Selected publications

• NIRPS tightens the mass estimate of GJ 3090 b and detects a planet near the stellar rotation period

  Astronomy and Astrophysics · 2026-01-05

  articleOpen access

  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.

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• Detailed Architecture of the L 98-59 System and Confirmation of a Fifth Planet in the Habitable Zone

  The Astronomical Journal · 2025-08-08 · 5 citations

  articleOpen accessCorresponding

  Abstract The L 98-59 system, identified by TESS in 2019, features three transiting exoplanets in compact orbits of 2.253, 3.691, and 7.451 days around an M3V star, with an outer 12.83 day nontransiting planet confirmed in 2021 using ESPRESSO. The planets exhibit a diverse range of sizes (0.8–1.6 R ⊕ ), masses (0.5–3 M ⊕ ), and likely compositions (Earth-like to possibly water-rich), prompting atmospheric characterization studies with Hubble Space Telescope and JWST. Here, we analyze 16 new TESS sectors and improve radial velocity (RV) precision of archival ESPRESSO and HARPS data using a line-by-line framework, enabling stellar activity detrending via a novel differential temperature indicator. We refine the radii of L 98-59 b, c, and d to 0.837 ± 0.019 R ⊕ , 1.329 ± 0.029 R ⊕ , and 1.627 ± 0.041 R ⊕ , respectively. Combining RVs with transit timing variations (TTVs) of L 98-59 c and d from TESS and JWST provides unprecedented constraints on the masses and eccentricities of the planets. We report updated masses of 0.46 ± 0.11 M ⊕ for b, 2.00 ± 0.13 M ⊕ for c, and 1.64 ± 0.07 M ⊕ for d, and a minimum mass of 2.82 ± 0.19 M ⊕ for e. We additionally confirm L 98-59 f, a nontransiting super-Earth with a minimal mass of 2.80 ± 0.30 M ⊕ on a 23.06 day orbit inside the Habitable Zone. The TTVs of L 98-59 c and d (&lt;3 minutes, P TTV = 396 days) constrain the eccentricities of all planets to near-circular orbits ( e ≲ 0.04). An internal structure analysis of the transiting planets reveals increasing water-mass fractions ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) with orbital distance, reaching <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>f</mml:mi> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">H</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.16</mml:mn> </mml:math> for L 98-59 d. We predict eccentricity-induced tidal heating in L 98-59 b with heat fluxes comparable to those of Io, potentially driving volcanic activity.

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• A complex structure of escaping helium spanning more than half the orbit of the ultra-hot Jupiter WASP-121 b

  Nature Communications · 2025-12-08 · 3 citations

  articleOpen access

  Atmospheric escape of close-in exoplanets, driven by stellar irradiation, influences their evolution, composition, and atmospheric dynamics. The near-infrared metastable helium triplet (10833 Å) has become a key probe of this process, enabling mass loss rate measurements for dozens of exoplanets. Only a few studies, however, have detected absorption beyond transit, supporting the presence of hydrodynamic outflows. None have yet precisely identified the physical extent of the out-of-transit signal, either due to non-continuous or short-duration observations. This strongly limits our ability to measure accurate mass-loss rates and to understand how the stellar environment shapes outflows. Here we present the continuous, full-orbit helium phase-curve observation of an exoplanet: the ultra-hot Jupiter WASP-121 b, obtained with the James Webb Space Telescope (JWST) and the Near Infrared Imager and Slitless Spectrograph (NIRISS). We detect significant helium absorption at > 3σ over nearly 60% of the orbit, revealing a persistent and large-scale outflow. The signal separates into a dense leading tail moving toward the star and a trailing tail pushed away by stellar irradiation. Both appear to remain collisional far from the planet, implying strong hydrodynamic escape. While qualitatively consistent with theoretical expectations, current models cannot reproduce the full spatial and kinematic structure, limiting precise mass-loss estimates. These results demonstrate JWST's ability to map exoplanet outflows in detail and highlight its synergy with ground-based spectroscopy.

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• Diversity in the haziness and chemistry of temperate sub-Neptunes

  Nature Astronomy · 2025-12-12 · 4 citations

  articleOpen access
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• NIRPS and TESS reveal a peculiar system around the M dwarf TOI-756: A transiting sub-Neptune and a cold eccentric giant

  Astronomy and Astrophysics · 2025-10-01 · 5 citations

  articleOpen access

  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.

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• Mapping Atmospheric Features of the Planetary-mass Brown Dwarf SIMP 0136 with JWST NIRISS

  The Astrophysical Journal · 2025-11-07 · 2 citations

  articleOpen accessCorresponding

  Abstract In this paper, we analyze James Webb Space Telescope Near-Infrared Imager and Slitless Spectrograph time-series spectroscopy data to characterize the atmosphere of the planetary-mass brown dwarf SIMP J01365662+093347. Principal component analysis reveals that 81% of spectral variations can be described by two components, implying that variability within a single rotational phase is induced by at least three distinct spectral regions. By comparing our data to a grid of Sonora Diamondback atmospheric models, we confirm that the time-averaged spectrum cannot be explained by a single model but requires a linear combination of at least three regions. Projecting these models onto the principal component plane shows that the overall variability is highly correlated with changes in temperature, cloud coverage, and possibly effective metallicity. We also extract brightness maps from the lightcurve and establish north–south asymmetry in the atmosphere. A combined multidimensional analysis of spectrophotometric variability links the three spectral regions to three atmospheric layers. Forsterite cloud and water abundance at each level form unique harmonics of atmospheric variability observed in different spectral bands. Atmospheric retrievals on the time-averaged spectrum are consistent with an optically thick iron cloud deck beneath a patchy forsterite cloud layer and with the overall adiabatic curve. We also demonstrate two new analysis methods: a regionally resolved spectra retrieval that relies on multiwavelength spherical harmonics maps, and a method to constrain brightness maps using Doppler information present in the spectra. Future observations of variable brown dwarfs of higher spectral resolution or those spanning multiple rotations should help break the mapping degeneracy.

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• Uniform Reanalysis of JWST MIRI 15 <i>μ</i>m Exoplanet Eclipse Observations Using Frame-normalized Principal Component Analysis

  The Astrophysical Journal Letters · 2025-08-06 · 3 citations

  articleOpen access

  Abstract James Webb Space Telescope (JWST) MIRI 15 μ m time-series eclipse photometry presents a powerful way to probe for the presence of atmospheres on low-temperature rocky exoplanets orbiting nearby stars. Here, we introduce a novel technique, frame-normalized principal component analysis (FN-PCA), to analyze and detrend these MIRI time-series observations. Using the FN-PCA technique, we perform a uniform reanalysis of the published MIRI 15 μ m observations of LHS 1478 b, TOI-1468 b, LHS 1140c, TRAPPIST-1 b, and TRAPPIST-1 c using our new data reduction pipeline ( Erebus ) and compare them to different potential atmospheric and surface compositions. We also investigate additional public data sets with the sole purpose of understanding the instrument systematics affecting MIRI. We identify and categorize important detector-level systematics in the observations that are generally present across all 17 analyzed eclipse observations, which we illustrate as eigenimage/eigenvalue pairs in the FN-PCA. One of these eigenimage/eigenvalue pairs corresponds to the prominent ramp effect at the beginning of the time-series observations, which has widely been reported for JWST and Spitzer photometry. For JWST/MIRI, we show that the detector settling timescales exponentially with the apparent magnitude of the target star <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>set</mml:mi> </mml:msub> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">[</mml:mo> <mml:mi>hr</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo>=</mml:mo> <mml:mn>0.063</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mi>exp</mml:mi> <mml:mrow> <mml:mn>0.427</mml:mn> <mml:mo>·</mml:mo> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>K</mml:mi> </mml:msub> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:mn>0.657</mml:mn> </mml:math> . This uniform reanalysis and investigation of JWST/MIRI systematics is done in preparation for the 500 hr Rocky Worlds Director’s Discretionary Time survey to demonstrate a data-driven systematic model usable across all MIRI 15 μ m data sets.

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• <i>JWST</i> NIRISS transmission spectroscopy of the super-Earth GJ 357b, a favourable target for atmospheric retention

  Monthly Notices of the Royal Astronomical Society · 2025-06-03 · 6 citations

  articleOpen access

  ABSTRACT We present a JWST Near Infrared Imager and Slitless Spectrograph/Single Object Slitless Spectroscopy transmission spectrum of the super-Earth GJ 357 b: the first atmospheric observation of this exoplanet. Despite missing the first $\sim$40 per cent of the transit due to using an out-of-date ephemeris, we still recover a transmission spectrum that does not display any clear signs of atmospheric features. We perform a search for Gaussian-shaped absorption features within the data but find that this analysis yields comparable fits to the observations as a flat line. We compare the transmission spectrum to a grid of atmosphere models and reject, to 3$\sigma$ confidence, atmospheres with metallicities $\lesssim 100\times$ solar ($\sim$4 g mol−1) with clouds at pressures down to 0.01 bar. We analyse how the retention of a secondary atmosphere on GJ 357 b may be possible due to its higher escape velocity compared to an Earth-sized planet and the exceptional inactivity of its host star relative to other M2.5V stars. The star’s XUV luminosity decays below the threshold for rapid atmospheric escape early enough that the volcanic revival of an atmosphere of several bars of CO$_2$ is plausible, though subject to considerable uncertainty. Finally, we model the feasibility of detecting an atmosphere on GJ 357 b with MIRI/LRS, MIRI photometry, and NIRSpec/G395H. We find that, with two eclipses, it would be possible to detect features indicative of an atmosphere or surface. Further to this, with three to four transits, it would be possible to detect a 1 bar nitrogen-rich atmosphere with 1000 ppm of CO$_2$.

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• Strict limits on potential secondary atmospheres on the temperate rocky exo-Earth TRAPPIST-1 d

  ArXiv.org · 2025-08-11 · 1 citations

  preprintOpen access

  The nearby TRAPPIST-1 system, with its seven small rocky planets orbiting a late-type M8 star, offers an unprecedented opportunity to search for secondary atmospheres on temperate terrestrial worlds. In particular, the 0.8 Earth-radii planet TRAPPIST-1 d lies at the edge of the habitable zone (equilibrium temperature ~262 K). Here we present the first 0.6-5.2 micron NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500-1,000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within $\pm$100-150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM's sensitivity to CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (greater than 3$σ$). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 to further reject high mean molecular weight compositions analogous to Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (greater than 95% confidence). If TRAPPIST-1 d retains an atmosphere, it is likely extremely thin or contains high-altitude aerosols, with water cloud formation at the terminator predicted by 3D global climate models. Alternatively, if TRAPPIST-1 d is airless, our evolutionary models indicate that TRAPPIST-1 b, c, and d must have formed with less than approximately 4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g.

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• Continuous helium absorption from both the leading and trailing tails of WASP-107 b

  Nature Astronomy · 2025-12-01 · 3 citations

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