SpeX: A medium-resolution 0.8-5.5 micron spectrograph and imager for the NASA Infrared Telescope Facility

We present the design, construction, and performance of SpeX, a medium-resolution 0.8-5.5 mum cryogenic spectrograph and imager, now in operation at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The design uses prism cross-dispersers and gratings to provide resolving powers up to Rsimilar to2000 simultaneously across 0.8-2.4, 1.9-4.2, or 2.4-5.5 mum, with a 15" long slit. A high-throughput low-resolution Rsimilar to200 prism mode is also provided for faint-object and occultation spectroscopy. Single-order 60" long-slit modes with resolving powers up to Rsimilar to2000 are available for extended objects. The spectrograph employs an Aladdin 3 1024x1024 InSb array and uses narrow slits and a spatial scale of 0".15 pixel(-1) for optimum sensitivity on point sources. An autonomous infrared slit viewer is used for object acquisition, infrared guiding, and scientific imaging in the wavelength range 0.8-5.5 mum. The imager employs an Aladdin 2 512x512 InSb array that covers a 60" x 60" field of view at 0".12 pixel. SpeX was successfully commissioned on IRTF during 2000 May, June, and July. Astronomical observations are presented to illustrate performance.