Assistant Research Scientist, Astronomy & Astrophysics department, University of California, San Diego
Exploring exoplanets with direct imaging and novel high-resolution spectroscopy techniques.
Studying the atmospheres of the coldest exoplanets and brown dwarfs with JWST
One of the next milestones in exoplanet science is the detection of gas giants that are similar to the ones in our own solar system. We are currently able to study the atmospheres of planets that are either 10 times closer to their star (mostly transit spectroscopy), or several times larger and further away (direct imaging). Measuring the composition of the first true solar system analogs would bridge the gap between these two populations. This is necessary to identify the trends in atmospheric composition that would allow us to better understand how they form. This might just be possible with JWST.
JWST presents a unique opportunity to observe directly imaged exoplanets and brown dwarfs at wavelengths >3 μm and thereby better constrain their composition and atmospheric physics. I have developed tools to enable the first moderate resolution spectra with NIRSpec (R~2,700; 2.9−5.2 μm) targeting substellar companions at high contrast, when the companion is much fainter and close to its star. The figure above features the faint T-dwarf companion HD 19467 B, which has clear spectral features of CO2, CH4, CO and H2O in its spectrum (Figure below). In order to mitigate systematics caused by spatial undersampling, we developed a framework to forward model the companion signal and host starlight directly in detector images. We demonstrated a sensitivity to companions that are 2x10-6 fainter than their stars at 1′′ (figure above). The achieved performance will enable detailed spectroscopy of most known directly imaged exoplanets, and even allow spectroscopy of sub-Jupiters up to ~1 Gyr at 10 pc and 1’’ separation.
Searching for exomoons
The development of novel instruments combining the power of high-resolution spectroscopy and high-contrast imaging is enabling the first direct radial velocity measurements of planets. This will allow us to detect wobble of these planets caused by orbiting satellites.
The figure below shows the future prospects for exomoon detections around the brown dwarf companion HR 7672 B. From ~1.5 nights of observations with the KPIC instrument, we have demonstrated a sensitivity to satellites with a mass ratio of 1-4% at separations similar to the Galilean moons (Dashed blue). The figure also includes simulated sensitivity for future instruments like Keck/KPIC II, Keck/HISPEC, and TMT/MODHIS (colored curves) assuming 6 nights of observations over a 25-day period.
The mass ratios of the Galilean satellites are shown as black dots for comparison. Their possible scaled-up mass ratios accounting for the larger mass of the brown dwarf compared to Jupiter are shown as grey crosses. The Roche limit is computed for both a rigid and a fluid satellite shown as the inner and outer greyed region respectively. The black dashed lines represent the astrometric sensitivity of VLTI/Gravity and the vertical gray scale bars represent direct imaging of satellites.
Measuring the composition of exoplanets
The formation of directly imaged planets, whether from accretion of planetesimals or from the collapse of the circumstellar disk, remains poorly understood. Different formation models predict different atmospheric compositions, so spectroscopic characterization of exoplanets might be used to inform their formation pathway.
Get in touch at jruffio at ucsd.edu