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

TLDR

We present SpeX, a medium‑resolution 0.8–5.5 µm cryogenic spectrograph and imager now operating on the 3.0 m NASA IRTF. SpeX uses prism cross‑dispersers and gratings to deliver R≈2000 across 0.8–5.5 µm with a 15″ slit, offers a low‑resolution prism mode, single‑order 60″ long‑slit modes, and employs Aladdin 3 and Aladdin 2 InSb arrays with an autonomous infrared slit viewer for acquisition and imaging. SpeX was commissioned on IRTF in May–July 2000, and subsequent observations demonstrate its performance.

Abstract

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 015 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 012 pixel -1. SpeX was successfully commissioned on IRTF during 2000 May, June, and July. Astronomical observations are presented to illustrate performance.