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E-ELT Instrument study for first light: OPTIMOS-DIORAMAS: mechanical concept study for slit masks system

The Seeing-limited, large multiplex, optical/near-IR spectrograph, Optimos-Dioramas, currently under study by a Consortium of Institutes from France, Italy, and Switzerland, is one of the possible candidates for first light on the EELT Telescope. The spectograph is designed to maximize the field of view and cover in one-shot the spectral range (0.37micron - 1.6micron). This paper describes the studies performed to establish a base-line conceptual design of the Slit Masks System for the Optimos-Dioramas spectrograph. This unit has been designed in order to better satisfy the limits of the allowed volume on the Nasmyth E-ELT platform, and it is also able to guarantee all the optical specifications needed to cover the overall field of view (7x7arcmin). In order to take and position the masks in the focal plane, the performed system is fully robotic and able to load/unload the masks in the proper quadrant. A central cross structure, about 8.33arcsec wide, is needed. Each mask will necessarily be larger than 719x719mm, i.e. 780x780mm. The system based on four 0.6mm thick (black painted steel) masks is fully feasible and complies with all specifications. Vignetting due to the focal plane curvature is minimized and the slits (cut via a stencil-laser machine) can have all shapes and sizes.