The MUSE (Multi Unit Spectroscopic Explorer) instrument is a second-generation integral-field spectrograph candidate for the VLT, operating in the visible and near IR wavelength range (0.465 - 0.93 μm). It is combining a large 1' x 1' Field of View with a spectral resolution of 3000 and a spatial resolution of 0.2" coupled to a sophisticated ground-layer Adaptive Optics (AO) system. After a brief summary of the major instrumental requirements, we will focus on the opto-mechanical design of MUSE, including core subsystems such as the Fore-Optics, the Image Slicers and the Spectrographs, the Structure and the Calibration Unit. The most creative trends of the instrument will be underlined, such as the specific choices adopted to reduce the costs, weight and volume of the Slicer and Spectrograph units, that need to be manufactured and installed on the VLT Nasmyth platform into twenty-four replicas. Finally, a realistic estimate of the expected performance (in both throughput and image quality), and the future development program for the forthcoming detailed design phase will be presented.
The Multi Unit spectroscopic Explorer (MUSE) is a second generation VLT panoramic integral-field spectrograph operating in the visible wavelength range. MUSE has a field of 1 x 1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by a ground layer adaptive optics system using four laser guide stars. The simultaneous spectral range is 0.465-0.93 μm, at a resolution of R~3000. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. This makes MUSE a unique and tremendously powerful instrument for discovering and characterizing objects that lie beyond the reach of even the deepest imaging surveys. MUSE has also a high spatial resolution mode with 7.5 x 7.5 arcse2 field of view sampled at 25 milli-arcsec. In this mode MUSE should be able to get diffraction limited data-cube in the 0.6-1 μm wavelength range. Although MUSE design has been optimized for the study of galaxy formation and evolution, it has a wide range of possible applications; e.g. monitoring of outer planets atmosphere, young stellar objects environment, supermassive black holes and active nuclei in nearby galaxies or massive spectroscopic survey of stellar fields.
The introduction of Image Slicers in Astronomy has been growing rapidly in the recent years. These optical devices allow the simultaneous observation on the same detector matrix of two-dimensional sky maps and the spectral decomposition of light on all of their angular samples, therefore dramatically reducing the observation times and getting rid of the spectro-photometric variations of the atmosphere. Today the implementation of Image Slicers is planned on various ground and space telescopes, covering a spectral domain ranging from blue to mid-IR wavelengths. Among such different projects, we describe the Image Slicer of MUSE (Multi Unit Spectroscopic Explorer), a second-generation Integral-Field Spectrograph for the VLT combining a 1’ x 1’ Field of View with a spatial resolution of 0.2” and a spectral resolution of 3000. The most efficient principle of an Image Slicer consists in a combination of several different optical channels, each made of three mini-mirrors having different tilts and curvatures. After a brief presentation of the MUSE Image Slicer requirements, we will explain the followed logic in order to optimize the opto-mechanical design and cost of the Slicer: indeed one of MUSE peculiarity is the total number of its individual modules, that is 24. The realization of such series at an affordable cost actually is a design driver of the study. The communication also deals with the used optical design models, the expected performance, the candidate technologies for the manufacturing of all the components, and the future development of a prototype of this critical optical subsystem.
SNIFS is an integral field spectrograph devoted to the observation of supernovae. This instrument is today in the manufacturing phase and should be able to observe supernovae at the end of this year (2003) on the 2.2m telescope of University Hawaii. The concept of SNIFS is to split the 6” x 6” field of view into 225 samples of 0.4” x 0.4” through a microlens array. Then the spectral decomposition of each sample is imaged on a 2k x 4k CCD. In order to cover all the large spectral range with a high resolution, the spectrograph is composed of two modules, one for the blue wavelengths (320 nm to 560nm)with a resolution around 1000 at 430 nm and one for the red wavelengths (520 nm to 1 µm) with a resolution around 1300 at 760 nm. First we will present the optical design and detail the function of each optical component. Then the mechanical design will be shown with some maps of the structure. Finally the first pictures taken during the alignments will be displayed.