Mathieu Cohen

The 4MOST instrument concept overview

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 >25x106 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~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 ~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical, control, data management and operations concepts; and initial performance estimates.

4MOST-4-metre Multi-Object Spectroscopic Telescope

4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with ~2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; ~1600 fibres go to two spectrographs with resolution R<5000 (λ~390-930 nm) and ~800 fibres to a spectrograph with R>18,000 (λ~392-437 nm and 515-572 nm and 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an 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, resulting in more than 25 million spectra of targets spread over a large fraction of the southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020. This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7].

ATLAS: the E-ELT laser tomographic adaptive optics system

ATLAS is a generic Laser Tomographic AO (LTAO) system for the E-ELT. Based on modular, relatively simple, and yet innovative concepts, it aims at providing diffraction limited images in the near infra-red for a close to 100 percent sky coverage.

Compact high resolution four wave lateral shearing interferometer

A simple, ultra-compact, four wave achromatic interferometric technique is used to measure with high accuracy and high transverse resolution wavefront of polychromatic lightsource. The wave front to be measured is replicated by a diffraction grating into four copies interfering together leading to an interference pattern very similar to the intensity distribution obtained in the focal plane of a Shack-Hartmann microlens array. The grating is made of optical glass modulated in depth on top of which a chromium mask is printed. The amplitude mask acts like a Hartmann plate. Used in association with the phase mask, it allows suppression of the unwanted zero and second orders. A CCD detector located in the vicinity of the grating records the interference pattern. This new wavefront sensor is able to resolve wavefront spatial frequencies 3 to 4 times higher than a conventional Shack-Hartmann technique using an equivalent CCD detector. Its dynamic is also much higher.

EAGLE: an MOAO fed multi-IFU working in the NIR on the E-ELT

EAGLE is an instrument for the European Extremely Large Telescope (E-ELT). EAGLE will be installed at the Gravity Invariant Focal Station of the E-ELT, covering a field of view of 50 square arcminutes. Its main scientific drivers are the physics and evolution of high-redshift galaxies, the detection and characterization of first-light objects and the physics of galaxy evolution from stellar archaeology. These key science programs, generic to all ELT projects and highly complementary to JWST, require 3D spectroscopy on a limited (~20) number of targets, full near IR coverage up to 2.4 micron and an image quality significantly sharper than the atmospheric seeing. The EAGLE design achieves these requirements with innovative, yet simple, solutions and technologies already available or under the final stages of development. EAGLE relies on Multi-Object Adaptive Optics (MOAO) which is being demonstrated in the laboratory and on sky. This paper provides a summary of the phase A study instrument design.

Overview of the GYES instrument: a multifibre high-resolution spectrograph for the prime focus of the Canada-France-Hawaii Telescope

ESAs cornerstone mission Gaia will construct a billion-star catalogue down to magnitude 20 but will only provide detailed chemical information for the brighter stars and will be lacking radial velocity at the faint end due to insufficient Signal-to-Noise Ratios (SNR). This calls for the deployment of a ground spectrograph under time scales coherent with those of Gaia for a complementary survey. The GYES instrument is a high resolution (~ 20,000) spectrometer proposed for installation on the Canada- France-Hawaii Telescope (CFHT) to perform this survey in the northern hemisphere. It exploits the large Field of View (FoV) available at the prime focus together with a high multiplex (~ 500 fibres) to achieve a SNR of 30 in two hours at magnitude 16 and render the survey possible on the order of 300 nights. The on-going feasibility study aims at jointly optimising all components of the system: the field corrector, the positioner, the fibres and the spectrograph. The key challenges consist in accommodating the components in the highly constrained environment of the primary focus, as well as in achieving maximum efficiency thanks to high transmission and minimum reconfiguration delays. Meanwhile, for GYES to have its first light at the time of Gaias initial data release (2014-2015), it is mandatory to keep its complexity down by designing a predominantly passive instrument.

High resolution spectrograph for the 4MOST facility

4MOST (4-metre Multi-Object Spectrograph Telescope) is a wide field and high multiplex fibre-fed spectroscopic facility continuously running a public survey on one of ESOs 4-metre telescopes (NTT or VISTA). It is currently undergoing a concept study and comprises a multi-object (300) high resolution (20 000) spectrograph whose purpose is to provide detailed chemical information in two wavelength ranges (395-456.5 nm and 587-673 nm). It will complement the data produced by ESAs space mission Gaia to form an unprecedented galactic-archaeology picture of the Milky Way as the result of the public survey. Building on the developments carried out for the GYES1 instrument on the Canada- France-Hawaii Telescope in 2010, the spectrograph is intended as being athermal and not featuring any motorised parts for high reliability and minimum maintenance, thereby allowing it to operate every night for five years. In addition to the fixed configuration which allows fine-tuning the spectrograph to a precise need, it features a dual-arm architecture with volume-phase holographic gratings to achieve the required dispersion at a maximum efficiency in each channel. By combining high yield time-wise and photon-wise, the spectrograph is expected to deliver more than a million spectra and make the most out of the selected 4-metre telescope.

MOSAIC optical relay module: optical design, performance, and flexure analysis

The Optical Relay Module of the MOSAIC multiple-object spectrograph is used to relay 400-1800nm light picked off from the ELT focal plane to either a fibre-based integral field unit or a natural guide star wavefront sensor. Here we present the preliminary optical design offering a telecentric exit beam with a focal-ratio of F/17.718 and the opto-mechanical analysis of flexures with a study of the impact in the optical layout performances such as: deviation of the PSF centroid, tip-tilt of the image focal plane, variations of the wavefront error, optical quality and pupil wandering at the deformable mirror position.

The achromatic chessboard, a new concept of a phase shifter for nulling interferometry III: experimental performances

Context. Dark fringe interferometry in the thermal infrared is one way to detect directly a planet orbiting a star, and so to characterize the planets atmosphere through spectroscopy. This method demands a phase shift of π1 in one arm of the interferometer. In order to detect various bio-tracers gases, a broad wavelength range (6-18 μm)2-3 is necessary, therefore an achromatic phase shift of π is required. The achromatic device presented here is a phase shifter made of two cellular mirrors, in which each cell induces a specific phase shift. Aims. We wish to demonstrate that this theoretical concept is experimentally valid. We present in this paper the setup and the very first results. Methods. In a first step, we have consolidated the theoretical ground and in a second step we developed an optical bench in the visible domain to test the concept and measure the performances of this device. Results. The preliminary experimental tests show evidences that such a device is working as expected in terms of nulling and achromatism: in spite of an error on one cell of the prototype, it provides a nulling of 2.10-3 at one wavelength, and this value is close to the expected value. Besides, a nulling of 1.10-2 in a 450 to 750 nm bandwidth: a hint that a perfect device should be achromatic.

The MICADO first-light imager for the ELT: towards the preliminary design review of the MICADO-MAORY SCAO

MICADO is the European ELT first-light imager, working in the near-infrared at the telescope diffraction limit. Provided by MAORY, the ELT first-light adaptive optics module (AO), MCAO will be the primary AO mode of MICADO, driving the design of the instrument. MICADO will also come with a SCAO capability. Developed under MICADO’s responsibility and jointly by MICADO and MAORY, SCAO will be the first AO mode to be tested at the telescope, in a phased approach of the AO integration at the ELT. The MICADO-MAORY SCAO preliminary design review (PDR) will occur in November 2018. We present here different activities and results we have had in the past two years preparing this PDR, covering several fields (opto-mechanics, electronics, real-time and control software, integration and tests, AO simulations and performance, prototyping) and the different SCAO subsystems (pyramid wavefront sensor, calibration unit, real-time computer, dichroic and the so-called Green Doughnut which hosts the SCAO assembly as well as the MAORY MCAO natural guide star wavefront sensors).