1,126 research outputs found

    Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parametrized, phase-equilibrium cloud formation code EDDYSED (article)

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    This is the final version. Available from OUP via the DOI in this recordThe dataset associated with this article is available in ORE: https://doi.org/10.24378/exe.1483We present results from 3D radiative-hydrodynamical simulations of HD 209458b with a fully coupled treatment of clouds using the EDDYSED code, critically, including cloud radiative feedback via absorption and scattering. We demonstrate that the thermal and optical structure of the simulated atmosphere is markedly different, for the majority of our simulations, when including cloud radiative effects, suggesting this important mechanism cannot be neglected. Additionally, we further demonstrate that the cloud structure is sensitive to not only the cloud sedimentation efficiency (termed fsed in EDDYSED), but also the temperature–pressure profile of the deeper atmosphere. We briefly discuss the large difference between the resolved cloud structures of this work, adopting a phase-equilibrium and parametrized cloud model, and our previous work incorporating a cloud microphysical model, although a fairer comparison where, for example, the same list of constituent condensates is included in both treatments is reserved for a future work. Our results underline the importance of further study into the potential condensate size distributions and vertical structures, as both strongly influence the radiative impact of clouds on the atmosphere. Finally, we present synthetic observations from our simulations reporting an improved match, over our previous cloud-free simulations, to the observed transmission, HST WFC3 emission, and 4.5 Όm Spitzer phase curve of HD 209458b. Additionally, we find all our cloudy simulations have an apparent albedo consistent with observations.Leverhulme TrustScience and Technology Facilities Council (STFC

    Observable signatures of wind-driven chemistry with a fully consistent three dimensional radiative hydrodynamics model of HD 209458b (article)

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    This is the final version of the article. Available from American Astronomical Society / IOP Publishing via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32579We present a study of the effect of wind-driven advection on the chemical composition of hot Jupiter atmospheres using a fully-consistent 3D hydrodynamics, chemistry and radiative transfer code, the Met Office Unified Model (UM). Chemical modelling of exoplanet atmospheres has primarily been restricted to 1D models that cannot account for 3D dynamical processes. In this work we couple a chemical relaxation scheme to the UM to account for the chemical interconversion of methane and carbon monoxide. This is done consistently with the radiative transfer meaning that departures from chemical equilibrium are included in the heating rates (and emission) and hence complete the feedback between the dynamics, thermal structure and chemical composition. In this letter we simulate the well studied atmosphere of HD 209458b. We find that the combined effect of horizontal and vertical advection leads to an increase in the methane abundance by several orders of magnitude; directly opposite to the trend found in previous works. Our results demonstrate the need to include 3D effects when considering the chemistry of hot Jupiter atmospheres. We calculate transmission and emission spectra, as well as the emission phase curve, from our simulations. We conclude that gas-phase non-equilibrium chemistry is unlikely to explain the model–observation discrepancy in the 4.5 ”m Spitzer/IRAC channel. However, we highlight other spectral regions, observable with the James Webb Space Telescope, where signatures of wind-driven chemistry are more prominent.BD and DKS acknowledge funding from the European Research Council (ERC) under the European Unions Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 336792. NJM is part funded by a Leverhulme Trust Research Project Grant. JM and IAB acknowledge the support of a Met Office Academic Partnership secondment. ALC is funded by an STFC studentship. DSA acknowledges support from the NASA Astrobiology Program through the Nexus for Exoplanet System Science. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility. This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure

    Protein Encapsulation Using Complex Coacervates: What Nature Has to Teach Us

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    Protein encapsulation is a growing area of interest, particularly in the fields of food science and medicine. The sequestration of protein cargoes is achieved using a variety of methods, each with benefits and drawbacks. One of the most significant challenges associated with protein encapsulation is achieving high loading while maintaining protein viability. This difficulty is exacerbated because many encapsulant systems require the use of organic solvents. By contrast, nature has optimized strategies to compartmentalize and protect proteins inside the cell—a purely aqueous environment. Although the mechanisms whereby aspects of the cytosol is able to stabilize proteins are unknown, the crowded nature of many newly discovered, liquid phase separated “membraneless organelles” that achieve protein compartmentalization suggests that the material environment surrounding the protein may be critical in determining stability. Here, encapsulation strategies based on liquid–liquid phase separation, and complex coacervation in particular, which has many of the key features of the cytoplasm as a material, are reviewed. The literature on protein encapsulation via coacervation is also reviewed and the parameters relevant to creating protein‐containing coacervate formulations are discussed. Additionally, potential opportunities associated with the creation of tailored materials to better facilitate protein encapsulation and stabilization are highlighted

    Erratum: A library of ATMO forward model transmission spectra for hot Jupiter exoplanets

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    This is the final version. Available from OUP via the DOI in this recordThe article to which this is the erratum is in ORE at http://hdl.handle.net/10871/30324The paper ‘A library of ATMO forward model transmission spectra for hot Jupiter exoplanets’ was published in MNRAS 474, 4, 5158–5185. In the original manuscript (Goyal et al. 2018), we presented a grid of forward model transmission spectra for hot Jupiter exoplanets. However, we recently identified an error in the treatment of rainout in our 1D atmosphere model ATMO. The correction of this error led to changes in the equilibrium chemical abundances using rainout condensation and thereby the transmission spectra. We note that this error only affects the online library2,3 that includes rainout condensation, the library with local condensation (without rainout) is unaffected. We further note that the gas phase equilibrium scheme used in ATMO has been compared by Drummond et al. (2016) with the analytical schemes of Burrows & Sharp (1999) and Heng & Tsai (2016). The gas phase chemistry with and without local condensation has also been verified in Baudino et al. (2017) against the petitCODE (Molliùre et al. 2015, 2017) and Exo-REM (Baudino et al. 2015) models. Therefore, issues with the previous version of the grid were confined to the implementation of rainout

    HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey

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    We report the discovery of HATS-1b, a transiting extrasolar planet orbiting the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet discovered by HATSouth, a global network of autonomous wide-field telescopes. HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve of HATS-1b has near continuous coverage over several multi-day periods, demonstrating the power of using a global network of telescopes to discover transiting planets.Comment: Submitted to AJ 10 pages, 5 figures, 6 table

    Interpol: An R package for preprocessing of protein sequences

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    <p>Abstract</p> <p>Background</p> <p>Most machine learning techniques currently applied in the literature need a fixed dimensionality of input data. However, this requirement is frequently violated by real input data, such as DNA and protein sequences, that often differ in length due to insertions and deletions. It is also notable that performance in classification and regression is often improved by numerical encoding of amino acids, compared to the commonly used sparse encoding.</p> <p>Results</p> <p>The software "Interpol" encodes amino acid sequences as numerical descriptor vectors using a database of currently 532 descriptors (mainly from AAindex), and normalizes sequences to uniform length with one of five linear or non-linear interpolation algorithms. Interpol is distributed with open source as platform independent R-package. It is typically used for preprocessing of amino acid sequences for classification or regression.</p> <p>Conclusions</p> <p>The functionality of Interpol widens the spectrum of machine learning methods that can be applied to biological sequences, and it will in many cases improve their performance in classification and regression.</p

    A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b

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    Exoplanets orbiting close to their parent stars could lose some fraction of their atmospheres because of the extreme irradiation. Atmospheric mass loss primarily affects low-mass exoplanets, leading to suggest that hot rocky planets might have begun as Neptune-like, but subsequently lost all of their atmospheres; however, no confident measurements have hitherto been available. The signature of this loss could be observed in the ultraviolet spectrum, when the planet and its escaping atmosphere transit the star, giving rise to deeper and longer transit signatures than in the optical spectrum. Here we report that in the ultraviolet the Neptune-mass exoplanet GJ 436b (also known as Gliese 436b) has transit depths of 56.3 +/- 3.5% (1 sigma), far beyond the 0.69% optical transit depth. The ultraviolet transits repeatedly start ~2 h before, and end >3 h after the ~1 h optical transit, which is substantially different from one previous claim (based on an inaccurate ephemeris). We infer from this that the planet is surrounded and trailed by a large exospheric cloud composed mainly of hydrogen atoms. We estimate a mass-loss rate in the range of ~10^8-10^9 g/s, which today is far too small to deplete the atmosphere of a Neptune-like planet in the lifetime of the parent star, but would have been much greater in the past.Comment: Published in Nature on 25 June 2015. Preprint is 28 pages, 12 figures, 2 table

    Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts

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    We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray induced photoemission spectroscopy turns out to be a valuable non-destructive diagnostic tool. We show that the observation of generic one-dimensional signatures in photoemission spectra of the valence band close to the Fermi level can be strongly affected by surface effects. Especially, great care must be exercised taking evidence for an unusual one-dimensional many-body state exclusively from the observation of a pseudogap.Comment: 11 pages, 12 figures, v2: minor changes in text and figure labellin

    The impact of mixing treatments on cloud modelling in 3D simulations of hot Jupiters

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    This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this recordData availability: The research data supporting this publication are openly available at https://doi.org/10.7910/DVN/NLT6MSWe present results of 3D hydrodynamical simulations of HD209458b including a coupled, radiatively-active cloud model (EddySed). We investigate the role of the mixing by replacing the default convective treatment used in previous works with a more physically relevant mixing treatment ( ) based on global circulation. We find that uncertainty in the efficiency of sedimentation through the sedimentation factor sed plays a larger role in shaping cloud thickness and its radiative feedback on the local gas temperatures – e.g. hot spot shift and day-to-night side temperature gradient – than the switch in mixing treatment. We demonstrate using our new mixing treatments that simulations with cloud scales which are a fraction of the pressure scale height improve agreement with the observed transmission spectra, the emission spectra, and the Spitzer 4.5 m phase curve, although our models are still unable to reproduce the optical and UV transmission spectra. We also find that the inclusion of cloud increases the transit asymmetry in the optical between the east and west limbs, although the difference remains small (. 1%).Leverhulme TrustScience and Technology Facilities Council (STFC)Medical Research Council (MRC
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