Entity

Time filter

Source Type

Brussels, Belgium

Grevesse N.,University of Liege | Asplund M.,Max Planck Institute for Astrophysics | Sauval A.J.,Observatoire Royal de Belgique | Scott P.,The Oskar Klein Center
Canadian Journal of Physics | Year: 2011

We have very recently re-determined the abundances of nearly all the available chemical elements in the solar photosphere, from lithium to thorium (Asplund et al. Annu. Rev. Astron. Astrophys. 47, 481 (2009)). This new complete and homogeneous analysis results from a very careful selection of spectral lines of all the indicators of the abundances present in the solar photospheric spectrum, from a discussion of the atomic and molecular data, and from an analysis of these lines based on a new 3D model of the solar outer layers, taking non-LTE effects into account when possible. We present these new results, compare them with other recent solar data as well as with recent results for the solar neighborhood, and discuss some of their most important implications as well as some of the atomic data we still urgently need. © 2011 Published by NRC Research Press.


Vu T.H.,Jet Propulsion Laboratory | Gloesener E.,Observatoire Royal de Belgique | Choukroun M.,Jet Propulsion Laboratory | Ibourichene A.,Ecole Normale Superieure de Paris | Hodyss R.,Jet Propulsion Laboratory
Journal of Physical Chemistry B | Year: 2014

Clathrate hydrates, ice-like crystalline compounds in which small guest molecules are enclosed inside cages formed by tetrahedrally hydrogen-bonded water molecules, are naturally abundant on Earth and are generally expected to exist on icy celestial bodies. A prototypical example is Saturn's moon Titan, where dissociation of methane clathrates, a major crustal component, could contribute significantly to the replenishment of atmospheric methane. Ammonia is an important clathrate inhibiting agent that may be present (potentially at high concentrations) in Titan's interior. In this study, low-temperature Raman experiments are conducted to examine the dissociation point of tetrahydrofuran clathrates, an ambient-pressure analogue of methane clathrates, over a wide range of ammonia concentrations from 0 to 25 wt %. A phase diagram for the H2O-THF-NH3 system is generated, showing two main results: (i) ammonia lowers the dissociation point of clathrate hydrates to a similar extent compared to the melting of water ice and (ii) THF clathrate exhibits a "liquidus-like" behavior in the presence of ammonia, with a eutectic temperature of about 203.6 K. As temperatures higher than this estimated eutectic are anticipated within Titan's icy crust, these results imply that partial dissociation of clathrates can occur readily and may contribute to outgassing from the interior. © 2014 American Chemical Society.


Scott P.,Imperial College London | Asplund M.,Australian National University | Grevesse N.,University of Liege | Bergemann M.,University of Cambridge | Sauval A.J.,Observatoire Royal de Belgique
Astronomy and Astrophysics | Year: 2015

We redetermine the abundances of all iron group nuclei in the Sun, based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (NLTE), stringent line selection procedures and high quality observational data. We have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. We find log ∈Sc = 3.16 ± 0.04, log ∈Ti = 4.93 ± 0.04, log ∈V = 3.89 ± 0.08, log ∈Cr = 5.62 ± 0.04, log ∈Mn = 5.42 ± 0.04, log ∈Fe = 7.47 ± 0.04, log ∈Co = 4.93 ± 0.05 and log ∈Ni = 6.20 ± 0.04. Our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and NLTE line formation). The new abundances are generally in good agreement with the CI meteoritic abundances but with some notable exceptions. This analysis constitutes both a full exposition and a slight update of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data we employed. © ESO 2014.


Grevesse N.,University of Liege | Scott P.,Imperial College London | Asplund M.,Australian National University | Sauval A.J.,Observatoire Royal de Belgique
Astronomy and Astrophysics | Year: 2015

We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data that we have employed. © ESO 2014.


Scott P.,Imperial College London | Grevesse N.,University of Liege | Asplund M.,Australian National University | Sauval A.J.,Observatoire Royal de Belgique | And 6 more authors.
Astronomy and Astrophysics | Year: 2015

The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geophysics: elemental abundances of essentially all astronomical objects are referenced to the solar composition, and basically every process involving the Sun depends on its composition. This article, dealing with the intermediate-mass elements Na to Ca, is the first in a series describing the comprehensive re-determination of the solar composition. In this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. We employ a highly realistic 3D hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational diagnostics. For comparison, and to quantify remaining systematic errors, we repeat the analysis using three different 1D hydrostatic model atmospheres (marcs, miss and Holweger & Müller 1974, Sol. Phys., 39, 19) and a horizontally and temporally-averaged version of the 3D model (〈3D〉). We account for departures from local thermodynamic equilibrium (LTE) wherever possible. We have scoured the literature for the best possible input data, carefully assessing transition probabilities, hyperfine splitting, partition functions and other data for inclusion in the analysis. We have put the lines we use through a very stringent quality check in terms of their observed profiles and atomic data, and discarded all that we suspect to be blended. Our final recommended 3D+NLTE abundances are: log εNa = 6:21 ± 0:04, log εMg = 7:59 ± 0:04, log εAl = 6:43 ± 0:04, log εSi = 7:51 ± 0:03, log εP = 5:41 ± 0:03, log εS = 7:13 ± 0:03, log εK = 5:04 ± 0:05 and log εCa = 6:32 ± 0:03. The uncertainties include both statistical and systematic errors. Our results are systematically smaller than most previous ones with the 1D semi-empirical Holweger & Müller model, whereas the 〈3D〉 model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the results presented in Asplund et al. (2009, ARA&A, 47, 481) for Na to Ca, and includes full details of all lines and input data used. © ESO 2014.

Discover hidden collaborations