The European Extremely Large Telescope (E-ELT) is expected to reveal a revolutionary view on the Universe enabling the study of extra-solar planets, of stellar populations in external galaxies, and of faint distant galaxies tracing the early history of the Universe. E-ELT observations will lead to breakthrough results addressing key issues like the origin of the first stars and galaxies, the nature of dark matter and dark energy, galactic evolution and the formation of stars and planets. The large collecting area of the 42m primary mirror and its novel five mirror design make the E-ELT perfectly suited to perform spectroscopic observations over a large field of view.
The E-ELT Science Working Group (SWG) recognized ``the very strong science case for an instrument which provides multi-object spectroscopy from the R to the H band, with a multiplex of at least 100, a field of view of 10 arcminutes, and a spectral resolution of R~3000, or more, subject to a trade-off. A goal would be to extend the spectral range further into the blue (and the red), and to include R = 5000 - 10000.'' The SWG further noted that JWST will have no capability in this domain.
OPTIMOS-EVE is a fibre-fed, optical-to-infrared multi-object spectrograph designed to explore the large field of view provided by the E-ELT at seeing limited conditions. Therefore, OPTIMOS-EVE is well suited to be used in the early operational phase of the E-ELT and also beyond, when the atmospheric conditions will not be optimal to provide full adaptive optics corrections (at least 30% of the time, depending on the telescope site). OPTIMOS-EVE is one of the few E-ELT instruments under study that will explore the visible to near-infrared wavelength region.
OPTIMOS-EVE has been designed for the E-ELT Nasmyth focus and provides low-, medium-, and high-resolution spectroscopy (R~5,000 – 30,000) from the ultraviolet to the near-infrared (0.37 to 1.7 mm) for multi-object studies of sources nearby and at cosmological distances. The fibre positioner provides the opportunity to observe over 200 single targets within the ≥ 7 arcmin field of view, or to combine the fibres into medium- or large-sized IFUs. The wavelength coverage of an individual spectrum (l/3 - l/6 in the visible and l/10 to l/20 in the IR) is a trade-off between spectral resolution, multiplex and detector cost. The baseline design includes a focal plate carousel and fibre positioner, two dual beam VIS/NIR optimized spectrographs where the beams are split by a dichroic. The 4 spectrographs have a very similar optical design and employ VPH gratings for optimal performance. The large wavelength coverage makes an ADC at the intermediate focus of the telescope desirable, especially for targets at large zenith distance (e.g. Magellanic Clouds); an ADC would provide enhanced performances, but is not essential to achieve the main scientific objectives.
The instrument top-level requirements were derived from the analysis of five key science cases provided by the Science Team. This led to a requirements matrix and the study of six optical designs, each with a different score on the scientific performance, the technical and operational feasibility, and the volume-, weight-, cost- and risk-budget. The design concept fully accounts for the feedback from the mid-term review and is compliant with the science expectations.
OPTIMOS-EVE may be a workhorse instrument for the E-ELT based on state-of-the-art technology and is able to address a major fraction of the E-ELT science cases, from extra-solar planets, stellar populations beyond the Local Group, properties of dark haloes, the intergalactic medium, up to the most distant galaxies accessible with the E-ELT. It will address the Design Reference Missions S3, S9, G4, C4, C7 and C10 (see RD1 and Table 1 in RD2). From its concept and design, it is a robust instrument, and it can be developed, manufactured and integrated using existing technologies. It will be ready for the early science operations of the E-ELT and should be considered for first generation. OPTIMOS-EVE provides unique capabilities, scientific potential and will be complimentary to future large ground-based (e.g. ALMA, SKA) and space-born (e.g. GAIA, JWST) facilities.
The OPTical Multi Object Spectrograph 'Extreme Visual Explorer' for the European - Extremely Large Telescope - Consortium partners: GEPI, NOVA, RAL, NBI, INAF, AIP, LSW, IAG, LNA, ON
