34th Meeting of the AAS Division on Dynamical Astronomy, May 2003
8 Extra-Solar Planetary Systems
Oral, Tuesday, May 6, 2003, 11:10-11:55am,

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[8.01] Student Stipend Recipient: Planet Scattering and Exoplanet Orbits

R.K. Barnes, T.R. Quinn (U. Washington)

We examine the large eccentricities of exoplanets. One possible origin of these orbits results from the ejection of an original companion. We examine systems which lie close to instability, and simulate configurations which eject planets within 106 years. We then compare the distributions of eccentricities of the remaining planet, with the observed distribution in single companion systems. We only examine planets whose orbits cannot be partially circularized by stellar tides (typically Porb {> \atop ~ 10 days, e {< \atop ~ 0.4). Only 4 planetary systems currently can eject a planet within the observed errors, HD12661, 47UMa, HD82943, and GJ876. For low eccentricities (e < 0.05) ejections predict too few planets, for intermediate eccentricities (0.05 < e <0.3), the rate is too high by nearly a factor of 2, but above 0.3, the relative frequencies are in good agreement. At low e planets are most likely not scattered, and their eccentricities result from dynamical friction during the final stage of planet formation. At high eccentricities the results suggest that scattering is the primary mechanism for high eccentricity. The results at intermediate eccentricity however suggest that either there are too few data (both of multiplanet systems and single planet systems) or that another mechanism alters eccentricity, such as collisions, which are not resolved in our simulations. We also find that, for a typical planetary system, semi-major axes do not change by more than 50% after an ejection.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.