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H. Kobayashi, S. Ida, H. Tanaka (Tokyo Institute of Technology)
We investigate the effects of a passing stellar encounter on a planetesimal disk through analytical calculations and numerical simulations, and derive the boundary radius (a\rm planet) outside which planet formation is inhibited by disruptive collisions with high relative velocities. We study orbital eccentricity (e) and inclination (i) of planetesimals pumped up by perturbations of a passing single star. We model a protoplanetary system as a disk of massless particles circularly orbiting a host star. The massless particles represent planetesimals. A single star as massive as the host star encounters the protoplanetary system. Numerical orbital simulations show that in the inner region at semimajor axis a \la 0.2 D where D is pericenter distance of the encounter, e and i have power-law and the longitudes are aligned, independent of the encounter parameters. In the outer region a \ga 0.2 D, the radial gradient is steeper. We analytically reproduce the power-law dependence and explicitly give numerical factors of the power-law dependence as functions of encounter parameters. We derive the boundary radius (a\rm planet) of planet forming region as a function of dynamical parameters of a stellar cluster, assuming the protoplanetary system belongs to the stellar cluster. We find a\rm planet ~ 40-60AU in the case of D ~150-200AU. D ~ 200AU may be likely to occur in a relatively dense cluster. We point out that the size of planetary systems (a\rm planet) born in a dense cluster may be necessarily restricted to that comparable to the size of planet region (~30-40AU) of our Solar system. We also investigate e and i of the particles in outer region. We show that the stellar encounter may cause the eccentric and inclined orbits of Kuiper Belt Objects.
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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.