Spiral Structure when Setting up Pericentre Glow: Possible Giant Planets at Hundreds of AU in the HD141569 Disk

摘要

This paper discusses the impact of introducing a planet on an eccentric orbitinto a planetesimal disk. That planet's secular perturbations cause the orbitsof the planetesimals to evolve in such a way that at any one time planetesimalsat the same distance from the star have common pericentres and eccentricities.This causes the surface density distribution of an extended planetesimal diskto exhibit two spirals, one exterior the other interior to the planet's orbit.These two spirals unwind in different directions and their structure isdescribed by two parameters: the time since the planet was introduced and theplanet's eccentricity. At late times the spirals become tightly wound and theoffset centre of symmetry of the pericentre glow approximation is recovered.Comparison with spiral structure seen in the HD141569 disk shows that itsspiral at 325 AU is similar to that caused by introducing a planet 5 Myr agowith a mass 0.2-2M_Jup orbiting at 235-250 AU with an eccentricity of 0.05-0.2;likewise a Saturn mass planet at 150 AU would cause structure like that seen at200 AU. More definitive statements about any planets orbiting HD141569 fromthis model could be made once the effect of the binary companion on the disk isknown, and once the disk's structure has been better characterised down to 100AU, including the location of the star within the disk. The relatively youngage of this system (~5 Myr) means that if giant planets really do exist athundreds of AU from HD141569, this provides a unique opportunity to setconstraints on the mechanism by which those planets came to be at such largedistances.