Thousands of extrasolar planets (exoplanets) have been discovered so far, indicating the ubiquity of planetary systems in our galaxy. These exoplanets have an enormous range of characteristics. While the formation mechanism for small planets is well-accepted and mostly understood, how giant planets form and evolve is still under debate. One approach towards understanding giant planet formation and evolution process is to study the associated debris disks. Debris disks are composed of dust produced by planetesimals that are in orbit around main sequence stars. The grain composition, dust distribution, and disk morphology can be used to infer the system’s dynamical history and even predict the possible existence of unseen exoplanets.

My thesis focuses on studying the debris disk around HD 131835 with multi-wavelength high-contrast imaging. Multi-wavelength imaging allows us to characterize the distribution of grains of various sizes since an observation is most sensitive to grains with the size similar to the probing wavelength. The target, HD 131835, is a ∼15 Myr A2 star in the Scorpius-Centaurus OB association at a distance of ∼120 parsec. I first report the discovery of the resolved disk around HD 131835 in mid-infrared at 11.7 μm and 18.3 μm with T-ReCS on Gemini South. Next, I present the first scattered-light image of the debris disk around HD 131835 using the Gemini Planet Imager (GPI). The disk is detected in H-band polarized light. Compared to its mid-infrared thermal emission, the disk in scattered light shows similar orientation but different morphology. Unlike the continuous and extended feature in thermal emission, the disk in scattered light has a cleared region inward of ∼ 75 AU. In addition, I discover a weak brightness asymmetry along the major axis that is only present in the scattered-light image. The results of my thesis work imply that the system has multiple grain populations, and those grains could be composed of a mixture of silicates and amorphous carbon. The brightness asymmetry and the richness in the morphological features indicate that the system is dynamic, possibly with strong interactions between dust and gas and perturbations from unseen objects. In the final chapters, I present my instrumentation work including developing the photometric calibration method in the polarimetry mode for the GPI coronagraphic observations and creating a more automatic process for aligning the focal plane mask to the star while observing.

Direct imaging and spectroscopy is fundamental to understanding the composition, evolution, and formation of exoplanets, and as such these techniques have been given high priority in the 2020 Decadal Survey on Astronomy and Astrophysics. At its heart, the field of exoplanet science has been driven by advancements in technology and data reduction methods. This thesis focuses on direct imaging techniques, including their applications to circumstellar debris disks and the instrumentation required therein, addressing the following questions: What can we learn about the formation and dynamical history of planetary systems through direct imaging of warped debris disks? How can we improve upon our ability to detect planets and disks through advancements in astronomical instrumentation?

To date, observers have found several debris disks containing asymmetries and warps. Dynamical interactions between planetesimals, dust, radiation, and possibly planets work in tandem to shape dust into distinct morphologies. I discuss the morphological characteristics of the edge-on debris disk around HD 110058 as seen in infrared scattered light by the Gemini Planet Imager, and attempt to probe the dynamical history of the system. The presence of an asymmetric warp in the disk at a radius of 0.35 arcseconds ($\sim$38 AU) is revealed in PSF-subtracted total-intensity images, reminiscent of the disk around $\beta$ Pictoris. We discuss the results of scattered-light modeling intended to constrain the three-dimensional morphology of the warp. This complex morphology suggests the existence of large-scale dynamical perturbations due to a possible unseen planet.

As we seek to learn more about the universe, we must continually build astronomical instruments that can uncover more of the inner workings of the physical processes that underlie. Detailed studies of exoplanets and debris disks, such as that of HD 110058, are only made possible by well designed astronomical instruments. Through a set of instrument focused projects I will illustrate the cycle of instrument development from design to data and scientific discovery. With the characterization of the upgraded NIRSPEC detector, I explain the process used to ensure the data taken with the instrument is well-understood. Finally, I illustrate the instrument design process and the steps taken to transform scientific inquiries into instrument designs with the Fabry-P�rot etalon calibration system concept for OSIRIS.

High-contrast imaging of circumstellar debris disks and exoplanets provides unique information about planetary system evolution. Several hundred nearby main-sequence stars are known to host debris disks: reservoirs of rock and ice that are thought to be coeval with planet formation. My dissertation research focused on detecting and characterizing such disks to gain new insight into circumstellar environments during the epoch of planet assembly. To view these systems on spatial scales down to a few astronomical units, I used near-infrared angular differential imaging data from the Keck NIRC2 and Gemini Planet Imager instruments. Detection of relatively faint disks and planets in these data is enhanced by image-processing algorithms that suppress the stellar signal, however, they also bias the brightnesses of these objects. I developed a new technique to forward-model and correct for this bias, thus allowing more accurate analysis of disk and planet properties. Applying this technique to scattered-light imaging of the HD 32297 debris disk, I used photometric and morphological measurements to infer physical characteristics of the disk and its constituent grains. I also investigated the HD 61005 debris disk and the role that an eccentric, inclined planet could play in shaping its unusual morphology. To expand the small samples of resolved disks and directly-imaged planets, I conducted a coronagraphic survey of 24 nearby stars, the preliminary results of which are reported herein. Concluding on the same theme of high-angular resolution imaging, my final project comprised tasks translating science requirements into design specifications for an upgraded Keck OSIRIS imager.

High-contrast imaging techniques have enhanced our capabilities in studying

the formation and evolution of exo-solar disks and planets. In my

research, I have studied the instrumentation, data reduction, and data

analysis involved in this area. Many high-contrast imagers operate in the near-infrared

wavelengths, the systems of which are rapidly developing with new

technology. To this end, I have characterized the infrared detector of

the upgraded Keck OSIRIS imager as well as explored methods for

blocking out infrared radiation from the telescope components which

pollute the desired scientific signal. Moving downstream from the data

collection, I improved data reduction methods for suppressing the

stellar signal from high-contrast images of disks and planets, as well

as writing publically available code to forward model biases

introduced from these subtraction methods. I generalized the code for

these methods such that they can be used for most high-contrast

imaging instruments, and optimized it for disks such that it

ran two order of magnitudes faster than code optimized for planet

detection. I studied the efficacy of

my forward modeling module in further efforts to make the code more generally

used by the scientific community. I used these techniques to study the

debris disk HR4796A using multi-wavelength integral field polarimetric data form the

Gemini Planet Imager (GPI). HR4796A hosts a well-studied debris disk with a long history due to

its high fractional luminosity and favorable inclination lending

itself well to both unresolved and resolved observations.

We modelled a purely geometric disk in order to extract geometry

parameters, polarized fraction and total intensity scattering phase

functions for these data. We find that conventional methods that are

used to model debris disks cannot produce a satisfactory model of the

phase functions of the disk, indicating the need for more

sophisticated grain models.

The goal of this thesis is to characterize circumstellar disks and substellar objects, from moons to brown dwarfs, by improving and applying techniques from high-contrast imaging. To do so, I led four projects, two of which expand the range of targets accessible by high-contrast imaging. In Project 1, I develop an improved algorithm for high-contrast imaging data processing, enabling detection of fainter, smaller planets; this algorithm uses both spatial and temporal information on the speckle noise present in high-contrast images, and will be especially useful for next-generation photon-counting detectors such as Microwave Kinetic Inductance Detectors (MKIDs). In Project 2, I demonstrate a new technique to detect and monitor ejections of ice particles from subsurface oceans on outer solar system bodies, such as Jupiter’s icy moon Europa, using ground-based polarimetric imaging. Such plumes have not been confirmed on Europa, but are of significant interest for astrobiology and planning for the upcoming Europa Clipper mission.

The remaining two projects use existing analysis techniques to investigate individual systems of interest that add to our understanding of planet formation. In Project 3, I characterize the atmosphere of a brown dwarf around HIP 93398, a recently discovered companion identified via the Hipparcos Gaia Catalog of Accelerations, using high-resolution spectra from SCExAO/CHARIS. With both a dynamical mass measurement and high-resolution spectroscopy, HIP 93398 B provides substantial constraints on models of brown dwarf evolution. In Project 4, I constrain the morphology and scattering properties of the debris disk around the bright star HD 155623, a unique “hybrid” debris disk that shows signs of youth despite its age, using polarimetric data from the Gemini Planet Imager. With the information from my investigation, the HD 156623 system can now serve as a benchmark for models aiming to explain how gas and dust interact during the later stages of planet formation.

These investigations both further innovation in exoplanet imaging techniques and, respectively, provide insight into detections of extrasolar planets, the nature of oceans beyond Earth, the mechanisms of planet formation, and the atmospheres of giant planets and brown dwarfs.