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M. Nagasawa (NASA Ames Research Center), D. N .C Lin (UCO/Lick Observatory, University of California), S. Ida (Tokyo Institute of Technology)
The evolution of eccentricity of non-resonant extrasolar planets due to the apsidal libration or circulation induced by both the secular interaction between them and the self gravity of their nascent disks is investigated.
Rates and amplitudes of eccentricity modulation are determined by the relative longitude of their periapse passage. For mature planets, the eigenfrequencies of this modulation is determined by their mass and semi major axis ratios. However, prior to disk depletion, self gravity of the planets' nascent disks dominates the planets' precession eigenfrequencies.
We analyze the evolution of planetary eccentricities in the Upsilon Andromedae and the HD168443 system during the epoch in which the protostellar disk outside the planets is gradually cleared. As these extrasolar planets are very massive, it would be reasonable to assume that the protostellar disk inside the orbit of these planets has been quickly removed after the completion of the planets. Using this model, we show that the gravity of the disk declines adiabatically with disk depletion, and the modulation amplitude of the planets' relative phase of periapse passage is approximately invariant despite the time-asymmetrical exchange of angular momentum between planets. We find that the disk depletion could cause a large change in planetary eccentricity ratios. However, the relatively large amplitude of the planets' eccentricities cannot be excited if all the planets around the same host star had small initial eccentricities. Although the effect is large or small, the exchange of angular momentum itself is inevitable in the multi-planetary system as long as the outer planet is more massive than the inner one. The eccentricities of extrasolar planets are not necessarily the original eccentricities at the time of their formation.
This work is supported in part by NASA through grant NAG5-10727 and NSF through AST-9987417 to D.N.C.L..
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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.