How can we characterize the atmospheres of brown dwarfs and exoplanets?
What are the formation pathways and environments of substellar objects?
How do atmospheric processes, such as cloud formation, operate in brown dwarfs and giant planets?
How do stellar abundances influence the formation and cloud properties of brown dwarfs?
How can observational and computational methods be combined to understand the atmospheric, physical, and chemical processes in exoplanets and brown dwarfs?
How can atmospheric retrieval techniques be used to characterize the atmospheres of individual exoplanetary and brown dwarf systems?
My Research
Fingerprints of Formation
Image Credit: NASA / JPL / SwRI / MSSS / Gerald Eichstädt / Thomas Thomopoulos CC BY 3.0
Clues about a planet’s formation history are encoded in its spectrum. I use spectra of young, directly imaged planets and brown dwarfs to determine their atmospheric characteristics—such as metallicity, carbon-to-oxygen ratio, isotopologue ratios, and cloud properties. These measurements help me uncover how, when, and where these planets formed.
Stellar Spectroscopy
A careful scrutiny of host stars is a critical approach to calibrating BD and exoplanet properties. Precisely measured host star abundances and metallicity values are key to correctly interpreting planetary atmospheric compositions and illuminating planet formation histories (e.g., initial formation locations and subsequent migration. I use high-resolution spectroscopic observations of solar-type stars to ground retrieval efforts of substellar companions
Image Credit: NASA/JPL-Caltech/T. Pyle (IPAC)
Clouds/Weather
Clouds have emerged as one of the most confounding issues for attempts to characterize substellar atmospheres in detail. The presence of dust clouds have the following impacts: obscuring atmospheric features be-low cloud layers, altering thermal structure, consuming elements, and changing key observables related to formation diagnostics. I use atmospheric retrievals to understand clouds of brown dwarfs and how they evolve.
Temperate Exoplanets
Are we alone? Detecting potential biosignatures and characterizing temperate world can provide us clues in the search for life. I have worked on detecting potential biosignatures such as ammonia (NH3) in the atmospheres of Hydrogen/Nitrogen dominated atmospheres with JWST and Twinkle
Research Highlights
The aim of this project was to perform retrieval analysis for a set of young, (<150 Myr), cloudy, low surface gravity planetary-mass objects that are analogs of directly imaged exoplanets (e.g. HR 8799bcde). The goal was to probe and further understand their formation pathways (via C/O ratios). As we performed the retrieval results, we found consistent difficulty in the retrieval constraints regardless of the signal to noise of the two objects and thermal profile parameterization used. Ultimately, we found further evidence for JWST is needed to guide and inform retrieval analysis in this regime.
Atmospheric Retrievals of Exoplanet Analogues: BD+60B and W0047
KEY RESULTS
- Found strong evidence for continued missing information in models
- Data strongly favored cloud models over cloudless models, consistent with red and variable nature of objects
I am leading atmospheric retrieval studies for three intermediate-mass (30 — 40 M Jup) brown dwarfs in the AB Doradus Moving Group (ABDMG) using the POSEIDON retrieval code. These three young (<150 Myr) objects share similar fundamental properties (mass, temperature, surface gravity). I am using a combination of archival ground-based and space-based data sets to investigate their atmospheric composition and formation pathways in comparison to the ABDMG environment.
Intermediate-Mass Brown Dwarfs in AB Doradus Moving Group: Formation and Composition for Early L-dwarfs.
I have worked on projects with Dr. Ji Wang on determining whether ammonia (a potential biosignature) in hydrogen and nitrogen dominated atmospheres of gas dwarfs is detectable with JWST and Twinkle. We sought gas dwarfs, as they are more amendable targets than Earth-like planets for transit observations because of their larger radii and atmospheric scale heights due to potentially hydrogen-dominated atmospheres. To learn more, please check out the papers below
Detecting Potential Biosignatures: Ammonia (NH3) in Temperate Gas Dwarfs
Stellar Abundances of FGK stars with Benchmark Brown Dwarfs
I performed a uniform stellar abundance analysis of FGK type stars with a high resolution optical spectrograph (Potsdam Echelle Polarimetric and Spectroscopic Instrument; PEPSI). In our sample, we observed ~32 stars that have benchmark wide-orbit brown dwarfs companions. In an effort to Know Thy Star, Know Thy Brown Dwarf , we uniformly report the abundances of C/O, Mg/Si and Ca/Al to (1) anchor future retrieval analysis for the brown dwarf companion and comment on the usability of abundances (other that assumed solar) for question of formation in brown dwarf and giant exoplanet science (2) predict cloud species to form in the brown dwarfs from host star Mg/Si chemistry, and (3) investigate the use the [Y/Mg] ratio as a stellar clock for our sample with wide age-estimates
KEY RESULTS
- PI of a 27.5 hour observing program with PEPSI on the Large Binocular Telescope
- Our sample has a spread in C/O ratios and [Fe/H] measurements beyond previously assumed solar values.
- Most of our systems predict enstatite and forsterite clouds with five systems also predicting quartz clouds, based on host star Mg/Si ratios
- We find for a number of systems, our derived ages from [Y/Mg] stellar clock in combination with fundamental parameters (bolometric luminosity or effective temperature ) provide mass estimates within 1σ of previous mass estimates
Currently I am advising Master’s student Malik Bossett (San Francisco State University) on determining rotational and radial velocities for a sample of solar-type host stars hosting wide-orbit brown dwarf companions. Malik is uniformly determining the rotational velocities using high-resolution optical data and the MCMC-based SMART code.