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Session 69 - Instabilities in Planetary Systems.
Display session, Friday, January 09
Exhibit Hall,

[69.05] Vertical Instabilities and Off-Plane Orbits in Circumbinary and Protoplanetary Disks

P. Erwin, L. S. Sparke (U.Wisconsin-Madison)

We show that several families of off-plane orbits around a circular binary or star-planet system are stable, and are accessible to particles orbiting in a circumbinary or protoplanetary disk. The presence of vertical instabilities in the family of planar orbits which supports circumbinary disks suggests that disk particles should be excited into off-plane motion; additional instabilities exist in planar orbits associated with major resonances.

We use a simple form of dissipation to mimic such effects as viscosity, gas drag, and Poynting-Robertson drag, allowing disk particles to spiral slowly inwards. We can then test the effects of resonances on particle motion, and explore the effects of nonzero binary eccentricity. For mass ratios 0.02 \le \mu \le 0.35 and eccentricity e < 0.01, the vertical resonance at r \approx 2.1a (3:1 commensurability) intercepts the majority of particles and excites them onto the stable off-plane orbits. For \mu \le 0.01, the neighboring planar instability dominates, forcing most particles onto asymmetric planar resonance orbits. For typical star-planet mass-ratios (\mu \le 0.001), neither of the outer resonances are strong enough to intercept a significant fraction of particles. For eccentric systems with e \sim 0.1 we find vertical excitation for particles on 1:3 orbits further out, branching from the main circumbinary orbits at the 4:1 commensurability.

We discuss possible applications to pre-main sequence binaries, \beta Pictoris systems, planetary system formation, and the Kuiper Belt. Some Kuiper belt objects may exist in highly inclined orbits, especially if Neptune migrated outward early in the Solar System.

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