We introduced the use of Artificial Neural Networks (ANN) for centroiding in Shack-Hartmann wavefront sensors in the presence of elongated spots, as it will occur in Extremely Large Telescopes. We showed in simulation that ANNs can outperform existing techniques, such as the Matched Filter. The main advantage of our technique is its ability to cope with changing conditions, as real atmospheric turbulence behaves. Here we present experimental results from the laboratory that confirm the findings in our original article, while at the same time they are useful to refine the ANN-based techniques.
FIDEOS (FIbre Dual Echelle Optical Spectrograph) is a fibre-fed bench-mounted high-resolution echelle spec- trograph for the 1-m telescope at ESO in La Silla, Chile. It is based on a 44.41 lines/mm 70° blaze angle
echelle grating in quasi-Littrow mode, providing spectral resolution of R ~ 42 000, covering the spectral range from 400 nm to 680 nm. The detector is a 2k×2k CCD with 15 μm pixels. The spectrograph will be fed by two 50
µm core diameter fibres for the astronomical object and the simultaneous calibration lamp, respectively. Alter- natively, an iodine cell will be mounted on the telescope-spectrograph interface, providing a secondary spectral calibration source. In addition, the instrument will be mounted on a fixed optical-bench without movable parts rather than the CCD shutter and its enclosure will be thermally controlled to ensure opto-mechanical stability. Since the FIDEOS will deliver high resolution and spectral stability, it will be optimized for precision radial velocities.
Free-atmosphere, and surface-layer optical-turbulence have been extensively monitored over the years. The
optical-turbulence inside a telescope enclosure en the other hand has yet to be as fully characterized. For this
latest purpose, an experimental concept, LOTUCE (LOcal TUrbulenCe Experiment) has been developed in
order to measure and characterise the so-called dome-seeing. LOTUCE2 is an upgraded prototype whose main
aim is to measure optical turbulence characteristics more precisely by minimising cross-contamination of signals.
This characterisation is both quantitative (optical turbulence strength) and qualitative (assessing the optical
turbulence statistical model). We present the new opto-mechanical design, with the theoretical capabilities and
limitations to the actual models.
The Durham adaptive Optics Real Time Controller (DARC)1 is a real-time system for astronomical adaptive optics systems originally developed at Durham University and in use for the CANARY instrument. One of its main strengths is to be a generic and high performance real-time controller running on an off-the-shelf Linux computer. We are using DARC for two different implementations: BEAGLE,2 a Multi-Object AO (MOAO) bench system to experiment with novel tomographic reconstructors and LOTUCE2,3 an in-dome turbulence instrument. We present the software architecture for each application, current benchmarks and lessons learned for current and future DARC developers.
We present the optical concept and design of a fiber-fed echelle spectrograph for precise radial velocity measurements in the near-infrared. The spectrograph is designed to achieve a nominal resolution λ/Δλ of the order of 40000 and to cover the range from 0.9μm to 1.7μm in a single exposure. This spectrum is to be recorded on a 2048×2048 infrared detector. The instrument is designed to be mounted at 1 to 2 m class telescopes for survey purposes. We present in the optical design and the instrument capability. We do emphasis particularly on optical aberrations and thus discuss the instrument expected limitations from the optical viewpoint.
The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The
optimization of the performances of these techniques requires a precise specification of the different components
of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly
the structure constante of the refractive index C2n(h) and the outer scale L0(h). New techniques based on the moon limb observation for the monitoring of the C2n(h) and L0(h) profiles with high vertical resolution will be
In this paper the Paranal Surface Layer characterization is presented. Causes, physics and behavior of the SL above
Paranal surface are discussed. The analysis is developed using data from different turbulence profilers operated during
several campaigns between 2007 and 2009. Instruments used are SL-SLODAR, DIMM, Elevated DIMM, MASS, Lunar
Scintillometer and Ultrasonic Anemometers with temperature sensors positioned at different strategic heights.
Between February and April 2009 a number of ultrasonic anemometers, temperature probes and dust sensors were
operated inside the CTIO Blanco telescope dome. These sensors were distributed in a way that temperature and
3 dimensional wind speeds were monitored along the line of sight of the telescope. During telescope operations,
occasional seeing measurements were obtained using the Mosaic CCD imager and the CTIO site monitoring MASS-DIMM
system. In addition, also a Lunar Scintillometer (LuSci) was operated over the course of a few nights inside the
dome. We describe the instrumental setup and first preliminary results on the linkage of the atmospheric conditions
inside the dome to the overall image quality.
MooSci is a linear array of photodiodes that measures time varying intensities of light reflected from the Moon, lunar
scintillation. The covariance between all possible pairs of photodiodes can be used to reconstruct the ground layer
turbulence profile from the ground up to a maximum height roughly determined by the distance between the furthest pair
of detectors. This technique of profile restoration will be used for site testing at various locations. This paper describes
the design of a lunar scintillometer and preliminary results from Las Campanas Peak.
High angular resolution observations of the sun are limited by atmospheric turbulence. The MISOLFA seeing monitor (still under construction) is developed to obtain spatial and temporal statistical properties of optical turbulence by analyzing local motions observed on solar edge images. The solar flying shadows used for angle-of-arrival spatio-temporal analysis are observed in the pupil plane image by mean of a rectangular thin slit positioned on the solar edge image. A numerical simulation of the light propagation in both the atmospheric turbulence medium and the MISOLFA optical system is carried out studying the relation of the measured intensity variations in the pupil plane to angle-of-arrival fluctuations in the non-isoplanatic case. First results are presented and discussed.