Design of the WIYN High Resolution Infrared Camera (WHIRC)

Abstract

ABSTRACTThe WIYN High Resolution Infrared Camera (WHIRC) is a high-resolution near-infrared imager (0.8–2.5 μm) designed to produce superb images over a moderate (3.3′ × 3.4′) field of view on the WIYN 3.5 m telescope at Kitt Peak National Observatory. It takes scientific advantage of the excellent image quality produced by the telescope and its image stabilization subsystem, the WIYN Tip-Tilt Module (WTTM), which is located on one of two Nasmyth ports. WHIRC mounts to WTTM and reimages the WTTM focal plane to a plate scale of 0.1″ pixel-1 at the WHIRC detector. Its straight-through optical path makes for a compact, very low mass, instrument—a necessity, given the stringent moment-loading requirement at the WTTM interface. The WHIRC optical path consists of a vacuum window, a five-element collimator, a dual filter wheel, a five-element achromatic camera, and a 2k2 Raytheon VIRGO mercury cadmium telluride (HgCdTe) detector. A novel all-aluminum lens cell design is used to achieve 13 μm lens centering tolerances between ambient and the 77 K operating temperature. A suite of 13 filters facilitates broadband (J, H, and Ks) imaging, as well as narrowband imaging tailored to a variety of astronomical investigations. The imaging performance of WHIRC is excellent. Irrespective of seeing, the telescope, and WTTM, WHIRC delivers 0.13″, 0.11″, and 0.08″ FWHM images in J, H, and Ks, respectively. On sky, the imaging is equally impressive yielding images as good as ∼0.25 FWHM in Ks. In this article we describe the WHIRC design in detail and present the predicted and measured instrument performance.