Pupil plane optimization for single-mode multiaxial optical interferometry with a large number of telescopes

Incoming optical interferometers will allow spectro-imaging at high angular resolution. Non-homothetic Fizeau concept combines good sensitivity and high spectral resolution capabilities. However, one critical issue is the design of the beam recombination scheme, at the heart of the instrument. We tackle the possibility of reducing the number of pixels that are coding the fringes by compressing the pupil plane. Shrinking the number of pixels -- which drastically increases with the number of recombined telescopes -- is indeed a key issue that enables to reach higher limiting magnitude, but also allows to lower the required spectral resolution and fasten the fringes reading process. By means of numerical simulations, we study the performances of existing estimators of the visibility with respect to the compression process. We show that, not only the model based estimator lead to better signal to noise ratio (SNR) performances than the Fourier ones, but above all it is the only one which prevent from introducing baseline mixing biases in the visibilities as the pupil plane compression rate increases. Furthermore, we show that moderate compression allows to keep the visibilities SNR unaffected. In the light of these conclusions, we propose an optimized pupil arrangements for 6 and 8 beam recombiners

First astrophysical results from AMBER/VLTI

The AMBER instrument installed at the Very Large Telescope (VLT) combines three beams from as many telescopes to produce spectrally dispersed fringes from milli-arcsecond angular scale in the near infrared. Two years after installation, first scientific observations have been carried out during the Science Demonstration Time and the Guaranteed Time mostly on bright sources due to some VLTI limitations. In this paper, we review these first astrophysical results and we show which types of completely new information is brought by AMBER. The first astrophysical results have been mainly focusing on stellar wind structure, kinematics, and its interaction with dust usually concentrated in a disk. Because AMBER has dramatically increased the number of measures per baseline, this instrument brings strong constraints on morphology and models despite a relatively poor (u, v) coverage for each object.Comment: SPIE 6268 proceeding

VITRUV - Imaging close environments of stars and galaxies with the VLTI at milli-arcsec resolution

The VITRUV project has the objective to deliver milli-arcsecond spectro-images of the environment of compact sources like young stars, active galaxies and evolved stars to the community. This instrument of the VLTI second generation based on the integrated optics technology is able to combine from 4 to 8 beams from the VLT telescopes. Working primarily in the near infrared, it will provide intermediate to high spectral resolutions and eventually polarization analysis. This paper summarizes the result from the concept study led within the Joint Research Activity advanced instruments of the OPTICON program.Comment: In "The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation VLTI Instrumentation", Allemagne (2005) in pres

The planar optics phase sensor: a study for the VLTI 2nd generation fringe tracker

In a few years, the second generation instruments of the Very Large Telescope Interferometer (VLTI) will routinely provide observations with 4 to 6 telescopes simultaneously. To reach their ultimate performance, they will need a fringe sensor capable to measure in real time the randomly varying optical paths differences. A collaboration between LAOG (PI institute), IAGL, OCA and GIPSA-Lab has proposed the Planar Optics Phase Sensor concept to ESO for the 2[SUP]nd[/SUP] Generation Fringe Tracker. This concept is based on the integrated optics technologies, enabling the conception of extremely compact interferometric instruments naturally providing single-mode spatial filtering. It allows operations with 4 and 6 telescopes by measuring the fringes position thanks to a spectrally dispersed ABCD method. We present here the main analysis which led to the current concept as well as the expected on-sky performance and the proposed design

An asymmetry detected in the disk of Kappa CMa with the AMBER/VLTI

International audienceAims. We study the geometry and kinematics of the circumstellar environment of the Be star Kappa CMa in the Br gamma emission line and its nearby continuum. Methods. We use the VLTI/AMBER instrument operating in the K band which provides a spatial resolution of about 6 mas with a spectral resolution of 1500 to study the kinematics within the disk and to infer its rotation law. In order to obtain more kinematical constraints we also use an high spectral resolution Pa beta line profile obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and we compile V/R line profile variations and spectral energy distribution data points from the literature. Results. Using differential visibilities and differential phases across the Br gamma line we detect an asymmetry in the disk. Moreover, we found that kappa CMa seems difficult to fit within the classical scenario for Be stars, illustrated recently by alpha Arae observations, i.e. a fast rotating B star close to its breakup velocity surrounded by a Keplerian circumstellar disk with an enhanced polar wind. Finally we discuss the possibility for kappa CMa to be a critical rotator with a Keplerian rotating disk and try to see if the detected asymmetry can be interpreted within the "one-armed" viscous disk framework

Traitement du signal en interferometrie monomode dans le cadre du projet AMBER. Application a l'observation interferometrique de l'environnement > circumstellaire des etoiles jeunes

Recent progresses of optical interferometry, in terms of spatial resolution, sensitivity and precision of the measurements, made this technique particularly well suited to study the close environment of young stars which hold the keys of stellar and planet formation. As a matter of fact, the first interferometric observations have unveiled many essential informations on the physical nature of the surrounding structure of these objects. The AMBER instrument, the near infrared three beams recombiner of the Very Large Telescope Interferometer (VLTI), will, by pioneering the era of interferometric imaging with both very high spatial and spectral resolution, allow to move one step forward in the understanding of the physical processes governing these stars. This work is organized around the AMBER instrument. After summarizing the general principles of optical interferometry in presence of atmospheric turbulence, I show why introducing waveguides in the recombination scheme allows, by taking advantage of their properties of spatial filtering, to increase the precision and the robustness of the measurements. From this theoretical basis, I then develop the AMBER data reduction procedures, with stressing the innovative specificities of the interferometric signal processing. The algorithms have been tested and validated though simulations and then applied to the observation of the Herbig Be star MWC 297 in medium spectral resolution. This young star presents a strong emission line due to the atomic transition of the hydrogen $\mathrm(Br)\gamma$. The study confirms the existence of an accretion disk around the star and reveal the presence of an atmospherical envelope, twice as broad as the disk, where the atomic transitions of the hydrogen occurs. At last, I analyze in a theoretical framework the methods that investigate the astrophysical parameters of a source observed with single mode interferometers, such as model fitting and image reconstruction techniques. I particularly emphasize the issues that restrain the capacity of AMBER to image circumstellar environment of young stars.Les recents progres de l'interferometrie optique, en termes de resolution spatiale, de sensibilite et de precision des mesures, ont rendu cette technique particulierement bien adaptee a l'etude de l'environnement proche des etoiles jeunes, etoiles qui possedent en leur sein les cles de la formation stellaire et planetaire. De fait, les premieres observations interferometriques ont revele nombre d'informations essentielles sur la nature de la structure etendue entourant ces objets. L'instrument AMBER, le recombinateur proche infra-rouge 3 telescopes du Very Large Telescope Interferometer (VLTI), va, en inaugurant l'ere de l'imagerie interferometrique a tres haute resolution spatiale et spectrale, permettre de franchir une nouvelle etape dans la comprehension des processus physiques regissant ces etoiles. Cette these s'articule autour de l'instrument AMBER. Apres un resume des principes generaux de l'interferometrie optique en presence de turbulence atmospherique, je montre en quoi l'introduction de guides d'ondes dans le schema de recombinaison permet, en utilisant leurs proprietes de filtrage spatial, d'augmenter la precision et la robustesse des mesures. Partant de ces bases theoriques, je developpe ensuite les procedures de reduction de donnees AMBER,soulignant les points specifiques et novateurs concernant le traitement du signal interferometrique. Ces algorithmes ont ete testes et valides a partir de simulations, puis appliques aux mesures a moyenne resolution spectrale de l'etoile de Herbig Be MWC 297, qui presente une forte raie d'emission relative a la transition atomique de l'hydrogene Brackett gamma. Cette etude confirme l'existence d'un disque d'accretion autour de l'etoile et met en evidence la presence d'une enveloppe atmospherique deux fois plus etendue correspondant a la raie d'hydrogene. Enfin j'analyse dans un contexte theorique global, les methodes d'investigation des parametres astrophysiques d'une source observee avec un interferometre optique monomode, respectivement par ajustement de modeles et par reconstruction d'images. Je repertorie notamment les difficultes majeures limitant les capacites d'AMBER en tant qu'imageur de l'environnement circumstellaire des etoiles jeunes

Feature extraction using multimodal convolutional neural networks for visual speech recogntiion

International audienc

Prise en charge de la fibrillation auriculaire en médecine générale

MONTPELLIER-BU Médecine UPM (341722108) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF