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Direct imaging studies have mainly used low-resolution spectroscopy (R ∼ 20-100) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances (e.g., carbon-to-oxygen ratio, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC (R ∼ 35,000 in the K band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS, we analyze the KPIC high-resolution spectrum (2.29-2.49 μm) and the archival low-resolution spectrum (1-2.2 μm) of the benchmark brown dwarf HD 4747 B (m = 67.2 ± 1.8 M Jup, a = 10.0 ± 0.2 au, T eff ≈ 1400 K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with those of its host star within 1σ-2σ. The retrieved parameters from the K-band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H2O, and CH4 (volume-mixing ratio of log(CH4) = −4.82 ± 0.23) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory.

We present a transmission spectrum for the warm (500-600 K) sub-Neptune HD 3167c obtained using the Hubble Space Telescope Wide Field Camera 3 infrared spectrograph. We combine these data, which span the 1.125-1.643 μm wavelength range, with broadband transit measurements made using Kepler/K2 (0.6-0.9 μm) and Spitzer/IRAC (4-5 μm). We find evidence for absorption by at least one of H2O, HCN, CO2, and CH4 (Bayes factor 7.4; 2.5σ significance), although the data precision does not allow us to unambiguously discriminate between these molecules. The transmission spectrum rules out cloud-free hydrogen-dominated atmospheres with metallicities ≤100 solar at >5.8σ confidence. In contrast, good agreement with the data is obtained for cloud-free models assuming metallicities >700 solar. However, for retrieval analyses that include the effect of clouds, a much broader range of metallicities (including subsolar) is consistent with the data, due to the degeneracy with cloud-top pressure. Self-consistent chemistry models that account for photochemistry and vertical mixing are presented for the atmosphere of HD 3167c. The predictions of these models are broadly consistent with our abundance constraints, although this is primarily due to the large uncertainties on the latter. Interior structure models suggest that the core mass fraction is >40%, independent of a rock or water core composition, and independent of atmospheric envelope metallicity up to 1000 solar. We also report abundance measurements for 15 elements in the host star, showing that it has a very nearly solar composition.

We present a transmission spectrum for the Neptune-size exoplanet HD 106315 cfrom optical to infrared wavelengths based on transit observations from theHubble Space Telescope/Wide Field Camera 3, K2, and Spitzer. The spectrum showstentative evidence for a water absorption feature in the $1.1 - 1.7\mu$mwavelength range with a small amplitude of 30 ppm (corresponding to just $0.8\pm 0.04$ atmospheric scale heights). Based on an atmospheric retrievalanalysis, the presence of water vapor is tentatively favored with a Bayesfactor of 1.7 - 2.6 (depending on prior assumptions). The spectrum is mostconsistent with either enhanced metallicity, high altitude condensates, orboth. Cloud-free solar composition atmospheres are ruled out at $>5\sigma$confidence. We compare the spectrum to grids of cloudy and hazy forward modelsand find that the spectrum is fit well by models with moderate cloud lofting orhaze formation efficiency, over a wide range of metallicities ($1 - 100\times$solar). We combine the constraints on the envelope composition with an interiorstructure model and estimate that the core mass fraction is $\gtrsim0.3$. Witha bulk composition reminiscent of that of Neptune and an orbital distance of0.15 AU, HD 106315 c hints that planets may form out of broadly similarmaterial and arrive at vastly different orbits later in their evolution.