75 research outputs found
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
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