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 μm 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 R~2000 simultaneously across 0.8-2.4, 1.9-4.2, or 2.4-5.5 μm, with a 15" long slit. A high-throughput low-resolution R~200 prism mode is also provided for faint-object and occultation spectroscopy. Single-order 60" long-slit modes with resolving powers up to R~2000 are available for extended objects. The spectrograph employs an Aladdin 3 1024×1024 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 μm. The imager employs an Aladdin 2 512×512 InSb array that covers a 60^''×60^'' field of view at 0.12" pixel^-1. SpeX was successfully commissioned on IRTF during 2000 May, June, and July. Astronomical observations are presented to illustrate performance.