ANIR : Atacama Near-Infrared Camera for the 1.0-m miniTAO Telescope release_q7saplubl5gh5ccr6oafbztptm

Abstract

We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in northern Chile. The camera provides a field of view of 5'.1 × 5'.1 with a spatial resolution of 0".298 /pixel in the wavelength range of 0.95 to 2.4 μm. Taking advantage of the dry site, the camera is capable of hydrogen Paschen-α (Paα, λ=1.8751 μm in air) narrow-band imaging observations, at which wavelength ground-based observations have been quite difficult due to deep atmospheric absorption mainly from water vapor. We have been successfully obtaining Paα images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters (N1875, N191) including the atmospheric absorption show larger dispersion ( 10 filters (a few in Precipitable Water Vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and derive that the median and the dispersion of the distribution of the PWV are 0.40+/-0.30 mm for N1875 and 0.37+/-0.21 mm for N191, which are remarkably smaller (49+/-38 the base of Cerro Chajnantor (5100 m alt.). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3-1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a "ground-based" Paα observation.
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