Applications of High-Contrast Imaging Techniques and Polarimetry to (Exo-)Planetary Science

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

Direct Imaging of Exoplanets with Project 1640

Project 1640 is a suite of instrumentation and software focused on high-contrast imaging of exoplanets, probing the parameter space of companion size > 1MJ and distance 5-50 AU around the host stars. The instrument consists of an apodized Lyot coronagraph, with a Mach-Zender interferometer and an integral field spectrograph, forming data cubes of dimensions right ascension, declination, and wavelength. P1640 is operated at Palomar Observatory in Southern California, in conjunction with their PALM-3000 adaptive optics system. Data reduction models out remaining speckle noise using principle component analysis and produces a residual cube, which can then be manually inspected for possible companions. For this summer project, data reduction using the Karhunen-Lo ́eve Image Projection (KLIP) algorithm was completed on many of the survey stars and inspected, in an effort to search for more candidates. At this time, two possible candidates have been found, and are awaiting further confirmation

Using blogs to make peer-reviewed research more accessible

Discipline-based education researchers produce knowledge that aims to help instructors improve student learning and educational outcomes. Yet, the information produced may not even reach the educators it is intended to influence. Prior work has found that instructors often face barriers to implementing practices in peer-reviewed literature. Some of these barriers are related to accessing the knowledge in the first place such as difficulty finding and understanding research and a lack of time to do so. To lower these barriers, we created an online blog, PERbites, that summarizes recent discipline-based education research in short posts that use plain language. Having covered nearly 100 papers to date, we conducted a survey to see if we were addressing the need we had originally set out to address. We posted a 23-item survey on our website and received 24 usable responses. The results suggested that readers do generally agree that we are meeting our original goals. Readers reported that our articles were easier to understand and used more plain language than a typical discipline-based education research (DBER) journal article. At the same time, readers thought that all the important information was still included. Finally, readers said that this approach helped them keep up with DBER studies and read about papers they otherwise would not have. However, most readers did not indicate they changed their teaching and research practice as a result of reading our blog. Our results suggest that alternative methods of sharing research (e.g., non-peer reviewed publications or conference talks) can be an effective method of connecting research with practitioners, and future work should consider how we as a community might build on these efforts to ensure education research can make meaningful changes in the classroom.Comment: Published in the Proceedings of the 2022 Physics Education Research Conference, Grand Rapids, MI, US July 13th - July 14t

Our Future in the Stars

After years of hard physical and mental training, they take their first steps to the shuttle, waving goodbye to all the spectators and Earth. These astronauts, originally scientists, teachers, pilots, and engineers, each endured at least three years of rigorous professional training before even applying to an astronaut program. Earning a bachelor’s degree is the minimum requirement for NASA positions, and the astronauts train beyond the classroom by swimming laps in a space suit to experience zero-gravity. A day in an astronaut’s life might start by climbing aboard the “vomit comet,” an aircraft that flies a parabolic path to simulate microgravity conditions. Astronauts also accustom themselves to move and work in weightlessness at the Neutral Buoyancy Lab in NASA’s Johnson Space Center (JSC). Behind the walls of this facility in Houston, Texas, these astronauts-in-training submerge themselves in a massive swimming pool while in clunky space suits. They navigate in full-scale underwater mockups of their shuttle and familiarize themselves with the life-size replica of the International Space Station (ISS). After years of training, these space pioneers stand at the launch pad with 1000 jet aircraft pilot-in-command hours in their pockets, thoroughly acquainted with every module on the ISS. NASA statistics claim that the launch shuttle sends our astronauts hurling into space at 18,000 mph, a speed nine times faster than the average rifle bullet. In just six hours, they arrive at the actual ISS, which spans about the width of an American football field. The docking process is actually the most complicated component of their journey; the spacecraft cannot dock without entering the correct orbit at the correct time, and there is no room for a mistake that might send the spacecraft crashing into the ISS. When the astronauts finally do make it onboard the ISS, they’ll find themselves inside a leviathan weighing nearly one million pounds. The astronauts have more space than a six-bedroom house and are required to exercise in the station’s gymnasium. They might walk through the main central truss and look through the 360o bay window, and then visit laboratories where physicists attempt to detect dark matter and biologists study muscle atrophy in zebrafish. To prevent loss of muscle and bone mass, our astronauts engage in scheduled exercise and various spaceship repairs every day, leaving them only an hour or two of free time in the mornings. Control center staff back on Earth likewise cannot sit back and relax. Orbital debris presents a constant, imminent danger to the wellbeing of the ISS. Station-crew and on-ground staff must do all that they can to protect this $150 billion flying space station from large debris while simultaneously conducting research and repairing the ship. The ISS is anything but permanent. Our astronauts’ toil will amount to nothing if we cannot raise the funds necessary to keep the station in orbit. Boeing predicts that the ISS’s parts can hold up through 2028, but the bigger issue is finding funding to keep the station alive. NASA and its partners in Russia, Japan, Canada, and other countries have committed to funding the station through 2020, but what its fate afterwards is uncertain. These countries are debating the question if the structure should be kept in orbit, allowing further research and providing a market for space transport companies like SpaceX and Sierra Nevada. Alternatively, they could choose to give up the mammoth, perhaps by letting it spiral down into the South Pacific for a watery death. Fortunately for ardent ISS supporters, there is some solace for the immediate future; NASA and White House officials announced plans to keep the station running till at least 2024. Still, it is time to look beyond this station. As famous and celebrated as it may be, new avenues for exploration must be built after the ISS becomes dysfunctional. As our society has look into our future in space, we have expanded our ideas, including plans to construct space colonies –stations with Earth-like features that function as permanent settlements. If these colonies successfully sustain human life, there are plans to build a mega-station called ‘Elysium’ – based off the movie – which could house a large portion of the human population. Such stations might very well be essential to mankind’s future in the stars. There are also plans to construct a new NASA vehicle, the Orion Multi-Purpose Crew Vehicle (MPCV), specifically for deep space exploration. Expected to meet the constantly growing needs of human space exploration programs, Orion may eventually carry astronauts to worlds far beyond Earth’s orbit which no man has ever seen or set foot on. This century marks the dawn of a new era in exploration, and if we can muster the manpower and financial support, humankind will advance further than we’ve ever been from our home planet

Speckle Space-Time Covariance in High-Contrast Imaging

We introduce a new framework for point-spread function (PSF) subtraction based on the spatio-temporal variation of speckle noise in high-contrast imaging data where the sampling timescale is faster than the speckle evolution timescale. One way that space-time covariance arises in the pupil is as atmospheric layers translate across the telescope aperture and create small, time-varying perturbations in the phase of the incoming wavefront. The propagation of this field to the focal plane preserves some of that space-time covariance. To utilize this covariance, our new approach uses a Karhunen-Lo\'eve transform on an image sequence, as opposed to a set of single reference images as in previous applications of Karhunen-Lo\'eve Image Processing (KLIP) for high-contrast imaging. With the recent development of photon-counting detectors, such as microwave kinetic inductance detectors (MKIDs), this technique now has the potential to improve contrast when used as a post-processing step. Preliminary testing on simulated data shows this technique can improve contrast by at least 10-20% from the original image, with significant potential for further improvement. For certain choices of parameters, this algorithm may provide larger contrast gains than spatial-only KLIP.Comment: Accepted to A

Can Extreme Bacteria Teach Us About Extraterrestrial Life?

Have you ever wondered if there is life beyond Earth? Scientists have been studying this topic for a long time and believe the answer might lie in extremophilic microbes, small organisms that thrive in extreme environments. In a 2022 study, scientists took extremophilic microbes from an analogue environment, or place on Earth similar to Mars, and put them in simulated Martian conditions. After exposing them to higher ultraviolet radiation levels, low oxygen levels, a dry atmosphere, and moisture-free Mars-like soil, these microbes still were able to survive. This research is important in helping us understand if Mars can house life and give us clues into what that life might look like beyond Earth

Astrobites as a Community-led Model for Education, Science Communication, and Accessibility in Astrophysics

Support for early career astronomers who are just beginning to explore astronomy research is imperative to increase retention of diverse practitioners in the field. Since 2010, Astrobites has played an instrumental role in engaging members of the community -- particularly undergraduate and graduate students -- in research. In this white paper, the Astrobites collaboration outlines our multi-faceted online education platform that both eases the transition into astronomy research and promotes inclusive professional development opportunities. We additionally offer recommendations for how the astronomy community can reduce barriers to entry to astronomy research in the coming decade

Surveying Nearby Brown Dwarfs with HGCA: Direct Imaging Discovery of a Faint, High-Mass Brown Dwarf Orbiting HD 176535 A

Brown dwarfs with well-measured masses, ages and luminosities provide direct benchmark tests of substellar formation and evolutionary models. We report the first results from a direct imaging survey aiming to find and characterize substellar companions to nearby accelerating stars with the assistance of the Hipparcos-Gaia Catalog of Accelerations (HGCA). In this paper, we present a joint high-contrast imaging and astrometric discovery of a substellar companion to HD 176535 A, a K3.5V main-sequence star aged approximately $3.59_{-1.15}^{+0.87}$ Gyrs at a distance of $36.99 \pm 0.03$ pc. In advance of our high-contrast imaging observations, we combined precision HARPS RVs and HGCA astrometry to predict the potential companion's location and mass. We thereafter acquired two nights of KeckAO/NIRC2 direct imaging observations in the $L'$ band, which revealed a companion with a contrast of $\Delta L'_p = 9.20\pm0.06$ mag at a projected separation of $\approx$0.\!\!''35 ($\approx$13 AU) from the host star. We revise our orbital fit by incorporating our dual-epoch relative astrometry using the open-source MCMC orbit fitting code $\tt orvara$. HD 176535 B is a new benchmark dwarf useful for constraining the evolutionary and atmospheric models of high-mass brown dwarfs. We found a luminosity of $\rm log(L_{bol}/L_{\odot}) = -5.26\pm0.06$ and a model-dependent effective temperature of $980 \pm 35$ K for HD 176535 B. Our dynamical mass suggests that some substellar evolutionary models may be underestimating luminosity for high-mass T dwarfs. Given its angular separation and luminosity, HD 176535 B would make a promising candidate for Aperture Masking Interferometry with JWST and GRAVITY/KPIC, and further spectroscopic characterization with instruments like the CHARIS/SCExAO/Subaru integral field spectrograph

Improving Undergraduate Astronomy Students' Skills with Research Literature via Accessible Summaries: A Case Study with Astrobites-based Lesson Plans

Undergraduate physics and astronomy students are expected to engage with scientific literature as they begin their research careers, but reading comprehension skills are rarely explicitly taught in major courses. We seek to determine the efficacy of lesson plans designed to improve undergraduate astronomy (or related) majors' perceived ability to engage with research literature by using accessible summaries of current research written by experts in the field. During the 2022-2023 academic year, twelve faculty members incorporated lesson plans using accessible summaries from Astrobites into their undergraduate astronomy major courses, surveyed their students before and after the activities, and participated in follow-up interviews with our research team. Quantitative and qualitative survey data clearly show that students' perceptions of their abilities with jargon, identifying main takeaways of a paper, conceptual understanding of physics and astronomy, and communicating scientific results all improved with use of the tested lesson plans. Additionally, students show evidence of increased confidence of their abilities within astronomy after exposure to these lessons, and instructors valued a ready-to-use resource to incorporate reading comprehension in their pedagogy. This case study with Astrobites-based lesson plans suggests that incorporating current research in the undergraduate classroom through accessible literature summaries may increase students' confidence and ability to engage with research literature, as well as their preparation for participation in research and applied careers.Comment: Submitted to PRPE