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Abstract High-resolution spectroscopy of exoplanet atmospheres provides insights into their composition and dynamics from the resolved line shape and depth of thousands of spectral lines. WASP-127 b is an extremely inflated sub-Saturn (R_p= 1.311R_Jup,M_p= 0.16M_Jup) with previously reported detections of H₂O and CO₂. However, the seeming absence of the primary carbon reservoir expected at WASP-127 b temperatures (T_eq∼1400 K) from chemical equilibrium, CO, posed a mystery. In this manuscript, we present the analysis of high-resolution observations of WASP-127 b with the Immersion Grating Infrared Spectrometer on Gemini South. We confirm the presence of H₂O (8.67σ) and report the detection of CO (4.34σ). Additionally, we conduct a suite of Bayesian retrieval analyses covering a hierarchy of model complexity and self-consistency. When freely fitting for the molecular gas volume mixing ratios, we obtain super-solar metal enrichment for H₂O abundance of log₁₀X ${}_{{\mathrm{H}}_2\mathrm{O}}$= −1.23 ${}_{-0.49}^{+0.29}$and a lower limit on the CO abundance of log₁₀X_CO≥–2.20 at 2σconfidence. We also report tentative evidence of photochemistry in WASP-127 b based upon the indicative depletion of H₂S. This is also supported by the data preferring models with photochemistry over free-chemistry and thermochemistry. The overall analysis implies a super-solar (∼39× Solar; [M/H] = ${1.59}_{-0.30}^{+0.30}$) metallicity for the atmosphere of WASP-127 b and an upper limit on its atmospheric C/O ratio as < 0.68. 

Abstract Ultra-hot Jupiters (UHJs) are among the best targets for atmospheric characterization at high spectral resolution. Resolving their transmission spectra as a function of orbital phase offers a unique window into the 3D nature of these objects. In this work, we present three transits of the UHJ WASP-121b observed with Gemini-S/IGRINS. For the first time, we measure the phase-dependent absorption signals of CO and H₂O in the atmosphere of an exoplanet, and we find that they are different. While the blueshift of CO increases during the transit, the absorption lines of H₂O become less blueshifted with phase, and even show a redshift in the second half of the transit. These measurements reveal the distinct spatial distributions of both molecules across the atmospheres of UHJs. Also, we find that the H₂O signal is absent in the first quarter of the transit, potentially hinting at cloud formation on the evening terminator of WASP-121b. To further interpret the absorption trails of CO and H₂O, as well as the Doppler shifts of Fe previously measured with VLT/ESPRESSO, we compare the data to simulated transits of WASP-121b. To this end, we post-process the outputs of the global circulation models with a 3D Monte-Carlo radiative transfer code. Our analysis shows that the atmosphere of WASP-121b is subject to atmospheric drag, as previously suggested by small hotspot offsets inferred from phase-curve observations. Our study highlights the importance of phase-resolved spectroscopy in unravelling the complex atmospheric structure of UHJs and sets the stage for further investigations into their chemistry and dynamics. 

Abstract Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4μm with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H₂O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of $\left(\frac{\mathrm{C}+\mathrm{O}}{\mathrm{H}}\right)=-{0.70}_{-0.93}^{+1.27}$, consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O $={0.80}_{-0.11}^{+0.07}$. We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1σbut favored a slightly more substellar metallicity and solar C/O ratio ( $\left(\frac{\mathrm{C}+\mathrm{O}}{\mathrm{H}}\right)=-{0.74}_{-0.17}^{+0.23}$and C/O $={0.59}_{-0.14}^{+0.13}$). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic (V_sys) and Keplerian (K_p) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshiftedV_sysfor H₂O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H₂O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.