105 research outputs found
Circumbinary Planet Formation in the Kepler-16 system. I. N-body Simulations
The recently discovered circumbinary planets (Kepler-16 b, Kepler-34 b,
Kepler-35 b) represent the first direct evidence of the viability of planet
formation in circumbinary orbits. We report on the results of N-body
simulations investigating planetesimal accretion in the Kepler-16 b system,
focusing on the range of impact velocities under the influence of both stars'
gravitational perturbation and friction from a putative protoplanetary disk.
Our results show that planet formation might be effectively inhibited for a
large range in semi-major axis (1.75 < a_P < 4 AU), suggesting that the
planetary core must have either migrated from outside 4 AU, or formed in situ
very close to its current location.Comment: 6 pages, 4 figures. Accepted for publication in ApJ. Additional
materials available at http://www.stefanom.org/?kep16
Third-order density-functional perturbation theory: a practical implementation with applications to anharmonic couplings in Si
We present a formulation of third-order density-functional perturbation
theory which is manifestly invariant with respect to unitary transfomations
within the occupied-states manifold and is particularly suitable for a
practical implementation of the so called `2n+1' theorem. Our implementation is
demonstrated with the calculation of the third-order anharmonic coupling
coefficients for some high-simmetry phonons in Silicon.Comment: 6 pages, Plane Tex, SISSA Ref. 78/94/CM/SC (June 94
Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
Quantum ESPRESSO is an integrated suite of computer codes for
electronic-structure calculations and materials modeling, based on
density-functional theory, plane waves, and pseudopotentials (norm-conserving,
ultrasoft, and projector-augmented wave). Quantum ESPRESSO stands for "opEn
Source Package for Research in Electronic Structure, Simulation, and
Optimization". It is freely available to researchers around the world under the
terms of the GNU General Public License. Quantum ESPRESSO builds upon
newly-restructured electronic-structure codes that have been developed and
tested by some of the original authors of novel electronic-structure algorithms
and applied in the last twenty years by some of the leading materials modeling
groups worldwide. Innovation and efficiency are still its main focus, with
special attention paid to massively-parallel architectures, and a great effort
being devoted to user friendliness. Quantum ESPRESSO is evolving towards a
distribution of independent and inter-operable codes in the spirit of an
open-source project, where researchers active in the field of
electronic-structure calculations are encouraged to participate in the project
by contributing their own codes or by implementing their own ideas into
existing codes.Comment: 36 pages, 5 figures, resubmitted to J.Phys.: Condens. Matte
Eclipsing Binary Trojan Asteroid Patroclus: Thermal Inertia from Spitzer Observations
We present mid-infrared (8-33 micron) observations of the binary L5-Trojan
system (617) Patroclus-Menoetius before, during, and after two shadowing
events, using the Infrared Spectrograph (IRS) on board the Spitzer Space
Telescope.F or the first time, we effectively observe changes in asteroid
surface temperature in real time, allowing the thermal inertia to be determined
very directly. A new detailed binary thermophysical model is presented which
accounts for the system's known mutual orbit, arbitrary component shapes, and
thermal conduction in the presence of eclipses. We obtain two local
thermal-inertia values, representative of the respective shadowed areas: 21+/14
MKS and 6.4+/-1.6 MKS. The average thermal inertia is estimated to be 20+/-15
MKS, potentially with significant surface heterogeneity. This first
thermal-inertia measurement for a Trojan asteroid indicates a surface covered
in fine regolith. The diameters of Patroclus and Menoetius are 106 +/- 11 and
98+/-10 km, respectively, in agreement with previous findings. Taken together
with the system's known total mass, this implies a bulk mass density of 1.08
+/-0.33 g/cm3, significantly below the mass density of L4-Trojan asteroid (624)
Hektor and suggesting a bulk composition dominated by water ice.Comment: in press to Icarus, 48 pages, 6 tables, 5 figure
Phonons and related properties of extended systems from density-functional perturbation theory
This article reviews the current status of lattice-dynamical calculations in
crystals, using density-functional perturbation theory, with emphasis on the
plane-wave pseudo-potential method. Several specialized topics are treated,
including the implementation for metals, the calculation of the response to
macroscopic electric fields and their relevance to long wave-length vibrations
in polar materials, the response to strain deformations, and higher-order
responses. The success of this methodology is demonstrated with a number of
applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic
OPTIMADE, an API for exchanging materials data
: The Open Databases Integration for Materials Design (OPTIMADE) consortium has designed a universal application programming interface (API) to make materials databases accessible and interoperable. We outline the first stable release of the specification, v1.0, which is already supported by many leading databases and several software packages. We illustrate the advantages of the OPTIMADE API through worked examples on each of the public materials databases that support the full API specification
OPTIMADE, an API for exchanging materials data.
The Open Databases Integration for Materials Design (OPTIMADE) consortium has designed a universal application programming interface (API) to make materials databases accessible and interoperable. We outline the first stable release of the specification, v1.0, which is already supported by many leading databases and several software packages. We illustrate the advantages of the OPTIMADE API through worked examples on each of the public materials databases that support the full API specification
Spin dynamics from time-dependent density functional perturbation theory
We present a new method to model spin-wave excitations in magnetic solids, based on the Liouville-Lanczos approach to time-dependent density functional perturbation theory. This method avoids computationally expensive sums over empty states and naturally deals with the coupling between spin and charge fluctuations, without ever explicitly computing charge-density susceptibilities. Spin-wave excitations are obtained with one Lanczos chain per magnon wave-number and polarization, avoiding the solution of the linear-response problem for every individual value of frequency, as other state-of-the-art approaches do. Our method is validated by computing magnon dispersions in bulk Fe and Ni, resulting in agreement with previous theoretical studies in both cases, and with experiment in the case of Fe. The disagreement in the case of Ni is also comparable with that of previous computations
The GAPS programme with HARPS-N at TNG. X. Differential abundances in the XO-2 planet-hosting binary
Binary stars hosting exoplanets are a unique laboratory where chemical tagging can be performed to measure the elemental abundances of both stellar components with high accuracy, with the aim to investigate the formation of planets and their subsequent evolution. Here, we present a high-precision differential abundance analysis of the XO-2 wide stellar binary based on high-resolution HARPS-N at TNG spectra. Both components are very similar K-dwarfs and host planets. Since they formed presumably within the same molecular cloud, we expect that they possess the same initial elemental abundances. We investigated whether planets can cause some chemical imprints in the stellar atmospheric abundances. We measure abundances of 25 elements for both stars with a range of condensation temperature TC = 40-1741 K, achieving typical precisions of ~0.07 dex. The northern component shows abundances in all elements higher by +0.067 ± 0.032 dex on average, with a mean difference of +0.078 dex for elements with TC > 800 K. The significance of the XO-2N abundance difference relative to XO-2S is at the 2σ level for almost all elements. We discuss that this result might be interpreted as the signature of the ingestion of material by XO-2N or depletion in XO-2S that is due to locking of heavy elements by the planetary companions. We estimate a mass of several tens of M⊕ in heavy elements. The difference in abundances between XO-2N and XO-2S shows a positive correlation with the condensation temperatures of the elements, with a slope of (4.7 ± 0.9) × 10-5 dex K-1, which could mean that both components have not formed terrestrial planets, but first experienced the accretion of rocky core interior to the subsequent giant planets. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the INAF - Fundación Galileo Galilei at the Roche de los Muchachos Observatory of the Instituto de Astrofísica de Canarias (IAC) in the framework of the large programme Global Architecture of Planetary Systems (GAPS; P.I. A. Sozzetti).Final reduced spectra (FITS) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/583/A135</A
VizieR Online Data Catalog: XO-2N and XO-2S spectra (Biazzo+, 2015)
Final reduced spectra used for the elemental abundance measurements. We observed both XO-2 components with the high resolution HARPS-N@TNG (R~115000, λ~3900-6900Å) spectrograph between November 20, 2012 and October 4, 2014. Solar spectra were also obtained through observations of the asteroid Vesta. The spectra reduction was obtained using the 2013 November version of the HARPS-N instrument data reduction software (DRS) pipeline. A detailed description of the observations and data reduction is reported in Paper II (Desidera et al., 2013A&A...554A..29D) (2 data files). <P /
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