David Horville

Maunakea Spectroscopic Explorer (MSE): the prime focus subsystems: requirements and interfaces

MSE will be a massively multiplexed survey telescope, including a segmented primary mirror which feeds fibers at the prime focus, including an array of approximately four thousand fibers, positioned precisely to feed banks of spectrographs several tens of meters away. We describe the process of mapping top-level requirements on MSE to technical specifications for subsystems located at the MSE prime focus. This includes the overall top-level requirements based on knowledge of similar systems at other telescopes and how those requirements were converted into specifications so that the subsystems could begin working on their Conceptual Design Phases. We then discuss the verification of the engineering specifications and the compiling of lower-level requirements and specifications into higher level performance budgets (e.g. Image Quality). We also briefly discuss the interface specifications, their effect on the performance of the system and the plan to manage them going forward. We also discuss the opto-mechanical design of the telescope top end assembly and refer readers to more details for instrumentation located at the top end.

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.

SST-GATE: an innovative telescope for very high energy astronomy

The Cherenkov Telescope Array (CTA) is an international collaboration that aims to create the worlds largest (ever) Very High Energy gamma-ray telescope array, consisting of more than 100 telescopes covering an area of several square kilometers to observe the electromagnetic showers generated by incoming cosmic gamma-rays with very high energies (from a few tens of GeV up to over 100 TeV). Observing such sources requires - amongst many other things - a large FoV (Field of View). In the framework of CTA, SST-GATE (Small Size Telescope - GAmma-ray Telescope Elements) aims to investigate and to build one of the two first CTA prototypes based on the Schwarzschild-Couder (SC) optical design that delivers a FoV close to 10 degrees in diameter. To achieve the required performance per unit cost, many improvements in mirror manufacturing and in other technologies are required. We present in this paper the current status of our project. After a brief introduction of the very high energy context, we present the opto-mechanical design, discuss the technological tradeoffs and explain the electronics philosophy that will ensure the telescopes cost is minimised without limiting its capabilities. We then describe the software nedeed to operate the telescope and conclude by presenting the expected telescope performance and some management considerations.

Multi-object spectroscopy with the European ELT: scientific synergies between EAGLE and EVE

The EAGLE and EVE Phase A studies for instruments for the European Extremely Large Telescope (E-ELT) originated from related top-level scientific questions, but employed different (yet complementary) methods to deliver the required observations. We re-examine the motivations for a multi-object spectrograph (MOS) on the E-ELT and present a unified set of requirements for a versatile instrument. Such a MOS would exploit the excellent spatial resolution in the near-infrared envisaged for EAGLE, combined with aspects of the spectral coverage and large multiplex of EVE. We briefly discuss the top-level systems which could satisfy these requirements in a single instrument at one of the Nasmyth foci of the E-ELT.

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.

Challenges of the opto-mechanical conceptual design of a small far-IR balloon experiment

Astronomers require more and more precise instruments for their observations. Here we describe the challenges encountered in the optical and mechanical designs of the CIDRE (Campagne d’Identification du Deutérium par Réception hEtérodyne) project, which was to be flown on a high altitude balloon at 40 km. The project aimed to measure the transitions of the HD molecule at 2.675 THz band and some other THz lines in our galaxy. The astronomers asked to fly the biggest possible telescope in a standard balloon gondola, and required high pointing accuracy (7 arcsec). In January 2014, the technical project, including the optical and mechanical designs, was evaluated to be of excellent standard, but, for all that, the project was cancelled because of financial constraints. Nevertheless the phase A study allowed us to identify the optical and mechanical challenges of balloon projects and we were able to come up with a simple design, that fulfilled all the requirements. The 900 mm primary mirror and the rest of the optics were designed to be supported by a sandwich-panel composite structure with carbon epoxy skins and aluminum honeycomb core to improve the mechanical stiffness and the thermal behavior of the instrument without increasing its mass or its complexity. In this paper, we describe the optical design and the mechanical structure of the instrument. Finite element analysis is carried out to estimate the gravitational flexure and the thermal deformations, which can both harm the pointing accuracy and the performances of the instrument. These simulations show that the proposed design would fulfill the different requirements (pointing accuracy, landing survival as well as the dynamic behavior).