496 research outputs found
Laboratory Testing the Layer Oriented Wavefront Sensor for the Multiconjugate Adaptive optics Demonstrator
The Multiconjugate Adaptive optics Demonstrator (MAD) for ESO-Very Large
Telescopes (VLT) will demonstrate on sky the MultiConjugate Adaptive Optics
(MCAO) technique. In this paper the laboratory tests relative to the first
preliminary acceptance in Europe of the Layer Oriented (LO) Wavefront Sensor
(WFS) for MAD will be described: the capabilities of the LO approach have been
checked and the ability of the WFS to measure phase screens positioned at
different altitudes has been experimented. The LO WFS was opto-mechanically
integrated and aligned in INAF - Astrophysical Observatory of Arcetri before
the delivering to ESO (Garching) to be installed on the final optical bench.
The LO WFS looks for up to 8 reference stars on a 2arcmin Field of View and up
to 8 pyramids can be positioned where the focal spot images of the reference
stars form, splitting the light in four beams. Then two objectives conjugated
at different altitudes simultaneously produce a quadruple pupil image of each
reference star.Comment: 12 pages,14 figures, Proceeding of Spie Conference "Advances in
Adaptive Optics II", Orlando 200
Impact of Sodium Layer variations on the performance of the E-ELT MCAO module
Multi-Conjugate Adaptive Optics systems based on sodium Laser Guide Stars may
exploit Natural Guide Stars to solve intrinsic limitations of artificial
beacons (tip-tilt indetermination and anisoplanatism) and to mitigate the
impact of the sodium layer structure and variability. The sodium layer may also
have transverse structures leading to differential effects among Laser Guide
Stars. Starting from the analysis of the input perturbations related to the
Sodium Layer variability, modeled directly on measured sodium layer profiles,
we analyze, through a simplified end-to-end simulation code, the impact of the
low/medium orders induced on global performance of the European Extremely Large
Telescope Multi-Conjugate Adaptive Optics module MAORY.Comment: 7 pages, 5 figures, SPIE conference Proceedin
Variability of Young Massive Stars in the Arches Cluster
We present preliminary results of the first near-infrared variability study
of the Arches cluster, using adaptive optics data from NIRI/Gemini and
NACO/VLT. The goal is to discover eclipsing binaries in this young (2.5 +- 0.5
Myr), dense, massive cluster for which we will determine accurate fundamental
parameters with subsequent spectroscopy. Given that the Arches cluster contains
more than 200 Wolf-Rayet and O-type stars, it provides a rare opportunity to
determine parameters for some of the most massive stars in the Galaxy.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
A method for space-variant deblurring with application to adaptive optics imaging in astronomy
Images from adaptive optics systems are generally affected by significant
distortions of the point spread function (PSF) across the field of view,
depending on the position of natural and artificial guide stars. Image
reduction techniques circumventing or mitigating these effects are important
tools to take full advantage of the scientific information encoded in AO
images. The aim of this paper is to propose a method for the deblurring of the
astronomical image, given a set of samples of the space-variant PSF. The method
is based on a partitioning of the image domain into regions of isoplanatism and
on applying suitable deconvolution methods with boundary effects correction to
each region. The effectiveness of the boundary effects correction is proved.
Moreover, the criterion for extending the disjoint sections to partially
overlapping sections is validated. The method is applied to simulated images of
a stellar system characterized by a spatially variable PSF. We obtain good
photometric quality, and therefore good science quality, by performing aperture
photometry on the deblurred images. The proposed method is implemented in IDL
in the Software Package "Patch", which is available on
http://www.airyproject.eu.Comment: 11 pages, 9 figures, 7 tables, accepted by A&
Historic evolution of the optical design of the Multi Conjugate Adaptive Optics Relay for the Extremely Large Telescope
The optical design of the Multi Conjugate Adaptive Optics Relay for the
Extremely Large Telescope experienced many modifications since Phase A
conclusion in late 2009. These modifications were due to the evolution of the
telescope design, the more and more accurate results of the performance
simulations and the variations of the opto-mechanical interfaces with both the
telescope and the client instruments. Besides, in light of the optics
manufacturing assessment feed-backs, the optical design underwent to a global
simplification respect to the former versions. Integration, alignment,
accessibility and maintenance issues took also a crucial role in the design
tuning during the last phases of its evolution. This paper intends to describe
the most important steps in the evolution of the optical design, whose
rationale has always been to have a feasible and robust instrument, fulfilling
all the requirements and interfaces. Among the wide exploration of possible
solutions, all the presented designs are compliant with the high-level
scientific requirements, concerning the maximum residual wavefront error and
the geometrical distortion at the exit ports. The outcome of this decennial
work is the design chosen as baseline at the kick-off of the Phase B in 2016
and subsequently slightly modified, after requests and inputs from alignment
and maintenance side
Laser Guide Stars for Extremely Large Telescopes: Efficient Shack-Hartmann Wavefront Sensor Design using Weighted center-of-gravity algorithm
Over the last few years increasing consideration has been given to the study
of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by
the atmosphere in optical and near-infrared astronomical observations from the
ground. A possible method for the generation of a LGS is the excitation of the
Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since
the Sodium layer is approximately 10 km thick, the artificial reference source
looks elongated, especially when observed from the edge of a large aperture.
The spot elongation strongly limits the performance of the most common
wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront
sensor, for instance, decreases proportionally to the elongation (in a photon
noise dominated regime). To compensate for this effect a straightforward
solution is to increase the laser power, i.e. to increase the number of
detected photons per subaperture. The scope of the work presented in this paper
is twofold: an analysis of the performance of the Weighted Center of Gravity
algorithm for centroiding with elongated spots and the determination of the
required number of photons to achieve a certain average wavefront error over
the telescope aperture.Comment: 10 pages, 14 figure
Valorizzazione dell'A. Nodosum tramite tecniche di bioliquefazione: studio e caratterizzazione
Più volte nel corso dell’ ultimo secolo la ricerca si è concentrata sulle alghe brune come piante alimentari dalle quali poter ricavare diversi prodotti. L’obiettivo del presente elaborato è dimostrare come sia possibile valorizzare e caratterizzare l'Ascophyllum nodosum destrutturando il tessuto vegetale attraverso l'utilizzo di biocatalizzatori enzimatici, al fine di liberare composti di interesse specifici da utilizzare in vari ambiti dell'industria (cosmetica, alimentare, agronomica). I risultati rivelano che l’attività alginasica svolge un’importante ruolo nel rilascio di antiossidanti; infatti, la grande quantità di alginati, tipica delle alghe brune, determina il rilascio di componenti chimiche che presentano il maggior potere antiossidante
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