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The chemical abundances of gas-giant exoplanet atmospheres hold clues to the formation and evolution pathways that sculpt the exoplanet population. Recent ground-based high-resolution spectroscopic observations of the non-transiting hot Jupiter $\tau$ Bo\"otis b from different instruments have resulted in a tension on the presence of water vapour in the planet's atmosphere, which impact the planet's inferred C/O and metallicity. To investigate this, we revisit the archival CRIRES observations of the planet's dayside in the wavelength range 2.28 to 2.33 $\mu$m. We reanalyse them using the latest methods for correcting stellar and telluric systematics, and free-chemistry Bayesian atmospheric retrieval. We find that a spurious detection of CH$_{4}$ can arise from inadequate telluric correction. We confirm the detection of CO and constrain its abundance to be near solar $\log_{10}(\mathrm{CO})$ = -3.44$^{+1.63}_{-0.85}$ VMR. We find a marginal evidence for H$_{2}$O with $\log_{10}(\mathrm{H_{2}O})$ = -5.13$^{+1.22}_{-6.37}$ VMR. This translates to super solar C/O (0.95$^{+0.06}_{-0.31}$), marginally sub-solar metallicity (-0.21 $^{+1.66}_{-0.87}$). Due to the relatively large uncertainty on H$_{2}$O abundance, we cannot confidently resolve the tension on the presence of H$_{2}$O and the super-solar atmospheric metallicity of $\tau$ Bo\"otis b. We recommend further observations of $\tau$ Bo\"otis b in the wavelength ranges simultaneously covering CO and $\mathrm{H_{2}O}$ to confirm the peculiar case of the planet's super-solar C/O and metallicity., Comment: 16 pages, 13 figures; Accepted for publication in MNRAS

High-resolution spectroscopic characterization of young super-Jovian planets enables precise constraints on elemental and isotopic abundances of their atmospheres. As part of the ESO SupJup Survey, we present high-resolution spectral observations of two wide-orbit super-Jupiters in YSES 1 (or TYC 8998-760-1) using the upgraded VLT/CRIRES+ (R~100,000) in K-band. We carry out free atmospheric retrieval analyses to constrain chemical and isotopic abundances, temperature structures, rotation velocities, and radial velocities. We confirm the previous detection of 13CO in YSES 1 b at a higher significance of 12.6{\sigma}, but point to a higher 12CO/13CO ratio of 88+/-13 (1{\sigma} confidence interval), consistent with the primary's isotope ratio 66+/-5. We retrieve a solar-like composition in YSES 1 b with a C/O=0.57+/-0.01, indicating a formation via gravitational instability or core accretion beyond the CO iceline. Additionally, the observations lead to detections of H2O and CO in the outer planet YSES 1 c at 7.3{\sigma} and 5.7{\sigma}, respectively. We constrain the atmospheric C/O ratio of YSES 1 c to be either solar or subsolar (C/O=0.36+/-0.15), indicating the accretion of oxygen-rich solids. The two companions have distinct vsini, 5.34+/-0.14 km/s for YSES 1 b and 11.3+/-2.1 km/s for YSES 1 c, despite their similar natal environments. This may indicate different spin axis inclinations or effective magnetic braking by the long-lived circumplanetary disk around YSES 1 b. YSES 1 represents an intriguing system for comparative studies of super-Jovian companions and linking present atmospheres to formation histories., Comment: 25 pages, 11 figure, accepted for publication in AJ. The extracted CRIRES+ spectra of the YSES-1 system can be found at https://doi.org/10.5281/zenodo.13664032

Exoplanets with masses between Earth and Neptune are amongst the most commonly observed, yet their properties are poorly constrained. Their transmission spectra are often featureless, which indicate either high-altitude clouds or a high atmospheric metallicity. The archetypical warm Neptune GJ 436b is such a planet showing a flat transmission spectrum in observations with the Hubble Space Telescope (HST). Ground-based high-resolution spectroscopy (HRS) effectively probes exoplanet atmospheres at higher altitudes and can therefore be more sensitive to absorption coming from above potential cloud decks. In this paper we aim to investigate this for the exoplanet GJ 436b. We present new CRIRES+ HRS transit data of GJ 436b. Three transits were observed, but since two were during bad weather conditions, only one transit was analyzed. The radiative transfer code petitRADTRANS was used to create atmospheric models for cross-correlation and signal-injection purposes, including absorption from H$_2$O, CH$_4$, and CO. No transmission signals were detected, but atmospheric constraints can be derived. Injection of artificial transmission signals indicate that if GJ 436b would have a cloud deck at pressures P>10 mbar and a <300$\times$ solar metallicity, these CRIRES+ observations should have resulted in a detection. We estimate that the constraints presented here from one ground-based HRS transit are slightly better than those obtained with four HST transits. Combining HRS data from multiple transits is an interesting avenue for future studies of exoplanets with high-altitude clouds., Comment: Accepted for publication by A&A on July 5th, 2024

Ultra-hot Jupiters are among the best targets for atmospheric characterization at high spectral resolution. Resolving their transmission spectra as a function of orbital phase offers a unique window into the 3D nature of these objects. In this work, we present three transits of the ultra-hot Jupiter WASP-121b observed with Gemini-S/IGRINS. For the first time, we measure the phase-dependent absorption signals of CO and H$_{\text{2}}$O in the atmosphere of an exoplanet, and we find that they are different. While the blueshift of CO increases during the transit, the absorption lines of H$_{\text{2}}$O become less blueshifted with phase, and even show a redshift in the second half of the transit. These measurements reveal the distinct spatial distributions of both molecules across the atmospheres of ultra-hot Jupiters. Also, we find that the H$_{\text{2}}$O signal is absent in the first quarter of the transit, potentially hinting at cloud formation on the evening terminator of WASP-121b. To further interpret the absorption trails of CO and H$_{\text{2}}$O, as well as the Doppler shifts of Fe previously measured with VLT/ESPRESSO, we compare the data to simulated transits of WASP-121b. To this end, we post-processes the outputs of global circulation models with a 3D Monte-Carlo radiative transfer code. Our analysis shows that the atmosphere of WASP-121b is subject to atmospheric drag, as previously suggested by small hotspot offsets inferred from phase-curve observations. Our study highlights the importance of phase-resolved spectroscopy in unravelling the complex atmospheric structure of ultra-hot Jupiters and sets the stage for further investigations into their chemistry and dynamics., Comment: 24 pages, 16 figures, accepted for publication in PASP

Numerous chemical constraints have been possible for exoplanetary atmospheres thanks to high-resolution spectroscopy (HRS) from ground-based facilities as well as low-resolution spectroscopy (LRS) from space. These two techniques have complementary strengths, and hence combined HRS and LRS analyses have the potential for more accurate abundance constraints and increased sensitivity to trace species. In this work we retrieve the atmosphere of the ultra-hot Jupiter WASP-76~b, using high-resolution CARMENES/CAHA and low-resolution HST WFC3 and Spitzer observations of the primary eclipse. As such hot planets are expected to have a substantial fraction of H$_2$O dissociated, we conduct retrievals including both H$_2$O and OH. We explore two retrieval models, one with self-consistent treatment of H$_2$O dissociation and another where H$_2$O and OH are vertically-homogeneous. Both models constrain H$_2$O and OH, with H$_2$O primarily detected by LRS and OH through HRS, highlighting the strengths of each technique and demonstrating the need for combined retrievals to fully constrain chemical compositions. We see only a slight preference for the H$_2$O-dissociation model given that the photospheric constraints for both are very similar, indicating $\log(\mathrm{OH/H_2O}) = 0.7^{+0.3}_{-0.3}$ at 1.5~mbar, showing that the majority of the H$_2$O in the photosphere is dissociated. However, the bulk O/H and C/O ratios inferred from the models differs significantly, and highlights the challenge of constraining bulk compositions from photospheric abundances with strong vertical chemical gradients. Further observations with JWST and ground-based facilities may help shed more light on these processes., Comment: 11 pages, 6 figures, 2 tables, accepted for publication in MNRAS

Direct atmospheric retrievals of exoplanets at high-resolution have recently allowed for a more detailed characterisation of their chemistry and dynamics from the ground. By monitoring the longitudinal distribution of species, as well as the varying vertical temperature structure and dynamics between the limbs of WASP-76b, across multiple transits, we aim to enhance our understanding of the 3D nature and chemical/dynamical evolution of such objects over the timescales of months/years. We present retrievals of three VLT/ESPRESSO observations of the ultra-hot Jupiter WASP-76b, including one not yet reported in the literature, from which we constrain the atmospheric abundances, vertical temperature structure, and atmospheric dynamics for both the leading and trailing limbs of the atmosphere separately, via novel rotational broadening kernels. We confirm the presence of VO recently reported in the atmosphere of WASP-76b. We find a uniform longitudinal distribution of Fe and Mg across the limbs of the atmosphere, for each of our transits, consistent with previous works as well as with stellar values. We constrain substellar Na/Fe and Cr/Fe ratios across each of our transits, consistent with previous studies of WASP-76b. Where constrained, V/Fe and VO/Fe ratios were also found to be broadly consistent between the limbs of the atmosphere for each of the transits, as well as with previous studies. However, for two of the transits, both V and VO were unconstrained in the leading limb, suggesting possible depletion due to recombination and condensation. The consistency of our constraints across multiple high-resolution observations, as well as with previous studies using varying modelling/retrieval frameworks and/or instruments, affirms the efficacy of high-resolution ground-based retrievals of exoplanetary atmospheres., Comment: Accepted for publication in Astronomy & Astrophysics. 23 pages, 16 figures (including appendix)

Observations of cooler atmospheres of super-Earths and Neptune sized objects often show flat transmission spectra. The most likely cause of this trend is the presence of aerosols (i.e. clouds and hazes) in the atmospheres of such objects. High-resolution spectroscopy provides an opportunity to test this hypothesis by targeting molecular species whose spectral line cores extend above the level of such opaque decks. In this work, we analyse high-resolution infrared observations of the warm Neptune GJ 3470 b taken over two transits using CARMENES (R $\sim$ 80,000) and look for signatures of H$_2$O (previously detected using HST WFC3+Spitzer observations) in these transits with a custom pipeline fully accounting for the effects of data cleaning on any potential exoplanet signal. We find that our data are potentially able to weakly detect ($\sim3\sigma$) an injected signal equivalent to the best-fit model from previous HST WFC3+Spitzer observations. However, we do not make a significant detection using the actual observations. Using a Bayesian framework to simultaneously constrain the H$_2$O Volume Mixing Ratio (VMR) and the cloud top pressure level, we select a family of models compatible with the non detection. These are either very high VMR, cloud-free models, solar-abundance models with a high cloud deck, or sub-solar abundance models with a moderate cloud deck. This is a broader range compared to published results from low-resolution spectroscopy, but is also compatible with them at a 1$\sigma$ level., Comment: 18 pages, 8 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal on April 9, 2024

Context: High-resolution spectrographs fed by adaptive optics (AO) provide a unique opportunity to characterize directly imaged exoplanets. Observations with such instruments allow us to probe the atmospheric composition, spin rotation, and radial velocity of the planet, thereby helping to reveal information on its formation and migration history. The recent upgrade of the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES+) at the VLT makes it a highly suitable instrument for characterizing directly imaged exoplanets. Aims: In this work, we report on observations of $\beta$ Pictoris b with CRIRES+ and use them to constrain the planets atmospheric properties and update the estimation of its spin rotation. Methods: The data were reduced using the open-source \textit{pycrires} package. We subsequently forward-modeled the stellar, planetary, and systematic contribution to the data to detect molecules in the planet's atmosphere. We also used atmospheric retrievals to provide new constraints on its atmosphere. Results: We confidently detected water and carbon monoxide in the atmosphere of $\beta$ Pictoris b and retrieved a slightly sub-solar carbon-to-oxygen ratio, which is in agreement with previous results. The interpretation is hampered by our limited knowledge of the C/O ratio of the host star. We also obtained a much improved constraint on its spin rotation of $19.9 \pm 1.0$ km/s, which gives a rotation period of $8.7 \pm 0.8$ hours, assuming no obliquity. We find that there is a degeneracy between the metallicity and clouds, but this has minimal impact on the retrieved C/O, $v\sin{i}$, and radial velocity. Our results show that CRIRES+ is performing well and stands as a highly useful instrument for characterizing directly imaged planets., Comment: Accepted for publication in A&A

Isotope ratios have recently been measured in the atmospheres of directly-imaged and transiting exoplanets from ground-based observations. The arrival of JWST allows us to characterise exoplanetary atmospheres in further detail and opens up wavelengths inaccessible from the ground. In this work we constrain the carbon and oxygen isotopes $^{13}$C, $^{18}$O and $^{17}$O from CO in the atmosphere of the directly-imaged companion VHS 1256 b through retrievals of the $\sim$4.1-5.3 $\mu$m NIRSpec G395H/F290LP observations from the early release science programme (ERS 1386). We detect and constrain $^{13}$C$^{16}$O, $^{12}$C$^{18}$O and $^{12}$C$^{17}$O at 32, 16 and 10$\sigma$ confidence respectively, thanks to the very high signal-to-noise observations. We find the ratio of abundances are more precisely constrained than their absolute values, with $\mathrm{^{12}C/^{13}C=62^{+2}_{-2}}$, in between previous measurements for companions ($\sim$30) and isolated brown dwarfs ($\sim$100). The oxygen isotope ratios are $\mathrm{^{16}O/^{18}O =425^{+33}_{-28}}$ and $\mathrm{^{16}O/^{17}O=1010^{+120}_{-100}}$. All of the ratios are lower than the local inter-stellar medium and Solar System, suggesting that abundances of the more minor isotopes are enhanced compared to the primary. This could be driven by isotope fractionation in protoplanetary disks, which can potentially alter the carbon and oxygen ratios through isotope selective photodissociation, gas/ice partitioning and isotopic exchange reactions. In addition to CO, we constrain $^{1}$H$_2$$^{16}$O and $^{12}$C$^{16}$O$_2$ (the primary isotopologues of both species), but find only upper limits on $^{12}$C$^1$H$_4$ and $^{14}$N$^{1}$H$_3$. This work highlights the power of JWST to constrain isotopes in exoplanet atmospheres, with great promise in determining formation histories in the future., Comment: 11 pages, 7 figures, 2 tables, accepted for publication in The Astrophysical Journal Letters

Ground-based high-resolution spectroscopy (HRS) has detected numerous chemical species and atmospheric dynamics in exoplanets, most notably ultra-hot Jupiters (UHJs). However, quantitative estimates on abundances have been challenging but are essential for accurate comparative characterisation and to determine formation scenarios. In this work we retrieve the atmospheres of six UHJs (WASP-76~b, MASCARA-4~b, MASCARA-2~b, WASP-121~b, HAT-P-70~b and WASP-189~b) with ESPRESSO and HARPS-N/HARPS observations, exploring trends in eleven neutral species and dynamics. While Fe abundances agree well with stellar values, Mg, Ni, Cr, Mn and V show more variation, highlighting the difficulty in using a single species as a proxy for metallicity. We find that Ca, Na, Ti and TiO are under-abundant, potentially due to ionisation and/or night-side rain-out. Our retrievals also show that relative abundances between species are more robust, consistent with previous works. We perform spatially- and phase-resolved retrievals for WASP-76~b and WASP-121~b given their high signal-to-noise observations, and find the chemical abundances in each of the terminator regions are broadly consistent. We additionally constrain dynamics for our sample through Doppler shifts and broadening of the planetary signals during the primary eclipse, with median blue shifts between $\sim$0.9-9.0~km/s due to day-night winds. Furthermore, we constrain spectroscopic masses for MASCARA-2~b and HAT-P-70~b consistent with their known upper limits, but we note that these may be biased due to degeneracies. This work highlights the importance of future HRS studies to further probe differences and trends between exoplanets., Comment: 26 pages, 11 figures, 5 tables, published in AJ

We have entered the era of the James Webb Space Telescope (JWST). We use the first JWST transmission spectrum of the hot Saturn-mass exoplanet, WASP-39 b, obtained with the NIRSpec instrument in the 3-5 $\mu$m range to investigate (a) what atmospheric constraints are possible with JWST-quality data in this spectral range, (b) requirements for atmospheric models used in retrievals, (c) effect of differences between data reduction pipelines on retrieved atmospheric properties, and (d) complementarity between JWST data in the 3-5 $\mu$m range and HST observations at shorter wavelengths. JWST spectra in the 3-5 $\mu$m range provide a promising avenue for chemical detections while encompassing a window in cloud opacity for several prominent aerosols. We confirm recent inferences of CO$_2$, SO$_2$, H$_2$O, and CO in WASP-39 b, report tentative evidence for H$_2$S, and retrieve elemental abundances consistent with Saturn's metallicity. We retrieve molecular abundances with $\sim$0.3-0.6 dex precision with this relatively limited spectral range. When considering the 3-5 $\mu$m data alone, reported differences in spectra with different reduction pipelines can affect abundance estimates by up to $\sim$1 dex and the detectability of less prominent species. Complementing with data at shorter wavelengths, e.g. with other JWST instruments or HST WFC3 ($\sim$0.8-1.7 $\mu$m), can significantly improve the accuracy and precision of the abundance estimates. The high data quality enables constraints on aerosol properties, including their composition, modal size and extent, motivating their consideration in retrievals. Our results highlight the promise of JWST exoplanet spectroscopy, while underscoring the importance of robust data reduction and atmospheric retrieval approaches in the JWST era., Comment: Accepted for publication in ApJ Letters

We present high-resolution dayside thermal emission observations of the exoplanet WASP-18b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, and we extract the planet signal via cross correlation with model spectra. We detect the atmosphere of WASP-18b at a signal-to-noise ratio (SNR) of 5.9 using a full chemistry model, measure H2O (SNR=3.3), CO (SNR=4.0), and OH (SNR=4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4$\sigma$) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultra-hot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature-pressure profile to freely adjust results in a moderately super-stellar carbon to oxygen ratio (C/O=0.75^{+0.14}_{-0.17}) and metallicity ([M/H]=1.03^{+0.65}_{-1.01}). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O=0.45^{+0.08}_{-0.10} and [M/H]=1.17^{+0.66}_{-1.01}. A retrieval that assumes radiative-convective-thermochemical-equilibrium and naturally accounts for thermal dissociation constrains C/O<0.34 (2$\sigma$) and [M/H]=0.48^{+0.33}_{-0.29}, in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalising signature of different Doppler shifts at the level of a few km/s for different molecules, which might probe dynamics as a function of altitude and location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to UHJ spectra., Comment: 27 pages, 18 figures, submitted to AAS Journals. Community feedback welcome

Detections of molecules in the atmosphere of gas giant exoplanets allow us to investigate the physico-chemical properties of the atmospheres. Their inferred chemical composition is used as tracer of planet formation and evolution mechanisms. Currently, an increasing number of detections is showing a possible rich chemistry of the hotter gaseous planets, but whether this extends to cooler giants is still unknown. We observed four transits of WASP-80 b, a warm transiting giant planet orbiting a late-K dwarf star with the near-infrared GIANO-B spectrograph installed at the Telescopio Nazionale Galileo and performed high resolution transmission spectroscopy analysis. We report the detection of several molecular species in its atmosphere. Combining the four nights and comparing our transmission spectrum to planetary atmosphere models containing the signature of individual molecules within the cross-correlation framework, we find the presence of H2O, CH4, NH3 and HCN with high significance, tentative detection of CO2, and inconclusive results for C2H2 and CO. A qualitative interpretation of these results, using physically motivated models, suggests an atmosphere consistent with solar composition and the presence of disequilibrium chemistry and we therefore recommend the inclusion of the latter in future modelling of sub-1000K planets., Comment: 12 pages, 4 figures. AJ, Accepted July 11th, 2022

Exoplanet atmospheres are inherently three-dimensional systems in which thermal/chemical variation and winds can strongly influence spectra. Recently, the ultra-hot Jupiter WASP-76 b has shown evidence for condensation and asymmetric Fe absorption with time. However, it is currently unclear whether these asymmetries are driven by chemical or thermal differences between the two limbs, as precise constraints on variation in these have remained elusive due to the challenges of modelling these dynamics in a Bayesian framework. To address this we develop a new model, HyDRA-2D, capable of simultaneously retrieving morning and evening terminators with day-night winds. We explore variations in Fe, temperature profile, winds and opacity deck with limb and orbital phase using VLT/ESPRESSO observations of WASP-76 b. We find Fe is more prominent on the evening for the last quarter of the transit, with $\log(X_\mathrm{Fe}) = {-4.03}^{+0.28}_{-0.31}$, but the morning shows a lower abundance with a wider uncertainty, $\log(X_\mathrm{Fe}) = {-4.59}^{+0.85}_{-1.0}$, driven by degeneracy with the opacity deck and the stronger evening signal. We constrain 0.1 mbar temperatures ranging from $2950^{+111}_{-156}$ K to $2615^{+266}_{-275}$ K, with a trend of higher temperatures for the more irradiated atmospheric regions. We also constrain a day-night wind speed of $9.8^{+1.2}_{-1.1}$ km/s for the last quarter, higher than $5.9^{+1.5}_{-1.1}$ km/s for the first, in line with general circulation models. We find our new spatially- and phase-resolved treatment is statistically favoured by 4.9$\sigma$ over traditional 1D-retrievals, and thus demonstrate the power of such modelling for robust constraints with current and future facilities., Comment: 18 pages, 15 figures, accepted for publication in MNRAS

Characterising the atmospheres of hot Jupiters is important in understanding the formation and migration of these exotic planets. However, there are still many open questions about the chemical and physical properties of these atmospheres. Here, we confirm the detection of water vapour in thermal emission from the non-transiting hot Jupiter {\tau} Bootis Ab with the high resolution NIR CARMENES spectrograph. Combining over 17 h of observations (560 spectra) and using a Bayesian cross-correlation to log-likelihood approach, we measure a systemic velocity of $V_{sys} = -11.51^{+0.59}_{-0.60}$ km/s and a radial velocity semi-amplitude of $K_{P} = 106.21^{+1.76}_{-1.71}$ km/s for the planet, which results in an absolute mass of $M_{P} = 6.24^{+0.17}_{-0.18} M_{J}$ and an orbital inclination of $41.6^{+1.0}_{-0.9}$ degrees. Our retrieved $V_{sys}$ shows a significant shift (+5 km/s) from the literature value, which could be caused by an inaccurate time of periastron. Within the explored model grid, we measure a preference for solar water abundance (VMR = $10^{-3}$) and no evidence for additional minor species in the atmosphere. Given the extensive orbital coverage of the data, we searched for a phase dependency in the water signal but found no strong evidence of variation with orbital phase. This detection is at odds with recent observations from SPIRou/CFHT and their tight upper limit on water abundance. We recommend further observations of the atmosphere {\tau} Bootis Ab to try and resolve these discrepancies., Comment: Accepted for publication in MNRAS

Measurements of the atmospheric carbon (C) and oxygen (O) relative to hydrogen (H) in hot Jupiters (relative to their host stars) provide insight into their formation location and subsequent orbital migration. Hot Jupiters that form beyond the major volatile (H2O/CO/CO2) ice lines and subsequently migrate post disk-dissipation are predicted have atmospheric carbon-to-oxygen ratios (C/O) near 1 and subsolar metallicities, whereas planets that migrate through the disk before dissipation are predicted to be heavily polluted by infalling O-rich icy planetesimals, resulting in C/O < 0.5 and super-solar metallicities. Previous observations of hot Jupiters have been able to provide bounded constraints on either H2O or CO, but not both for the same planet, leaving uncertain the true elemental C and O inventory and subsequent C/O and metallicity determinations. Here we report spectroscopic observations of a typical transiting hot Jupiter, WASP-77Ab. From these, we determine the atmospheric gas volume mixing ratio constraints on both H2O and CO (9.5$\times 10^{-5}$ - 1.5$\times 10^{-4}$ and 1.2$\times 10^{-4}$ - 2.6$\times 10^{-4}$, respectively). From these bounded constraints, we are able to derive the atmospheric C/H (0.35$^{+0.17}_{-0.10}$ $\times$ Solar) and O/H (0.32 $^{+0.12}_{-0.08}$ $\times$ Solar) abundances and the corresponding atmospheric carbon-to-oxygen ratio (C/O=0.59$\pm$0.08; the solar value is 0.55). The sub-solar (C+O)/H (0.33$^{+0.13}_{-0.09}$ $\times$ Solar) is suggestive of a metal-depleted atmosphere relative to what is expected for Jovian-like planets while the near solar value of C/O rules out the disk-free migration/C-rich atmosphere scenario., Comment: This is the accepted "pre-proof" version. Minor editorial reference/figure/abstract differences from published version. Published version here: https://www.nature.com/articles/s41586-021-03912-6

The atmospheres of gaseous giant exoplanets orbiting close to their parent stars (hot Jupiters) have been probed for nearly two decades. They allow us to investigate the chemical and physical properties of planetary atmospheres under extreme irradiation conditions. Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour and carbon monoxide in their atmospheres; this has been studied in terms of scaled solar composition under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there and subsequently refuted. Here we report observations of HD 209458b that indicate the presence of water (H2O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (CH4), ammonia (NH3) and acetylene (C2H2), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards. Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions., Comment: As part of the Springer Nature Content Sharing Initiative, it is possible to access a view-only version of this paper by using the following SharedIt link: https://rdcu.be/cifrz

We provide a new framework to model the day side and night side atmospheres of irradiated exoplanets using 1-D radiative transfer by incorporating a self-consistent heat flux carried by circulation currents (winds) between the two sides. The advantages of our model are its physical motivation and computational efficiency, which allows for an exploration of a wide range of atmospheric parameters. We use this forward model to explore the day and night side atmosphere of WASP-76~b, an ultra-hot Jupiter which shows evidence for a thermal inversion and Fe condensation, and WASP-43~b, comparing our model against high precision phase curves and general circulation models. We are able to closely match the observations as well as prior theoretical predictions for both of these planets with our model. We also model a range of hot Jupiters with equilibrium temperatures between 1000-3000~K and reproduce the observed trend that the day-night temperature contrast increases with equilibrium temperature up to $\sim$2500~K beyond which the dissociation of H$_2$ becomes significant and the relative temperature difference declines., Comment: 20 pages, 7 figures, accepted for publication in MNRAS

In the last decade ground based high resolution Doppler spectroscopy (HRS) has detected numerous species in transiting and non-transiting hot Jupiters, and is ideally placed for atmospheric characterisation of warm Neptunes and super Earths. Many of these cooler and smaller exoplanets have shown cloudy atmospheres from low resolution near infrared observations, making constraints on chemical species difficult. We investigate how HRS can improve on these given its sensitivity to spectral line cores which probe higher altitudes above the clouds. We model transmission spectra for the warm Neptune GJ~3470~b and determine the detectability of H$_2$O with the CARMENES, GIANO and SPIRou spectrographs. We also model a grid of spectra for another warm Neptune, GJ~436~b, over a range of cloud-top pressure and H$_2$O abundance. We show H$_2$O is detectable for both planets with modest observational time and that the high H$_2$O abundance-high cloud deck degeneracy is broken with HRS. However, meaningful constraints on abundance and cloud-top pressure are only possible in the high metallicity scenario. We also show that detections of CH$_4$ and NH$_3$ are possible from cloudy models of GJ~436~b. Lastly, we show how the presence of the Earth's transmission spectrum hinders the detection of H$_2$O for the most cloudy scenarios given that telluric absorption overlaps with the strongest H$_2$O features. The constraints possible with HRS on the molecular species can be used for compositional analysis and to study the chemical diversity of such planets in the future., Comment: 13 pages, 9 figures, accepted for publication in MNRAS, Posting of this manuscript on the arXiv was coordinated with C. Hood et al

Ultra hot jupiters (UHJs), giant exoplanets with equilibrium temperatures above 2000 K, are ideal laboratories for studying metal compositions of planetary atmospheres. At these temperatures the thermal dissociation of metal-rich molecules into their constituent elements makes these atmospheres conducive for elemental characterisation. Several elements, mostly ionized metals, have been detected in UHJs recently using high resolution transit spectroscopy. Even though a number of neutral transition metals (e.g., Fe, Ti, V, Cr) are expected to be strong sources of optical/NUV opacity and, hence, influence radiative processes in the lower atmospheres of UHJs, only Fe I has been detected to date. We conduct a systematic search for atomic species in the UHJ WASP-121 b. Using theoretical models we present a metric to predict the atomic species likely to be detectable in such planets with high resolution transmission spectroscopy. We search for the predicted species in observations of WASP-121 b and report the first detections of neutral transition metals Cr I and V I in an exoplanet at 3.6 $\sigma$ and 4.5 $\sigma$, respectively. We confirm previous detections of Fe I and Fe II. Whereas Fe II was detected previously in the NUV, we detect it in the optical. We infer that the neutral elements Fe I, V I, and Cr I are present in the lower atmosphere, as predicted by thermochemical equilibrium, while Fe II is a result of photoionisation in the upper atmosphere. Our study highlights the rich chemical diversity of UHJs., Comment: Accepted for publication in ApJL

Recent detections of thermal inversions in the dayside atmospheres of some hot Jupiters are motivating new avenues to understand the interplay between their temperature structures and other atmospheric conditions. In particular, TiO has long been proposed to cause thermal inversions in hot Jupiters, depending on other factors such as stellar irradiation, C/O, and vertical mixing. TiO also has spectral features in the optical and near-infrared that have been detected. However, interpretations of TiO signatures rely on the accuracy of TiO opacity used in the models. The recently reported Toto TiO line list provides a new opportunity to investigate these dependencies, which is the goal of the present work. First, we investigate how the Toto line list affects observable transmission and emission spectra of hot Jupiters at low and high resolution. The improvement in the Toto line list compared to a previous line list results in observable differences in the model spectra, particularly in the optical at high resolution. Secondly, we explore the interplay between temperature structure, irradiation and composition with TiO as the primary source of optical opacity, using 1D self-consistent atmospheric models. Among other trends, we find that the propensity for thermal inversions due to TiO peaks at C/O$\sim$0.9, consistent with recent studies. Using these models, we further assess metrics to quantify thermal inversions due to TiO, compared to frequently-used Spitzer photometry, over a range in C/O, irradiation, metallicity, gravity and stellar type., Comment: Accepted for publication in MNRAS, 19 pages, 14 figures

Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures $\gtrsim$2000~K have been observed recently. Many of these planets show largely featureless thermal spectra in the near-infrared observed with the HST WFC3 spectrograph (1.1-1.7~$\mu$m) even though this spectral range contains strong H$_2$O opacity. Recent works have proposed the possibility of H- opacity masking the H$_2$O feature and/or thermal dissociation of H$_2$O causing its apparent depletion at the high temperatures of UHJs. In this work we test these hypotheses using observations of the exoplanet WASP-18b as a case study. We report detailed atmospheric retrievals of the planet using the HyDRA retrieval code, extended to include the effects of H- opacity and thermal dissociation. We report constraints on the H$_2$O, CO and H- abundances as well as the pressure-temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each dataset. We find that the H$_2$O and H- abundances are relatively unconstrained given the featureless WFC3 spectra. We do not conclusively detect H- in the planet contrary to previous studies which used equilibrium models to infer its presence. The constraint on the CO abundance depends on the combination of WFC3 and Spitzer data, ranging from solar to super-solar CO values. We additionally see signs of a thermal inversion from two of the datasets. Our study demonstrates the potential of atmospheric retrievals of UHJs including the effects of H- and thermal dissociation of molecules., Comment: 19 pages, 10 figures, accepted for publication in The Astronomical Journal

High resolution spectroscopy (HRS) has been used to detect a number of species in the atmospheres of hot Jupiters. Key to such detections is accurately and precisely modelled spectra for cross-correlation against the R$\gtrsim$20,000 observations. There is a need for the latest generation of opacities which form the basis for high signal-to-noise detections using such spectra. In this study we present and make publicly available cross sections for six molecular species, H$_2$O, CO, HCN, CH$_4$, NH$_3$ and CO$_2$ using the latest line lists most suitable for low- and high-resolution spectroscopy. We focus on the infrared (0.95-5~$\mu$m) and between 500-1500~K where these species have strong spectral signatures. We generate these cross sections on a grid of pressures and temperatures typical for the photospheres of super Earth, warm Neptunes and hot Jupiters using the latest H$_2$ and He pressure broadening. We highlight the most prominent infrared spectral features by modelling three representative exoplanets, GJ~1214~b, GJ~3470~b and HD~189733~b, which encompass a wide range in temperature, mass and radii. In addition, we verify the line lists for H$_2$O, CO and HCN with previous high resolution observations of hot Jupiters. However, we are unable to detect CH$_4$ with our new cross sections from HRS observations of HD~102195~b. These high accuracy opacities are critical for atmospheric detections with HRS and will be continually updated as new data becomes available., Comment: 16 pages, 11 figures, accepted for publication in MNRAS

The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of $39.1^{+2.7}_{-2.6}$ Earth masses and a density of $5.2^{+0.7}_{-0.8}$ grams per cubic centimetre, similar to Earth's. Interior structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than $3.9^{+0.8}_{-0.9}$ per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet., Comment: Published in Nature. This is a preprint of the article, before minor changes made during the refereeing and editing process. The published PDF is at https://www.nature.com/articles/s41586-020-2421-7 and can be accessed for free by following this link: https://rdcu.be/b5miB . Abstract updated to match published version

High resolution spectroscopy (R > 20,000) is currently the only known method to constrain the orbital solution and atmospheric properties of non-transiting hot Jupiters. It does so by resolving the spectral features of the planet into a forest of spectral lines and directly observing its Doppler shift while orbiting the host star. In this study, we analyse VLT/CRIRES (R = 100,000) L-band observations of the non-transiting giant planet HD 179949 b centred around 3.5 microns. We observe a weak (3.0 sigma, or S/N = 4.8) spectral signature of H2O in absorption contained within the radial velocity of the planet at superior-conjunction, with a mild dependence on the choice of line list used for the modelling. Combining this data with previous observations in the K-band, we measure a detection significance of 8.4 sigma for an atmosphere that is most consistent with a shallow lapse-rate, solar C/O ratio, and with CO and H2O being the only major sources of opacity in this wavelength range. As the two sets of data were taken three years apart, this points to the absence of strong radial-velocity anomalies due, e.g., to variability in atmospheric circulation. We measure a projected orbital velocity for the planet of KP = (145.2 +- 2.0)kms^{-1} (1 sigma) and improve the error bars on this parameter by ~70%. However, we only marginally tighten constraints on orbital inclination (66.2 +3.7 -3.1 degrees) and planet mass (0.963 +0.036 -0.031 Jupiter masses), due to the dominant uncertainties of stellar mass and semi-major axis. Follow ups of radial-velocity planets are thus crucial to fully enable their accurate characterisation via high resolution spectroscopy., Comment: Accepted for publication in MNRAS; 13 pages, 10 figures

The class of ultra-hot Jupiters comprises giant exoplanets undergoing intense irradiation from their host stars. They have proved to be a particularly interesting population for their orbital and atmospheric properties. One such planet, WASP-121~b, is in a highly misaligned orbit close to its Roche limit, and its atmosphere exhibits a thermal inversion. These properties make WASP-121~b an interesting target for additional atmospheric characterization. In this paper, we present analysis of archival high-resolution optical spectra obtained during transits of WASP-121~b. Artifacts from the Rossiter-McLaughlin effect and Center-to-Limb Variation are deemed negligible. However, we discuss scenarios where these effects warrant more careful treatment by modeling the WASP-121 system and varying its properties. We report a new detection of atmospheric absorption from H$\alpha$ in the planet with a transit depth of $1.87\pm0.11\%$. We further confirm a previous detection of the Na I doublet, and report a new detection of Fe I via cross-correlation with a model template. We attribute the H$\alpha$ absorption to an extended Hydrogen atmosphere, potentially undergoing escape, and the Fe I to equilibrium chemistry at the planetary photosphere. These detections help to constrain the composition and chemical processes in the atmosphere of WASP-121~b., Comment: 15 pages, 14 figures, submitted to MNRAS after addressing reviewer comments

High-resolution Doppler spectroscopy has been used to detect several chemical species in exoplanetary atmospheres. Such detections have traditionally relied on cross correlation of observed spectra against spectral model templates, an approach that is successful for detecting chemical species but not optimised for constraining abundances. Recent work has explored ways to perform atmospheric retrievals on high-resolution spectra (HRS) and combine them with retrievals routinely performed for low-resolution spectra (LRS) by developing a mapping from the cross correlation function to a likelihood metric. We build upon previous studies and report HyDRA-H, a hybrid retrieval code for simultaneous analysis of low- and high- resolution thermal emission spectra of exoplanets in a fully Bayesian approach. We demonstrate HyDRA-H on the hot Jupiter HD 209458b as a case study. We validate our HRS retrieval capability by confirming previous results and report a simultaneous hybrid retrieval using both HRS and LRS data. The LRS data span the HST WFC3 (1.1-1.7 $\mu$m) and Spitzer photometry (IRAC 3.6-8 $\mu$m) bands, while the HRS data were obtained with CRIRES on VLT at 2.3 $\mu$m. The constraints on the composition and temperature profiles for the hybrid retrieval are more stringent than retrievals with either LRS or HRS datasets individually. We retrieve abundances of $\log(\mathrm{H_2O)} = -4.11^{+0.91}_{-0.30}$ and $\log(\mathrm{CO}) = {-2.16}^{+0.99}_{-0.47}$, and $\mathrm{C/O} = 0.99^{+0.01}_{-0.02}$, consistent with previous works. We constrain the photospheric temperature to be $1498^{+216}_{-57}$ K, consistent with the equilibrium temperature. Our results demonstrate the significant advantages of hybrid retrievals by combining strengths of both HRS and LRS observations which probe complementary aspects of exoplanetary atmospheres., Comment: 16 pages, 9 figures, accepted for publication in The Astronomical Journal

Thermal emission spectra of hot Jupiters have led to key constraints on thermal inversions (or 'stratospheres') in their atmospheres with important implications for their atmospheric processes. Canonically, thermal inversions in hot Jupiters have been suggested to be caused by species such as TiO and VO which have strong visible opacity to absorb incident starlight. We explore two new avenues for thermal inversions in hot Jupiters, exploring both the visible and infrared opacities in their atmospheres. Firstly, by exploring a range of metal-rich species we find that four species (AlO, CaO, NaH and MgH) provide visible opacities comparable to TiO/VO and can cause strong inversions with reasonable abundances. Secondly, we show that a low infrared opacity caused by a low H$_2$O abundance, e.g. through a C/O~1, can also lead to strong thermal inversions even with low abundances of the visible absorbers mentioned above. We find that increasing the C/O ratio towards unity requires almost 2 orders of magnitude lower abundances for the visible absorbers in order for an inversion to form. Finally, we explore the thermal inversion in WASP-121b and find that it can be explained by all the visible absorbers listed above for different C/O ratios. Our study demonstrates the importance of both the refractory and volatile species in governing the physicochemical processes in hot Jupiter atmospheres. Spectroscopic observations in the visible have the potential to detect the newly proposed refractory species that can cause thermal inversions in addition to TiO and VO., Comment: 16 pages, 10 figures, accepted for publication in MNRAS

High-resolution doppler spectroscopy provides a powerful means for chemical detections in exoplanetary atmospheres. This approach involves monitoring hundreds of molecular lines in the planetary spectrum doppler shifted by the orbital motion of the planet. The molecules are detected by cross-correlating the observed spectrum of the system with a model planetary spectrum. The method has led to molecular detections of H2O, CO, and TiO in hot Jupiters using large ground-based telescopes. Critical to this method, however, is the accurate removal of the stellar and telluric features from the observed spectrum, also known as detrending. Previous molecular detections have relied on specific choices of detrending methods and parameters. However, the robustness of molecular detections across the different choices has not been investigated in detail. We conduct a systematic investigation of the effect of detrending algorithms, parameters, and optimizations on chemical detections using high-resolution spectroscopy. As a case study, we consider the hot Jupiter HD 189733 b. Using multiple methods, we confirm high-significance detections of H2O (4.8$\sigma$) and CO (4.7$\sigma$). Additionally, we report evidence for HCN at high significance (5.0$\sigma$). On the other hand, our results highlight the need for improved metrics and extended observations for robust confirmations of such detections. In particular, we show that detection significances of $\gtrsim$ 4$\sigma$ can be obtained by optimizing detrending at incorrect locations in the planetary velocity space; such false positives can occur in nearly 30\% of cases. We discuss approaches to help distinguish molecular detections from spurious noise., Comment: 15 pages, 16 figures, Accepted for publication in MNRAS

Transmission spectroscopy of exoplanets has the potential to provide precise measurements of atmospheric chemical abundances, in particular of hot Jupiters whose large sizes and high temperatures make them conducive to such observations. To date, several transmission spectra of hot Jupiters have revealed low amplitude features of water vapour compared to expectations from cloud-free atmospheres of solar metallicity. The low spectral amplitudes in such atmospheres could either be due to the presence of aerosols that obscure part of the atmosphere or due to inherently low abundances of H$_2$O in the atmospheres. A recent survey of transmission spectra of ten hot Jupiters used empirical metrics to suggest atmospheres with a range of cloud/haze properties but with no evidence for H$_2$O depletion. Here, we conduct a detailed and homogeneous atmospheric retrieval analysis of the entire sample and report the H$_2$O abundances, cloud properties, terminator temperature profiles, and detection significances of the chemical species. Our present study finds that the majority of hot Jupiters have atmospheres consistent with sub-solar H$_2$O abundances at their day-night terminators. The best constrained abundances range from $\mathrm{log(H_2O)}$ of $-5.04^{+0.46}_{-0.30}$ to $-3.16^{+0.66}_{-0.69}$, which compared to expectations from solar-abundance equilibrium chemistry correspond to $0.018^{+0.035}_{-0.009}\times$ solar to $1.40^{+4.97}_{-1.11}\times$ solar. Besides H$_2$O we report statistical constraints on other chemical species and cloud/haze properties, including cloud/haze coverage fractions which range from $0.18^{+0.26}_{-0.12}$ to $0.76^{+0.13}_{-0.15}$. The retrieved H$_2$O abundances suggest sub-solar oxygen and/or super-solar C/O ratios, and can provide important constraints on the formation and migration pathways of hot giant exoplanets., Comment: 18 pages, 7 figures, MNRAS, in press

Molecular species in planetary atmospheres provide key insights into their atmospheric processes and formation conditions. In recent years, high-resolution Doppler spectroscopy in the near-infrared has allowed detections of H$_2$O and CO in the atmospheres of several hot Jupiters. This method involves monitoring the spectral lines of the planetary thermal emission Doppler-shifted due to the radial velocity of the planet over its orbit. However, aside from CO and H$_2$O, which are the primary oxygen- and carbon-bearing species in hot H$_2$-rich atmospheres, little else is known about molecular compositions of hot Jupiters. Several recent studies have suggested the importance and detectability of nitrogen-bearing species in such atmospheres. In this Letter, we confirm potential detections of CO and H$_2$O in the hot Jupiter HD 209458b using high-resolution spectroscopy. We also report a cross-correlation peak with a signal-to-noise ratio of $4.7$ from a search for HCN. The results are obtained using high-resolution phase-resolved spectroscopy with the Very Large telescope CRyogenic high-resolution InfraRed Echelle Spectrograph (VLT CRIRES) and standard analysis methods reported in the literature. A more robust treatment of telluric contamination and other residuals would improve confidence and enable unambiguous molecular detections. The presence of HCN could provide constraints on the C/O ratio of HD~209458b and its potential origins., Comment: 8 pages, 5 figures, published in ApJL

Thermal emission spectra of exoplanets provide constraints on the chemical compositions, pressure-temperature (P-T) profiles, and energy transport in exoplanetary atmospheres. Accurate inferences of these properties rely on the robustness of the atmospheric retrieval methods employed. While extant retrieval codes have provided significant constraints on molecular abundances and temperature profiles in several exoplanetary atmospheres, the constraints on their deviations from thermal and chemical equilibria have yet to be fully explored. Our present work is a step in this direction. We report HyDRA, a disequilibrium retrieval framework for thermal emission spectra of exoplanetary atmospheres. The retrieval code uses the standard architecture of a parametric atmospheric model coupled with Bayesian statistical inference using the Nested Sampling algorithm. For a given dataset, the retrieved compositions and P-T profiles are used in tandem with the GENESIS self-consistent atmospheric model to constrain layer-by-layer deviations from chemical and radiative-convective equilibrium in the observable atmosphere. We demonstrate HyDRA on the Hot Jupiter WASP-43b with a high-precision emission spectrum. We retrieve an H2O mixing ratio of log(H2O) = -3.54^{+0.82}_{-0.52}, consistent with previous studies. We detect H2O and a combined CO/CO2 at 8-sigma significance. We find the dayside P-T profile to be consistent with radiative-convective equilibrium within the 1-sigma limits and with low day-night redistribution, consistent with previous studies. The derived compositions are also consistent with thermochemical equilibrium for the corresponding distribution of P-T profiles. In the era of high precision and high resolution emission spectroscopy, HyDRA provides a path to retrieve disequilibrium phenomena in exoplanetary atmospheres., Comment: 20 pages, 13 figures, Accepted for publication in MNRAS

As an exoplanet transits its host star, some of the light from the star is absorbed by the atoms and molecules in the planet's atmosphere, causing the planet to seem bigger; plotting the planet's observed size as a function of the wavelength of the light produces a transmission spectrum. Measuring the tiny variations in the transmission spectrum, together with atmospheric modelling, then gives clues to the properties of the exoplanet's atmosphere. Chemical species composed of light elements$-$such as hydrogen, oxygen, carbon, sodium and potassium$-$have in this way been detected in the atmospheres of several hot giant exoplanets, but molecules composed of heavier elements have thus far proved elusive. Nonetheless, it has been predicted that metal oxides such as titanium oxide (TiO) and vanadium oxide occur in the observable regions of the very hottest exoplanetary atmospheres, causing thermal inversions on the dayside. Here we report the detection of TiO in the atmosphere of the hot-Jupiter planet WASP-19b. Our combined spectrum, with its wide spectral coverage, reveals the presence of TiO (to a confidence level of 7.7{\sigma}), a strongly scattering haze (7.4{\sigma}) and sodium (3.4{\sigma}), and confirms the presence of water (7.9{\sigma}) in the atmosphere., Comment: Main article: 9 pages, 3 figures. Methods: 21 pages, 7 extended data figures, 3 extended data tables. Published in Nature

We are entering the era of high-precision and high-resolution spectroscopy of exoplanets. Such observations herald the need for robust self-consistent spectral models of exoplanetary atmospheres to investigate intricate atmospheric processes and to make observable predictions. Spectral models of plane-parallel exoplanetary atmospheres exist, mostly adapted from other astrophysical applications, with different levels of sophistication and accuracy. There is a growing need for a new generation of models custom-built for exoplanets and incorporating state-of-the-art numerical methods and opacities. The present work is a step in this direction. Here we introduce GENESIS, a plane-parallel, self-consistent, line-by-line exoplanetary atmospheric modelling code which includes (a) formal solution of radiative transfer using the Feautrier method, (b) radiative-convective equilibrium with temperature correction based on the Rybicki linearisation scheme, (c) latest absorption cross sections, and (d) internal flux and external irradiation, under the assumptions of hydrostatic equilibrium, local thermodynamic equilibrium and thermochemical equilibrium. We demonstrate the code here with cloud-free models of giant exoplanetary atmospheres over a range of equilibrium temperatures, metallicities, C/O ratios and spanning non-irradiated and irradiated planets, with and without thermal inversions. We provide the community with theoretical emergent spectra and pressure-temperature profiles over this range, along with those for several known hot Jupiters. The code can generate self-consistent spectra at high resolution and has the potential to be integrated into general circulation and non-equilibrium chemistry models as it is optimised for efficiency and convergence. GENESIS paves the way for high-fidelity remote sensing of exoplanetary atmospheres at high resolution with current and upcoming observations., Comment: 24 pages, 16 figures, Published in MNRAS

The formation mechanisms and chemical compositions of brown dwarfs likely span a diverse range. If they are formed predominantly in isolation by gravitational collapse like dwarf stars then their compositions might follow those of dwarf stars, spanning a relatively narrow range in metallicities (~ -0.4 to +0.4 dex) and predominantly oxygen-rich (C/O <~ 0.7). On the other hand, giant planets in the solar system are all super-solar in metallicity ([C/H] > 0.5~dex), which is thought to be a consequence of formation by core-accretion in a circumstellar disk. In this study we determine the atmospheric chemical compositions of three brown dwarfs and find them to be neither characteristic of dwarf stars nor giant planets. We derive high-precision atmospheric chemical abundances using high-S/N HST near-infrared spectra of three mid T Dwarfs which, together with two previously studied objects, display distinctly sub-solar metallicities and span C/O ratios of 0.4-1.0. These abundance patterns indicate either an old sub-stellar population and a multitude of formation environments or objects formed in circumstellar disks followed by ejection later. We show that for a simple synthetic model population of brown dwarfs with the same spectral-type as our sample the predicted age distribution is predominantly older than the Sun and, hence, more metal poor, consistent with our derived abundances. The diverse C/O ratios we find are indicative of either different chemical reservoirs in their formation environments or different formation pathways. Our results open the possibility that cool brown dwarfs may provide important probes of early galactic chemical evolution and inhomogeneity., Comment: Submitted to ApJ on Oct 5, 2016. Comments welcome