Testing the validity of the ray-tracing code GYOTO

In the next few years, the near-infrared interferometer GRAVITY will be able to observe the Galactic center. Astrometric data will be obtained with an anticipated accuracy of 10 $\mu$as. To analyze these future data, we have developed a code called GYOTO to compute orbits and images. We want to assess the validity and accuracy of GYOTO in a variety of contexts, in particular for stellar astrometry in the Galactic center. Furthermore, we want to tackle and complete a study made on the astrometric displacements that are due to lensing effects of a star of the central parsec with GYOTO. We first validate GYOTO in the weak-deflection limit (WDL) by studying primary caustics and primary critical curves obtained for a Kerr black hole. We compare GYOTO results to available analytical approximations and estimate GYOTO errors using an intrinsic estimator. In the strong-deflection limit (SDL), we choose to compare null geodesics computed by GYOTO and the ray-tracing code named Geokerr. Finally, we use GYOTO to estimate the apparent displacements of a star for different angles from Sagittarius A* (Sgr A*). We have demonstrated that GYOTO is accurate to a very high level, orders of magnitude better than the GRAVITY requirements. GYOTO is also valid in weak- and strong-deflection regimes and for very long integrations. At the astrometric precision that GRAVITY is aiming for, lensing effects must always be taken into account when fitting stellar orbits in the central parsec of the Galaxy.Comment: 11 pages, 12 figure

The GRAVITY instrument software / High-level software

GRAVITY is the four-beam, near- infrared, AO-assisted, fringe tracking, astrometric and imaging instrument for the Very Large Telescope Interferometer (VLTI). It is requiring the development of one of the most complex instrument software systems ever built for an ESO instrument. Apart from its many interfaces and interdependencies, one of the most challenging aspects is the overall performance and stability of this complex system. The three infrared detectors and the fast reflective memory network (RMN) recorder contribute a total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data per night. The detectors, the two instrument Local Control Units (LCUs) as well as the five LCUs running applications under TAC (Tools for Advanced Control) architecture, are interconnected with fast Ethernet, RMN fibers and dedicated fiber connections as well as signals for the time synchronization. Here we give a simplified overview of all subsystems of GRAVITY and their interfaces and discuss two examples of high-level applications during observations: the acquisition procedure and the gathering and merging of data to the final FITS file.Comment: 8 pages, 7 figures, published in Proc. SPIE 9146, Optical and Infrared Interferometry IV, 91462

Multiple star systems in the Orion nebula

This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge

Elaboration et caractérisation de revêtements base Ni, obtenus par projection, pour outils de coupe agricoles

Driven by technological and demographic development, farms have evolved and agricultural equipment has improved. The machines are heavily used and maintenance operations are limited. As cutting tools are wearing parts, their durability has become a strategic issue. The application of Cermet composite coating is then widely used industrially, in particular by flame-powder spraying. To improve the performance of the tools, this study aims to increase the resistance of this coating to the degradation mechanisms. The laser cladding technology which can applying coatings with high carbide content has great potential. A comparison is made between the two deposition technologies, then a parametric study is carried out on the powder applied by laser cladding. The effect of the composition of the NiCrBSi matrix, the bulk density of the tungsten carbide powder, its mass ratio and its particle size are studied on the physicochemical, mechanical, tribological and functional properties of the coatings. Laser technology prevents carbide decarburization, refines the matrix structure and promotes intermetallic phase precipitation over flame - powder spraying without a clear improvement in deposit strength. The parametric study showed that the use of a dense and hard carbide powder, a carbide mass content of 50% and a fine particle size improves the resistance of the coating during friction and cutting tests.Sous l’impulsion du développement technologique et démographique, les exploitations agricoles ont évolué et les équipements agricoles se sont perfectionnés. Les machines sont fortement sollicitées, ainsi la durabilité des outils de coupe étant des pièces d’usure est devenue un enjeu stratégique. L’application d’un revêtement Cermet (céramique-metal) est alors largement utilisée industriellement, notamment par projection flamme-poudre. Dans une optique d’amélioration de la performance des outils, cette étude vise à augmenter la résistance de ce revêtement. La technologie de rechargement laser, qui permet d’appliquer des revêtements à forte teneur en carbure dans une matrice nickel, présente un fort potentiel. Un comparatif est réalisé entre les deux technologiques de dépôt, puis, une étude paramétrique est menée sur la poudre appliquée par rechargement laser. Les effets de la composition de la matrice, de la densité apparente de la poudre de carbure de tungstène, de sa proportion massique et de sa granulométrie sur les propriétés physico – chimiques, mécaniques, tribologiques et fonctionnelles des revêtements sont étudiés. Le laser prévient la décarburation, affine la microstructure et favorise la précipitation de phases intermétalliques par rapport à la flamme sans amélioration claire de la résistance du dépôt. L’étude paramétrique a montré que l’utilisation d’une poudre de carbure dense et dure, une teneur massique en carbure de 50 % et une granulométrie fine améliore la résistance du revêtement lors des essais de frottement et de coupe

Development and characterization of sprayed Ni based coatings, for agricultural cutting tools

Sous l’impulsion du développement technologique et démographique, les exploitations agricoles ont évolué et les équipements agricoles se sont perfectionnés. Les machines sont fortement sollicitées, ainsi la durabilité des outils de coupe étant des pièces d’usure est devenue un enjeu stratégique. L’application d’un revêtement Cermet (céramique-metal) est alors largement utilisée industriellement, notamment par projection flamme-poudre. Dans une optique d’amélioration de la performance des outils, cette étude vise à augmenter la résistance de ce revêtement. La technologie de rechargement laser, qui permet d’appliquer des revêtements à forte teneur en carbure dans une matrice nickel, présente un fort potentiel. Un comparatif est réalisé entre les deux technologiques de dépôt, puis, une étude paramétrique est menée sur la poudre appliquée par rechargement laser. Les effets de la composition de la matrice, de la densité apparente de la poudre de carbure de tungstène, de sa proportion massique et de sa granulométrie sur les propriétés physico – chimiques, mécaniques, tribologiques et fonctionnelles des revêtements sont étudiés. Le laser prévient la décarburation, affine la microstructure et favorise la précipitation de phases intermétalliques par rapport à la flamme sans amélioration claire de la résistance du dépôt. L’étude paramétrique a montré que l’utilisation d’une poudre de carbure dense et dure, une teneur massique en carbure de 50 % et une granulométrie fine améliore la résistance du revêtement lors des essais de frottement et de coupe.Driven by technological and demographic development, farms have evolved and agricultural equipment has improved. The machines are heavily used and maintenance operations are limited. As cutting tools are wearing parts, their durability has become a strategic issue. The application of Cermet composite coating is then widely used industrially, in particular by flame-powder spraying. To improve the performance of the tools, this study aims to increase the resistance of this coating to the degradation mechanisms. The laser cladding technology which can applying coatings with high carbide content has great potential. A comparison is made between the two deposition technologies, then a parametric study is carried out on the powder applied by laser cladding. The effect of the composition of the NiCrBSi matrix, the bulk density of the tungsten carbide powder, its mass ratio and its particle size are studied on the physicochemical, mechanical, tribological and functional properties of the coatings. Laser technology prevents carbide decarburization, refines the matrix structure and promotes intermetallic phase precipitation over flame - powder spraying without a clear improvement in deposit strength. The parametric study showed that the use of a dense and hard carbide powder, a carbide mass content of 50% and a fine particle size improves the resistance of the coating during friction and cutting tests

CARIM – Profil Migratoire : Algérie

Written on the basis of CARIM database and publicationsEcrit à partir de la base de données du CARIM et de ses publicationsEuro-Mediterranean Consortium for Applied Research on International Migration (CARIM)CARIM is co-financed by the European University Institute and the European UnionCARIM est co-financé par l'Institut Universitaire Européen et l'Union Européenn

CARIM – Profil Migratoire : Niger

Written on the basis of CARIM database and publicationsEcrit à partir de la base de données du CARIM et de ses publicationsEuro-Mediterranean Consortium for Applied Research on International Migration (CARIM)CARIM is co-financed by the European University Institute and the European UnionCARIM est co-financé par l'Institut Universitaire Européen et l'Union Européenn