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In my research, I seek to understand how molecules evolve throughout the planet forming process. I use a combination of techniques in both theoretical and observational astrochemistry.
In my research, I seek to understand how molecules evolve throughout the planet forming process. I use a combination of techniques in both theoretical and observational astrochemistry.
Planet Forming Regions
Planet Forming Regions
In space, planet formation occurs when a molecular gas cloud collapses to from a protoplanetary disk. Over time, icy dust particles in the disk will stick together and get bigger and bigger to form planets. Understanding the chemical evolution in these planet forming regions is essential to understanding not only the origins of planets, but also in understanding the chemical pool available to planets. This knowledge helps us determine the habitability of planets beyond our Solar System and understand the history and origins of biological precursors.
In my research, I use a combination of astronomy, infrared astronomy, and chemical models to understand the global evolution of molecular species throughout the planet forming process. By combining each of these techniques, I am able to gain a comprehensive view of disk chemistry.
Infrared Astronomy
Infrared Astronomy
Infrared (IR) astronomy traces the vibrational and ro-vibrational transitions. I use observations from the James Webb Space Telescope (JWST), which traces the hot gas emitting in the inner disk (<10au). I use radiative transfer 'slab' models to fit column density, temperature, and emitting area of molecular species. These observations tell us about the chemical environment where terrestrial planets form.
Vibrational transitions of water. Gif Credit: Water Structure and Science by Martin Chaplin
Some topics I am using JWST data to explore include:
How does chemistry evolve throughout the disk lifetime?
What organic molecules are present where terrestrial planets form, and can they be inherited by forming planets?
Which disk properties are more or less likely to shape chemical evolution (includes chemical disk modeling)?
Stay tuned for more updates. My first JWST publication is in prep now!
Radio Astronomy
Radio Astronomy
Radio observations (millimeter/submillimeter wavelengths) trace the rotations of molecular species and are used to observe molecules in the cold gas in the outer regions (>10au) of protoplanetary disks. I have used data from interferometers, like the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA) to observe gas-phase emission.
I specialize in time-domain radio observations (including target of opportunity) and coordination with other telescopes.
Line Profiles and Keplerian Motion
Line Profiles and Keplerian Motion
The Keplerian rotation of disks broadens line emission, and a double peaked line is often observed in disks. We can use the shape of lines to learn about the distribution of gasses, even if we don't have the spatial resolution to distinguish disk features or structures. We can study variations in line shape and profile to better understand minor fluctuations in chemical abundances and temperature.
Interferometers
Interferometers
Interferometers are made up of lots of individual dishes, and the configuration of the dishes impacts what the telescope 'sees'. For example, in the graphic on the right, you can see what ALMA would see in a compact, intermediate, and extended configuration if ALMA were to observe a picture of a cat. This graphic was made using the friendlyVRI tool developed by Cormac R. Purcell and Roy Truelove.
Since I often compare observations taken at different points in time (and in different telescope configurations), I am an intimately familiar with imaging tools and techniques to mimic interferometric artifacts.
Baby Suns, X-rays, and Flares (PhD Dissertation)
Baby Suns, X-rays, and Flares (PhD Dissertation)
Young baby stars, known as T-tauri stars, are known be X-ray bright. High X-ray emission is attributed to hot ionized gas trapped in magnetic fields on the stellar surface. However, these magnetic loops can undergo re-connection events, resulting in a burst or 'flare' of X-ray photons (imaged above). T-tauri stars are known to be X-ray variable on relatively short (days-weeks) time scales, so it is important to that we have an accurate understanding of X-ray flaring events to also understand how this variability can drive disk chemistry and physics.
X-ray Light Curve Generator: XGEN
X-ray Light Curve Generator: XGEN
XGEN is a model written by me! XGEN models flaring events using a random number generator, where flare energy is determined by a power-law distribution. Below is an example light curve (considered typical for a T-tauri star) produced by XGEN (flare statistics taken from Wolk et al. 2005), and a schematic demonstrating how XGEN works. This model is described in further detail in Waggoner & Cleeves (2022) and is publicly available on GitHbub.
Combining Flares and Disk Chemistry
Combining Flares and Disk Chemistry
X-ray photons are known to drive chemistry in astronomical settings, like protoplanetary disks, via the ionization of H2 and helium. Ionized H2+ can then either collide with another H2 molecule, resulting the in the fluorescence of UV photon, or abstract a proton from H2 to form H and H3+. Each of these three products are known to chemical evolution in planet forming regions.
Unfortunately, X-ray ionization rates are non-constant over time due to flaring events. My research aims to use both models and observations to better understand how variable X-ray ionization rates drive chemical evolution in protoplanetary disks.
If you are interested to know more about my work modeling flare driven chemistry, please refer to my PhD dissertation and publications tab.
Undergraduate:
Harvard-Smithsonian
CfA REU
Undergraduate:
Harvard-Smithsonian
CfA REU
During the Summer of 2017, I began my first astrochemistry project at the SMA-Havard Smithsonian Center for Astrophysics REU program. During this time, I worked with Ilse Cleeves (who also became my PhD advisor) and modeled X-ray flare driven water variability in protoplanetary disks. This REU was the foundation of my astrochemistry career, because this project became the inspiration for my graduate research and the topic of my first first author publication.
Undergraduate:
Ball State University
Undergraduate:
Ball State University
At Ball State University I worked with Dr. James Poole studying physical organic chemistry from 2015-2018. During this time, I performed both experimental and theoretical research on radical chemistry. My experimental project explored regioselectivity of hydroxyl radical reactions with aromatic hydrocarbons to better constrain the importance of OH addition or H abstraction in the presence of functional groups on aromatic rings. My theory project modeled possible reaction pathways of Bpin reactions with various aromatic rings.
Interested in my work? Please reach out to me at awaggoner2@wisc.edu!
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