OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the Spanish Day One instrument for the Gran Telescopio Canarias (GTC). Sensitive in the wavelength range from 365 through 1000 nm, OSIRIS is a multiple purpose instrument for imaging and low-resolution long slit and multiple object spectroscopy (MOS). Imaging can be done using broad band filters or narrow band tunable filters with FWHM ranging from 0.2 to 1.3 nm at 365 nm, through 0.9 to 5.4 nm at 1000 nm. OSIRIS observing modes include also fast photometry and spectroscopy. OSIRIS field of view is of 8.5x8.5 arcminutes and the maximum nominal spectral resolution is of 5000 for a slit width of 0.6 arcsec. MOS incorporates detector charge shuffling co-ordinated with telescope nodding for an excellent sky subtraction. The use of tunable filters is a completely new feature in 8-10m class telescopes that will allow observing the very faint and distant emission line objects.
OSIRIS scientific Key Project is OTELO.
