Influence of the mixing conditions on the rheological behavior of a biscuit dough

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Active control of a large deformable mirror for future E-ELT

International audienceIncreasing dimensions of ground based telescopes and adaptive optics needs for these instruments require wide deformable mirrors with a high number of actuators to compensate the effects of the atmospheric turbulence on the wave fronts. The new dimensions and characteristics of these deformable mirrors lead to the apparition of structural vibrations, which may reduce the rejection band width of the adaptive optics control loop. The aim of this paper is the study of the dynamic behavior of a 1-meter prototype of E-ELT's deformable mirror in order to identify its eigenmodes and to propose some ways to control its vibrations. We first present the first eigenmodes of the structure determined by both finite element analysis and experimental modal analysis. Then we present the frequency response of the prototype to a tilt excitation to estimate the effects of its vibrations on the adaptive optics loop. Finally we suggest a method to control the dynamics of the deformable mirror

Performance of the Mechanical Structure of the SST-2M GCT Telescope for the Cherenkov Telescope Array

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Performance of the Mechanical Structure of the SST-2M GCT Telescope for the Cherenkov Telescope Array

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Modeling of a large deformable mirror for future E-ELT

International audienceIncreasing dimensions of ground based telescopes while implementing Adaptive Optics systems to cancel both structural deformations and atmospheric effects require very large diameters deformable mirrors (DM) and a high number of actuators with large strokes. This has led for the future E-ELT to a 2.5 m diameter DM getting about 8000 actuators. This paper presents a local and a global model of the DM in order to both study its influence function and its dynamical behavior. In the first part, influence function of the mirror is calculated. Results obtained by an analytical way are compared to those obtained numerically. In the second part, modal analysis of the mirror is presented. Results are limited to the first modes. Modal analysis is also only made for the base plate to derive the specific influence of DM's components on the global dynamic behavior. In the last part, optimization methods are used to help designing a 1 m prototype of the DM

A Langsdorf cloud chamber as a complementary educational material to Cherenkov telescopes for the observation of cosmic rays

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ARENA Solar Astrophysics Working Group Reporting on Dome C Exceptional Potential for Solar Observations

International audienceThe ARENA Solar Astrophysics Working Group (WG6) is reviewing the exceptional site conditions prevailing at Dome C/Concordia making it a unique place on Earth for solar observations: excellent seeing, low sky brightness, low water vapour and high duty cycle. These qualities open science programmes which can combine very high resolution, coronagraphy, infrared access, and long time series (continuity). Major objectives accessible are the chromosphere-corona interface at very high resolution, direct magnetic field measurements in the chromosphere (prominences) and in the corona, 2D imaging spectroscopy and waves. A first mid-size facility is proposed and described, AFSIIC (Antarctica Facility for Solar Interferometric Imaging and Coronagraphy), using 3×Ø50 cm off-axis telescopes (1.4 m equivalent telescope) to access these objectives with the proper flux, angular resolution and coronagraphic potential. Support infrastructure and logistics have been studied and are discussed, noticeably a 30 m tower to place the observatory over the very thin surface turbulent layer of Dome C

SST-GATE telescope: an innovative dual-mirror prototype for the Cherenkov Telescope Array

International audienceThe Observatoire de Paris is involved in the Cherenkov Telescope Array (CTA) project by designing and constructing on the site of Meudon a Small Size Telescope prototype, named SST-GATE, in collaboration with the CHEC team (Compact High Energy Camera) which is providing the camera. The telescope structure is based on the Schwarzschild- Couder optical design which has never been adopted before in the design of a ground-based telescope. This concept allows a larger field of view and cheaper and smaller telescope and camera design with improved performance compared to the Davies-Cotton design traditionally used in very high energy gamma-ray telescopes. The SST-GATE telescope has been designed with the prime objectives of being light, versatile and simple to assemble with a minimal maintenance cost. This papers aims at reviewing the SST-GATE telescope structure from mechanics to optics along with the control command architecture; several innovative developments implemented within the design are discussed. Updates of the project status and perspectives are made