Direct imaging with highly diluted apertures. I. Field of view limitations

Future optical interferometric instrumentation mainly relies on the availability of an efficient cophasing system: once available, what has so far postponed the relevance of direct imaging with an interferometer will vanish. This paper focuses on the actual limits of snapshot imaging, inherent to the use of a sparse aperture: the number of telescopes and the geometry of the array impose the maximum extent of the field of view and the complexity of the sources. A second limitation may arise from the beam combination scheme. Comparing already available solutions, we show that the so called hypertelescope mode (or densified pupil) is ideal. By adjusting the direct imaging field of view to the useful field of view offered by the array, the hypertelescope makes an optimal use of the collected photons. It optimizes signal to noise ratio, drastically improves the luminosity of images and makes the interferometer compatible with coronagraphy, without inducing any loss of useful field of view.Comment: 13 pages, 6 figures, accepted for publication in MNRAS. Full-resolution version available at http://www.obs-hp.fr/~lardiere/publi/2006-Lardiere-MNRAS.pd

Fringe tracking performance monitoring: FINITO at VLTI

Since April 2011, realtime fringe tracking data are recorded simultaneously with data from the VLTI/AMBER interferometric beam combiner. Not only this offers possibilities to post-process AMBER reduced data to obtain more accurate interferometric quantities, it also allows to estimate the performance of the fringe tracking a function of the conditions of seeing, coherence time, flux, etc. First we propose to define fringe tracking performance metrics in the AMBER context, in particular as a function of AMBER's integration time. The main idea is to determine the optimal exposure time for AMBER: short exposures are dominated by readout noise and fringes in long exposures are completely smeared out. Then we present this performance metrics correlated with Paranal local ASM (Ambient Site Monitor) measurements, such as seeing, coherence time or wind speed for example. Finally, we also present some preliminary results of attempts to model and predict fringe tracking performances, using Artificial Neural Networks.Comment: SPIE conference, Optical and Infrared Interferometry II

Direct imaging with highly diluted apertures. II. Properties of the point spread function of a hypertelescope

In the future, optical stellar interferometers will provide true images thanks to larger number of telescopes and to advanced cophasing subsystems. These conditions are required to have sufficient resolution elements (resel) in the image and to provide direct images in the hypertelescope mode. It has already been shown that hypertelescopes provide snapshot images with a significant gain in sensitivity without inducing any loss of the useful field of view for direct imaging applications. This paper aims at studying the properties of the point spread functions of future large arrays using the hypertelescope mode. Numerical simulations have been performed and criteria have been defined to study the image properties. It is shown that the choice of the configuration of the array is a trade-off between the resolution, the halo level and the field of view. A regular pattern of the array of telescopes optimizes the image quality (low halo level and maximum encircled energy in the central peak), but decreases the useful field of view. Moreover, a non-redundant array is less sensitive to the space aliasing effect than a redundant array.Comment: 10 pages paper with referee in A&

Wavefront outer scale deduced from interferometric dispersed fringes

Astronomy and Astrophysics, v. 448, p. 1225-1234, 2006. http://dx.doi.org/10.1051/0004-6361:20052806International audienc

The Measurement Bench for the LHC Spool Corrector Magnets in Industry

The LHC accelerator will be equipped with more than 3500 superconducting spool corrector magnets. CERN has awarded the contract for the series production and testing of these corrector magnets to industry. Magnetic field measurements are done at the factory. Dedicated magnetic measurement benches have been built to test these corrector magnets in the resistive state at room temperature. The benches allow to measure the strength of the main field, normal and skew harmonics, the magnetic axis position and orientation of the main field with respect to the mechanical reference points of the magnet. This paper presents the objectives, a description and the performances obtained with the benches during first measurements at industry

First experimental demonstration of temporal hypertelescope operation with a laboratory prototype

In this paper, we report the first experimental demonstration of a Temporal HyperTelescope (THT). Our breadboard including 8 telescopes is firstly tested in a manual cophasing configuration on a 1D object. The Point Spread Function (PSF) is measured and exhibits a dynamics in the range of 300. A quantitative analysis of the potential biases demonstrates that this limitation is related to the residual phase fluctuation on each interferometric arm. Secondly, an unbalanced binary star is imaged demonstrating the imaging capability of THT. In addition, 2D PSF is recorded even if the telescope array is not optimized for this purpose.Comment: Accepted for publication in MNRAS. 11 pages, 25 figure

RESEARCHES ON ONION AND GARLIC WEED CONTROL

Onion and garlic crops are highly susceptible to weed infestation because theygrow slowly on the first stages and can be easily compromised by weeds. Our study was made at the Didactical research Station of Banu maracine which belongs to the University of Craiova, Romania. We have tried three herbicide active ingredients: metolachlor, pendimetalin and oxyfluorfen. The crops were: sown onion, planted onion and planted garlic. On postemergence we have tried four concentrations of oxyfluoerfen as Goal 2E herbicide. The reason why we tried these substances is that the information on the herbicide leaflet does not provide enough knowledge for postemergent application on sown onion and planted garlic. Our resilts have shown that the sown onion and garlic can not be sprayed by 5 ml in 5 litres water while planted onion resists to even 33 ml in 5 litres water

On the Binarity of LBV Stars

We report on the binarity of luminous blue variable stars observed with a set of techniques and instruments. Among them, observations at high angular resolution with the VLT-NACO, the VLTI-AMBER and with spectrographs such as the VLT-XSHOOTER allowed us to find several LBV stars as binaries or having a potential companion. In particular the LBV Pistol Star clearly presents radial velocity variations and line profiles modifications (double peak appearance). In addition, the absorption component of the P Cygni lines varies as well with the time indicating a potential wind structure variability. Our observations also show directly for the first time a companion to at least one of the observed LBVs (HD 168625). This one seems to affect the environment of the system. This system is known to be surrounded by several rings similar to those of SN1987A, possibly indicating a future supernova occurrence for this Galactic object. These results show that Eta Car is no longer unique

The 10th VLTI School of Interferometry: Premiering a Fully Online Format

International audienceVery Large Telescope Inerferometer (VLTI) schools have nearly a 20-year history and have trained a significant fraction of today's optical interferometrists who use high-angular-resolution techniques on a regular basis. Very early in the development of the VLTI, training was identified by the community as a necessary tool, as the expertise in optical long-baseline interferometry was limited to a few groups in France and Germany (in those early years the UK was not an ESO member state). The first VLTI school took place in Les Houches, France, in 2002 and since then VLTI schools have been organised in several locations (France, Germany, Hungary, Poland, Portugal) roughly every two years, the previous one being held in 2018 in Lisbon. The VLTI schools are funded and coordinated through the European Interferometry Initiative (Eii)

Progress of the CHARA/SPICA project

This is the final version. Available from SPIE via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation conference, 14 - 18 December 2020, Online OnlyCHARA/SPICA (Stellar Parameters and Images with a Cophased Array) is currently being developed at Observatoire de la Cote d'Azur. It will be installed at the visible focus of the CHARA Array by the end of 2021. It has been designed to perform a large survey of fundamental stellar parameters with, in the possible cases, a detailed imaging of the surface or environment of stars. To reach the required precision and sensitivity, CHARA/SPICA combines a low spectral resolution mode R = 140 in the visible and single-mode fibers fed by the AO stages of CHARA. This setup generates additional needs before the interferometric combination: the compensation of atmospheric refraction and longitudinal dispersion, and the fringe stabilization. In this paper, we present the main features of the 6-telescopes fibered visible beam combiner (SPICA-VIS) together with the first laboratory and on-sky results of the fringe tracker (SPICA-FT). We describe also the new fringe-tracker simulator developed in parallel to SPICA-FT.National Science Foundation (NSF)GSU College of Arts and SciencesGSU Office of the Vice President for Research and Economic DevelopmentEuropean Union Horizon 2020Onera’s Direction Scientifique General