Imaging Spectrograph for the Hubble Space Telescope

The Space Telescope Imaging Spectrograph (STIS) has been selected by NASA as a second-generation instrument for the Hubble Space Telescope (HST). Its main advantage over the first-generation spectrographs, i.e., the Faint-Object Spectrograph (FOS) and the Goddard High-Resolution Spectrograph (GHRS), lies in the use of area detectors. Two of these are 51.2 mm × 51.2 mm, 2048 × 2048 pixel Multiple-Anode Microchannel Arrays (MAMA), covering the wavelength ranges 105 nm - 170 nm (Band I, CsI photocathode) and 170 nm - 300 nm (Band II, CsTe photocathode). The other two are 55.3 mm × 55.3 mm, 2048 × 2048 pixel CCDs for the wavelength ranges 300 nm - 600 nm (Band III) and 550 nm - 1100 nm (Band IV). Each detector serves five or six different modes of operation, including low and medium-resolution first-orderspectral imaging (R = 1000 and R = 14,000), medium and high-resolution echelle modes (R = 15,000 and R = 120,000) and also a 50 arcsec × 50 arcsec camera. The optical system consists of a collimator, a grating/mirror wheel and separate refocussing optics for each individual mode. The collimator is an off-axis elliptical toroid, preceded by a 25-position slit selector.