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Register a new userA new chemical scheme for giant planet thermochemistry. Update of the methanol chemistry and new reduced chemical scheme
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Several chemical networks have been developed to study warm (exo)planetary atmospheres. The kinetics of the reactions related to the methanol chemistry included in these schemes have been questioned. The goal of this paper is to update the methanol chemistry for such chemical networks thanks to recent publications in the combustion literature. We aim also at studying the consequences of this update on the atmospheric compositions of (exo)planetary atmospheres and brown dwarfs. We have performed an extensive review of combustion experimental studies and revisited the sub-mechanism describing methanol combustion in the scheme of Venot et al. (2012, A&A 624, A58). The updated scheme involves 108 species linked by a total of 1906 reactions. We have then applied our 1D kinetic model with this new scheme to several case studies (HD 209458b, HD 189733b, GJ 436b, GJ 1214b, ULAS J1335+11, Uranus, Neptune), and compared the results obtained with those obtained with the former scheme. The update of the scheme has a negligible impact on hot Jupiters atmospheres. However, the atmospheric composition of warm Neptunes and brown dwarfs is modified sufficiently to impact observational spectra in the wavelength range JWST will operate. Concerning Uranus and Neptune, the update of the chemical scheme modifies the abundance of CO and thus impacts the deep oxygen abundance required to reproduce the observational data. For future 3D kinetics models, we also derived a reduced scheme containing 44 species and 582 reactions. Chemical schemes should be regularly updated in order to maintain a high level of reliability on the results of kinetic models and be able to improve our knowledge on planetary formation.
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As astronomical photometric surveys continue to tile the sky repeatedly, the potential to pushdetection thresholds to fainter limits increases; however, traditional digital-tracking methods cannotachieve this efficiently beyond time scales where motion is approximately linear. In this paper weprototype an optimal detection scheme that samples under a user defined prior on a parameterizationof the motion space, maps these sampled trajectories to the data space, and computes an optimalsignal-matched filter for computing the signal to noise ratio of trial trajectories. We demonstrate thecapability of this method on a small test data set from the Dark Energy Camera. We recover themajority of asteroids expected to appear and also discover hundreds of new asteroids with only a fewhours of observations. We conclude by exploring the potential for extending this scheme to larger datasets that cover larger areas of the sky over longer time baselines.
OGLE III and MOA II are discovering 600-1000 Galactic Bulge microlens events each year. This stretches the resources available for intensive follow-up monitoring of the lightcurves in search of anomalies caused by planets near the lens stars. We advocate optimizing microlens planet searches by using an automatic prioritization algorithm based on the planet detection zone area probed by each new data point. This optimization scheme takes account of the telescope and detector characteristics, observing overheads, sky conditions, and the time available for observing on each night. The predicted brightness and magnification of each microlens target is estimated by fitting to available data points. The optimisation scheme then yields a decision on which targets to observe and which to skip, and a recommended exposure time for each target, designed to maximize the planet detection capability of the observations. The optimal strategy maximizes detection of planet anomalies, and must be coupled with rapid data reduction to trigger continuous follow-up of anomalies that are thereby found. A web interface makes the scheme available for use by human or robotic observers at any telescope. We also outline a possible self-organising scheme that may be suitable for coordination of microlens observations by a heterogeneous telescope network.
It is still being debated whether the well-known metallicity - giant planet correlation for dwarf stars is also valid for giant stars. For this reason, having precise metallicities is very important. Different methods can provide different results that lead to discrepancies in the analysis of planet hosts. To study the impact of different analyses on the metallicity scale for evolved stars, we compare different iron line lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolved stars with planets. With these new homogeneous parameters, we revisit the metallicity - giant planet connection for evolved stars. A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performed through the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one built for cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting, using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributions of various different samples of evolved stars and red giants. All parameters compare well using a line list set, designed specifically for cool and solar-like stars to provide more accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for future analysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a bias in giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravity stars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicity enhancement is found for red giants with planets ($log g < 3.0$,dex) with respect to red giants without planets.
We propose a new performance indicator to evaluate the productivity of research institutions by their disseminated scientific papers. The new quality measure includes two principle components: the normalized impact factor of the journal in which paper was published, and the number of citations received per year since it was published. In both components, the scientific impacts are weighted by the contribution of authors from the evaluated institution. As a whole, our new metric, namely, the institutional performance score takes into account both journal based impact and articles specific impacts. We apply this new scheme to evaluate research output performance of Turkish institutions specialized in astronomy and astrophysics in the period of 1998-2012. We discuss the implications of the new metric, and emphasize the benefits of it along with comparison to other proposed institutional performance indicators.
Numerical solutions of the cosmic-ray (CR) magneto-hydrodynamic equations are dogged by a powerful numerical instability, which arises from the constraint that CRs can only stream down their gradient. The standard cure is to regularize by adding artificial diffusion. Besides introducing ad-hoc smoothing, this has a significant negative impact on either computational cost or complexity and parallel scalings. We describe a new numerical algorithm for CR transport, with close parallels to two moment methods for radiative transfer under the reduced speed of light approximation. It stably and robustly handles CR streaming without any artificial diffusion. It allows for both isotropic and field-aligned CR streaming and diffusion, with arbitrary streaming and diffusion coefficients. CR transport is handled explicitly, while source terms are handled implicitly. The overall time-step scales linearly with resolution (even when computing CR diffusion), and has a perfect parallel scaling. It is given by the standard Courant condition with respect to a constant maximum velocity over the entire simulation domain. The computational cost is comparable to that of solving the ideal MHD equation. We demonstrate the accuracy and stability of this new scheme with a wide variety of tests, including anisotropic streaming and diffusion tests, CR modified shocks, CR driven blast waves, and CR transport in multi-phase media. The new algorithm opens doors to much more ambitious and hitherto intractable calculations of CR physics in galaxies and galaxy clusters. It can also be applied to other physical processes with similar mathematical structure, such as saturated, anisotropic heat conduction.
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