Luc Bazinet

Tracing the compositional link between terrestrial super-Earths and their host stars provides clues about their dominant formation pathway. By constraining the stellar abundances of refractory elements, we can predict the core mass fractions (CMFs) of their super-Earths. The level of agreement between this prediction and the planetary CMF derived from their masses and radii can reveal past formation processes, such as mantle stripping and water-rich formation plus sequestration in the planet core. We present the first results from the Near Infrared Planet Searcher (NIRPS) GTO CMF subprogram: an intensive radial velocity campaign to refine masses and compute host stellar abundances of three hot super-Earths around M dwarfs (GJ1132 b, GJ1252 b, and LTT 3780 b). We calculated masses of 1.69 ± 0.15 M _⊕ , 1.54 ± 0.18 M _⊕ , and 2.34 ± 0.10 M _⊕ respectively. We measured the CMFs of these and six further hot super-Earths with masses already available in the literature to a precision of 10–15%. We compared them to CMF predictions made from measuring the Fe, Mg, and Si abundances of their host stars measured from the NIRPS spectra. The CMFs of these planets are smaller than expected from their host stellar abundances to a statistically significant degree. This discrepancy is suggestive of significant reservoirs of water, and while these planets are too hot to harbor surface water, they likely have interior water mass fractions of ~1%.

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.

We present an updated characterization of the planetary system orbiting the nearby M2 dwarf GJ 3090 (TOI-177; d =22 pc), based on new high-precision radial velocity (RV) observations from NIRPS and HARPS. With an orbital period of 2.85 d, the transiting sub-Neptune GJ 3090 b has a mass we refine to 4.52 ± 0.47 M _⊕ , which, combined with our derived radius of 2.18 ± 0.06 R _⊕ , yields a density of 2.40 _−0.30 ^+0.33 g∉cm ⁻³ . The combined interior structure and atmospheric constraints indicate that GJ 3090 b is a compelling water-world candidate, with a volatile-rich envelope in which water likely represents a significant fraction. We also confirm the presence of a second planet, GJ 3090 c, a sub-Neptune with a 15.9 d orbit and a minimum mass of 10.0 ± 1.3 M _⊕ , which does not transit. Despite its proximity to the star’s 18 d rotation period, our joint analysis using a multidimensional Gaussian process (GP) model that incorporates TESS photometry and differential stellar temperature measurements distinguishes this planetary signal from activity-induced variability. In addition, we place new constraints on a non-transiting planet candidate with a period of 12.7 d, suggested in earlier RV analyses. This candidate remains a compelling target for future monitoring. These results highlight the crucial role of multidimensional GP modelling in disentangling planetary signals from stellar activity, enabling the detection of a planet near the stellar rotation period that could have remained undetected with traditional approaches.

Context. The Near InfraRed Planet Searcher (NIRPS) joined HARPS on the 3.6-m ESO telescope at La Silla Observatory in April 2023, dedicating part of its Guaranteed Time Observations (GTO) program to the radial velocity follow-up of TESS planet candidates to confirm and characterize transiting planets around M dwarfs. Aims. We present the “Sub-Neptunes” subprogram of the NIRPS-GTO, aimed at investigating the composition and formation of sub-Neptunes orbiting M dwarfs. We report the first results of this program with the characterization of the TOI-756 system, which consists of TOI-756 b, a transiting sub-Neptune candidate detected by TESS, as well as TOI-756 c, an additional non-transiting planet discovered by NIRPS and HARPS. Methods. We analyzed TESS and ground-based photometry, high-resolution imaging, and high-precision radial velocities (RVs) from NIRPS and HARPS to characterize the two newly discovered planets orbiting TOI-756, as well as to derive the fundamental properties of the host star. A dedicated approach was employed for the NIRPS RV extraction to mitigate telluric contamination, particularly when the star’s systemic velocity was shown to overlap with the barycentric Earth radial velocity. Results. TOI-756 is a M1V-type star with an effective temperature of T_eff ~ 3657 K and a super-solar metallicity ([Fe/H]) of 0.20±0.03 dex. TOI-756 b is a 1.24-day period sub-Neptune with a radius of 2.81 ± 0.10 R_⊕ and a mass of 9.8_−1.6^+1.8 M_⊕. TOI-756 c is a cold eccentric (e_c = 0.45 ± 0.01) giant planet orbiting with a period of 149.6 days around its star with a minimum mass of 4.05 ± 0.11 M_Jup. Additionally, a linear trend of 146 m s⁻¹ yr⁻¹ is visible in the radial velocities, hinting at a third component, possibly in the planetary or brown dwarf regime. Conclusions. We present the discovery and characterization of the transiting sub-Neptune TOI-756 b and the non-transiting eccentric cold giant TOI-756 c. This system is unique in the exoplanet landscape, standing as the first confirmed example of such a planetary architecture around an M dwarf. With a density of 2.42 ± 0.49 g cm⁻³, the inner planet, TOI-756 b, is a volatile-rich sub-Neptune. Assuming a pure H/He envelope, we inferred an atmospheric mass fraction of 0.023 and a core mass fraction of 0.27, which is well constrained by stellar refractory abundances derived from NIRPS spectra. It falls within the still poorly explored radius cliff and at the lower boundary of the Neptune desert, making it a prime target for a future atmospheric characterization with JWST to improve our understanding of this population.

The intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. In this work we present the simultaneous detections of H₂O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned Near InfraRed Planet Searcher (NIRPS). We retrieved a photospheric abundance ratio of log₁₀(OH/H₂O) = −0.15 ± 0.20, indicating that there is about as much OH as H₂O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compared the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of 4.79_−0.97^+0.93 km s⁻¹ in the H₂O signal, which is not reproduced by current global circulation models. Finally, in addition to H₂O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we inferred a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, thus paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.

Context. Stellar activity variability is one of the main obstacles to the detection of Earth-like planets using the radial velocity (RV) method. Aims. The aim of this work is to measure the effect of activity in the spectra of M dwarfs and detect activity-sensitive lines in the near-infrared (NIR) to help improve exoplanet detection and characterisation and contribute to further stellar activity analysis in the NIR. Methods. We took advantage of the simultaneous observations of HARPS and the newly commissioned NIRPS spectrograph to carry out a blind search of the most activity-sensitive spectral lines in the NIR using NIRPS spectra and known activity indicators in the optical from HARPS as a reference. We analysed the spectra of Proxima (M5.5V) and Gl 581 (M3V), two M dwarfs with different activity levels and internal structures. Spectral lines were identified for both stars and their profiles were fitted using different models. Results. We found hundreds of lines sensitive to activity for both stars; the Proxima spectra were more affected. For Proxima, around 32% of the identified lines can be used to measure the rotation period of the star, while for Gl 581 the numbers drops to 1%. The fraction of lines sensitive to activity increases with increasing line depth for both stars. A list of 17 lines with rotation period detection for both stars is provided. Conclusions. Stellar activity is able to affect a significant number of spectral lines in the NIR, and methods should be developed to mitigate those effects at the spectral level. The line distortions detected here are expected to come mainly from the flux effect due to temperature contrasts between active regions and the quiet photosphere; however, we cannot rule out the possibility that core-emission from chromospheric activity or Zeeman splitting are also affecting some lines. The new line lists presented here can be used to improve the RV extraction and the detection of RV variability due to stellar activity signals, and to help false positive detection and the modelling of activity variability, thereby enhancing exoplanet detection in the NIR.

Context. Near-infrared high-resolution échelle spectrographs unlock access to fundamental properties of exoplanets, from their atmospheric escape and composition to their orbital architecture, which can all be studied simultaneously from transit observations. Aims. We present the first results of the newly commissioned ESO near-infrared spectrograph, Near-InfraRed Planet Searcher (NIRPS), from three transits of the well-studied warm Saturn WASP-69b. Our goals are to measure the orbital architecture of the planet through the Rossiter-McLaughlin (RM) effect and its atmospheric escape through the 1083 nm helium triplet. Methods. We used the RM Revolutions technique to better constrain the orbital architecture of the system. We extracted the high-resolution helium absorption profile to study its spectral shape and temporal variations. Then, we made 3D simulations from the EVE code to fit the helium absorption time series. Results. We measure a slightly misaligned orbit for WASP-69 b (3D spin-orbit angle of 28.7_−5.3^+6.1 ∘). We confirm the detection of helium with an average excess absorption of 3.17±0.05% (maximum of 4.02%). The helium absorption is spectrally and temporally resolved, extends to high altitudes and has a strong velocity shift up to −29.5±2.5 km s⁻¹ 50 minutes after egress. The signature cannot be explained by a thermosphere alone and thus requires 3D modeling of the thermosphere and exosphere. EVE simulations put constraints on the mass loss of 2.25 · 10¹¹ g s⁻¹ and hint at reactive chemistry within the cometary-like tail and interaction with the stellar winds that allow the metastable helium to survive longer than expected. Conclusions. Our results suggest that WASP-69 b is going through a transformative phase of its history by losing mass while evolving on a misaligned orbit, similar to a growing number of Neptunian worlds. This work shows how combining multiple observational tracers such as orbital architecture, atmospheric escape, and composition is critical to understand exoplanet demographics and their formation and evolution. We demonstrate that NIRPS in the near-infrared can reach precisions similar to HARPS in the optical for RM studies, and the high data quality of NIRPS leads to unprecedented atmospheric characterization. Therefore, the addition of NIRPS to HARPS on the ESO 3.6 m makes it the driving force of such new studies. The high stability of NIRPS combined with the large Guaranteed Time Observation (GTO) available for its consortium enables in-depth studies of exoplanets as well as large population surveys.

We obtained 420 high-resolution spectra of Proxima, over 159 nights, using the Near Infra Red Planet Searcher (NIRPS). We derived 149 nightly binned radial velocity measurements with a standard deviation of 1.69 ms ⁻¹ and a median uncertainty of 55 cms ⁻¹ , and performed a joint analysis combining radial velocities, spectroscopic activity indicators, and ground-based photometry, to model the planetary and stellar signals present in the data, applying multi-dimensional Gaussian process regression to model the activity signals. We detect the radial velocity signal of Proxima b in the NIRPS data. All planetary characteristics are consistent with those previously derived using visible light spectrographs. In addition, we find evidence of the presence of the sub-Earth Proxima d in the NIRPS data. When combining the data with the HARPS observations taken simultaneous to NIRPS, we obtain a tentative detection of Proxima d and parameters consistent with those measured with ESPRESSO. By combining the NIRPS data with simultaneously obtained HARPS observations and archival data, we confirm the existence of Proxima d, and demonstrate that its parameters are stable over time and against change of instrument. We refine the planetary parameters of Proxima b and d, and find inconclusive evidence of the signal attributed to Proxima c (P = 1900 d) being present in the data. We measure Proxima b and d to have minimum masses of 1.055 ± 0.055 M _⊕ , and 0.260 ± 0.038 M _⊕ , respectively. Our results show that, in the case of Proxima, NIRPS provides more precise radial velocity data than HARPS, and a more significant detection of the planetary signals. The standard deviation of the residuals of NIRPS after the fit is ~80 cm s ⁻¹ , showcasing the potential of NIRPS to measure precise radial velocities in the near-infrared.

Context. Ultra-hot Jupiters showcase one-of-a-kind extreme atmospheric conditions, including the dissociation of molecules into atomic species, ionisation, and significant day-to-night temperature contrasts. The proximity to their host stars exposes ultra-hot Jupiters to intense stellar irradiation, enabling high temperatures that drive noteworthy contributions to the overall opacity by hydride ions (H⁻), potentially obscuring features of metals in the near-infrared transmission spectrum. Aims. This work aims to detect atomic, ionic, and molecular species in the atmosphere of WASP-189b (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe⁺, Ti⁺, TiO, H₂O, CO, and OH). A focus is placed on (i) understanding the role of H⁻ as a source of absorption continuum opacity, and (ii) retrieving the relative hydride-to-Fe abundance using combined optical and near-infrared data. Methods. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and in the near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect a planet’s absorption features and to increase the signal-to-noise ratio of potential detections. Additionally, atmospheric retrievals quantified relative abundances by fitting the overall metallicity, and abundance proxies for TiO, H⁻, and e⁻. Results. Only atomic iron is detected in HARPS data (S/N~5.5). However, no Fe is detected at near-infrared wavelengths, likely due to the H⁻ continuum dampening. Atmospheric retrievals on HARPS only and HARPS+NIRPS combined suggest that the hydride-to-Fe ratio exceeds equilibrium model predictions by ~0.5 dex, hinting at a strong ionisation rate for hydrogen atoms. Including NIRPS data helps to constrain the H⁻ abundance, as well as set an upper limit on the free electron density, which is unconstrained from the HARPS-only retrieval. These results emphasise the impact of H⁻ as a non-negligible source of continuum absorption opacity impeding the detection of planetary absorption features in the near-infrared transmission spectrum of WASP-189b.