A high-resolution spectroscopic survey of directly imaged planets, brown dwarf companions, and hot Jupiters with Keck/KPIC

The Keck Planet Imager and Characterizer (KPIC) is a fiber-fed spectrograph for exoplanet characterization. We have collected K-band high-resolution spectra (1.9-2.5 µm, R~35,000) for about 30 directly imaged exoplanets (m < 13 M_Jup) and brown dwarf companions (m > 13 M_Jup), as well as 10 hot Jupiters. I overview science results from three years of KPIC. First, I present new high resolution KPIC spectra of the most challenging imaged planets (e.g. HR 8799 bcde, AF Lep b). Then, I showcase a population-level analysis of the compositions of ~10 planetary-mass companions (m~10-30 M_Jup) with orbital separations spanning ~50-350 AU and Teff~1500-2500 K. We find C/O~0.5-0.7 and near-solar metallicities for this ensemble of companions. Assuming solar abundances for their young host stars, which is typical of the star-forming regions they are in, these results indicate that widely separated m~10-30 M_Jup companions are more consistent with forming via direct gravitational collapse instead of core accretion. This is in contrast to the imaged giant planets, for which there is evidence of metal enrichment compared to their host stars. I also summarize six new ¹²CO/¹³CO measurements from KPIC, which more than doubles the literature measurements, and discuss the potential of ¹²CO/¹³CO as a formation tracer. Finally, I highlight initial results from the KPIC hot Jupiter survey. We find that hot Jupiters have a more diverse range in C/O (~0.3 to 0.8) and generally metal-enriched atmospheres, which is characteristic of core accretion in a protoplanetary disk.