Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Astronomy

Supervisor

Prof. Paul A. Wiegert

Abstract

Structures observed in circumstellar disks may be caused by gravitational interaction with planetary or stellar companions. These perturbed disks are often signposts of planet birth in exoplanetary systems, and offer insights into the properties of both the disk and the perturbing planets. Therefore, structures observed in these disks provide a powerful tool for detecting and studying extrasolar planetary systems. In this work, we examine the link between disk structures and nearby/embedded planets using numerical simulations of both hypothetical and observed disk systems.

We demonstrate that gaps can be opened in dynamically cold debris disks at the mean-motion resonances (MMRs) of an orbiting planet. These gaps are opened away from the orbit of the planet itself, revealing that not all disk gaps need contain a planetary body. These gaps are large and deep enough to be detectable in resolved disk images for a wide range of reasonable disk-planet parameters. The gap location, shape, and size are diagnostic of the planet location, eccentricity and mass, and allow one to infer the existence of unseen planets, as well as calculate many important parameters of both seen and unseen planets in these systems. We suggest that the widths, locations, and shapes of the two most prominent resonances, the 2:1 and 3:1 MMRs, could be used to determine: 1) the position of any unseen planets for more efficient targeted searches, and 2) the mass, semimajor axis and eccentricity of the planetary perturber, and present an algorithm for doing so.

We apply our dynamical model of planet-disk interactions to the protoplanetary disk around the young pre-main sequence star HL Tauri which was observed recently in unprecedented detail by the \textit{Atacama Large Millimeter/submillimeter Array} (ALMA). We determine that the disk structures that are likely sculpted by yet-to-be detected planets embedded in this gas-rich disk can be reproduced to a large extent using a simple particle-only model. For example, the number of planets in the HL Tau system remains a matter of debate; however, our results show that at least 5 of the observed gaps could be produced with only 3 planets in the system, where the additional gaps are due to mean-motion resonances. Our fitting of planetary masses and distances are also consistent with those in the literature. Therefore, we conclude that a particle-only treatment of gas-rich disks may be useful in understanding disk-planet dynamical interactions in some cases, and provide `low-cost' initial parameter determinations which can ultimately be used as a starting point for investigating protoplanetary disks more thoroughly using computationally expensive hydrodynamic models.

In the present study, we show that numerical simulations of circumstellar disks provide a powerful tool for the study of planets and planetary systems which can ultimately help in understanding their formation and evolution.


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