EMIR is the NIR multi-object imager and spectrograph for the GTC (Gran Telescopio Canarias). The instrument PDR phase was held successfully in March 2003, and we are at present in the middle of the ADR (Advanced Design Phase) during which a number of mechanical concepts will be tested on development prototypes to ensure the feasibility of the PDR proposed design. This presentation contains a technical description of the mechanical design of the instrument, as well as the prototypes development. The mechanical design is essentially built around the optical layout by providing an optical bench for mounting the optomechanics, the mechanisms and the detector, all this inside a custom-designed vacuum vessel and with the corresponding cooling system. One of its main design features is the use of a cryogenic reconfigurable slit mechanism to generate a multi-slit configuration, a long slit or an imaging aperture at the telescope focal plane. This feature will permit to maintain the instrument in operation conditions for a long time and take advantages in both a classically scheduled and a queued service observing schemes

EMIR, currently entering into its fabrication and AIV phase, will be one of the first common user instruments for the GTC, the 10 meter telescope under construction by GRANTECAN at the Roque de los Muchachos Observatory (Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofísica de Canarias (IAC). EMIR is designed to realize one of the central goals of 10m class telescopes, allowing observers to obtain spectra for large numbers of faint sources in an time-efficient manner. EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 µm. It is equipped with two innovative subsystems: a robotic reconfigurable multislit mask and disperssive elements formed by the combination of high quality difracction grating and conventional prisms, both at the heart of the instrument. The present status of development, expected performances, schedule and plans for scientific exploitation are described and discussed. The development and fabrication of EMIR is funded by GRANTECAN and the Plan Nacional de Astronomía y Astrofísica (National Plan for Astronomy and Astrophysics, Spain).

This paper shows the different design concepts and techniques employed in the structural and thermal analysis of EMIR (Espectrógrafo Multiobjeto Infrarrojo), nowadays under development at the Instituto de Astrofísica de Canarias.

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EMIR is a NIR multiobject spectrograph with imaging capabilities to be used at the GTC. A general description of instrument performances, as well as the updated optical and mechanical layouts, can be found elsewhere on these proceedings (reference documents 4, 6 and 7). After the successful results of the Preliminary Design Review in March 2003, EMIR optical design is now complete. Some specific features of the optical components make it particularly difficult to mount them in the instrument. For example, the first collimator lens in EMIR is one of the largest Fused Silica lenses ever mounted to work under cryogenic conditions, and some other lenses in the system present features such as aspheric surfaces, tight centering tolerances etc. The analysis of the testing being done in order to validate three different lens mounting design concepts is presented here, as well as the detailed status of the lens mounting design solutions adopted.