We present here the analysis of 30 gaseous extrasolar planets, with temperatures between 600 and 2400 K and radii between 0.35 and 1.9 R Jup . The quality of the HST/WFC3 spatially scanned data combined with our specialized analysis tools allow us to study the largest and most self-consistent sample of exoplanetary transmission spectra to date and examine the collective behavior of warm and hot gaseous planets rather than isolated case-studies. We define a new metric, the Atmospheric Detectability Index (ADI) to evaluate the statistical significance of an atmospheric detection and find statistically significant atmospheres around 16 planets out of the 30 analysed. For most of the Jupiters in our sample, we find the detectability of their atmospheres to be dependent on the planetary radius but not on the planetary mass. This indicates that planetary gravity plays a secondary role in the state of gaseous planetary atmospheres. We detect the presence of water vapour in all of the statistically detectable atmospheres, and we cannot rule out its presence in the atmospheres of the others. In addition, TiO and/or VO signatures are detected with 4 σ confidence in WASP-76 b, and they are most likely present in WASP-121 b. We find no correlation between expected signal-to-noise and atmospheric detectability for most targets. This has important implications for future large-scale surveys.

Many methods have been proposed for efficient storage of molecular hydrogen for fuel cell applications. However, despite intense research efforts, the twin U.S. Department of Energy goals of 6.5% mass ratio and 62 kg͞m 3 volume density has not been achieved either experimentally or via theoretical simulations on reversible model systems. Carbon-based materials, such as carbon nanotubes, have always been regarded as the most attractive physisorption substrates for the storage of hydrogen. Theoretical studies on various model graphitic systems, however, failed to reach the elusive goal. Here, we show that insufficiently accurate carbon-H 2 interaction potentials, together with the neglect and incomplete treatment of the quantum effects in previous theoretical investigations, led to misleading conclusions for the absorption capacity. A proper account of the contribution of quantum effects to the free energy and the equilibrium constant for hydrogen adsorption suggest that the U.S. Department of Energy specification can be approached in a graphite-based physisorption system. The theoretical prediction can be realized by optimizing the structures of nano-graphite platelets (graphene), which are lightweight, cheap, chemically inert, and environmentally benign. equilibrium constants ͉ hydrogen storage ͉ quantum effects A recent report on hydrogen clathrate hydrate (1) shows that under high pressure, molecular hydrogen can be trapped in the clathrate cavities reaching a mass ratio close to that defined by the U.S. Department of Energy (DOE) (2). However, the hydrogen clathrate is only stable under high pressure or at very low temperature. Simple sterical considerations suggest that the use of a ''help gas'' to stabilize the clathrate hydrate under less severe thermodynamic conditions would lead to the deterioration of the hydrogen storage mass ratio and may not be viable for mobile applications. On the other hand, there have also been numerous experimental studies on the binding capacity of molecular hydrogen with graphitic substrates (3, 4). At technologically viable conditions, reliably reproducible results are still far from the DOE goal (3, 4). In the attempt to understand and improve the storage capacity of graphitic materials, calculations have been made on many models. Some of the calculations were based on empirical interaction potentials (5-9), and the others used potentials derived from quantum mechanical calculations (10-16). The role of quantum behavior of molecular hydrogen at low temperatures has also been investigated (6,8,(17)(18)(19). Unfortunately, the binding capacity for hydrogen at near-ambient conditions has not been calculated, including the quantum effects and accurate, ab initio-based interaction potentials. To date, there has not been a reliable theoretical study indicating that the DOE goal of 6.5% mass ratio can or cannot be achieved in pure graphitic materials.The interaction of nonpolar H 2 molecules with physisorption substrates in graphitic system is mainly the London dispersion. Accurate...

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The ExoMol database (www.exomol.com) provides extensive line lists of molecular transitions which are valid over extended temperature ranges. The status of the current release of the database is reviewed and a new data structure is specified. This structure augments the provision of energy levels (and hence transition frequencies) and Einstein A coefficients with other key properties, including lifetimes of individual states, temperature-dependent cooling functions, Land? g-factors, partition functions, cross sections, k-coefficients and transition dipoles with phase relations. Particular attention is paid to the treatment of pressure broadening parameters. The new data structure includes a definition file which provides the necessary information for utilities accessing ExoMol through its application programming interface (API). Prospects for the inclusion of new species into the database are discussedPeer reviewe

In the past decade, observations from space and ground have found H 2 O to be the most abundant molecular species, after hydrogen, in the atmospheres of hot, gaseous, extrasolar planets 1-5 . Being the main molecular carrier of oxygen, H 2 O is a tracer of the origin and the evolution mechanisms of planets. For temperate, terrestrial planets, the presence of H 2 O is of great significance as an indicator of habitable conditions. Being small and relatively cold, these planets and their atmospheres are the most challenging to observe, and therefore no atmospheric spectral signatures have so far been detected 6 . Super-Earths -planets lighter than ten M ⊕ -around later-type stars may provide our first opportunity to study spectroscopically the characteristics of such planets, as they are best suited for transit observations. Here we report the detection of an H 2 O spectroscopic signature in the atmosphere of K2-18 b -an eight M ⊕ planet in the habitable-zone of an M-dwarf 7 -with high statistical confidence (ADI 5 = 5.0, ∼3.6σ 8,9 ). In addition, the derived mean molecular weight suggests an atmosphere still containing some hydrogen. The observations were recorded with the Hubble Space Telescope/WFC3 camera, and analysed with our dedicated, publicly avail-1 arXiv:1909.05218v1 [astro-ph.EP] 11 Sep 2019 able, algorithms 5, 9 . While the suitability of M-dwarfs to host habitable worlds is still under discussion 10-13 , K2-18 b offers an unprecedented opportunity to get insight into the composition and climate of habitable-zone planets. Atmospheric characterisation of super-Earths is currently within reach of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST), combined with the recently implemented spatial scanning observational strategy 14 . The spectra of three hot transiting planets with radii less than 3.0 R ⊕ have been published so far: GJ-1214 b 15 , HD 97658 b 16 and 55 Cnc e 17 . The first two do not show any evident transit depth modulation with wavelength, suggesting an atmosphere covered by thick clouds or made of molecular species heavier than hydrogen, while only the spectrum of 55 Cnc e has revealed a light-weighted atmosphere, suggesting H/He still being present. In addition, transit observations of six temperate Earth-size planets around the ultra-cool dwarf TRAPPIST-1 -planets b, c, d, e, f 6 , and g 18 -have not shown any molecular signatures and have excluded the presence of cloud-free, H/He atmospheres around them. K2-18 b was discovered in 2015 by the Kepler spacecraft 7 , and it is orbiting around an M2.5 ([Fe/H] = 0.123 ± 0.157 dex, T eff = 3457 ± 39 K, M * = 0.359 ± 0.047 M , R * = 0.411±0.038 R ) 19 dwarf star, 34 pc away from the Earth. The star-planet distance of 0.1429 AU 19suggests a planet within the star's habitable zone (∼ 0.12 -0.25 AU) 20 , with effective temperature between 200 K and 320 K, depending on the albedo and the emissivity of its surface and/or its atmosphere. This crude estimate accounts for neither possible tidal energy sources 21 nor atmospheric heat ...

A new line list for H 2 16 O is presented. This line list, which is called POKAZATEL, includes transitions between rotation-vibrational energy levels up to 41 000 cm −1 in energy and is the most complete to date. The potential energy surface (PES) used for producing the line list was obtained by fitting a high-quality ab initio PES to experimental energy levels with energies of 41 000 cm −1 and for rotational excitations up to J = 5. The final line list comprises all energy levels up to 41 000 cm −1 and rotational angular momentum J up to 72. An accurate ab initio dipole moment surface (DMS) was used for the calculation of line intensities and reproduces high-precision experimental intensity data with an accuracy close to 1%. The final line list uses empirical energy levels whenever they are available, to ensure that line positions are reproduced as accurately as possible. The POKAZATEL line list contains over 5 billion transitions and is available from the ExoMol website (www.exomol.com) and the CDS database.

Context. Opacities of molecules in exoplanet atmospheres rely on increasingly detailed line-lists for these molecules. The line lists available today contain for many species up to several billions of lines. Computation of the spectral line profile created by pressure and temperature broadening, the Voigt profile, of all of these lines is becoming a computational challenge. Aims. We aim to create a method to compute the Voigt profile in a way that automatically focusses the computation time into the strongest lines, while still maintaining the continuum contribution of the high number of weaker lines. Methods. Here, we outline a statistical line sampling technique that samples the Voigt profile quickly and with high accuracy. The number of samples is adjusted to the strength of the line and the local spectral line density. This automatically provides high accuracy line shapes for strong lines or lines that are spectrally isolated. The line sampling technique automatically preserves the integrated line opacity for all lines, thereby also providing the continuum opacity created by the large number of weak lines at very low computational cost. Results. The line sampling technique is tested for accuracy when computing line spectra and correlated-k tables. Extremely fast computations (∼ 3.5 · 10 5 lines per second per core on a standard current day desktop computer) with high accuracy (≤ 1% almost everywhere) are obtained. A detailed recipe on how to perform the computations is given.

We present 'BYTe', a comprehensive 'hot' line list for the ro-vibrational transitions of ammonia, 14NH3, in its ground electronic state. This line list has been computed variationally using the program suite TROVE, a new spectroscopically-determined potential energy surface and an ab initio dipole moment surface. BYTe, is designed to be used at all temperatures up to 1500K. It comprises 1137650964 transitions in the frequency range from 0 to 12000 cm-1, constructed from 1366519 energy levels below 18000 cm-1 having J values below 36. Comparisons with laboratory data confirm the accuracy of the line list which is suitable for modelling a variety of astrophysical problems including the atmospheres of extrasolar planets and brown dwarfs.Comment: the paper has been submitted to MNRA