Ying Shu

Hot Jupiters are expected to be tidally locked and synchronously rotating due to their short orbital periods. These conditions create large day–night temperature contrasts and are thought to drive eastward superrotating jets. Indeed, the majority of hot Jupiters are observed to have the hottest region of the planet either at the substellar point or offset in the eastern direction. However, the full phase curve of CoRoT-2 b, observed with the Spitzer Space Telescope, exhibits robust evidence of a western hotspot offset. To determine the origin of this peculiar hotspot offset, we present phase-resolved high-resolution observations of CoRoT-2 b from the CRIRES+ spectrograph on the Very Large Telescope and the IGRINS spectrograph on Gemini South, covering both pre- and posteclipse phases (0.34–0.63). We detect the signal from the planet (signal-to-noise ratio > 4) in both pre- and posteclipse phases separately, and therefore perform separate cross-correlation and retrieval analyses at the two epochs. The phase-resolved retrievals show highly consistent abundances and C/Os, but prefer a hotter and more isothermal temperature–pressure profile at posteclipse phases, consistent with the phase-curve observations that indicated a western hotspot offset. By testing multiple hypotheses invoked to drive a western hotspot offset, we find the most likely explanation to be subsynchronous planetary rotation. We measure the planet’s rotational broadening to be 2.2 4 − 0.77 + 0.81 km s ⁻¹ , whereas the expectation from tidally locked rotation is 4.37 ± 0.13 km s ⁻¹ (2.6 σ discrepant). Other observations, such as high-precision phase curves or eclipse mapping, would help to further confirm the western hotspot offset and subsynchronous rotation.

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 H ₂ O with a confidence level of 2.6 σ and an abundance of log ₁₀ − 5.0 8 − 0.43 + 0.43 , as well as CO with 2.3 σ confidence and an abundance of log ₁₀ − 4.2 1 − 0.81 + 0.48 in CoRoT-2b’s atmosphere, using two fully independent data reduction and retrieval pipelines. No significant detections of CH ₄ , CO ₂ , 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 H ₂ O 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 μ m, potentially due to high-altitude absorbers such as H ⁻ , clouds, or observational systematics. From our retrieved abundances of CO and H ₂ O, we constrain a supersolar C/O ratio of 0.9 1 − 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.

Although exoplanetary science was not initially projected to be a substantial part of the Spitzer mission, its exoplanet observations set the stage for current and future surveys with JWST and Ariel. We present a comprehensive reduction and analysis of Spitzer’s 4.5 μm phase curves of 29 hot Jupiters on low-eccentricity orbits. The analysis, performed with the Spitzer Phase Curve Analysis pipeline, confirms that BLISS mapping is the best detrending scheme of the three independent schemes we tested for most, but not all, observations. Visual inspection remains necessary to ensure consistency across detrending methods due to the diversity of phase-curve data and systematics. Regardless of the model selection scheme, whether using the lowest BIC or a uniform detrending approach, we observe the same trends, or lack thereof. We explore phase-curve trends as a function of irradiation temperature, orbital period, planetary radius, mass, and stellar effective temperature. We discuss the trends that are robustly detected and provide potential explanations for those that are not observed. While it is almost tautological that planets receiving greater instellation are hotter, we are still far from confirming dynamical theories of heat transport in hot Jupiter atmospheres due to the sample’s diversity. Even among planets with similar temperatures, other factors like rotation and metallicity vary significantly. Larger, curated sample sizes and higher-fidelity phase-curve measurements from JWST and Ariel are needed to firmly establish the parameters governing day–night heat transport on synchronously rotating planets.