About Me

I am a fourth year graduate student and NSF Graduate Research Fellow at The University of Texas at Austin pursuing a PhD in Astronomy. My advisor is Prof. Brendan Bowler. We work on using long-term astrometric accelerations detected between Hipparcos and Gaia to complement direct imaging of exoplanets and brown dwarfs. I am interested in how this combination of techniques can improve our understanding of the formation, demographics, and atmospheric evolution of wide-separation planet and brown dwarf companions. To this end, I have focused on two main projects at UT: measuring the dynamical mass of the brown dwarf companion HD 984 B and launching a multi-facility survey of young accelerating stars to image new planets. Before coming to UT, I majored in Physics with a minor in Computer Science at the University of Michigan. There, I worked with Prof. David Gerdes on finding new minor planets in the outer solar system that were detected serendipitously as part of the Dark Energy Survey. Outside of astronomy, I love to play music. I play clarinet, piano, and the guitar; was in the marching band at Michigan; and even conducted a clarinet choir at one point!

Here is my CV, which contains an updated publication list.

Research

My research uses the combination of Hipparcos and Gaia to study exoplanets and brown dwarfs on wide orbits amenable to direct imaging. Long-period substellar companions induce small astrometric accelerations on their host stars from their reflux motion. The unprecedented sensitivity of Gaia combined with the 25 year time-baseline between the two missions enables the detection of small proper motion changes caused by planets and brown dwarfs at separations accessible to high-contrast imaging. This astrometric information is key to both better characterizing known substellar companions through the measurement of precise dynamical masses and imaging new planets and brown dwarfs around stars for which their astrometric accelerations betray the presence of undiscovered companions.

Dynamical Mass of HD 984 B

The masses of directly imaged planets and brown dwarfs are typically not directly determined. Instead, they are inferred using evolutionary models that leverage the cooling of substellar companions over time to predict an object's mass given its luminosity and age. This leaves most of these objects with relatively uncertain masses that are highly dependent on the choice of model, limiting their effectiveness in studying planet and brown dwarf formation and evolution. Benchmark substellar companions where we can directly determine their masses are needed to test these evolutionary models and their underlying assumptions about the atmospheric and internal physics of low-mass objects. It is challenging to obtain these valuable benchmarks, however, as they require knowledge of the acceleration induced by the companion on the host star. Only about fifeteen dynamical masses of imaged substellar companions have been measured thus far.

One way to obtain a precise dynamical mass is to couple observations of the relative motion of the companion with absolute astrometry of the host star, provided by Hipparcos and Gaia proper motions. In June of 2019, we realized that the star HD 984 exhibits a significant proper motion difference between Hipparcos and Gaia. HD 984 is a young (30-200 Myr) F7 star with an imaged low-mass companion, which at the time had model-dependent masses that ranged from 30 MJup to 90 MJup, spanning both the brown dwarf and low-mass star regimes. The astrometric acceleration detection enables the measurement of a precise dynamical mass of the companion. To extend the previously short orbital arc (2012-2015), we obtained high-contrast imaging with NIRC2 at Keck Observatory of the system in July 2019 and July 2020. Additionally, to constrain the radial direction of the acceleration, we obtained precision radial velocities of the host star with the Habitable-Zone Planet Finder on the Hobby-Eberly Telescope. Performing a joint orbit fit of the relative astrometry, radial velocities, and Hipparcos-Gaia proper motions yields a dynamical mass of 61 ± 4 MJup. This places the companion firmly in the brown dwarf regime. HD 984 B joins a small but growing list of benchmark substellar companions with measured dynamical masses and well-constrained ages and luminosities. Here's our recent paper on this measurement.

Imaging Giant Planets around Accelerating Stars

Over the last quarter-century, the census of planetary systems has exploded from the single case study of our solar system to over three thousand planetary systems. This has revolutionized our picture of planetary formation, evolution, atmospheres, composition, and orbital demographics. High-contrast imaging has played an important role in constructing this picture. It is the only detection method well-suited to studying planets on wide orbits (>10 AU), providing a crucial complement to detection methods biased towards close-in exoplanets. Furthermore, by directly collecting photons emitted in giant planet atmospheres, this technique provides unparalleled information on the composition, internal structure, and atmospheric properties of extrasolar gas giants.

Despite extensive campaigns to image planets around nearby young stars with state-of-the-art extreme AO facilities (e.g., GPIES, SHINE), only about a dozen long-period planets have been imaged, owing to the low occurrence rate of wide-separation exoplanets (~1%; Bowler 2016). While these detections have been valuable in constructing and testing theories of their atmospheric properties and origins, by number, they pale in comparison to the thousands of planets detected via radial velocities or transits. Hipparcos-Gaia proper motions provide a means to overcome this low occurrence rate by focusing on stars that exhibit low-amplitude astrometric accelerations that may be produced by unseen planets that can be directly imaged.

I am conducting a multi-facility survey to image planets around the most promising stars for harboring substellar companions, selected from their Hipparcos-Gaia astrometric accelerations. The primary contaminant for this type of program is binaries, which can produce the same low-amplitude astrometric accelerations as closer-in planets and brown dwarfs. To remove these binary interlopers, the first phase of this program is observationally vetting our sample with shallow high-resolution imaging via facilities including SOAR, WIYN/NESSIE, and Keck/NIRC2. Following this, we will obtain deep high-contrast imaging of the stars that emerge from the binary vetting, to hopefully discover new planets and brown dwarfs! This survey is well underway, with hundreds of stars that have already undergone binary vetting. Our hope is that this new, efficient program will significantly add to the currently small list of imaged planets.