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M dwarf systems offer a unique opportunity to study terrestrial exoplanetary atmospheres due to their smaller size and cooler temperatures. However, due to the extreme conditions these host stars impose, it is unclear whether their small, close-in rocky planets are able to retain any atmosphere at all. The Hot Rocks Survey aims to answer this question by targeting nine different M dwarf rocky planets spanning a range of planetary and stellar properties. LHS 1478 b orbits an M3-type star, has an equilibrium temperature of Teq = 585 K and experiences an instellation 21 times greater than that of Earth. We observe two secondary eclipses using photometric imaging at 15 um using the Mid-Infrared Instrument on the James Webb Space Telescope (JWST MIRI) to measure thermal emission from the dayside of the planet. We then compare these values to different atmospheric scenarios to evaluate potential heat transport and CO2 absorption signatures. We find a secondary eclipse depth of 146 +/- 56 ppm based on the first observation, while the second observation results in a non-detection due to significantly larger unexplained systematics. Based on the first observation alone, we can reject the null hypothesis of the dark (zero Bond albedo) no atmosphere bare rock model with a confidence level of 3.4 sigma. For an airless body with a Bond albedo of A=0.2, the significance decreases to 2.9 sigma. The secondary eclipse depth is consistent with the majority of atmospheric scenarios we considered, which all involve atmospheres which include different concentrations of CO2, and surface pressures from 0.1 to 10 bar. However, we stress that the two observations from our program do not yield consistent results, and more observations are needed to verify our findings. The Hot Rocks Survey serves as a relevant primer for future endeavors such as the Director's Discretionary Time (DDT) Rocky Worlds program., Comment: Submitted to A&A

Motivated by the observed ~30% variations in flux from the L7 dwarf VHS 1256 b, we subjected its time-resolved Hubble Space Telescope (HST) WFC3 spectra (measured in two epochs in 2018 and 2020), as well as medium-resolution Very Large Telescope (VLT) X-shooter and Early Release Science James Webb Space Telescope (JWST) spectra to a suite of both standard Bayesian (nested sampling) and machine-learning (random forest) retrievals. We find that both HST and VLT data require vertically varying abundance profiles of water in order to model the spectra accurately. Despite the large flux variations observed in the HST data, the temporal variability cannot be attributed to a single varying atmospheric property. The retrieved atmospheric quantities are consistent with being invariant across time. However, we find that model grids provide generally poor fits to the measured HST spectra and are unsuitable for quantifying the temporal variability of atmospheric properties. Additionally, our analysis of JWST spectra using model grids indicates consistency in retrieved properties across different wavelength channels. Despite the temporal variability in flux, the retrieved properties between HST and VLT, as well as between HST and JWST, are consistent within the respective posterior uncertainties. Such an outcome bodes well for future retrieval analyses of exoplanetary atmospheres, which are expected to exhibit weaker flux variations., Comment: Accepted by A&A. 16 pages, 14 figures, 3 tables

Modern spectroscopic surveys can only target a small fraction of the vast amount of photometrically cataloged sources in wide-field surveys. Here, we report the development of a generative AI method capable of predicting optical galaxy spectra from photometric broad-band images alone. This method draws from the latest advances in diffusion models in combination with contrastive networks. We pass multi-band galaxy images into the architecture to obtain optical spectra. From these, robust values for galaxy properties can be derived with any methods in the spectroscopic toolbox, such as standard population synthesis techniques and Lick indices. When trained and tested on 64x64-pixel images from the Sloan Digital Sky Survey, the global bimodality of star-forming and quiescent galaxies in photometric space is recovered, as well as a mass-metallicity relation of star-forming galaxies. The comparison between the observed and the artificially created spectra shows good agreement in overall metallicity, age, Dn4000, stellar velocity dispersion, and E(B-V) values. Photometric redshift estimates of our generative algorithm can compete with other current, specialized deep-learning techniques. Moreover, this work is the first attempt in the literature to infer velocity dispersion from photometric images. Additionally, we can predict the presence of an active galactic nucleus up to an accuracy of 82%. With our method, scientifically interesting galaxy properties, normally requiring spectroscopic inputs, can be obtained in future data sets from large-scale photometric surveys alone. The spectra prediction via AI can further assist in creating realistic mock catalogs., Comment: Code is available here: https://github.com/LarsDoorenbos/generate-spectra

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project's detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet's high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.

WASP-39b was observed using several different JWST instrument modes and the spectra were published in a series of papers by the ERS team. The current study examines the information content of these spectra measured using the different instrument modes, focusing on the complexity of the temperature-pressure profiles and number of chemical species warranted by the data. We examine if H2O, CO, CO2, K, H2S, CH4, and SO2 are detected in each of the instrument modes. Two Bayesian inference methods are used to perform atmospheric retrievals: standard nested sampling and supervised machine learning of the random forest (trained on a model grid). For nested sampling, Bayesian model comparison is used as a guide to identify the set of models with the required complexity to explain the data. Generally, non-isothermal transit chords are needed to fit the transmission spectra of WASP-39b, although the complexity of the Tp-profile required is mode-dependent. The minimal set of chemical species needed to fit a spectrum is mode-dependent as well, and also depends on whether grey or non-grey clouds are assumed. When a non-grey cloud model is used to fit the G395H spectrum, it generates a spectral continuum that compensates for the H2O opacity. The same compensation is absent when fitting the non-grey cloud model to the PRISM spectrum (which has broader wavelength coverage), suggesting that it is spurious. The interplay between the cloud spectral continuum and the H2O opacity determines if SO2 is needed to fit either spectrum. The inferred elemental abundances of carbon and oxygen and the carbon-to-oxygen (C/O) ratios are all mode- and model-dependent, and should be interpreted with caution. Bayesian model comparison does not always offer a clear path forward for favouring specific retrieval models (e.g. grey versus non-grey clouds) and thus for enabling unambiguous interpretations of exoplanet spectra., Comment: Accepted by A&A. 25 pages, 26 figures, 3 tables

Optical phase curves of hot Jupiters can reveal global scattering properties. We implement a Bayesian inference framework for optical phase curves with flux contributions from: reflected light from a potentially inhomogeneous atmosphere, thermal emission, ellipsoidal variations, Doppler beaming, and stellar rotation via a Gaussian process in the time domain. We probe for atmospheric homogeneity and time-variability using the reflected light inferences for highly precise Kepler light curves of five hot Jupiters. We also investigate the scattering properties which constrain the most likely condensates in the inhomogeneous atmospheres. Cross validation prefers inhomogeneous albedo distributions for Kepler-7 b and Kepler-41 b, and a weak preference for inhomogeneity for KOI-13 b. None of the five planets exhibit significant variations in geometric albedo on one-year timescales, in agreement with theoretical expectations. We show that analytic reflected light phase curves with isotropic multiple scattering are in excellent agreement with full Rayleigh multiple scattering calculations, allowing for accelerated and analytic inference. In a case study of Kepler-41 b, we identify perovskite, forsterite, and enstatite as possible scattering species consistent with the reflected light phase curves, with condensate particle radii in the range 0.01-0.1 micron., Comment: Accepted in A&A

Carbon monoxide was recently reported in the atmosphere of the hot Jupiter WASP-39b using the NIRSpec PRISM transit observation of this planet, collected as part of the JWST Transiting Exoplanet Community Early Release Science (JTEC ERS) Program. This detection, however, could not be confidently confirmed in the initial analysis of the higher resolution observations with NIRSpec G395H disperser. Here we confirm the detection of CO in the atmosphere of WASP-39b using the NIRSpec G395H data and cross-correlation techniques. We do this by searching for the CO signal in the unbinned transmission spectrum of the planet between 4.6 and 5.0 $\mu$m, where the contribution of CO is expected to be higher than that of other anticipated molecules in the planet's atmosphere. Our search results in a detection of CO with a cross-correlation function (CCF) significance of $6.6 \sigma$ when using a template with only ${\rm ^{12}C^{16}O}$ lines. The CCF significance of the CO signal increases to $7.5 \sigma$ when including in the template lines from additional CO isotopologues, with the largest contribution being from ${\rm ^{13}C^{16}O}$. Our results highlight how cross-correlation techniques can be a powerful tool for unveiling the chemical composition of exoplanetary atmospheres from medium-resolution transmission spectra, including the detection of isotopologues., Comment: Accepted for publication in The Astrophysical Journal Letters

The enigmatic nature of 55 Cancri e has defied theoretical explanation. Any explanation needs to account for the observed variability of its secondary eclipse depth, which is at times consistent with zero in the visible/optical range of wavelengths -- a phenomenon that does not occur with its also variable infrared eclipses. Yet, despite this variability its transit depth remains somewhat constant in time and is inconsistent with opaque material filling its Hill sphere. The current study explores the possibility of a thin, transient, secondary atmosphere on 55 Cancri e that is sourced by geochemical outgassing. Its transient nature derives from the inability of outgassing to be balanced by atmospheric escape. As the outgassed atmosphere escapes and is replenished, it rapidly adjusts to radiative equilibrium and the temperature fluctuations cause the infrared eclipse depths to vary. Atmospheres of pure carbon dioxide or carbon monoxide produce sufficient Rayleigh scattering to explain the observed optical/visible eclipse depths, which vanish in the absence of an atmosphere and the presence of a dark rocky surface. Atmospheres of pure methane are ruled out because they produce insufficient Rayleigh scattering. Upcoming observations by the James Webb Space Telescope will potentially allow the atmospheric temperature and surface pressure, as well as the surface temperature, to be measured., Comment: Accepted by Astrophysical Journal Letters (ApJL). 8 pages, 4 figures, 1 table

When observing transmission spectra produced by atmospheres of ultra-hot Jupiters, large telescopes are typically the instrument of choice due to the very weak signal of the planet's atmosphere. This study aims to alleviate the desire for large telescopes by illustrating that the same science is possible with smaller telescope classes. We use the cross-correlation technique to showcase the potential of the high-resolution spectrograph FOCES at Wendelstein Observatory and demonstrate its potential to resolve the atmosphere of the ultra-hot Jupiter, KELT-9 b. A performance comparison is conducted between FOCES and HARPS-N spectrographs, considering both single transit and combined observations over three nights. With FOCES, we have detected seven species in KELT-9 b's atmosphere: Ti II, Fe I, Fe II, Na I, Mg I, Na II, Cr II, Sc II. Although HARPS-N surpasses FOCES in performance, our results reveal that smaller telescope classes are capable of resolving ultra-hot Jupiter atmospheres. This broadens the scope of potential studies, allowing for investigations into phenomena like temporal variations in atmospheric signals and the atmospheric loss characteristics of these close-in planets.

Understanding differences between sub-stellar spectral data and models has proven to be a major challenge, especially for self-consistent model grids that are necessary for a thorough investigation of brown dwarf atmospheres. Using the supervised machine learning method of the random forest, we study the information content of 14 previously published model grids of brown dwarfs (from 1997 to 2021). The random forest method allows us to analyze the predictive power of these model grids, as well as interpret data within the framework of Approximate Bayesian Computation (ABC). Our curated dataset includes 3 benchmark brown dwarfs (Gl 570D, {\epsilon} Indi Ba and Bb) as well as a sample of 19 L and T dwarfs; this sample was previously analyzed in Lueber et al. (2022) using traditional Bayesian methods (nested sampling). We find that the effective temperature of a brown dwarf can be robustly predicted independent of the model grid chosen for the interpretation. However, inference of the surface gravity is model-dependent. Specifically, the BT-Settl, Sonora Bobcat and Sonora Cholla model grids tend to predict logg ~3-4 (cgs units) even after data blueward of 1.2 {\mu}m have been disregarded to mitigate for our incomplete knowledge of the shapes of alkali lines. Two major, longstanding challenges associated with understanding the influence of clouds in brown dwarf atmospheres remain: our inability to model them from first principles and also to robustly validate these models., Comment: Accepted for publication in The Astrophysical Journal

The atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. Secondary atmospheres, such as those of Earth, Mars and Venus, are sourced by outgassing. Persistent outgassing into long-lived, primordial, hydrogen-helium envelopes produces hybrid atmospheres of which there are no examples in the Solar System. We construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium and nitrogen content. Non-ideal gases (quantified by the fugacity coefficient) and non-ideal mixing of gaseous components (quantified by the activity coefficient) are considered. Both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. The abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by James Webb Space Telescope spectra in the near future. Methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding $\sim 10$ bar, a reduced (poorly oxidised) mantle and diminished magma temperatures (compared to modern Earth). Future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. Exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super Earths and sub-Neptunes; such an empirical relationship already exists for Solar System bodies., Comment: Accepted by ApJ. 31 pages, 24 figures, 4 tables

Carbonate precipitation in oceans is essential for the carbonate-silicate cycle (inorganic carbon cycle) to maintain temperate climates. By considering the thermodynamics of carbonate chemistry, we demonstrate that the ocean pH decreases by approximately 0.5 for a factor of 10 increase in the atmospheric carbon dioxide content. The upper and lower limits of ocean pH are within 1-4 of each other, where the upper limit is buffered by carbonate precipitation and defines the ocean pH when the carbon cycle operates. If the carbonate compensation depth (CCD) resides above the ocean floor, then carbonate precipitation and the carbon cycle cease to operate. The CCD is deep (>40 km) for high ocean temperature and high atmospheric carbon dioxide content. Key divalent carbonates of magnesium, calcium and iron produce an increasingly wider parameter space of deep CCDs, suggesting that chemical diversity promotes the carbon cycle. The search for life from exoplanets will benefit by including chemically more diverse targets than Earth twins., Comment: Published in ApJ Letters (updated missing journal information)

Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 \mu$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator., Comment: 48 pages, 12 figures, 2 tables. Under review at Nature

Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date. Recent observations from the JWST Transiting Exoplanet Early Release Science Program found a spectral absorption feature at 4.05 $\mu$m arising from SO$_2$ in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M$_J$) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of $\sim$1100 K. The most plausible way of generating SO$_2$ in such an atmosphere is through photochemical processes. Here we show that the SO$_2$ distribution computed by a suite of photochemical models robustly explains the 4.05 $\mu$m spectral feature identified by JWST transmission observations with NIRSpec PRISM (2.7$\sigma$) and G395H (4.5$\sigma$). SO$_2$ is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H$_2$S) is destroyed. The sensitivity of the SO$_2$ feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of $\sim$10$\times$ solar. We further point out that SO$_2$ also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations., Comment: 39 pages, 14 figures, accepted to be published in Nature

Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution, and high precision that, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0 - 4.0 $\mu$m, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous H$_2$O in the atmosphere and place an upper limit on the abundance of CH$_4$. The otherwise prominent CO$_2$ feature at 2.8 $\mu$m is largely masked by H$_2$O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100$\times$ solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere., Comment: 35 pages, 13 figures, 3 tables, Nature, accepted

Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R$\sim$600) transmission spectrum of an exoplanet atmosphere between 3-5 $\mu$m covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO$_2$ (28.5$\sigma$) and H$_2$O (21.5$\sigma$), and identify SO$_2$ as the source of absorption at 4.1 $\mu$m (4.8$\sigma$). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO$_2$, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range., Comment: 44 pages, 11 figures, 3 tables. Resubmitted after revision to Nature

Benchmark brown dwarf companions with well-determined ages and model-independent masses are powerful tools to test substellar evolutionary models and probe the formation of giant planets and brown dwarfs. Here, we report the independent discovery of HIP~21152~B, the first imaged brown dwarf companion in the Hyades, and conduct a comprehensive orbital and atmospheric characterization of the system. HIP~21152 was targeted in an ongoing high-contrast imaging campaign of stars exhibiting proper motion changes between Hipparcos and Gaia, and was also recently identified by Bonavita et al. (2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of HIP~21152 revealed a comoving companion at a separation of $0.37^{\prime\prime}$ (16 au). We perform a joint orbit fit of all available relative astrometry and radial velocities together with the Hipparcos-Gaia proper motions, yielding a dynamical mass of $24^{+6}_{-4}\,\mathrm{M_{Jup}}$, which is $1{-}2{\sigma}$ lower than evolutionary model predictions. Hybrid grids that include the evolution of cloud properties best reproduce the dynamical mass. We also identify a comoving wide-separation ($1837^{\prime\prime}$ or $7.9 \times 10^4 \, \mathrm{au}$) early-L dwarf with an inferred mass near the hydrogen-burning limit. Finally, we analyze the spectra and photometry of HIP~21152~B using the Saumon & Marley (2008) atmospheric models and a suite of retrievals. The best-fit grid-based models have $f_{\mathrm{sed}}=2$, indicating the presence of clouds, $T_{\mathrm{eff}}=1400 \, \mathrm{K}$, and $\log{g}=4.5 \, \mathrm{dex}$. These results are consistent with the object's spectral type of $\mathrm{T0\pm1}$. As the first benchmark brown dwarf companion in the Hyades, HIP~21152~B joins the small but growing number of substellar companions with well-determined ages and dynamical masses., Comment: 40 pages, 19 figures, accepted to AJ

The atmospheres of ultra hot Jupiters (UHJs) are prime targets for the detection of molecules and atoms at both low and high spectral resolution. We study the atmospheres of the UHJs WASP-121b and WASP-189b by performing 3D general circulation models (GCMs) of these planets using high temperature correlated-k opacity schemes with ultra-violet (UV) absorbing species included. The GCM results are then post-processed at low and high spectral resolutions and compared to available data. The high resolution results are cross-correlated with molecular and atomic templates to produce mock molecular detections. Our GCM models produce similar temperature-pressure (T-p) structure trends to previous 1D radiative-convective equilibrium models of UHJs. Furthermore, the inclusion of UV opacities greatly shapes the thermal and dynamical properties of the high-altitude, low-pressure regions of the UHJ atmospheres, with sharp T-p inversions due to the absorption of UV light. This suggests that optical wavelength, high-resolution observations probe a dynamically distinct upper atmospheric region, rather than the deeper jet forming layers., Comment: MNRAS accepted: 8 August 2022, published 11 August 2022

KELT-11b is an inflated sub-Saturn with a hot atmosphere and that orbits a bright evolved subgiant star, making it a prime choice for atmospheric characterization, but that transits its host star for more than seven hours. We observed this system in series of three consecutive nights with the HARPS spectrograph and report on the analysis of the transmission spectrum obtained from this dataset. Our results highlight the potential for independent observations of a long-transiting planet over consecutive nights. Our study reveals a sodium excess absorption of $0.28 \pm 0.05 \%$ and $0.50 \pm 0.06 \%$ in the Na D1 and D2 lines, respectively. This corresponds to 1.44 and 1.69 times the white-light planet radius in the line cores. Wind pattern modeling tends to prefer day-to-night side winds with no vertical winds, which is surprising considering the planet bloatedness. The modeling of the Rossiter-Mclaughlin effect yields a significantly misaligned orbit, with a projected spin-orbit angle of ${\lambda} = -77.86^{+2.36}_{-2.26}{}^\circ$. The characteristics of KELT-11 b, notably its extreme scale height and long transit, make it an ideal and unique target for next-generation telescopes. Our results as well as recent findings from HST, TESS, and CHEOPS observations could make KELT-11 b a benchmark exoplanet in atmospheric characterization., Comment: 19 pages, 18 figures, 8 tables. Accepted for publication in Astronomy & Astrophysics

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2 but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS). The data used in this study span 3.0 to 5.5 {\mu}m in wavelength and show a prominent CO2 absorption feature at 4.3 {\mu}m (26{\sigma} significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 {\mu}m that is not reproduced by these models., Comment: 27 pages, 6 figures, Accepted for publication in Nature, data and models available at https://doi.10.5281/zenodo.6959427

We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright ($T = 8.5$ mag), high proper motion ($\sim\,200$ mas yr$^{-1}$), low metallicity ([Fe/H]$\approx\,-0.28$) K-dwarf with a mass of $0.68\pm0.05$ M$_{\odot}$ and a radius of $0.67\pm0.01$ R$_{\odot}$. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a $1.70\pm0.07$ R$_{\oplus}$ super-Earth in a 3.82 day orbit, placing it directly within the so-called 'radius valley'. The outer planet, TOI-836 c, is a $2.59\pm0.09$ R$_{\oplus}$ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of $4.5\pm0.9$ M$_{\oplus}$ , while TOI-836 c has a mass of $9.6\pm2.6$ M$_{\oplus}$. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.

The construction and implementation of atmospheric model grids is a popular tool in exoplanet characterisation. These typically vary a number of parameters linearly, containing one model for every combination of parameter values. Here we investigate alternative methods of sampling parameters, including random sampling and Latin hypercube (LH) sampling, and how these compare to linearly sampled grids. We use a random forest to analyse the performance of these grids for two different models, as well as investigate the information content of the particular model grid from Goyal et al. 2019. We also use nested-sampling to implement mock atmospheric retrievals on simulated JWST transmission spectra by interpolating on linearly sampled model grids. Our results show that random or LH sampling out-performs linear sampling in parameter predictability for our higher dimensional models, requiring fewer models in the grid, and thus allowing for more computationally intensive forward models to be used. We also find that using a traditional retrieval with interpolation on a linear grid can produce biased posterior distributions, especially for parameters with non-linear effects on the spectrum. In particular, we advise caution when performing linear interpolation on the C/O ratio, cloud properties, and metallicity. Finally, we find that the information content analysis of the grid from Goyal et al. 2019 is able to highlight key areas of the spectra where the presence or absence of certain molecules can be detected, providing good indicators for parameters such as temperature and C/O ratio., Comment: 14 pages, 8 figures. Accepted for publication in ApJ

A large suite of 228 atmospheric retrievals is performed on a curated sample of 19 brown dwarfs spanning the L0 to T8 spectral types using the open-source Helios-r2 retrieval code, which implements the method of short characteristics for radiative transfer and a finite-element description of the temperature-pressure profile. Surprisingly, we find that cloud-free and cloudy (both gray and non-gray) models are equally consistent with the archival SpeX data from the perspective of Bayesian model comparison. Only upper limits for cloud properties are inferred if log-uniform priors are assumed, but the cloud optical depth becomes constrained if a uniform prior is used. Water is detected in all 19 objects and methane is detected in all of the T dwarfs, but no obvious trend exists across effective temperature. As carbon monoxide is only detected in a handful of objects, the inferred carbon-to-oxygen ratios are unreliable. The retrieved radius generally decreases with effective temperature, but the values inferred for some T dwarfs are implausibly low and may indicate missing physics or chemistry in the models. For the early L dwarfs, the retrieved surface gravity depends on whether the gray or non-gray cloud model is preferred. Future data are necessary for constraining cloud properties and the vertical variation of chemical abundances, the latter of which is needed for distinguishing between the chemical instability versus traditional cloud interpretation of the L-T transition., Comment: Accepted for publication in ApJ. The complete figure sets will be available in the online journal

Rocky planets hosted by close-in extrasolar systems are likely to be tidally locked in 1:1 spin-orbit resonance, a configuration where they exhibit permanent dayside and nightside. Because of the resulting day-night temperature gradient, the climate and large-scale circulation of these planets are strongly determined by their atmospheric stability against collapse, which designates the runaway condensation of greenhouse gases. To better constrain the surface conditions of rocky planets located in the habitable zone of their host star, it is therefore crucial to elucidate the mechanisms that govern the day-night heat redistribution. As a first attempt to bridge the gap between multiple modelling approaches ranging from idealised models to 3-D General Circulation Models (GCM), we developed a General Circulation Meta-Model (GCMM) able to reproduce both the closed-form solutions provided by analytical models and the numerical solutions obtained from GCM simulations. We used this approach to characterise the atmospheric stability of Earth-sized rocky planets with dry atmospheres containing CO2, and we benchmarked it against 3-D GCM simulations using THOR GCM. We observe that the collapse pressure below which collapse occurs can vary by ~40% around the value predicted by analytical scaling laws depending on the mechanisms taken into account among radiative transfer, atmospheric dynamics, and turbulent diffusion. Particularly, we find (i) that the turbulent diffusion taking place in the dayside planetary boundary layer (PBL) globally tends to warm up the nightside surface hemisphere except in the transition zone between optically thin and optically thick regimes, (ii) that the PBL also significantly affects the day-night advection timescale, and (iii) that the slow rotator approximation holds from the moment that the normalised equatorial Rossby deformation radius is greater than 2., Comment: 32 pages, 16 figures, accepted for publication in Astronomy & Astrophysics

Ground-based, high-resolution spectrographs are providing us with an unprecedented view of the dynamics and chemistry of the atmospheres of planets outside the Solar System. While there is a large number of stable and precise high-resolution spectrographs on modest-size telescopes, it is the spectrographs at observatories with apertures larger than 3.5 metres that dominate the atmospheric follow-up of exoplanets. In this work, we explore the potential of characterising exoplanetary atmospheres with FIES, a high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit of KELT-9 b to search for atomic iron, a species that has been recently discovered in both neutral and ionised forms in the atmospheres of these ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we detect a signal of Fe II at the $4.5\sigma$ and $4.0\sigma$ level in the transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the $8.5\sigma$ level. Although we do not find any significant Doppler shift in the signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the feature in KELT-9 b, which might be a manifestation of high-velocity winds transporting Fe II from the planetary dayside to the nightside. Our work demonstrates the feasibility of investigating exoplanet atmospheres with FIES, potentially unlocking a wealth of additional atmosphere detections with this and other high-resolution spectrographs mounted on similar-size telescopes., Comment: 9 pages, 6 figures, accepted to A&A

Context: TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young ($340\pm80$ Myr) K-type star. Although a validated planetary system, the orbits of the two outer planets were unconstrained as only two non-consecutive transits were seen in TESS photometry. This left 11 and 7 possible period aliases for each. Aims: To reveal the true orbits of these two long-period planets, precise photometry targeted on the highest-probability period aliases is required. Long-term monitoring of transits in multi-planet systems can also help constrain planetary masses through TTV measurements. Methods: We used the MonoTools package to determine which aliases to follow, and then performed space-based and ground-based photometric follow-up of TOI-2076 c and d with CHEOPS, SAINT-EX, and LCO telescopes. Results: CHEOPS observations revealed a clear detection for TOI-2076 c at $P=21.01538^{+0.00084}_{-0.00074}$ d, and allowed us to rule out three of the most likely period aliases for TOI-2076 d. Ground-based photometry further enabled us to rule out remaining aliases and confirm the $P=35.12537\pm0.00067$ d alias. These observations also improved the radius precision of all three sub-Neptunes to $2.518\pm0.036$, $3.497\pm0.043$, and $3.232\pm0.063$ $R_\oplus$. Our observations also revealed a clear anti-correlated TTV signal between planets b and c likely caused by their proximity to the 2:1 resonance, while planets c and d appear close to a 5:3 period commensurability, although model degeneracy meant we were unable to retrieve robust TTV masses. Their inflated radii, likely due to extended H-He atmospheres, combined with low insolation makes all three planets excellent candidates for future comparative transmission spectroscopy with JWST., Comment: 18 pages, 7 figure, 8 tables. Accepted for publication in Astronomy & Astrophysics. Photometry available on CDS/Vizier. Python package presented for modelling duotransiting planet candidates available at https://github.com/hposborn/MonoTools. Modelling & figure-creation code available at https://github.com/hposborn/TOI2076

General circulation models (GCMs) provide context for interpreting multi-wavelength, multi-phase data of the atmospheres of tidally locked exoplanets. In the current study, the non-hydrostatic THOR GCM is coupled with the HELIOS radiative transfer solver for the first time, supported by an equilibrium chemistry solver (FastChem), opacity calculator (HELIOS-K) and Mie scattering code (LX-MIE). To accurately treat the scattering of radiation by medium-sized to large aerosols/condensates, improved two-stream radiative transfer is implemented within a GCM for the first time. Multiple scattering is implemented using a Thomas algorithm formulation of the two-stream flux solutions, which decreases the computational time by about 2 orders of magnitude compared to the iterative method used in past versions of HELIOS. As a case study, we present four GCMs of the hot Jupiter WASP-43b, where we compare the temperature, velocity, entropy, and streamfunction, as well as the synthetic spectra and phase curves, of runs using regular versus improved two-stream radiative transfer and isothermal versus non-isothermal layers. While the global climate is qualitatively robust, the synthetic spectra and phase curves are sensitive to these details. A THOR+HELIOS WASP-43b GCM (horizontal resolution of about 4 degrees on the sphere and with 40 radial points) with multi-wavelength radiative transfer (30 k-table bins) running for 3000 Earth days (864,000 time steps) takes about 19-26 days to complete depending on the type of GPU., Comment: 31 pages, 24 figures, accepted for publication at MNRAS

We report the discovery and characterisation of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in TESS photometry. To characterise the system, we performed and retrieved CHEOPS, TESS, and ground-based photometry, HARPS high-resolution spectroscopy, and Gemini speckle imaging. We characterise the host star and determine $T_{\rm eff, \star}=4734\pm67$ K, $R_{\star}=0.726\pm0.007$ $R_{\odot}$, and $M_{\star}=0.748\pm0.032$ $M_{\odot}$. We present a novel detrending method based on PSF shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of $P_{\rm b}=6.44387\pm0.00003$ d, a radius of $R_{\rm b}=2.59\pm0.04$ $R_{\oplus}$, and a mass of $M_{\rm b}=13.5_{-1.8}^{+1.7}$ $M_{\oplus}$, whilst TOI-1064 c has an orbital period of $P_{\rm c}=12.22657^{+0.00005}_{-0.00004}$ d, a radius of $R_{\rm c}=2.65\pm0.04$ $R_{\oplus}$, and a 3$\sigma$ upper mass limit of 8.5 ${\rm M_{\oplus}}$. From the high-precision photometry we obtain radius uncertainties of $\sim$1.6%, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterised sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further RVs are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass-radius space, and it allows us to identify a trend in bulk density-stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets., Comment: 30 pages, 24 figures, 6 tables including the Appendix; accepted for publication in MNRAS

The temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber exists that causes a temperature inversion. Ozone plays this role in the Earth`s atmosphere. In the atmospheres of highly irradiated exoplanets, shortwave absorbers are predicted to be titanium oxide (TiO) and vanadium oxide (VO). Detections of TiO and VO have been claimed using both low and high spectral resolution observations, but later observations have failed to confirm these claims or overturned them. Here we report the unambiguous detection of TiO in the ultra-hot Jupiter WASP-189b using high-resolution transmission spectroscopy. This detection is based on applying the cross-correlation technique to many spectral lines of TiO from 460 to 690 nm. Moreover, we report detections of metals, including neutral and singly ionised iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe, Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. This is direct observational evidence for the three-dimensional thermo-chemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy., Comment: Published in Nature Astronomy on 27 January 2022, accepted on 1 December 2021 (32 pages, 21 figures, 3 tables)

We report the discovery of an ultrahot Jupiter with an extremely short orbital period of $0.67247414\,\pm\,0.00000028$ days ($\sim$16 hr). The $1.347 \pm 0.047$ $R_{\rm Jup}$ planet, initially identified by the Transiting Exoplanet Survey Satellite (TESS) mission, orbits TOI-2109 (TIC 392476080): a $T_{\rm eff} \sim 6500$ K F-type star with a mass of $1.447 \pm 0.077$ $M_{\rm Sun}$, a radius of $1.698 \pm 0.060$ $R_{\rm Sun}$, and a rotational velocity of $v\sin i_* = 81.9 \pm 1.7$ km s$^{-1}$. The planetary nature of TOI-2109b was confirmed through radial velocity measurements, which yielded a planet mass of $5.02 \pm 0.75$ $M_{\rm Jup}$. Analysis of the Doppler shadow in spectroscopic transit observations indicates a well-aligned system, with a sky-projected obliquity of $\lambda = 1\overset{\circ}{.}7 \pm 1\overset{\circ}{.}7$. From the TESS full-orbit light curve, we measured a secondary eclipse depth of $731 \pm 46$ ppm, as well as phase-curve variations from the planet's longitudinal brightness modulation and ellipsoidal distortion of the host star. Combining the TESS-band occultation measurement with a $K_s$-band secondary eclipse depth ($2012 \pm 80$ ppm) derived from ground-based observations, we find that the dayside emission of TOI-2109b is consistent with a brightness temperature of $3631 \pm 69$ K, making it the second hottest exoplanet hitherto discovered. By virtue of its extreme irradiation and strong planet-star gravitational interaction, TOI-2109b is an exceptionally promising target for intensive follow-up studies using current and near-future telescope facilities to probe for orbital decay, detect tidally driven atmospheric escape, and assess the impacts of H$_2$ dissociation and recombination on the global heat transport., Comment: 30 pages, 17 figures, published in AJ

Thermal phase curves of exoplanet atmospheres have revealed temperature maps as a function of planetary longitude, often by sinusoidal decomposition of the phase curve. We construct a framework for describing two-dimensional temperature maps of exoplanets with mathematical basis functions derived for a fluid layer on a rotating, heated sphere with drag/friction, which are generalizations of spherical harmonics. These basis functions naturally produce physically-motivated temperature maps for exoplanets with few free parameters. We investigate best practices for applying this framework to temperature maps of hot Jupiters by splitting the problem into two parts: (1) we constrain the temperature map as a function of latitude by tuning the basis functions to reproduce general circulation model (GCM) outputs, since disk-integrated phase curve observations do not constrain this dimension; and (2) we infer the temperature maps of real hot Jupiters using original reductions of several Spitzer phase curves, which directly constrain the temperature variations with longitude. The resulting phase curves can be described with only three free parameters per bandpass -- an efficiency improvement over the usual five or so used to describe sinusoidal decompositions of phase curves. Upon obtaining the hemispherically averaged dayside and nightside temperatures, the standard approach would be to use zero-dimensional box models to infer the Bond albedo and redistribution efficiency. We elucidate the limitation of these box models by demonstrating that negative Bond albedos may be obtained due to a choice of boundary condition on the nightside temperature. We propose generalized definitions for the Bond albedo and heat redistribution efficiency for use with two-dimensional (2D) temperature maps. Open-source software called kelp is provided to efficiently compute these phase curves., Comment: Accepted in A&A

General circulation models are often used to explore exoclimate parameter spaces and classify atmospheric circulation regimes. Models are tuned to give reasonable climate states for standard test cases, such as the Held-Suarez test, and then used to simulate diverse exoclimates by varying input parameters such as rotation rates, instellation, atmospheric optical properties, frictional timescales and so on. In such studies, there is an implicit assumption that the model which works reasonably well for the standard test case will be credible at all points in an arbitrarily wide parameter space. Here, we test this assumption using the open-source general circulation model THOR to simulate atmospheric circulation on tidally locked Earth-like planets with rotation periods of 0.1 to 100 days. We find that the model error, as quantified by the ratio between physical and spurious numerical contributions to the angular momentum balance, is extremely variable across this range of rotation periods with some cases where numerical errors are the dominant component. Increasing model grid resolution does improve errors but using a higher-order numerical diffusion scheme can sometimes magnify errors for finite-volume dynamical solvers. We further show that to minimize error and make the angular momentum balance more physical within our model, the surface friction timescale must be smaller than the rotational timescale., Comment: 8 pages, 5 figures, accepted by ApJ

We present an update of the open-source photochemical kinetics code VULCAN (Tsai et al. 2017; https://github.com/exoclime/VULCAN) to include C-H-N-O-S networks and photochemistry. Additional new features are advection transport, condensation, various boundary conditions, and temperature-dependent UV cross-sections. First, we validate our photochemical model for hot Jupiter atmospheres by performing an intercomparison of HD 189733b models between Moses et al. (2011), Venot et al. (2012), and VULCAN, to diagnose possible sources of discrepancy. Second, we set up a model of Jupiter extending from the deep troposphere to upper stratosphere to verify the kinetics for low temperature. Our model reproduces hydrocarbons consistent with observations, and the condensation scheme successfully predicts the locations of water and ammonia ice clouds. We show that vertical advection can regulate the local ammonia distribution in the deep atmosphere. Third, we validate the model for oxidizing atmospheres by simulating Earth and find agreement with observations. Last, VULCAN is applied to four representative cases of extrasolar giant planets: WASP-33b, HD 189733b, GJ 436b, and 51 Eridani b. We look into the effects of the C/O ratio and chemistry of titanium/vanadium species for WASP-33b; we revisit HD 189733b for the effects of sulfur and carbon condensation; the effects of internal heating and vertical mixing ($K_{\textrm{zz}}$) are explored for GJ 436b; we test updated planetary properties for 51 Eridani b with S$_8$ condensates. We find sulfur can couple to carbon or nitrogen and impact other species such as hydrogen, methane, and ammonia. The observable features of the synthetic spectra and trends in the photochemical haze precursors are discussed for each case., Comment: 50 pages, 41 figures, accepted for publication in ApJ

Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior, and orbital properties of the planetary companions. $\nu^2$ Lupi (HD 136352) is a naked-eye ($V = 5.78$) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity monitoring (Udry et al. 2019). The two inner planets (b and c) were recently found to transit (Kane et al. 2020), prompting a photometric follow-up by the brand-new $CHaracterising\:ExOPlanets\:Satellite\:(CHEOPS)$. Here, we report that the outer planet d is also transiting, and measure its radius and mass to be $2.56\pm0.09$ $R_{\oplus}$ and $8.82\pm0.94$ $M_{\oplus}$, respectively. With its bright Sun-like star, long period, and mild irradiation ($\sim$5.7 times the irradiation of Earth), $\nu^2$ Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b likely has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the $\nu^2$ Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets., Comment: Published in Nature Astronomy. 60 pages, 18 Figures, 6 Tables. This is the authors' version of the manuscript. The final authenticated version is available online at https://www.nature.com/articles/s41550-021-01381-5

We carried out a systematic study of full-orbit phase curves for known transiting systems in the northern ecliptic sky that were observed during Year 2 of the TESS primary mission. We applied the same methodology for target selection, data processing, and light-curve fitting as we did in our Year 1 study. Out of the 15 transiting systems selected for analysis, seven - HAT-P-7, KELT-1, KELT-9, KELT-16, KELT-20, Kepler-13A, and WASP-12 - show statistically significant secondary eclipses and day-night atmospheric brightness modulations. Small eastward dayside hotspot offsets were measured for KELT-9b and WASP-12b. KELT-1, Kepler-13A, and WASP-12 show additional phase-curve variability attributed to the tidal distortion of the host star; the amplitudes of these signals are consistent with theoretical predictions. We combined occultation measurements from TESS and Spitzer to compute dayside brightness temperatures, TESS-band geometric albedos, Bond albedos, and phase integrals for several systems. The new albedo values solidify the previously reported trend between dayside temperature and geometric albedo for planets with $1500

White dwarf spectroscopy shows that nearly half of white dwarf atmospheres contain metals that must have been accreted from planetary material that survived the red giant phases of stellar evolution. We can use metal pollution in white dwarf atmospheres as flags, signalling recent accretion, in order to prioritize an efficient sample of white dwarfs to search for transiting material. We present a search for planetesimals orbiting six nearby white dwarfs with the CHEOPS spacecraft. The targets are relatively faint for CHEOPS, $11$ mag $< G < 12.8$ mag. We use aperture photometry data products from the CHEOPS mission as well as custom PSF photometry to search for periodic variations in flux due to transiting planetesimals. We detect no significant variations in flux that cannot be attributed to spacecraft systematics, despite reaching a photometric precision of $<2$ ppt in 60 s exposures on each target. We simulate observations to show that the small survey is sensitive primarily to Moon-sized transiting objects with periods $3$ hr $< P < 10$ hr, with radii $R \gtrsim 1000$ km., Comment: 10 pages, accepted as a Letter to the Editor in A&A

Studying the albedos of the planets and moons of the Solar System dates back at least a century. Of particular interest is the relationship between the albedo measured at superior conjunction, known as the ``geometric albedo", and the albedo considered over all orbital phase angles, known as the ``spherical albedo". Determining the relationship between the geometric and spherical albedos usually involves complex numerical calculations and closed-form solutions are restricted to simple reflection laws. Here we report the discovery of closed-form solutions for the geometric albedo and integral phase function, which apply to any law of reflection that only depends on the scattering angle. The shape of a reflected light phase curve, quantified by the integral phase function, and the secondary eclipse depth, quantified by the geometric albedo, may now be self-consistently inverted to retrieve globally averaged physical parameters. Fully Bayesian phase curve inversions for reflectance maps and simultaneous light curve detrending may now be performed due to the efficiency of computation. Demonstrating these innovations for the hot Jupiter Kepler-7b, we infer a geometric albedo of $0.25^{+0.01}_{-0.02}$, a phase integral of $1.77 \pm0.07$, a spherical albedo of $0.44^{+0.02}_{-0.03}$ and a scattering asymmetry factor of $0.07^{+0.12}_{-0.11}$., Comment: 12 pages, 8 figures, 2 tables. This is a post-peer-review, pre-copyedit version of an article published in Nature Astronomy. The final authenticated version is available online at: https://www.nature.com/articles/s41550-021-01444-7. Equations (1) to (43) have not changed since v1. Differences between v1 and this version (v4) are in Figure 4 and the inferred parameter values associated with it

Due to its proximity to Earth, Jupiter of the Solar System serves as a unique case study for gas-giant exoplanets. In the current study, we perform fits of ab initio, reflective, semi-infinite, homogeneous model atmospheres to 61 phase curves from 0.40 to 1.00 $\mu$m, obtained from the Cassini spacecraft, within a Bayesian framework. We reproduce the previous finding that atmospheric models using classic reflection laws (Lambertian, Rayleigh, single Henyey-Greenstein) provide poor fits to the data. Using the double Henyey-Greenstein reflection law, we extract posterior distributions of the single-scattering albedo and scattering asymmetry factors and tabulate their median values and uncertainties. We infer that the aerosols in the Jovian atmosphere are large, irregular, polydisperse particles that produce strong forward scattering together with a narrow backscattering lobe. The near-unity values of the single-scattering albedos imply that multiple scattering of radiation is an important effect. We speculate that the observed narrow backscattering lobe is caused by coherent backscattering of radiation, which is usually associated with Solar System bodies with solid surfaces and regolith. Our findings demonstrate that precise, multi-wavelength phase curves encode valuable information on the fundamental properties of cloud/haze particles. The method described in this Letter enables single-scattering albedos and scattering asymmetry factors to be retrieved from James Webb Space Telescope phase curves of exoplanets., Comment: Accepted by ApJL. 8 pages, 4 figures, 1 table. Data of the 61 Cassini phase curves and Python script used for fitting are available as supplementary material for the final journal version. Key reference updated

Computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. Since the underlying spectroscopic line lists are constantly expanding and currently include up to ~ 10^10 - 10^11 transition lines, the opacity calculator codes need to become more powerful. Here we present major upgrades to the HELIOS-K GPU-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. Besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets: from downloading and pre-processing the data to performing the opacity calculations in a user-friendly way. HELIOS-K supports line lists from ExoMol, HITRAN, HITEMP, NIST, Kurucz and VALD3. By matching the resolution of 0.1 cm^-1 and cutting length of 25 cm^-1 used by the ExoCross code for timing performance (251 seconds excluding data read-in time), HELIOS-K can process the ExoMol BT2 water line list in 12.5 seconds. Using a resolution of 0.01 cm^-1, it takes 45 seconds - equivalent to about 10^7 lines per second. As a wavenumber resolution of 0.01 cm^-1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species, and make them freely available on the open-access DACE database. For the opacity calculations of the database, we use a cutting length of 100 cm^-1 for molecules and no cutting length for atoms. Our opacities are available for downloading from https://dace.unige.ch/opacityDatabase and may be visualized using https://dace.unige.ch/opacity., Comment: Published in The Astrophysical Journal Supplement Series

Compartmental transmission models have become an invaluable tool to study the dynamics of infectious diseases. The Susceptible-Infectious-Recovered (SIR) model is known to have an exact semi-analytical solution. In the current study, the approach of Harko et al. (2014) is generalised to obtain an approximate semi-analytical solution of the Susceptible-Exposed-Infectious-Recovered (SEIR) model. The SEIR model curves have nearly the same shapes as the SIR ones, but with a stretch factor applied to them across time that is related to the ratio of the incubation to infectious periods. This finding implies an approximate characteristic timescale, scaled by this stretch factor, that is universal to all SEIR models, which only depends on the basic reproduction number and initial fraction of the population that is infectious., Comment: This is a post-peer-review, pre-copyedit version of an article published in Scientific Reports (Springer Nature; www.nature.com/scientificreports). The final authenticated version is available online at: https://doi.org/10.1038/s41598-020-76563-8

WASP-127b is one of the puffiest exoplanets found to date, with a mass only $3.4$ Neptune masses, but a radius larger than Jupiter. It is also located at the border of the Neptune desert, which describes the lack of highly-irradiated Neptune-sized planets, and which remains poorly understood. Its large scale height and bright host star make the transiting WASP-127b a valuable target to characterise in transmission spectroscopy. We use combined EulerCam and TESS light curves to recalculate the system's parameters. Additionally, we present an in-depth search for sodium in four transit observations of WASP-127b, obtained as part of the Hot Exoplanet Atmosphere Resolved with Transit Spectroscopy (HEARTS) survey with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. Two nights from this dataset were analysed independently by another team, claiming a detection of sodium incompatible with previous studies of data from both ground and space. We show that this large sodium detection is actually due to contamination from telluric sodium emissions and the low S/N in the core of the deep stellar sodium lines. When properly accounting for these effects, the previous sodium signal is reduced to an absorption of $0.46\pm0.20\%$ ($2.3\sigma$), which is compatible with analyses of WASP-127b transits carried out with other instruments. We can fit a Gaussian to the D2 line, however, the D1 line was not detected, indicating an unusual line ratio if sodium exists in the atmosphere. Follow-up of WASP-127 at both high-resolution and with high sensitivity will be required to firmly establish the presence of sodium and analyse its line shape., Comment: 11 pages, 11 figures, published in A&A

The CHaracterising ExOPlanet Satellite (CHEOPS) was selected in 2012, as the first small mission in the ESA Science Programme and successfully launched in December 2019. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys and to following phase curves. CHEOPS will provide prime targets for future spectroscopic atmospheric characterisation. Requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars in the magnitude range between 6 and 9 by achieving a photometric precision of 20 ppm in 6 hours of integration. For K stars in the magnitude range between 9 and 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration. This is achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter telescope. The 280 kg spacecraft has a pointing accuracy of about 1 arcsec rms and orbits on a sun-synchronous dusk-dawn orbit at 700 km altitude. The nominal mission lifetime is 3.5 years. During this period, 20% of the observing time is available to the community through a yearly call and a discretionary time programme managed by ESA., Comment: Submitted to Experimental Astronomy