Mimir: A Near-Infrared Wide-Field Imager, Spectrometer, and Polarimeter

Mimir, a new facility-class near-infrared instrument for the 1.8 m Perkins telescope on Anderson Mesa outside Flagstaff, Arizona, was commissioned and has been operating for three years. Mimir is multifunction, performing wide-field (F=5) and narrow-field (F=17) imaging, long-slit spectroscopy, and imaging polarimetry. The F=5 mode images at 0.59" per pixel onto the 1024 × 1024 pixel ALADDIN III InSb array detector, giving a 10 0 × 10 0 field of view. In the F=17 mode, the plate scale is 0.18" per pixel. Optically, Mimir is a refractive reimager for the F=17:5 Perkins beam. A six-lens collimator produces an achromatic 25 mm pupil, which is imaged by a five-lens camera (F=5), a four-lens camera (F=17), or a two-lens pupil viewer onto the detector. Three filter wheels precede the pupil, one follows the pupil. The wheels contain a rotating half-wave plate, broadband filters, narrowband filters, grisms, long-pass filters, a wire grid, and thermal IR blockers. The first telescope focus is within Mimir, where a slit and decker unit, consisting of two linear motion cars, selects one of 13 slit scenes. The slit and decker cars, the four filter wheels, the half-wave plate rotation, and the camera selector are all driven by stepper motors within the cold vacuum space. Cooling is provided by a CTI 1050 two-stage, closed-cycle helium refrigerator, keeping the optics, filters, and internal surfaces between 65 and 75 K and the detector at 33.5 K. Switching between Mimir's different modes takes only a few seconds, making it a versatile tool for conducting a wide range of investigations and for quickly reacting to changing observing conditions. Mimir on the Perkins telescope achieves imaging sensitivities 2-4 mag deeper than 2MASS, moderate resolution (R ∼ 700) JHK spectra of virtually any 2MASS source, high- precision wide-field imaging polarimetry, and L 0 and M 0 band imaging and spectroscopy.