Katie Crotts

Topic

Expedition Unknown: Characterizing and Modelling Perturbed Debris Disks in Search for Elusive Planets

Department of Physics and Astronomy

Date & location

• Thursday, July 11, 2024

• 8:30 A.M.

• Elliott Building

• Room 038

Reviewers

Supervisory Committee

• Dr. Brenda Matthews, Department of Physics and Astronomy, University of Victoria (Co-Supervisor)

• Dr. Ruobing Dong, Department of Physics and Astronomy, UVic (Co-Supervisor)

• Dr. Gaspard Duchêne, Department of Astronomy, University of California, Berkeley(Outside Member) 

External Examiner

• Dr. Jean-Charles Augereau, Institut de Planétologie et d’Astrophysique de Grenoble,

  Université Grenoble Alpes 

Chair of Oral Examination

• Dr. Asad Kiyani, Faculty of Law, UVic

   

Abstract

Debris disks, which are defined as optically thin, dusty disks around main sequence stars, are intimately connected with planets in their systems. Not only does the mere existence of a debris disk suggest the presence of planets, as they efficiently stir the orbits of planetesimals leading to collisional evolution, but they can also easily shape the morphologies of their disk. To better understand planet-disk interactions, one crucial step is to uncover the variation in disk morphologies that are present in currently resolved disks. Further studies can then be done to understand how these disk morphologies are related to known or unknown planets.

In my thesis, I conducted a uniform, empirical analysis of 23 debris disks imaged with the Gemini Planet Imager (GPI) in polarized intensity. For this study, I characterized each disk through multi-wavelength, near-IR data to identify any asymmetries present. I find that the majority of disks (19/23) present a significant asymmetry in either geometry, surface brightness, disk color, or a combination of the three. These findings suggest that perturbations in our sample, as seen in scattered light, are common. Some of these perturbations are consistent with planet-disk interactions, including surface brightness asymmetries, eccentric disks, and warps. Additionally, I identified several possible trends between disk properties and stellar properties that may give further insight into debris disk evolution. This includes a trend between disk color and stellar temperature, and trends between the disk vertical aspect ratio and stellar temperature in tandem with the disk radius.

Within the GPI disk sample, I identify one of the most asymmetric disks, HD 111520. In another empirical analysis, I take a closer look at the HD 111520 debris disk to better understand its complex morphology. Using both polarized and total intensity multi-wavelength GPI observations, alongside observations taken with the Hubble Space Telescope (HST), I confirm that the disk hosts a variety of asymmetrical features and structures. This includes the strong 2 to 1 brightness asymmetry observed in previous studies, as well as a significant disk color asymmetry, a distinct 4° degree warp from the disk midplane past ∼180 au, and a bifurcation or “fork”-like structure on the NW side. While the color asymmetry and extreme brightness asymmetry suggests that the disk may have undergone a recent giant collision, the warp and fork structures strongly suggests the presence of an unseen planet.

Once these complex disk structures/features are identified, the disk morphology can effectively be used to probe unseen planets. In the final part of my thesis, I used the n-body code REBOUND, in an attempt to simulate the features of the highly asymmetrical disk around HD 111520 via planet-disk interactions. I find that a planet with a mass of ≈1 M_jup, that is on an eccentric and inclined orbit outside of the warp location, can create a similar radial asymmetry, warp, and “fork”-like structure in the disk as seen in observations. This work demonstrates how disk morphologies can be used to constrain the mass and orbit of a hidden planet in a perturbed debris disk system.