One 8 meter telescope is fine, but why not use four 8 meter telescopes at the same time? I use the K-band (2-2.5 micron) beam combining instrument GRAVITY at the Very Large Telescope Interferometer (VLTI) to study exoplanets and brown dwarfs as a member of the ExoGRAVITY collaboration. Using optical interferometry, we make very precise measurements of the orbital motion of giant planets, and collect spectra containing information about the abundances of carbon and oxygen bearing molecules in their atmospheres. I used these techniques to study the orbit, composition, and formation of one of the lowest mass exoplanets directly imaged from teh ground, AF Leporis b. In my first author paper on the system, I showed that the planet’s orbit is effectively circular, and the planet’s atmosphere is cloudy and strongly vertically mixed. I also evaluated some degeneracies in the Bayesian modeling of the atmosphere, showing why previous studies had overestimated the planet’s metallicity (hint: it’s always the fault of the clouds). This ensemble of results indicates not only that AF Lep b likely formed via core accretion, but that it hasn’t been disturbed by other planets or passing stars since it formed 25 million years ago.
Jan 1, 0001
As a member of the JWST Telescope Scientist Team (JWST-TST), I used guaranteed time observations planned by our high contrast imaging group at STScI to reveal the atmospheres of the iconic HR 8799 planets at never-before-seen wavelengths of light. The data is described in a first author paper I published in March 2025. The paper had a press release, found here. This result validates the findings of our ExoGRAVITY collaboration paper on the system, that the four gas giants in the HR 8799 system appear to be metal rich compared to their host star, indicating that they formed via core accretion. In order to block the light from the bright host star and reveal these faint planets, we used a novel mode of the Near Infrared Camera (NIRCam) coronagraph, placing all the observations at the narrowest end of the underutilized wedge shaped mask.
Jan 1, 0001
In particular, our JWST observations show clear carbon dioxide absorption (CO2) in the spectrum of each planet in the HR 8799 system, which, compared to the clear carbon monoxide absorption (CO), gives us a handle on the relative enrichment of heavy elements in these planet’s atmospheres. We also observed the young, Jupiter-mass planet 51 Eri b. Despite how faint this planet is, we were able to detect it at a wavelength of 4.1 microns, which tells us indirectly about how hot the planet is, and how much CO2 is in its atmosphere. Based on these measurements, we can say that these planets likely formed via core accretion. We hope to apply these techniques to characterize more systems in the near future. I was awarded about 23 hours of additional JWST observing time to repeat this experiment in four additional directly imaged systems. That means four more beautiful images of giant exoplanets from JWST coming soon!
Jan 1, 0001
I recently led a JWST Cycle 2 DD program with William Balmer to characterize the atmosphere of AF Lep b with JWST/NIRCam 4.4 micron imaging. At a separation of 320 mas, AF Lep b is a challenging planet to recover with JWST. At these wavelengths, AF Lep b is only two resolution elements (five NIRCam pixels) away from the host star. Furthermore, over 90% of the light from the planet is blocked by the coronograph at this separation. Despite these challenges, we successfully recovered the planet at a high significance at its expected location. The resulting photometry produced clear evidence for the presence of disequilibrium chemistry and enhanced metallicity in the atmosphere of AF Lep b. This is an exciting technical achievement for NIRCam coronagraphy — AF Lep b is now the closest separation planet successfully imaged with JWST!
Jan 1, 0001