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Direct detection of cold exoplanets with JWST

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If you have a question about this talk, please contact Dr Emily Sandford.

Observing substellar companions with multiple techniques allows for the best possible understanding of their formation, evolution, and atmospheric physics. Radial velocity (RV) observations are biased toward planets on short orbits, while high contrast imaging (HCI) is biased towards planets on very long orbits: in general, RV and HCI data are not available for the same substellar companions. In rare cases, however, long-term dynamical accelerations allow us to pinpoint prime HCI systems, and directly detect their substellar companions. This combination provides a rare but exceptionally detailed view of these companions: we can simultaneously measure precise dynamical masses, bolometric luminosities, and atmospheric compositions, and characterize the orbits of these companions. Mass/luminosity measurements have indicated a confusing tension: several brown dwarfs appear to be over- or under-luminous relative to their dynamical mass. Orbital measurements, meanwhile, indicate that brown dwarf companions are typically much more eccentric than their giant planet counterparts, shedding light on the diverse formation paths of these objects. In some cases, circumstellar debris disks can be directly detected and characterized, and their interactions with giant planets in the system constrained.

To date, the RV+HCI technique has only been possible for brown dwarf companions, and for the very youngest exoplanets – but with JWST this technique will likely allow for the first coronagraphic images of a solar-age exoplanet, paving the way to detailed characterization of cool (300K) exoplanet atmospheres through spectroscopic observations and photometric variability campaigns. I will present my work to identify long-term RV trends, and use Hipparcos and Gaia astrometric information to further select and characterize the best HCI targets. I will particularly highlight some early results from my recent JWST program, where we collected coronagraphic images of the nearby Eps Ind A, a 4Gyr star with a massive radial velocity companion (~3Mj), in the hopes of directly detecting that planet. I will also discuss an ongoing VLT /SPHERE program to identify new brown dwarfs based on RV trends, and also highlight a particularly puzzling object identified via this method: the HD4113C brown dwarf, which shows a striking and as-yet unexplained mass/luminosity tension. I will also present our work to image systems with circumstellar debris dust, and to characterize the disks themselves through scattered light imaging.

This talk is part of the Exoplanet Seminars series.

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