273 research outputs found
"Advanced" data reduction for the AMBER instrument
The amdlib AMBER data reduction software is meant to produce AMBER data
products from the raw data files that are sent to the PIs of different
proposals or that can be found in the ESO data archive. The way defined by ESO
to calibrate the data is to calibrate one science data file with a calibration
one, observed as close in time as possible. Therefore, this scheme does not
take into account instrumental drifts, atmospheric variations or
visibility-loss corrections, in the current AMBER data processing software,
amdlib. In this article, we present our approach to complement this default
calibration scheme, to perform the final steps of data reduction, and to
produce fully calibrated AMBER data products. These additional steps include:
an overnight view of the data structure and data quality, the production of
night transfer functions from the calibration stars observed during the night,
the correction of additional effects not taken into account in the standard
AMBER data reduction software such as the so-called "jitter" effect and the
visibility spectral coherence loss, and finally, the production of fully
calibrated data products. All these new features are beeing implemented in the
modular pipeline script amdlibPipeline, written to complement the amdlib
software.Comment: 10 pages, will be published in the proceeding of the SPIE conference
"astronomical Telescopes and Instrumentation: Optical and Infrared
Interferometry", held in Marseille from 23 to 27 june 200
AMBER closure and differential phases: accuracy and calibration with a Beam Commutation
The first astrophysical results of the VLTI focal instrument AMBER have shown
the importance of the differential and closure phase measures, which are
supposed to be much less sensitive to atmospheric and instrumental biases than
the absolute visibility. However there are artifacts limiting the accuracy of
these measures which can be substantially overcome by a specific calibration
technique called Beam Commutation. This paper reports the observed accuracies
on AMBER/VLTI phases in different modes, discusses some of the instrumental
biases and shows the accuracy gain provided by Beam Commutation on the
Differential Phase as well as on the Closure Phase.Comment: This paper will be published in the proceeding of SPIE ``astronomical
Telescopes and Instrumentation: Optical and Infrared Interferometry'
Statistical characterization of polychromatic absolute and differential squared visibilities obtained from AMBER/VLTI instrument
In optical interferometry, the visibility squared modulus are generally
assumed to follow a Gaussian distribution and to be independent of each other.
A quantitative analysis of the relevance of such assumptions is important to
help improving the exploitation of existing and upcoming multi-wavelength
interferometric instruments. Analyze the statistical behaviour of both the
absolute and the colour-differential squared visibilities: distribution laws,
correlations and cross-correlations between different baselines. We use
observations of stellar calibrators obtained with AMBER instrument on VLTI in
different instrumental and observing configurations, from which we extract the
frame-by-frame transfer function. Statistical hypotheses tests and diagnostics
are then systematically applied. For both absolute and differential squared
visibilities and under all instrumental and observing conditions, we find a
better fit for the Student distribution than for the Gaussian, log-normal and
Cauchy distributions. We find and analyze clear correlation effects caused by
atmospheric perturbations. The differential squared visibilities allow to keep
a larger fraction of data with respect to selected absolute squared
visibilities and thus benefit from reduced temporal dispersion, while their
distribution is more clearly characterized. The frame selection based on the
criterion of a fixed SNR value might result in either a biased sample of frames
or in a too severe selection.Comment: A&A, 13 pages and 9 figure
Three recipes for improving the image quality with optical long-baseline interferometers: BFMC, LFF, \& DPSC
We present here three recipes for getting better images with optical
interferometers. Two of them, Low- Frequencies Filling and Brute-Force Monte
Carlo were used in our participation to the Interferometry Beauty Contest this
year and can be applied to classical imaging using V 2 and closure phases.
These two addition to image reconstruction provide a way of having more
reliable images. The last recipe is similar in its principle as the
self-calibration technique used in radio-interferometry. We call it also
self-calibration, but it uses the wavelength-differential phase as a proxy of
the object phase to build-up a full-featured complex visibility set of the
observed object. This technique needs a first image-reconstruction run with an
available software, using closure-phases and squared visibilities only. We used
it for two scientific papers with great success. We discuss here the pros and
cons of such imaging technique.Comment: 9 pages, to be published in SPIE proceedings; Optical and Infrared
Interferometry III, Amsterdam : Netherlands (2012
Impact des véhicules électrifiés sur le dimensionnement du réseau HTA
Le développement annoncé des Véhicules Electriques et des Véhicules Hybrides Rechargeables va augmenter la consommation électrique, notamment dans le secteur résidentiel, ainsi que les pertes dans les lignes. Cette augmentation doit être prise en compte dans le dimensionnement de la section des conducteurs. En effet, un gestionnaire de réseau de distribution dimensionne celle-ci en cherchant l'optimum économique entre le coût du matériau conducteur et le coût des pertes par effet Joule capitalisées sur la durée de vie de la ligne. Dans cette contribution, nous estimons ce nouvel optimum et le surcoût engendré par la pénétration de véhicules électrifiés pour une ligne HTA. Nous montrons que ce surcoût peut être réduit en choisissant des profils de recharge adaptés. Ensuite une étude de la sensibilité du résultat aux paramètres montre que parmi ceux-ci, le choix du taux d'actualisation des pertes futures est prépondérant. Enfin est évalué l'impact de la production photovoltaïque distribuée sur le dimensionnement. Les résultats montrent que l'impact des véhicules électrifiés est environ 4 fois plus important que l'impact de la production photovoltaïque
The 2010 Interferometric Imaging Beauty Contest
We present the results of the fourth Optical/IR Interferometry Imaging Beauty
Contest. The contest consists of blind imaging of test data sets derived from
model sources and distributed in the OI-FITS format. The test data consists of
spectral data sets on an object "observed" in the infrared with spectral
resolution. There were 4 different algorithms competing this time: BSMEM the
Bispectrum Maximum Entropy Method by Young, Baron & Buscher; RPR the Recursive
Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo
algorithm by Baron, Monnier & Kloppenborg; and, WISARD the Weak-phase
Interferometric Sample Alternating Reconstruction Device by Vannier & Mugnier.
The contest model image, the data delivered to the contestants and the rules
are described as well as the results of the image reconstruction obtained by
each method. These results are discussed as well as the strengths and
limitations of each algorithm.Comment: To be published in SPIE 2010 "Optical and infrared interferometry II
PAINTER: a spatio-spectral image reconstruction algorithm for optical interferometry
International audienceAstronomical optical interferometers sample the Fourier transform of the intensity distribution of a source at the observation wavelength. Because of rapid perturbations caused by atmospheric turbulence, the phases of the complex Fourier samples (visibilities) cannot be directly exploited. Consequently, specific image reconstruction methods have been devised in the last few decades. Modern polychromatic optical interferometric instruments are now paving the way to multiwave-length imaging. This paper is devoted to the derivation of a spatio-spectral ("3D") image reconstruction algorithm, coined PAINTER (Polychromatic opticAl INTErferometric Reconstruction software). The algorithm relies on an iterative process, which alternates estimation of polychromatic images and of complex visibilities. The complex visibilities are not only estimated from squared moduli and closure phases, but also differential phases, which helps to better constrain the polychromatic reconstruction. Simulations on synthetic data illustrate the efficiency of the algorithm and in particular the relevance of injecting a differential phases model in the reconstruction
Estimating the phase in ground-based interferometry: performance comparison between single-mode and multimode schemes
In this paper we compare the performance of multi and single-mode
interferometry for the estimation of the phase of the complex visibility. We
provide a theoretical description of the interferometric signal which enables
to derive the phase error in presence of detector, photon and atmospheric
noises, for both multi and single-mode cases. We show that, despite the loss of
flux occurring when injecting the light in the single-mode component (i.e.
single-mode fibers, integrated optics), the spatial filtering properties of
such single-mode devices often enable higher performance than multimode
concepts. In the high flux regime speckle noise dominated, single-mode
interferometry is always more efficient, and its performance is significantly
better when the correction provided by adaptive optics becomes poor, by a
factor of 2 and more when the Strehl ratio is lower than 10%. In low light
level cases (detector noise regime), multimode interferometry reaches better
performance, yet the gain never exceeds 20%, which corresponds to the
percentage of photon loss due to the injection in the guides. Besides, we
demonstrate that single-mode interferometry is also more robust to the
turbulence in both cases of fringe tracking and phase referencing, at the
exception of narrow field of views (<1 arcsec).Comment: 9 pages (+ 11 online material appendices) -- 8 Figures. Accepted in
A&
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