Joost P. Wardenier

We present a Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 phase-curve observation of the ultrashort-period rocky planet TOI-2431 b and detect its secondary eclipse in the near-infrared. Combined with the TESS optical eclipse, these measurements constrain the planet’s dayside brightness temperature, reflected light contribution, albedo, and heat redistribution. We detect the eclipse in the optical and near-infrared wavelengths of TESS and HST/WFC3 G141, with a planet-to-star flux ratio of 37 ± 10 ppm and 6 9 − 13 + 14 ppm , respectively. Assuming negligible reflected light, the joint TESS+HST fit yields a brightness temperature T b , joint = 252 4 − 84 + 77 K and a brightness temperature ratio of R joint = T b , joint / T p , max = 0.98 0 − 0.034 + 0.032 consistent with the zero-albedo, no-redistribution limit T p , max = 257 4 − 35 + 36 K . The HST phase curve is consistent with zero nightside emission and no measurable hotspot offset, consistent with inefficient day-night heat distribution. Under this thermal-dominated interpretation, TOI-2431 b lies at the zero-albedo, no-redistribution limit and contrasts with previously observed lava worlds. At optical and near-infrared wavelengths, however, thermal emission is degenerate with reflected light. For a geometric albedo of A _g = 0.1, reflected light would contribute approximately 11 ppm in each bandpass, reducing the temperature to T b , joint ( A g = 0.1 ) = 240 7 − 102 + 91 K . Longer-wavelength observations are required to isolate the thermal component. Planned JWST/MIRI LRS observations are expected to substantially reduce this degeneracy and provide more direct constraints on heat redistribution and possible silicate-atmosphere spectral features. This marks the first secondary eclipse detection of a rocky exoplanet using HST and establishes TOI-2431 b as a benchmark target for studying properties of lava worlds.

Context. Exoplanetary magnetic fields govern atmospheric escape and circulation but have eluded detection in close-in planets. In the ultra-hot Jupiter KELT-9b, atmospheric dynamo is predicted to generate atmospheric fields of 400−4000 G. Aims. We searched for the circular polarization in atomic lines that a magnetic field would imprint, through the Zeeman effect, on the transmission spectrum of KELT-9b. Methods. We observed three transits with SPIRou at the CFHT, on 07 September 2025 and 03 and 06 July 2026, and applied least squares deconvolution to 1398 atomic lines to map the transit-averaged Stokes V and null spectra against the orbital semi-amplitude, K _p , and systemic velocity, v _sys . Results. The 2025 transit shows a Stokes V signature of V / I _c = 9.3 × 10 ⁻⁵ at K _p = 219 ± 11 km s ⁻¹ , v = −34.0 ± 1.2 km s ⁻¹ , close to the expected planetary velocity. Its false-alarm probability is 1.9 × 10 ⁻⁴ , and thus it is formally a marginal detection. Both 2026 transits are of comparable sensitivity but neither exhibits a signal at that location, setting 3 σ limits of 4.9 and 6.0 × 10 ⁻⁵ ; the 2025 amplitude would have been recovered at 4.9 σ and 4.0 σ . Conclusions. The 2025 signature is robust to the tests we applied to it but qualifies as a marginal detection at best. Spurious signals of comparable strengths occur elsewhere in our Stokes V and null maps, and we cannot rule out that our marginal detection is excess noise. It is not reproduced ten months later.

The TRAPPIST-1 system is well known for its seven transiting Earth-sized exoplanets. It has been extensively studied and characterized, notably with transit timing variations (TTVs), to precisely measure the mass of the planets. Using near-infrared spectroscopic observations obtained as part of the SPIRou Legacy Survey and the NIRPS Guaranteed Time Observation programs, we aimed to verify those values through radial velocity (RV) measurements of the system. Our RV analysis reveals that the current data do not have the precision required to individually detect the TRAPPIST-1 planets. However, we confidently detect (Δ ln 𝒵 = 7.53, 1860:1 odds) the combined RV signature of the planets by using the relative masses derived from the TTV analysis, with TRAPPIST-1 b as a proxy for the whole system. For the first time, the RV signal of the TRAPPIST-1 system is recovered: we find a RV semi-amplitude of K _b = 3.65 _−0.83 ^+0.78 m s ⁻¹ . This corresponds to a planetary mass of M _{p , b} = 1.31 ± 0.29 M _⊕ and demonstrates that the RV measurements are consistent with the TTV model ( M _{p , b; TTV} = 1.374 ± 0.069 M _⊕ ). Additionally, the NIRPS RVs constrain the presence of giant planets beyond the snow line, excluding Saturn-mass planets out to 2.7-yr orbits and Neptune-mass objects out to 20 d. Through RV, we determined the stellar activity period to be of 3.22 _−0.20 ^+0.22 d. Its agreement with photometric measurements (K2 and TESS) confirms stellar rotation as the origin of the ~3.3-d periodicity observed for TRAPPIST-1. We further investigated stellar activity with SPIRou polarimetric measurements, and placed an upper limit on the longitudinal field (| B _l | < 40 G, 3 σ ). This limit is compatible with a weak multipolar large-scale magnetic geometry, as observed in some of the later-type rapidly rotating M dwarfs.

Context. Ground-based spectrographs operating in the near-infrared (NIR) regime are hampered by various absorption and emission features of Earth’s atmosphere. While considerable attention has been paid to mitigating telluric absorption, correcting telluric emission features remains non-trivial and can significantly affect the observation of faint targets. Aims. We aim to develop and implement automated algorithms for sky background emission correction in the context of high-resolution spectroscopy. These empirical-based algorithms have been officially integrated into both NIRPS data reduction pipelines: NIRPS DRS and APERO DRS. The NIRPS DRS algorithm is additionally functional at the telescope site, enabling quick, real-time telluric-corrected data processing. Designed for flexibility, these techniques can be incorporated into the reduction workflow of any high-resolution spectrograph to improve the radial velocity (RV) performance. Methods. In our approach, a reference sky spectrum is first created by deep-stacking NIRPS sky calibration frames on a common wavelength grid and calculating the weighted median flux per pixel, separately for both the high-accuracy and high-efficiency instrument modes. This process is repeated for all spectral orders and for both the object and sky-calibration fibres: fibre A and fibre B, respectively. In this reference sky spectrum, the sky emission lines can be identified and used to construct a static library. During the data reduction process, the emission features in the library are individually scaled in terms of flux using two distinct techniques, each specific to the two DRS pipelines. Finally, they are locally subtracted from the science observations to minimise their noise contribution to the final spectrum Results. We find that the correction algorithms significantly improve the RV measurements obtained using both the cross-correlation function and line-by-line techniques, enabling NIRPS to achieve submetre-per-second precision in the NIR. The techniques have been successfully validated and demonstrated on both bright (Proxima Centauri) and faint (TOI-406, TOI-3494, TOI-4552) targets, as well as in both high-efficiency and high-accuracy instrument modes. Conclusions. We present the first attempts at empirically subtracting emission line features from high-resolution spectra. These algorithms can be applied independently of the instrumentation and implemented into the data reduction workflow of any high-resolution instrument with minimal modifications required.

Sulfur chemistry has emerged as an important probe of exoplanet atmospheres in the JWST era, although observational constraints have thus far been largely limited to SO ₂ and H ₂ S in warm and hot exoplanets. Recent JWST observations have revealed CS ₂ in several cooler gas giant exoplanets, yielding a new tracer of sulfur chemistry. However, the detailed chemical pathways responsible for the formation of CS ₂ remain poorly understood. Here, we use TOI-6894 b, a temperate gas giant with evidence for CS ₂ , as a test case for one-dimensional photochemical kinetic-transport modeling and sensitivity analyses of CS ₂ chemistry. We show that CS ₂ is produced through coupled thermochemical and photochemical processes involving CH ₄ and H ₂ S as the primary carbon and sulfur reservoirs, with S ₂ photolysis driving disequilibrium sulfur chemistry. Our models provide a physically consistent explanation for the observed CS ₂ feature in TOI-6894 b. Extending our analysis to gas giant exoplanets spanning a wide range of T _eq , we find that CS ₂ abundance peaks in temperate to warm atmospheres ( T _eq ∼ 500–700 K), and declines toward both lower and higher temperatures. This temperature dependence provides a unified framework for interpreting current CS ₂ observations, accounting for reported detections in temperate to warm planets and the lack of detections in colder and hotter giant exoplanets. Our results establish CS ₂ as a complementary probe of sulfur inventories and atmospheric metallicity in cool gas giant exoplanets.

The angle between stellar spin axis and planetary orbital plane can provide key insights into the formation and dynamical evolution of planetary systems. In particular, this measurement in multi-planet systems can be used to further discriminate between different competing migration scenarios. We present six transit observations of the sub-Neptune GJ 3090 b obtained with NIRPS and HARPS. GJ 3090 b is the inner planet of a confirmed multi-planet system orbiting an M dwarf (M2). Using high spectral resolution and high temporal cadence spectroscopic observations, we analyzed the Rossiter-McLaughlin (RM) effect induced by GJ 3090 b to determine its orbital obliquity. Through the RM revolutions technique, we find that the planet is on a retrograde orbit with a derived 3D obliquity of ψ = 136 ⁺²⁴ ₋₁₈ deg. We find no evidence of massive outer planetary or wide stellar binary companions, which disfavors scenarios involving gravitational perturbations from a massive body and instead points toward a primordial misalignment of the protoplanetary disk. Our results establish GJ 3090 b as the first planet on a retrograde orbit discovered around an M dwarf and the first highly misaligned confirmed multi-planet system without a known massive companion. We further propose late secondary disk accretion around GJ 3090, in which the disk is not expected to be aligned with the stellar spin axis, followed by disk-driven migration as the most likely mechanisms to explain the observed architecture. This work also illustrates the capability of the RM revolutions technique when applied to near-infrared data to probe orbital architectures of the smallest planets around M dwarfs that have remained mostly inaccessible.

Context . High-resolution thermal emission spectroscopy provides a powerful probe of atmospheric circulation in ultra-hot Jupiters (UHJs), with Doppler shifts encoding information about the 3D wind field across the planet disk. Retrieving these wind properties from phase-dependent emission spectra requires a forward model that is both physically motivated and computationally tractable. Aims . We aim to investigate what 3D wind information is contained in the thermal emission spectra of UHJs in the first place, and whether the complicated 3D atmospheric structure of these planets can be captured by a simplified forward model with a small number of parameters. Methods . We present dopplerkernel , a new forward model that parametrizes the projected line-of-sight velocity field on the planet disk using four wind parameters (an equatorial jet speed v _jet and width σ _jet , a source-to-sink flow speed v _wind , and a flow convergence longitude φ _sink ) and constructs a broadening kernel via weighted kernel-density estimation. We applied this framework in a Bayesian retrieval to synthetic K -band emission spectra of WASP-76b generated from three global circulation models (GCMs) that span a range of atmospheric drag strengths. We performed retrievals across multiple spectral resolutions and orbital phase coverages. Results . Our retrievals successfully recovered the equatorial jet in the drag-free GCM to within ∼1 km/s of the zonal mean and infer day-to-night wind speeds in good agreement with GCM averages at 1–10 mbar for all three drag regimes. We find that spectral resolutions of R ∼ 100 000 offer an optimal trade-off: sufficient to resolve global wind features while avoiding spurious detections caused by model–data mismatches at higher resolution. Combining pre- and post-eclipse phases yields more reliable constraints than either alone, particularly on the orientation of the source-to-sink flow. Experiments with more complex weight functions reveal a degeneracy between the velocity field and the thermal weighting, cautioning against overparametrization. Conclusions . A parametric broadening-kernel model with a small number of physically interpretable parameters can accurately reproduce the phase-dependent line shifts, shapes, and strengths in UHJ emission spectra. However, the fundamental degeneracy between the velocity distribution and the thermal weight function means that adding model complexity does not necessarily improve wind inference and may introduce spurious features. Bayesian model comparison is essential when applying this framework to real observations.

Ultrahot Jupiters (UHJs; T _eq ≳ 2000 K) enable simultaneous detection of volatile (ice-forming) and refractory (rock-forming) elements in planetary atmospheres, providing a powerful diagnostic of planet formation and atmospheric processing. We present a comprehensive high-resolution cross-correlation spectroscopy analysis of the UHJ MASCARA-1 b ( T _eq ≈ 2600 K) using the IGRINS and IGRINS-2 spectrographs. We detect robust (signal-to-noise ratio > 4) signals from H ₂ O, CO, OH, Fe i , Mg i , Ca i , and Ti i , marking the most complete atmospheric inventory of MASCARA-1 b to date. Using a chemically consistent atmospheric inference framework, we constrain elemental abundances to a typical precision of ≈0.2 dex, retrieving a solar atmospheric metallicity ([M/H] _⊙ = 0.0 7 − 0.13 + 0.17 ≈1.2 × solar), a C/O ratio (C/O = 0.6 5 − 0.08 + 0.08 ) consistent with solar value (C/O = 0.59), an enhanced refractory abundance ([ R /H] _⊙ = 0.4 0 − 0.17 + 0.23 ≈ 2.5 × solar; ≈3.8 × stellar), and a moderately supersolar refractory-to-volatile ratio ([ R / V ] _⊙ = 0.3 6 − 0.09 + 0.11 ≈ 2.3× solar). Comparison with formation models suggests that MASCARA-1 b most likely accreted material between the soot–H ₂ O or H ₂ O–CO snowlines (at 68% confidence). We additionally find stellar values for atmospheric Ti/Fe and Ca/Fe ratios (at 68% confidence). The Mg/Fe is also found to be consistent with stellar value at 95% confidence. Therefore, we do not find strong indication of nightside cold trapping in MASCARA-1 b. As homogeneous refractory-to-volatile measurements expand across the UHJ population, particularly with upcoming Extremely Large Telescopes, these diagnostics will enable statistically robust tests of emerging trends in giant planet formation and atmospheric evolution.

Context . Condensates are ubiquitous to all Solar System planets with significant ( > 10 mbar) atmospheres. The same is true for most exoplanets with characterised atmospheres, with even ultra-hot exoplanets being able to form clouds on their cooler nightsides. One high-interest condensate is titanium, a highly refractory element that as an oxide (TiO) is a potent optical absorber long believed to be a driver of thermal inversions in highly irradiated exoplanet atmospheres. Observations have shown that some ultra-hot Jupiters have strong thermal inversions despite being significantly Ti-depleted, likely due to cold trapping, raising doubts about whether TiO is the main cause of their inverted temperature structures. Aims . Our aim was to retrieve the titanium-to-iron ratio of the dayside atmosphere of the ultra-hot Jupiter WASP-189b to determine whether the full titanium budget is accounted for in the gas phase. Methods . We analysed thermal emission observations of WASP-189b taken with the HARPS and NIRPS spectrographs using different atmospheric retrieval prescriptions to infer the planet’s atmospheric thermal structure and composition. Results . We observed Fe and Ti signals in cross-correlation and measured a sub-solar Ti/Fe ratio for WASP-189b using both free and chemical equilibrium retrieval approaches. We find the Ti/Fe of the planetary atmosphere to be between 28% and 81% (1- σ bounds) that of the stellar value. Conclusions . The slight underabundance of Ti with respect to Fe on the dayside atmosphere of WASP-189b suggests that some titanium is missing from the gas phase, potentially due to a partial nightside cold trap. In the context of the ultra-hot Jupiter population, the onset of titanium in exoplanetary atmospheres appears to occur progressively, coinciding not with when thermal inversions begin but rather when the vapourisation threshold of titanium is reached on the nightside.

Ultrahot Jupiters (UHJs) are exceptional laboratories for studying planetary atmospheres under extreme irradiation conditions. With close-in tidally locked orbits, these planets can have daysides hot enough for metals to be significantly ionized while still maintaining nightsides cold enough for refractory species to potentially condense. We present an analysis of the UHJ HAT-P-70b taken with the MAROON-X high-resolution spectrograph. Using cross correlations, we detect 14 neutral and singly ionized species, including Fe I , Fe II , Ti I , Ca I , Ca II , Cr I , Na I , V I , Mn I , Ni I , Mg I , Ba II , O I , and Sr I , with tentative evidence for H I , Co I , and K I . The absorption signals exhibit blueshifts on the order of a few kilometers per second, consistent with day-to-night winds. We further constrain relative abundances with atmospheric retrievals and demonstrate that some inferred elemental abundance ratios depend strongly on modeling assumptions. In particular, we show that a well-mixed retrieval approach neglecting ionization can strongly bias highly ionizable elements such as Ca and Ti. Accounting for the effects of equilibrium chemistry and thermal ionization generally results in inferred elemental abundance ratios that are closer to expectations for a solar-like composition, although not in all cases. Interestingly, we find a distinct nickel enrichment on HAT-P-70b, adding to the growing number of UHJ studies where the Ni abundance is seemingly enhanced. Our results underline the importance of considering physical and chemical atmospheric processes such as ionization when interpreting high-resolution transmission spectra of UHJs.