SpeX: A Medium‐Resolution 0.8–5.5 Micron Spectrograph and Imager for the NASA Infrared Telescope Facility

ABSTRACT. We present the design, construction, and performance of SpeX, a medium-resolution 0.8–5.5 mm 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 mm, 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 �1 Aladdin 3 1024 # 1024 InSb array and uses narrow slits and a spatial scale of 0�.15 pixel 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 mm. The imager employs an Aladdin 2 512 # 512 InSb array that ′ ′ ′ ′ �1 covers a 60 # 60 field of view at 0�.12 pixel. SpeX was successfully commissioned on IRTF during 2000