Aurora Y. Kesseli

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.

Intense high-energy irradiation of close-in gaseous exoplanets drives the rapid escape of their atmospheres, fundamentally shaping planetary demographics. While atmospheric loss is routinely observed via transit absorption in atomic hydrogen, helium, and metal ions, the underlying physical properties, specifically the thermal structure, outflow dynamics, and mass-loss rate, remain poorly constrained due to inherent degeneracies in the transmission geometry. Here we report the first detection of atomic hydrogen emission from the escaping atmosphere of a gas giant. Using high-resolution spectroscopy of the ultrahot Jupiter KELT-9 b, we detect a hydrogen Balmer line (H α 6564.6 Å) emission signature originating from the planetary dayside. The emission line profile features a distinctive double-peaked shape with 0.1%–0.15% peak amplitudes at ±30 km s ⁻¹ and central self-absorption. This profile breaks transmission degeneracies, providing direct observational constraints on the vertical thermal structure, excited-state hydrogen populations, and wind dynamics in the upper atmosphere of KELT-9 b. Initial modeling reveals a vigorous outflow with a mass-loss rate above 10 ¹³ g s ⁻¹ , among the highest measured to date for gaseous exoplanets. Our results establish hydrogen airglow emission as a powerful diagnostic of atmospheric escape, opening a new observational window into the evolution of worlds in extreme radiation environments.

We introduce the Keck Planet Finder (KPF) Spectroscopy of the Upper Atmospheres and Refractory Species in Ultrahot Planets (SURFS-UP) Survey, a high-resolution survey to investigate the atmospheric composition and dynamics of a sample of ultrahot Jupiters with the KPF. Due to the unique design of KPF, we developed a publicly available pipeline for KPF that performs blaze removal, continuum normalization, order stitching, science spectra combination, telluric correction, and atmospheric detection via cross correlation. As a first demonstration, we applied this pipeline to a transit of WASP-76 b and achieved some of the highest signal-to-noise ratio (SNR) detections of refractory species in WASP-76 b to date (e.g., Fe I is detected at an SNR of 14.5). We confirm previous observations of an asymmetry in Fe I absorption, but find no measurable ingress–egress asymmetry in Na I and Ca II . Together, these results suggest variations within different layers of the atmosphere of WASP-76 b: neutral metals such as Fe I trace deeper regions with stronger asymmetries, while Na I and Ca II probe regions higher in the atmosphere where the ingress–egress asymmetries are weaker. Unlike some other ultrahot Jupiters, our results are qualitatively consistent with general circulation model predictions of decreasing velocity asymmetry with altitude and do not require a high-altitude superrotating jet that has been invoked for other planets (e.g., WASP-121 b). These results suggest that atmospheric circulation patterns in ultrahot Jupiters may be more diverse than previously thought, highlighting the need for broader surveys to study how atmospheric dynamics depend on planetary and stellar properties.

Measuring the chemical and isotopic compositions of gas giants and brown dwarfs provides insights into their formation pathways and birth environments. 2MASS J0249-0557c is an L2-type planetary mass companion (∼12 M _Jup ) orbiting a pair of brown dwarfs in the β Pictoris young moving group and vicinity. ^{7 7} While E. L. Shkolnik et al. (2017) and T. J. Dupuy et al. (2018) have attributed 2MASS J0249-0557AB to the β Pic young moving group, work by K. L. Luhman (2024) has attributed 2MASS J0249-0557AB to the 32 Ori young moving group, which spatially overlaps with the β Pic young moving group. The two groups have been proposed to be physically connected (J. Gagné et al. 2021). Its mass places it at the intersection of planets and brown dwarfs, making it an interesting target for constraining formation pathways at the planet–brown dwarf boundary. Using high-resolution spectroscopic data of the planet acquired with CRIRES+ mounted on the Very Large Telescope, we conduct atmospheric retrieval with the radiative transfer code petitRADTRANS and the nested sampling tool PyMultiNest. We retrieve a C/O ratio of 0.57 ± 0.01, a metallicity of [M/H] = 0.18 ± 0.05, and a ¹² CO/ ¹³ CO ratio of 9 5 − 17 + 23 . We also retrieve atmospheric compositions for two benchmark brown dwarfs in the β Pic YMG, 2MASSI J0443+0002 and SIPS J2000-7523, using CRIRES+ data and find consistent compositions. Together with 2MASS J0249-0557 c’s wide separation from its host, its compositional consistency with benchmark brown dwarfs supports gravitational collapse in a star-like manner as its most likely formation mechanism. These results deliver a homogeneous comparison of three substellar members in the β Pic YMG and vicinity. Their solar-like abundances provide a baseline for exoplanet members in the same moving group, such as β Pic b, 51 Eri b, and AF Lep b, whose host stellar compositions are difficult to measure. Future comparisons of atmospheric compositions among this moving group offer the potential to distinguish between formation mechanisms for its planetary members.

Stellar photospheric heterogeneity is a dominant astrophysical systematic impacting exoplanet transmission spectroscopy. NASA’s Pandora SmallSat Mission is designed to address this challenge through contemporaneous visible-band photometry and near-infrared spectroscopy of exoplanet host stars. Here, we present an end-to-end simulation study quantifying Pandora’s ability to infer stellar photospheric properties and correct stellar contamination using out-of-transit observations. We construct eight representative stellar activity scenarios and generate 160 simulated Pandora datasets, incorporating time-dependent stellar spectra, instrument response, and noise. Given accurate models, Bayesian retrievals of joint visible photometry (0.4–0.7 μ m) and near-infrared spectroscopy (0.9–1.6 μ m, R ≈ 120) recover photospheric temperatures with typical uncertainties of ≈30 K, with no significant bias. Models with two spectral components (i.e., a quiescent photosphere and spots) are strongly favored in 95% of cases; one-component models are preferred when true spot filling factors fall below a detection threshold of ≈0.3%. We propagate the true and inferred stellar parameters to compute true, inferred, and residual contamination signals under physically motivated spot geometries. For simple spot distributions, contamination signals of 10 ² –10 ³ ppm are reduced to ≲10 ppm—well below Pandora’s expected transmission spectroscopy precision (30–100 ppm). For more complex spot distributions, geometric degeneracies limit deterministic corrections, leaving residual contamination at the 10 ³ ppm level that must be mitigated using additional constraints, such as spot-crossing events and joint stellar–planetary retrievals of transmission spectra. These results define regimes in which stellar contamination can be corrected from stellar observations alone and show how Pandora stellar observations can identify cases where additional information is required.

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.

The TESS Input Catalog (TIC) was built on Gaia Data Release 2 (DR2). To date, there has not been an update to the TIC to incorporate Gaia Data Release 3 (DR3) IDs. In this Research Note, we outline how we cross-matched the TIC with Gaia DR3 IDs, its immediate applications to exoplanet research, and lessons learned when dealing with such large datasets. A full TIC/Gaia DR3 cross-match table is available for download on the Exoplanet Follow-up Observing Program website, and a Jupyter Notebook with instructions to reproduce the table is available on GitHub.

Pandora is a SmallSat mission dedicated to understanding exoplanets and their host stars by disentangling the impact of stellar heterogeneity on exoplanet transmission spectra. Selected as a NASA Astrophysics Pioneers mission in 2021, Pandora will provide simultaneous long-term visible photometric monitoring (0.4–0.7 μ m) and low-resolution near-infrared (NIR) spectroscopy (0.9–1.6 μ m) of transiting systems for the purposes of monitoring host star variability and characterizing exoplanetary atmospheres. Pandora’s year-long prime mission from 2026 to 2027 coincides with the middle of a decade defined by targeted efforts for atmospheric characterization of exoplanets, offering a key opportunity to leverage this new resource to maximize science with JWST and other observatories. Here we investigate Pandora’s anticipated performance for the general exoplanet population accessible to transit spectroscopy, from hot Jupiters to temperate sub-Neptunes. By modeling the atmospheres of five test cases broadly consistent with the bulk properties of HD 209458b, HD 189733b, WASP-80 b, HAT-P-18 b, and K2-18 b, we find that Pandora may provide abundance constraints as precise as ∼1.0 dex for main atmospheric absorbers such as H ₂ O and CH ₄ . Then, we explore the synergies between Pandora and JWST. Our results suggest that targets with JWST data in the NIR can benefit from the addition of Pandora observations and result in more reliable abundance estimates than with JWST data alone. Moreover, Pandora can serve the community by providing precursory observations of targets of interest for JWST atmospheric characterization. We conclude by outlining strategies for the use of Pandora as a standalone observatory and in synergy with JWST.

Context . The distinct formation pathways proposed for directly imaged exoplanets and isolated brown dwarfs might leave imprints in the inherited chemical composition. Elemental and isotopic tracers could help inform the suspected histories, but this requires a careful characterisation of the sub-stellar atmospheres. In particular, objects at the L-T transition exhibit signs of dynamics that can drive their atmospheres out of chemical equilibrium. Aims . In this work, we studied the nearest L-T brown dwarfs, Luhman 16A and B, to assess the chemical disequilibrium in their atmospheres. We also investigated the elemental and isotopic compositions in the context of their probable formation history within the Oceanus moving group. Methods . As part of the ESO SupJup Survey, we obtained spatially resolved CRIRES ⁺ K-band spectra of the binary. These high-resolution observations were analysed using an atmospheric retrieval framework that couples the radiative transfer code petitRADTRANS to the MultiNest sampling algorithm. Results . We detect and retrieve the abundances of ¹² CO, H ₂ O, CH ₄ , NH ₃ , H ₂ S, HF, and the ¹³ CO isotopologue. We find that both atmospheres are in chemical disequilibrium with somewhat stronger vertical mixing in Luhman 16A compared to B ( K _zz,A ~ 10 ^8.7 vs K _zz,B ~ 10 ^8.2 cm ² s ⁻¹ ). The tested chemical models, free-equilibrium and disequilibrium chemistry, yield consistent mixing ratios and agree with earlier work at shorter wavelengths. The free-chemistry gaseous C/O ratios show evidence of oxygen trapping in silicate-oxide clouds. While the C/O ratios are consistent with the solar composition, the metallicities are modestly enhanced with [C/H] ~ 0.15. The carbon isotope ratios are measured at ¹² C/ ¹³ C _A = 74 ₋₂ ⁺² and ² C/ ¹³ C _B = 74 ₋₃ ⁺³ . Conclusions . The coincident constraints of metallicities and isotopes across the binary provide further evidence in favour of a common formation. The ¹² C/ ¹³ C ratios are aligned with the present-day interstellar medium but lower than the Solar System value. This suggests a recent inheritance and corroborates the relatively young age (~500 Myr) of Luhman 16A and B as members of the Oceanus moving group.