Overview

My research interests concern the origin and formation of planets and Brown Dwarfs (objects often referred to as “failed stars” although their origin and nature are often much more complicated that that). The big questions that drive my research are “how do solar systems like our own form,” “how do planetary systems form generally,” and “how unique is our solar system in the context of planet formation?” I have used big telescopes, special optics, and computer algorithms to study the orbital properties and photometric variability of low mass embedded companions: peering inside planetary cradles to observe infant exoplanets growing inside circumstellar disks. I also have used smaller telescopes to observe young and low mass stars, leveraging a plethora of methods to understand the growth of pre-main-sequence stars and the accretion process. Currently, I am using interferometry and spectroscopy to characterize the atmospheres of Brown Dwarfs and exoplanets. Put simply- I love observational astronomy.

Most of my work during my undergraduate studies involved direct imaging, simulations of direct imaging, and the aggregation of direct imaging results. There’s a visceral satisfaction in taking a picture of something hundreds of light years away (especially if that something is a planet) and using that picture to understand something deeper about the physics of the universe.

Giant Accreting Protoplanets Survey (GAPLanetS)

A six panel schematic. Panel one shows three blobs which are labeled as being 1 parsec in diameter. These blobs represent molecular, star forming clouds. Panel two shows a single blob, now more circular, which has arrows pointing inwards towards the core of the blob. This represents the contraction of protostellar cores into a protostar. Panel three shows a protostar with a thick, flared disk and circumstellar envelope. Panel four shows a smaller, flatter circumstellar disk and a Pre-Main-Sequence star; the disk is labeled as being 100au in diameter. Panel five shows a disk with rings and no circumstellar envelope (again labeled as being 100au in diameter). Panel six shows a diagram of a solar system with three planets in a single plane and a highly inclined comet or planet on an eccentric orbit around a Main-Sequence star (this panel is labeled as being 50au in diameter).

In jargon-y, technical terms, I used a handful of direct imaging detection methods to observe accreting protoplanets embedded within circumstellar disks. The survey I worked on focuses on transition disks and the planets that form within them. Transition disks are circumstellar disks which exhibit significant material and morphological evolution when compared to younger protoplanetary disks. Transition disks boast wide gaps and striking spiral arms indicative of planet formation, and observations of these systems can reveal information about the composition of planetary building blocks, and the dynamical evolution of planet formation. Important high contrast observations over the past two decades continue to overturn our understanding of the planet formation process. The image to the right is a schematic of the star formation process, the byproduct of which is a circumstellar disk and eventually a solar system.

There are a lot of contentious claims about planet formation and direct imaging, plenty of competing theories, and so many open questions, which is what makes the field so exciting. These kinds of studies also require methods and instruments which exist on the bleeding edge of observational and computational innovation. It’s an exciting time to be an astronomer interested in these kinds of questions!

A good analogy to help understand the problem of direct imaging goes something like: trying to image a Jupiter sized planet around a sun-like star is like trying to take a picture of a firefly next to a lighthouse on the West Coast of Turtle Island, all the way from the East Coast.

Image credit: NASA Space Place

This has been accomplished! Astronomers to date have been able to take direct images of widely separated, massive planets by using big telescopes, clever algorithms, and specialized optics. Giant, widely separated planets (more massive than Jupiter, but on Neptune sized orbits) are rare when compared to close in, less massive worlds like the Earth. This means direct imaging has only produced a handful of results when compared with other detection methods. Meme pages like “Exoplanet Memes for Habitable Teens” make this abundantly clear. Still, direct imaging is the only way to fully characterize exoplanet properties (like atmospheric composition), and observe populations of exoplanets that other methods are not sensitive to. Advancements in technology will allow astronomers in the near future to directly image more common exoplanets, and gather more detections. But how do astronomers currently circumvent these limitations and directly observe these rare, massive, and widely separated exoplanets?

An artist interpretation of a transition disks, where newly formed planets have carved a large inner cavity. Image credit: NAOJ

Planets form from circumstellar disks, which are the “leftovers” of the star formation process that settle into rotation around a protostar. These “cradles” of planet formation swaddle young planets which grow within the disk. We know circumstellar disks host planets because we can observe the dynamical footprint of planets carving rings and spirals into the disks and because we’ve been able to discover exoplanets within circumstellar disks (more on that in a moment). Dust within the disk coagulates to form pebbles, which form rocks, boulders, planetesimals, and so on. Gas giant planets, like Jupiter, likely begin as icy, rocky cores which grow massive enough to pull tons of hydrogen gas from the disk into their atmospheres.

This accretion process, by which a giant planet gains mass, causes the accreting molecular hydrogen gas to heat up; upon recombination, the gas will emit light of very specific and predictable colors corresponding to the energy of the electrons in the gas. An accreting planet will shine brightly at these colors- bright enough in comparison to its host star to be detectable by the current generation of telescopes. Importantly, heated hydrogen gas shines brightly in visible light, which doesn’t require an exceedingly large telescope to resolve. By taking an image in a hydrogen line filter (which captures signal from the star and the planet’s accretion), and then a nearby, boring filter (capturing only the starlight) we can subtract the two images, leaving us with an image of the planet and the accretion signal, and no more pesky starlight (or confounding disk signal).

This image visualizes the SDI technique I employ to observe accreting planets. While starlight and the distortions caused by the atmosphere are of equal brightness between the two wavelengths of light, the accretion signal from the giant planet is brighter in an emission band characteristic of Hydrogen. By subtracting the two images, astronomers can isolate the signal from the growth of the young planet. Pictured is the giant, accreting planet LkCa 15b, which was discovered by my undergraduate advisor Kate Follette. Image credit: Follette Lab

Another limiting factor is our ability to resolve sources through the distortion of Earth’s atmosphere. In order to combat this, astronomers use deform-able mirrors to cancel out the distortion of the atmosphere. This technique is referred to as “adaptive-optics” (AO). The Magellan telescope, the source of GAPlanetS data, boasts the Magellan Adaptive Optics (MagAO) system. There’s a great online resource on adaptive optics written by a professor at RIT here. I’ve included some cool explainer images in the gallery below as well.

I remove starlight and spurious disk signals from adaptive optics images in a process referred to as “PSF subtraction.” I use angular differential imaging (ADI), leveraging the rotational diversity of a time series of observations and spectral differential imaging (SDI), leveraging the excess luminosity exhibited by objects undergoing accretion to remove starlight and disk structure from images via the python implementation of the fancy sounding Karhunen-Loeve Image Processing (pyKLIP) algorithm. Another analogy: I essentially use a form of facial recognition to create a model of the host’s starlight, which I subtract from images to reveal growing planets. I do this work under the tutelage of Dr. Kate Follette, who is the PI of the Giant Accreting Protoplanet Survey (GAPlanetS).

After uncovering planet signal using adaptive optics, angular and spectral differential imaging, and the KLIP principle component analysis algorithm, I use a pyKLIP forward modeling technique to determine the position and brightness of a detected planet over time. This allows for a more nuanced understanding of their properties, evolutionary history, and how they shape the environment of their host transition disks.

This image shows the ADI+SDI reduction of beta Pictoris b, a Jupiter sized exoplanet, and the model of that image. The model is a great fit, because the residual map (data minus model) on the far left is essentially featureless. I use the same modeling technique, albeit on a different target system. Image credit: Wang et al. 2016

Q: “What is your website logo?”

A: Good question! An artifact of the KLIP PSF subtraction process is “self-subtraction” which occurs because the modeled PSF is constructed from a finite series of images (good explanation here). So when you reveal a planet using KLIP or a similar ADI algorithm, the signal of the planet is this emblematic little butterfly thing, with the planet light surrounded by two self-subtraction lobes. My website logo in particular is one of the results of my undergraduate thesis research.

Simulating Exozodi Yield

During the summer of 2020 (amid other things) I worked remotely with Dmitry Savranski in the Space Imaging and Optical Systems Lab (SIOS Lab) at Cornell University. I used EXOSIMS, a direct imaging simulation suite developed by SIOS lab, to predict the yield of the miniaturized Distributed Occulting Telescope (mDOT), a novel cubesat proposed by some very smart people at Stanford University which will demonstrate the effectiveness of an occulting star shade in negating starlight to observe exoplanets and circumstellar dust. You can view slides from a presentation I gave on this research here.

Transition Disk Database

The Transition Disk Database (TDD) is an aggregation of transition disk morphology and properties. I presented the results of this literature review at the 235th meeting of the American Astronomical Society (see my “betterposter” design here).

This is a picture of me presenting my poster on the TDD at the 235th meeting of the AAS in Honolulu, HI. Nice shirt, too!

Very Low Mass Variability

I observed very low mass (VLM) stars using the Half-Degree-Imager on the WIYN 0.9m telescope atop Kitt Peak National Observatory on the Tohono O’odham Nation. I presented some of this research with my collaborator Lena Treiber to the Five College Astronomy Department (who paid for my trip to KPNO). You can see our poster and some very beautiful images of the Taurus star forming cloud below. I kept an online journal during the spring semester, which you can read here.

Teachers Assistant work and Star Clusters

I worked as a TA for many of the astronomy course offerings at Amherst College (ASTR 112: Alien Worlds, ASTR 337: Observational Techniques I, and ASTR 341: Obs. Tech. II). I set up and operated the 11in Cassegrain telescopes atop the New Science Center’s observatory, working under one of the coolest people I know, Sarah Betti. We’ve gotten some pretty good data, given local weather conditions and elevation, which I’ve used to fit isochrones to open clusters.