Kaitlyn Hessel

Topic

From Orbit Modeling to Speckle Suppression: A Study of Exoplanet Motion and Coherent Differential Imaging for High Contrast Exoplanet Observations

Department of Physics and Astronomy

Date & location

• Monday, August 10, 2026
• 9:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Christian Marois, Department of Physics and Astronomy, University of Victoria (Co-Supervisor)
• Dr. Kim Venn, Department of Physics and Astronomy, UVic (Co-Supervisor)

External Examiner

• Dr. Susan Redmond, Jet Propulsion Laboratory, Caltech

Chair of Oral Examination

• Dr. Donald Juzwishin, School of Health Information Science, UVic

Abstract

Directly imaging faint exoplanets orbiting bright host stars requires a combination of techniques that include target selection, orbit prediction and post-processing among other specialized approaches. Identifying promising systems and determining where to search within them depends on accurate orbit modeling, which combines multiple data types to estimate an exoplanet’s position over time and to assess the likelihood of there being additional unseen companions. Using a Julia-based, orbit modeling code called Octofitter, the work in this thesis estimates the impact of the choice of Bayesian prior on orbit prediction. It demonstrates that Observable priors are more predictive of an exoplanet’s orbit than the traditionally used Uniform priors, particularly for low orbit coverage systems such as those common for direct imaging. Additionally, this works highlights the importance of using orbit modeling codes such as Octofitter to guide direct imaging campaigns for detection and characterization of both known and undetected exoplanets.

Even with accurate orbit predictions, direct imaging observations are dominated by scattered stellar light known as quasi-static speckles that obscure or mimic exoplanet signals. Post-processing is therefore essential for isolating faint targets, however, established techniques suffer from exoplanet self-subtraction and can be unsuitable for extended sources such as protoplanetary disks. This thesis outlines the implementation of Coherent Differential Imaging (CDI) using a Self-Coherent Camera (SCC) on the Subaru Pathfinder Instrument for Detecting Exoplanets and Retrieving Spectra (SPIDERS) currently located at the Subaru Telescope. Due to the optical incoherence of exoplanet and stellar light, CDI can identify and remove the stellar speckle field without impacting planetary features, a disk or point source, removing the issue of self-subtraction or disk morphing. On the SPIDERS bench, CDI reached a contrast improvement of ∼30x and on-sky demonstrated improvements of up to ∼6x under challenging observing conditions, including 40 m/s wind speeds and 0.8-1.2′′ of atmospheric seeing.

The orbit modeling and post-processing tools presented in this thesis will improve the planning and execution of direct imaging campaigns for exoplanet detection and characterization. Together, CDI and orbit modeling form a powerful end-to-end plan for the field of direct imaging that can be employed on upcoming instruments such as Gemini Planet Imager 2 at the Gemini North Observatory and NASA’s next flagship mission, the Habitable Worlds Observatory.