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Measuring the abundances of carbon- and oxygen-bearing molecules has been a primary focus in studying the atmospheres of hot Jupiters, as doing so can help constrain the carbon-to-oxygen (C/O) ratio. The C/O ratio can help reveal the evolution and formation pathways of hot Jupiters and provide a strong understanding of the atmospheric composition. In the last decade, high-resolution spectral analyses have become increasingly useful in measuring precise abundances of several carbon- and oxygen-bearing molecules. This allows for a more precise constraint of the C/O ratio. We present four transits of the hot Jupiter WASP-43b observed between 1.45 and 2.45 μ m with the high-resolution Immersion GRating InfraRed Spectrometer on the Gemini-S telescope. We detected H _2 O at a signal-to-noise ratio of 3.51. We tested for the presence of CH _4 , CO, and CO _2 , but we did not detect these carbon-bearing species. We ran a retrieval for all four molecules and obtained a water abundance of ${\mathrm{log}}_{10}({\rm{H}\,}_{2}\,\rm{O})=-2.2{4}_{-0.48}^{+0.57}$ . We obtained an upper limit on the C/O ratio of C/O < 0.95. These findings are consistent with previous observations from the Hubble Space Telescope and the James Webb Space Telescope.

A primary goal of exoplanet science is to measure the atmospheric composition of gas giants in order to infer their formation and migration histories. Common diagnostics for planet formation are the atmospheric metallicity ([M/H]) and the carbon-to-oxygen (C/O) ratio as measured through transit or emission spectroscopy. The C/O ratio in particular can be used to approximately place a planet’s initial formation radius from the stellar host, but a given C/O ratio may not be unique to formation location. This degeneracy can be broken by combining measurements of both the C/O ratio and the atmospheric refractory-to-volatile ratio. We report the measurement of both quantities for the atmosphere of the canonical ultrahot Jupiter WASP-121 b using the high-resolution ( R = 45,000) IGRINS instrument on Gemini South. Probing the planet’s direct thermal emission in both pre- and post-secondary eclipse orbital phases, we infer that WASP-121 b has a significantly superstellar C/O ratio of ${0.70}_{-0.10}^{+0.07}$ and a moderately superstellar refractory-to-volatile ratio at ${3.83}_{-1.67}^{+3.62}\times $ stellar. This combination is most consistent with formation between the soot line and H _2 O snow line, but we cannot rule out formation between the H _2 O and CO snow lines or beyond the CO snow line. We also measure velocity offsets between H _2 O, CO, and OH, potentially an effect of chemical inhomogeneity on the planet dayside. This study highlights the ability to measure both C/O and refractory-to-volatile ratios via high-resolution spectroscopy in the near-IR H and K bands.

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 2.4 μ m with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H _2 O, 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 $\left[\tfrac{{\rm{C}}+{\rm{O}}}{{\rm{H}}}\right]=-{0.70}_{-0.93}^{+1.27}$ , 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 1 σ but favored a slightly more substellar metallicity and solar C/O ratio ( $\left[\tfrac{{\rm{C}}+{\rm{O}}}{{\rm{H}}}\right]=-{0.74}_{-0.17}^{+0.23}$ 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 redshifted V _sys for H _2 O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H _2 O 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.

We present high-resolution dayside thermal emission observations of the exoplanet WASP-18 b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross-correlation with model spectra. We detect the atmosphere of WASP-18 b at a signal-to-noise ratio (S/N) of 5.9 using a full chemistry model, measure H _2 O (S/N = 3.3), CO (S/N = 4.0), and OH (S/N = 4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4 σ ) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultrahot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature–pressure profile to adjust freely results in a moderately super-stellar carbon-to-oxygen ratio (C/O = ${0.75}_{-0.17}^{+0.14}$ ) and metallicity ([M/H] = ${1.03}_{-1.01}^{+0.65}$ ). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O = ${0.45}_{-0.10}^{+0.08}$ and [M/H] = ${1.17}_{-1.01}^{+0.66}$ . A retrieval that assumes radiative–convective–thermochemical equilibrium and naturally accounts for thermal dissociation constrains C/O < 0.34 (2 σ ) and [M/H] = ${0.48}_{-0.29}^{+0.33}$ , in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalizing signature of different Doppler shifts at the level of a few kilometers per second for different molecules, which might probe dynamics as a function of altitude and/or location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to the spectra of UHJs.

Close-in lava planets represent an extreme example of terrestrial worlds, but their high temperatures may allow us to probe a diversity of crustal compositions. The brightest and most well-studied of these objects is 55 Cancri e, a nearby super-Earth with a remarkably short 17 hr orbit. However, despite numerous studies, debate remains about the existence and composition of its atmosphere. We present upper limits on the atmospheric pressure of 55 Cnc e derived from high-resolution time-series spectra taken with Gemini-N/MAROON-X. Our results are consistent with current crustal evaporation models for this planet which predict a thin ∼100 mbar atmosphere. We conclude that, if a mineral atmosphere is present on 55 Cnc e, the atmospheric pressure is below 100 mbar.