Atmospheric Metallicity and C/O of HD 189733 b from High-resolution Spectroscopy

We present high-resolution K-band emission spectra of the quintessential hot Jupiter HD 189733 b from the Keck Planet Imager and Characterizer. Using a Bayesian retrieval framework, we fit the dayside pressure-temperature profile, orbital kinematics, mass-mixing ratios of H2O, CO, CH4, NH3, HCN, and H2S, and the (CO)-C-13/(CO)-C-12 ratio. We measure mass fractions of logH(2)O = -2.0(-0.4)(+0.4) and logCO = -2.2(-0.5)(+0.5), and place upper limits on the remaining species. Notably, we find logCH(4) < -4.5 at 99% confidence, despite its anticipated presence at the equilibrium temperature of HD 189733 b assuming local thermal equilibrium. We make a tentative (similar to 3 sigma) detection of (CO)-C-13, and the retrieved posteriors suggest a C-12/C-13 ratio similar to or substantially less than the local interstellar value. The possible C-13 enrichment would be consistent with accretion of fractionated material in ices or in the protoplanetary disk midplane. The retrieved abundances correspond to a substantially substellar atmospheric C/O = 0.3 +/- 0.1, while the carbon and oxygen abundances are stellar to slightly superstellar, consistent with core-accretion models which predict an inverse correlation between C/O and metallicity. The specific combination of low C/O and high metallicity suggests significant accretion of solid material may have occurred late in the formation process of HD 189733 b.