RV measurements of directly imaged brown dwarfs to characterize companions and search for exomoons with KPIC

Exoplanet demographic studies emphasize the wide diversity of planets that populate our Milky Way, such as Super-Earths, mini-Neptunes, and hot Jupiters. Such a diversity could be expected for extrasolar satellites, or exomoons, but this population remains to be measured beyond our own solar system. Using the Keck Planet Imager and Characterizer (KPIC), a high contrast imaging suite attached to a high resolution spectrograph (1.9-2.5 microns, R~35,000), we carry out the spectral characterization of exoplanets through measuring planetary radial velocities and atmospheric parameters. I present the first dedicated exomoon radial velocity search using high-contrast, high-resolution observations of directly imaged substellar companion, GQ Lup B. Over 10 epochs, we find a median RV error of 1 km/s, most likely limited by systematic fringing, or oscillations in the spectrum’s continuum as a function of wavelength due to transmissive optics in KPIC. With this RV precision, KPIC is sensitive to exomoons 4.7% the mass of GQ Lup B at a separation of 65 Jupiter radii, or the extent of the cavity measured in the circumplanetary disk (CPD) detected around GQ Lup B. Using simulations of HISPEC, a high resolution infrared spectrograph planned to debut at the W.M. Keck Observatory in 2025, we estimate future exomoon sensitivity to increase by over an order of magnitude at separations within the CPD.