Research
Here are descriptions of my first-author projects!
The TRAPPIST-1 e/b program -- coming soon!
TRAPPIST-1 is one of the best known exoplanetary systems, and it's small size makes it the best candidate for observations of terrestrial, rocky exoplanets. However, early observations with JWST show significant stellar contamination that we cannot confidently model. The TRAPPIST-1 system contains a possible solution to overcome this stellar contamination. Using the multiplicative effect of the stellar contamination signal to our advantage, we propose to observe close (but not overlapping) transits of TRAPPIST-1 b and TRAPPIST-1 e. The ratio of the resulting transmission spectrum will correct for the signal from the stellar contamination, and leave only the ratio of their atmospheric opacities. Assuming little to no atmospheric signal from TRAPPIST-1 b based on the thermal emission observations, we expect this ratio to result in the transmission spectrum of TRAPPIST-1 e normalized by the flat transit depth of TRAPPIST-1 b. Using this method, we can detect an Earthlike atmosphere on TRAPPIST-1 e using 15 close transits of TRAPPIST-1 b and e to 3 sigma significance.
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We have already published our initial study of TRAPPIST-1 e, based on four transits from the TST-DREAMS GTO program (PI Nikole Lewis). We find a tentative persistent signal between visits, which may be indicative of an atmosphere, but may also be due to stellar noise. Our new program will provide an answer to the atmospheric state of TRAPPIST-1 e, implications of which go beyond the TRAPPIST-1 system to the likelihood of atmospheric survival of rocky planets in the habitable zones of M dwarfs across the universe.
Read our original paper on TRAPPIST-1 e paper from the TST-DREAMS GTO program here
Hot Rocks Survey IV: Emission from LTT 3780 b Is Consistent with a Bare Rock
It is an open question whether small planets around M dwarfs are able to maintain atmospheres. The Hot Rocks Survey aims to address this question by observing nine rocky exoplanets orbiting M dwarfs with MIRI emission photometry to constrain the onset of atmospheres. In this paper, we present two MIRI F1500W (15 μm) eclipses of LTT 3780 b, an ultrashort-period super-Earth (P = 0.768 days, R = 1.325 R⊕, M = 2.46 M⊕) that receives 111× Earth’s instellation, the highest in the survey. We find a combined eclipse depth of 312 ± 38 ppm, which is consistent between different data reduction and analysis assumptions, bolstering our confidence in the eclipse detection. This eclipse depth is consistent with the thermal emission from a bare rock surface, with a dayside temperature of 1143±100 K, 98% ± 9% of the maximum temperature predicted for a zero-albedo, zero heat redistribution blackbody. We are able to confidently rule out CO2-based atmospheres down to a 0.01 bar surface pressure to greater than 3σ (ruling out an approximately Mars-like atmosphere). We are unable to rule out a pure H2O 1 bar atmosphere, though we argue that this composition is unlikely on such a highly irradiated planet, nor O2 atmospheres due to the lack of features in the bandpass, though we can put constraints on CO2-mixture atmospheres. As a potential bare rock, we consider a variety of surface composition models, but are unable to distinguish between them. However, LTT 3780 b is an excellent target for follow-up JWST observations to determine its surface composition and rule out additional atmospheric compositions.
HST SHEL: Enabling Comparative Exoplanetology with HST/STIS
The Hubble Space Telescope (HST) has been our most prolific tool to study exoplanet atmospheres. As the age of JWST begins, there are a wealth of HST archival data that are useful to strengthen our inferences from JWST. Notably, HST/Space Telescope Imaging Spectrograph (STIS), with its 0.3–1 μm wavelength coverage, extends past JWST’s 0.6 μm wavelength cutoff and holds an abundance of potential information: alkali (Na, K) and molecular (TiO, VO) species opacities, aerosol information, and the presence of stellar contamination. However, time-series observations with HST suffer from significant instrumental systematics and can be highly dependent on choices made during the transit fitting process. This makes comparing transmission spectra of planets with different data reduction methodologies challenging, as it is difficult to discern whether an observed trend is caused by differences in data reduction or underlying physical processes. Here we present the Sculpting Hubble’s Exoplanet Legacy (SHEL) program, which aims to build a consistent data reduction and light-curve analysis methodology and associated database of transmission spectra from archival HST observations. The data reduction pipeline and tutorials are available on Github and Zenodo.
ACCESS: Transmission Spectrum of hot Saturn HATS-5 b
HATS-5 b is an interesting hot Saturn which has an equilibrium temperature of ~1025 K, which is a regime of predicted clear atmospheres at the pressures probed by transmission spectroscopy. As part of the ACCESS collaboration, we observed HATS-5 b over 5 nights with the IMACS instrument on the Magellan/Baade telescope. From these observations, we obtained the transmission spectrum and uncovered evidence of a clear, solar-metallicity, sub-solar C/O atmosphere with a tentative detection of water! We also see evidence for a depleted abundance for alkalis Na and K, which has been tentatively predicted around this temperature range. Future observations with JWST would be able to confirm this water detection as well as superbly constrain the atmospheric parameters.
Read the paper here (and see another great ACCESS paper I'm part of here).
The Formation of Earth's Largest Impact Crater
The Vredefort crater is Earth's largest verified impact crater. Though it is quite old (~2 billion years old) and thus has gone through extensive erosion, it was believed to originally have a diameter of 250-300 km. I used iSALE, a shock physics impact code, to simulate the impactor that created the crater. Our finding of an asteroid 20-25 km in diameter with an impact speed of 15-25 km/s was in disagreement with past simulation results, but is a better fit to the characteristics found in the crater. This impactor is even larger than the one that killed the dinosaurs, and would have caused similarly catastrophic effects globally, but only single-cellular life existed at the time. Additionally, using an ejecta layer found in Karelia, Russia, we were able to use the ejecta predictions from the simulations to constrain the landmasses of South Africa and Russia to have been ~2000 km apart 2 billion years ago - much further back than our current simulations can predict.
Star Formation and Stellar Outflows: Characterizing NGC 1333 and HH 7-11
NGC 1333 is likely the largest nearby star formation region (d~300 pc). As common in active star formation areas, contained within it are a number of Herbig Haro (HH) objects, tracing the stellar outflows of young stellar objects. HH 7-11 is a particularly striking and famous example, and is the subject of the study. I used Spitzer and Hubble Space Telescope observations to study these objects in detail, and using the MAPPINGS shock simulation program I determined the outflow characteristics of the HH 7-11 shock. Using this information, we estimated the total energy and momentum feedback from the outflow, which will eventually be done for all outflows in NGC 1333 in an attempt to determine the eventual fate of the natal cloud.