The preslit system of GIANO-TNG

GIANO-TNG is an ultra-stable infrared (0.9-2.5 μm) high resolution cross-dispersed spectrometer designed to operate at a fixed position relative to the telescope axis. It therefore requires a pre-slit opto-mechanical system which takes care of field de-rotation and auto-guiding. Taking advantage of the structure already existing for SARG (the high resolution optical spectrometer of the Telescopio Nazionale Galileo, TNG) we are developing a system which provides a large (2 arcmin) field of view for offset guiding and includes, as separate and selectable elements, a gas absorption cell and a polarimetric module where the analyzers work in a collimated beam.