Jean-Baptiste Ruffio

David & Ellen Lee Prize Postdoctoral Fellow, California Institute of Technology

Exploring exoplanets with direct imaging and novel high-resolution spectroscopy techniques.

As an astronomer interested in extra-solar planets, I strive to better understand planet formation and pave the way for the first detections of bio-signatures around Earth analogs. I am interested in planets across all ages: from their cradle as they actively accrete material from their protoplanetary disk to the mature planets similar to our own solar system. I explore these new worlds through the largest direct imaging surveys by developing novel statistical tools and instrumentation techniques. Moderate to high-resolution spectroscopy for high-contrast science is particularly exciting. It will for example unravel the mysteries of planet formation by measuring trends in atmospheric compositions, detect new populations of exoplanets including their moons, or even map their surface features with Doppler imaging. While the past decade was marked by the discovery of thousands of exoplanets, the next frontier will be population studies of their atmospheres for comparative exoplanetology.

Steps leading to the detection of water (H2O) and carbon monoxide (CO) in the atmospheres of the HR 8799 planets using the OSIRIS instrument at the Keck observatory and the new data reduction framework that I developed during my PhD. It allowed the study of planets that were so far inaccessible and enabled the measurements of the radial velocities of the planets themselves. I am developing a Python module for high-contrast imaging at high spectral resolution called BREADS (

(left) Using over a decade of Keck/OSIRIS observations, we have obtained the best moderate resolution spectra of the HR 8799 planets. (Right) While classical core accretion models predict super-stellar C/O, we showed that the four planets have similar C/O ratio and consistent with stellar.

A particularly exciting prospect for high-contrast imaging has been the recent development of dedicated high-resolution spectroscopic facilities. I have been working on the Keck planet imager and characterizer (KPIC; R=35000), which is the first instrument of its kind to come online. After two years on sky, our team has already opened new frontiers for exoplanet characterization. We have detected 20+ low-mass companions at high spectral resolution and measured the first spins of the HR 8799 planets. Exciting applications of high-resolution spectroscopy include the direct detection of new populations of planets, the characterization of their atmospheres, spin measurements and mapping their surface features with Doppler imaging, and even the search for exomoons from measurement of their radial velocities. It is a very active area of instrument development and innovative data analysis techniques.

During my PhD at Stanford University with Bruce Macintosh, I designed a statistically motivated planet detection algorithm for high-contrast imaging based on forward modeling and matched filtering. The open-source package is publicly available in python ( I analyzed the data for one of the largest and most sensitive searches for young gas giant planets around 524 nearby stars (Gemini Planet Imager Exoplanet Survey) enabling its derivation of planet occurrence rates. We showed that giant planets are more common around higher-mass stars and form a distinct population from brown-dwarf companions suggesting that they form differently.

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