June
2026
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2026AJ....171..333S
Authors
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Shu, Ying
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Dang, Lisa
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Darveau-Bernier, Antoine
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Kesseli, Aurora
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Bazinet, Luc
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Lipper, Justin
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Pelletier, Stefan
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Allart, Romain
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Cowan, Nicolas B.
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Lafreniére, David
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Rauscher, Emily
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Sánchez-López, Alejandro
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Benneke, Björn
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Boucher, Anne
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Doyon, René
Abstract
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We present ground-based high-resolution spectroscopic pre-eclipse observations of the hot Jupiter CoRoT-2b obtained with the IGRINS spectrograph on Gemini South. Using cross-correlation analysis, we detect the Doppler-shifted signature of the planet's thermal emission with a signal-to-noise ratio of 4.32. Our independent analyses confirm the presence of H2O with a confidence level of 2.6σ and an abundance of log10 −5.08−0.43+0.43 , as well as CO with 2.3σ confidence and an abundance of log10 −4.21−0.81+0.48 in CoRoT-2b's atmosphere, using two fully independent data reduction and retrieval pipelines. No significant detections of CH4, CO2, TiO, or VO are reported. While our cross-correlation analysis tentatively suggests the presence of HCN and OH, retrieval analysis does not confirm these molecules. The detected H2O and CO features indicate that CoRoT-2b's dayside spectrum is not featureless, as previously inferred from lower-resolution observations, but instead reveals a complex atmospheric structure. Interestingly, we find a lack of significant molecular features at wavelengths shorter than 1.7 μm, potentially due to high-altitude absorbers such as H−, clouds, or observational systematics. From our retrieved abundances of CO and H2O, we constrain a supersolar C/O ratio of 0.91−0.17+0.08 and a subsolar metallicity. This study provides the first high-resolution constraints on the atmospheric composition of CoRoT-2b and serves as the foundation for future investigations into its peculiar westward hot spot offset. Further phase-resolved observations will be required to explore the underlying atmospheric dynamics in more detail.
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