Publications

2024

1. Nature

   Sulphur dioxide in the mid-infrared transmission spectrum of WASP-39b

   Diana Powell, Adina D. Feinstein, Elspeth K. H. Lee, and 70 more authors

   Nature, Jan 2024

   LINK
2. NatureAstro

   Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b

   Taylor J. Bell, Nicolas Crouzet, Patricio E. Cubillos, and 80 more authors

   Nature Astronomy, Apr 2024

   ABSTRACT LINK

   Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5 μm to 12 μm with the JWST’s Mid-Infrared Instrument. The spectra reveal a large day–night temperature contrast (with average brightness temperatures of 1,524 ± 35 K and 863 ± 23 K, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase-curve shape and emission spectra strongly suggest the presence of nightside clouds that become optically thick to thermal emission at pressures greater than  100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2 σ upper limit of 1–6 ppm, depending on model assumptions). Our results provide strong evidence that the atmosphere of WASP-43b is shaped by disequilibrium processes and provide new insights into the properties of the planet’s nightside clouds. However, the remaining discrepancies between our observations and our predictive atmospheric models emphasize the importance of further exploring the effects of clouds and disequilibrium chemistry in numerical models.

3. APJ

   Is the Atmosphere of the Ultra-hot Jupiter WASP-121 b Variable?

   Q. Changeat, J. W. Skinner, J. Y-K. Cho, and 12 more authors

   The Astrophysical Journal Supplement Series, Feb 2024

   ABSTRACT LINK

   We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere of WASP-121 b, an ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations with a uniform methodology and addressing the biases from instrument systematics, sophisticated atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a strong thermal inversion beginning at ∼10 4 Pa on the dayside, solar to subsolar metallicity Z (i.e., − 0.77 < log ( Z ) < 0.05 ), and supersolar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly, utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following unambiguous time-varying signals in the data: (i) a shift of the putative hotspot offset between the two phase curves and (ii) varying spectral signatures in the transits and eclipses. By simulating the global dynamics of WASP-121 b’s atmosphere at high resolution, we show that the identified signals are consistent with quasiperiodic weather patterns, hence atmospheric variability, with signatures at the level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in the simulations, the weather patterns arise from the formation and movement of storms and fronts, causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.

4. Nature

   SO2, silicate clouds, but no CH4 detected in a warm Neptune

   Achrène Dyrek, Michiel Min, Leen Decin, and 43 more authors

   Nature, Jan 2024

   LINK
5. A&A

   Transiting exoplanets with the Mid-InfraRed Instrument on board JWST: From simulations to observations

   A. Dyrek, E. Ducrot, P.-O. Lagage, and 4 more authors

   Astronomy & Astrophysics, Mar 2024

   ABSTRACT LINK

   Context . The James Webb Space Telescope (JWST) has now started its exploration of exoplanetary worlds. In particular, the Mid-InfraRed Instrument (MIRI) with its Low-Resolution Spectrometer (LRS) carries out transit, eclipse, and phase-curve spectroscopy of exoplanetary atmospheres with an unprecedented precision in a so far almost uncharted wavelength range. Aims . The precision and significance in the detection of molecules in exoplanetary atmospheres relies on a thorough understanding of the instrument itself and on accurate data reduction methods. This paper aims to provide a clear description of the instrumental systematics that affect observations of transiting exoplanets through the use of simulations. Methods . We carried out realistic simulations of transiting-exoplanet observations with the MIRI LRS instrument that included the model of the exoplanet system, the optical path of the telescope, the MIRI detector performances, and instrumental systematics and drifts that could alter the atmospheric features we are meant to detect in the data. After we introduce our pipeline, we show its performance on the transit of L 168-9b, a super-Earth-sized exoplanet observed during the commissioning of the MIRI instrument. Results . This paper provides a better understanding of the data themselves and of the best practices in terms of reduction and analysis through comparisons between simulations and real data. We show that simulations validate the current data-analysis methods. Simulations also highlight instrumental effects that impact the accuracy of our current spectral extraction techniques. These simulations are proven to be essential in the preparation of JWST observation programs and help us to assess the detectability of various atmospheric and surface scenarios.

6. Nature

   A high internal heat flux and large core in a warm neptune exoplanet

   Luis Welbanks, Taylor J. Bell, Thomas G. Beatty, and 16 more authors

   Nature, May 2024

   LINK

2023

1. Nature

   Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST

   Thomas P. Greene, Taylor J. Bell, Elsa Ducrot, and 3 more authors

   Nature, Jun 2023

   LINK
2. A&A

   Spitzer thermal phase curve of WASP-121 b

   G. Morello, Q. Changeat, A. Dyrek, and 2 more authors

   Astronomy & Astrophysics, Aug 2023

   ABSTRACT LINK

   Aims. We analyse unpublished Spitzer observations of the thermal phase-curve of WASP-121 b, a benchmark ultra-hot Jupiter. Methods. We adopted the wavelet pixel-independent component analysis technique to remove challenging instrumental systematic effects in these datasets and we fit them simultaneously with parametric light-curve models. We also performed phase-curve retrievals to better understand the horizontal and vertical thermal structure of the planetary atmosphere. Results. We measured planetary brightness temperatures of  2700 K (dayside) and  700–1100 K (nightside), along with modest peak offsets of 5.9° ± 1.6 (3.6 µm) and 5.0° −3.1 +3.4 (4.5 µm) after mid-eclipse. These results suggest inefficient heat redistribution in the atmosphere of WASP-121 b. The inferred atmospheric Bond albedo and circulation efficiency align well with observed trends for hot giant exoplanets. Interestingly, the measured peak offsets correspond to a westward hot spot, which has rarely been observed. We also report consistent transit depths at 3.6 and 4.5 µm, along with updated geometric and orbital parameters. Finally, we compared our Spitzer results with previous measurements, including recent JWST observations. Conclusions. We extracted new information on the thermal properties and dynamics of an exoplanet atmosphere from an especially problematic dataset. This study probes the reliability of exoplanet phase-curve parameters obtained from Spitzer observations when state-of-the-art pipelines are adopted to remove the instrumental systematic effects. It demonstrates that Spitzer phase-curve observations provide a useful baseline for comparison with JWST observations, and shows the increase in parameters precision achieved with the newer telescope.

3. arXiv

   A First Look at the JWST MIRI/LRS Phase Curve of WASP-43b

   Taylor J. Bell, Laura Kreidberg, Sarah Kendrew, and 7 more authors

   Aug 2023

   Version Number: 1

   ABSTRACT LINK

   We observed a full-orbit phase curve of the hot Jupiter WASP-43b with MIRI/LRS as part of the Transiting Exoplanet Community Early Release Science Program. Here we report preliminary findings for the instrument performance from the team’s MIRI Working Group. Overall we find that MIRI’s performance for phase curve observations is excellent, with a few minor caveats. The key takeaways for Cycle 2 planning with MIRI/LRS are: (1) long-duration observations (> 24 hours) have now been successfully executed; (2) for phase curves, we recommend including a one-hour burn-in period prior to taking science data to mitigate the effects of the ramp systematic; and (3) we do not yet recommend partial phase curve observations. In addition, we also find that: the position of the spectrum on the detector is stable to within 0.03 pixels over the full 26.5-hour observation; the light curves typically show a systematic downward ramp that is strongest for the first 30 minutes, but continues to decay for hours; from 10.6-11.8 microns, the ramp effect has remarkably different behavior, possibly due to a different illumination history for the affected region of the detector; after trimming the integrations most affected by the initial ramps and correcting the remaining systematics with analytic models, we obtain residuals to the light-curve fits that are typically within 25% of the photon noise limit for 0.5-micron spectroscopic bins; non-linearity correction is not a significant source of additional noise for WASP-43, though it may be an issue for brighter targets; the gain value of 5.5 electrons/DN currently on CRDS and JDox is known to be incorrect, and the current best estimate for the gain is approximately 3.1 electrons/DN; new reference files for the JWST calibration pipeline reflecting these findings are under development at STScI.

4. Nature

   A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve

   Eliza M.-R. Kempton, Michael Zhang, Jacob L. Bean, and 30 more authors

   Nature, Aug 2023

   LINK
5. A&A

   In search of gravity mode signatures in main sequence solar-type stars observed by \textitKepler

   S. N. Breton, H. Dhouib, R. A. García, and 7 more authors

   Astronomy & Astrophysics, Nov 2023

   ABSTRACT LINK

   Gravity modes ( g modes), mixed gravito-acoustic modes (mixed modes), and gravito-inertial modes ( gi modes) possess unmatched properties as probes for stars with radiative interiors. The structural and dynamical constraints that they are able to provide cannot be accessed by other means. While they provide precious insights into the internal dynamics of evolved stars as well as massive and intermediate-mass stars, their non-detection in main sequence (MS) solar-type stars make them a crucial missing piece in our understanding of angular momentum transport in radiative zones and stellar rotational evolution. In this work, we aim to apply certain analysis tools originally developed for helioseismology in order to look for g -mode signatures in MS solar-type stars. We select a sample of the 34 most promising MS solar-type stars with Kepler four-year long photometric time series. All these stars are well-characterised late F-type stars with thin convective envelopes, fast convective flows, and stochastically excited acoustic modes ( p modes). For each star, we compute the background noise level of the Fourier power spectrum to identify significant peaks at low frequency. After successfully detecting individual peaks in 12 targets, we further analyse four of them and observe distinct patterns of surrounding peaks with a low probability of being noise artifacts. Comparisons with the predictions from reference models suggest that these patterns are compatible with the presence of non-asymptotic low-order pure g modes, pure p modes, and mixed modes. Given their sensitivity to both the convective core interface stratification and the coupling between p - and g -mode resonant cavities, such modes are able to provide strong constraints on the structure and evolutionary states of the related targets. Considering the granulation and activity background of the stars in our sample, we subsequently compute the corresponding mode velocity necessary to trigger a detectable luminosity fluctuation. We use it to estimate the surface velocity, ⟨ v r ⟩, of the candidate modes we have detected. In this case, we find ⟨ v r ⟩∼10 cm s −1 . These results could be extremely useful for characterising the deep interior of MS solar-type stars, as the upcoming PLATO mission will considerably expand the size of the available working sample.

2022

1. MNRAS

   Is binning always sinning? The impact of time-averaging for exoplanet phase curves

   Giuseppe Morello, Achrène Dyrek, and Quentin Changeat

   Monthly Notices of the Royal Astronomical Society, Oct 2022

   ABSTRACT LINK

   We explore how finite integration time or temporal binning can affect the analysis of exoplanet phase curves. We provide analytical formulae to account for this effect or, if neglected, to estimate the potential biases in the retrieved parameters. As expected, due to their smoother variations over longer time-scales, phase curves can be binned more heavily than transits without causing severe biases. In the simplest case of a sinusoidal phase curve with period P, the integration time Δt reduces its amplitude by the scaling factor sinc(πΔt/P), without altering its phase or shape. We also provide formulae to predict reasonable parameter error bars from phase-curve observations. Our findings are tested with both synthetic and real data sets, including unmodelled astrophysical signals and/or instrumental systematic effects. Tests with the Spitzer data show that binning can affect the best-fitting parameters beyond predictions, due to the correction of high-frequency correlated noise. Finally, we summarize key guidelines for speeding up the analysis of exoplanet phase curves without introducing significant biases in the retrieved parameters.

2. SPIE

   Characterization of the MIRIm double prism assembly at short wavelengths: implications for transit observations of exoplanets

   Patrice Bouchet, René Gastaud, Pierre-Olivier Lagage, and 12 more authors

   In Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave , Aug 2022

   LINK

2020

1. SPIE

   A cryogenic actuator for the image derotator on ELT-METIS

   Olivier Corpace, Jean-Christophe Barrière, Ayoub Bounad, and 12 more authors

   In Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV , Dec 2020

   LINK