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PhD Proposal Defense - Erika Nesvold

Erika successfully defended her PhD Proposal on November 21, 2011.

A Collisional Algorithm for Modeling Debris Disks

Many stars harbor disks of debris, in the form of dust and planetesimals, left over from planet formation. Any planets orbiting in these debris disks will gravitationally perturb the planetesimals, creating morphological features in the disk. These features have a large angular extent on the sky compared to planets, and can be more easily resolved than the planets themselves. We can therefore use images of a resolved debris disk to predict the presence of a perturbing planet and constrain its mass and orbital elements, even when the planet is too faint to be observed.

But to use this planet-finding technique, we need accurate models of the evolution of the disk as it is shaped by the planet. This problem has previously been addressed using N-body integrators to simulate the dynamics of a planet-disk system, but these models neglect or over-approximate the effects of catastrophic collisions between planetesimals. Such collisions affect the dynamics of the planetesimals as well as their size distribution as the kinetic energy of the colliding planetesimals is used to shatter them into smaller fragments.

I propose to develop a debris disk model that combines an N-body integrator to solve the equations of motion for the planetesimals and planets in a disk and a collisional algo- rithm to correct the trajectories of colliding planetesimals and calculate the evolution of the planetesimal size distribution as fragments are created. My model will take as its inputs various parameters such as planetary and stellar mass, the planets’ initial orbital elements, and the initial distribution of planetesimals. The output of my model will be simulated images of the evolved disk. After the model has been completed and tested, I will apply it to archived data of several different resolved debris disks to constrain the mass and orbital elements of confirmed planets and to predict the presence, mass, and orbits of undetected planets.