20, 2013
Fomalhaut\'s Main Belt Structure and the Eccentric Orbit of Fomalhaut b
Kalas, Paul (UC Berkeley)
Graham, James R. (UC Berkeley)
Fitzgerald, Michael C. (UCLA)
Clampin, Mark (NASA GSFC)
We present a significant update to the observations and understanding of the planetary system sur- rounding the nearby, 440 Myr old, A3V star Fomalhaut. Our latest HST/STIS high-contrast optical images confirm that the low-mass object Fomalhaut b has a hightly eccentric orbit (e∼0.8). Its periapse is near 30 AU and in the sky-plane projection Fomalhaut b will begin crossing the main belt (a∼140 AU) two decades in the future. An MCMC analysis of the astrometry indicates apsidal alignment between Fomalhaut b and the belt, but the mutual inclination is not necessarily coplanar. We find that only 12 per cent of Fomalhaut bís ascending and descending nodes would physically encounter the belt. The non-detections of Fomalhaut b at infrared wavelengths suggest that its mass is less than a Jupiter mass, and its optical luminosity may be due to a circumplanetary dust ring or an irregular satellite cloud. We suggest that Fomalhaut bís minimum mass is a few times that of the dwarf planet Ceres in order for the circumplanetary cloud to survive shearing during periapse passage. In addition, we give observational evidence that the main belt may have an azimuthal dust depletion approximately 50 AU wide. Taken together, the eccentric orbit of Fomalhaut b and the main belt struc- ture indicate that other, yet-to-be-detected planet-mass objects may dynamically influence the system.
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