Search

A status overview of 4MOST is presented, a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's VISTA telescope at Paranal. Its key specifications are: a large field of view of 4.4 deg2 and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). The 4MOST system integration has commenced and the selection process for ESO community survey programmes has been started. This overview presents the expected performance of the instrument, the science the consortium expects to carry out, and the unique operational scheme of 4MOST.

The 4MOST([1]) instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the ESO VISTA telescope designed to perform a massive (initially >25x10(6) spectra in 5 years) combined all-sky public survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of galaxies, X-ray AGN/galaxy evolution to z similar to 5, Galactic X-ray sources and resolving the Galactic edge; Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of similar to 1600 targets at R similar to 5,000 from 390-900nm and similar to 800 targets at R>18,000 in three channels between similar to 395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of similar to 4.1 degrees2. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: opto-mechanical, control, data management and operations concepts; and initial performance estimates.

Polarimetry is a particularly powerful technique when imaging circumstellar environments. Currently most telescopes include more or less advanced polarimetric facilities and large telescopes count on it for their planet-finder instruments like SPHERE-ZIMPOL on the VLT or EPICS on the future E-ELT. One of the biggest limitations of this technique is the instrumental polarization (IP) generated in the telescope optical path, which can often be larger than the signal to be measured. In most cases this instrumental polarization changes over time and is dependent on the errors affecting the optical elements of the system. We have modeled the VLT and E-ELT telescope layouts to characterize the instrumental polarization generated on their optical paths using the M&m's code, an error budget and performance simulator for polarimetric systems. In this study we present the realistic Mueller matrices calculated with M&m's for both systems, with and without the setups to correct for the IP, showing that correction can be achieved, allowing for an accurate polarimetric performance.

MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) will be a mid-infrared spectro-interferometer combining the beams of up to four telescopes of the European Southern Observatory Very Large Telescope Interferometer (ESO VLTI), providing phase closure and image reconstruction. Matisse will produce interferometric spectra in the LM and in the N band (2.3 to 13.5 micron) and is as such a successor of MIDI. The instrument will be developed by a consortium consisting of Observatoire de Nice (warm optics), NOVA-ASTRON (cold optics), MPI-A (cryostats) and MPIfR (detectors). Beams of up to four Unit Telescopes or Auxiliary Telescopes (UT - AT) pass the warm pre-optics and in the cold optics all beams recombine on the detector where they create a spectral interference pattern. An innovative MAIT plan drastically shortens the MAIT phase and therefore reduces cost. The MAIT plan comprises the assembly and alignment procedure of about 220 cryogenic optical components for which a mirror mount clip has been developed. Alignment accuracy and stability specifications are of the order of nanometers and arcsec, which requires over 50 degrees of freedom in cryogenic alignment mechanisms for e.g. Tip/Tilt and detector Tip/Tilt/Focus. The design, realization and test results of these mechanisms are presented. A cryogenic electrical switch significantly reduces the complexity of the electronic cabling and improves reliability.

This paper presents the specifications, design, construction and evaluation of a piezo-driven tip/tilt/focus mechanism which can align a detector or any other optical component in a cryogenic environment. Even with a no-adjustment design philosophy, usually one or two components have to be adjusted in order to compensate for the total of optical and mechanical tolerances in an optical cryogenic instrument. Normally these adjustments are made by means of shims or stiff screw mechanisms and are applied at room temperature. In order to adjust the particular component(s), mostly by just a few microns, the high-risk and time-consuming operation of opening a cryostat is required. For a large cryostat the typical cycle of cooling, testing, warm-up, opening, adjustment, closing and cooling again, takes roughly two weeks. Often the cycle needs to be repeated a few times before the required position is obtained. ASTRON developed a piezo driven tip/tilt/focus mechanism which can adjust a detector or any other optical component in both the ambient and cryogenic (

During the last ten years, Astron has been a major contractor for the design and manufacturing of astronomical instruments for Space- and Earth based observatories, such as VISIR, MIDI, SPIFFI, X-Shooter and MIRI. Driven by the need to reduce the weight of optically ultra-stiff structures, two promising techniques have been developed in the last years: ASTRON Extreme Lightweighting [1][2] for mechanical structures and an improved Polishing Technique for Aluminum Mirrors. Using one single material for both optical components and mechanical structure simplifies the design of a cryogenic instrument significantly, it is very beneficial during instrument test and verification, and makes the instrument insensitive to temperature changes. Aluminum has been the main material used for cryogenic optical instruments, and optical aluminum mirrors are generally diamond turned. The application of a polishable hard top coating like nickel removes excess stray light caused by the groove pattern, but limits the degree of lightweighting of the mirrors due to the bi-metal effect. By directly polishing the aluminum mirror surface, the recent developments at Astron allow for using a non-exotic material for light weighted yet accurate optical mirrors, with a lower surface roughness (~1nm RMS), higher surface accuracy and reduced light scattering. This paper presents the techniques, obtained results and a global comparison with alternative lightweight mirror solutions. Recent discussions indicate possible extensions of the extreme light weight technology to alternative materials such as Zerodur or Silicon Carbide.

The SPHERE is an exo-solar planet imager, which goal is to detect giant exo-solar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made of an extreme-Adaptive Optics (AO) turbulence correction, pupil tracker and interferential coronagraphs. At its back end, an Infra-Red Dual-beam Imaging and Spectroscopy science module and an integral field spectrograph work in the Near Infrared (NIR) Y, J, H and Ks bands (0.95 - 2.32μm) and a high resolution polarization camera covers the visible (0.6 - 0.9 μm) region. We describe briefly the science goals of the instrument and deduce the top-level requirements. This paper presents the system architecture, and reviews each of the main sub-systems. The results of the latest end-to-end simulations are shown and an update of the expected performance is given. The project has been officially kicked-off in March 2006, it is presently undergoing Preliminary Design Review and is scheduled for 1st light in early 2011. This paper reviews the present design of SPHERE but focuses on the changes implemented since this project was presented the last time to this audience.

The GLAS (Ground-layer Laser Adaptive-optics System) project is to construct a common-user Rayleigh laser beacon that will work in conjunction with the existing NAOMI adaptive optics system, instruments (near IR imager INGRID, optical integral field spectrograph OASIS, coronagraph OSCA) and infrastructure at the 4.2-m William Herschel Telescope (WHT) on La Palma. The laser guide star system will increase sky coverage available to high-order adaptive optics from ~1% to approaching 100% and will be optimized for scientific exploitation of the OASIS integral-field spectrograph at optical wavelengths. Additionally GLAS will be used in on-sky experiments for the application of laser beacons to ELTs. This paper describes the full range of engineering of the project ranging through the laser launch system, wavefront sensors, computer control, mechanisms, diagnostics, CCD detectors and the safety system. GLAS is a fully funded project, with final design completed and all equipment ordered, including the laser. Integration has started on the WHT and first light is expected summer 2006.

SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. SPHERE commissioning is foreseen in 2013 on the VLT. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light (600-900 nm) from extrasolar planets. It is located behind an extreme AO system (SAXO) and a stellar coronagraph. We present the first high contrast polarimetric results obtained for the fully integrated SPHERE-ZIMPOL system. We have measured the polarimetric high contrast performance of several coronagraphs: a Classical Lyot on substrate, a suspended Classical Lyot and two 4 Quadrant Phase Mask coronagraphs. We describe the impact of crucial system parameters – Adaptive Optics, Coronagraphy and Polarimetry - on the contrast performance.

We present an overview of the 4MOST project at the Preliminary Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of ESO. 4MOST has a broad range of science goals ranging from Galactic Archaeology and stellar physics to the high-energy physics, galaxy evolution, and cosmology. Starting in 2021, 4MOST will deploy 2436 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. The fibres will feed one high-resolution (R similar to 20,000) and two medium-resolution (R similar to 5000) spectrographs with fixed 3-channel designs and identical 6k x 6k CCD detectors. 4MOST will have a unique operations concept in which 5-year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept, showing that we can expect to observe more than 25 million objects in each 5-year survey period and will eventually be used to plan and conduct the actual survey.