FourStar: The Near-Infrared Imager for the 6.5 m Baade Telescope at Las Campanas Observatory

ABSTRACT The FourStar Infrared Camera is a 4 K × 4 K near-infrared (1.0-2.4 μ m) imager built for the Magellan 6.5 m Baade Telescope at Las Campanas Observatory, Chile. FourStar has an all-refractive optical system, four HAWAII-2RG detectors, and Teledyne electronics. The pixel scale of 0.159″ pixel-1 produces a 10.8′ × 10.8′ field of view. Ten filters are available across the Y, J, H, and Ks bands. We present the optical, mechanical, thermal, electronic, and software design choices and their associated engineering implementations. The detector readout electronics, control system, and the automatic data acquisition hardware are also described. Laboratory and on-sky performance data are presented. FourStar has excellent image quality, easily meeting the requirement of critically sampling the median seeing disk. The throughput is ≈0.5-0.6 across its wavelength coverage. Some early science results are presented.