Imaging Performance of Near Infrared (NIR) channel in Infrared Camera (IRC) on board ASTRO-F

摘要

The Infrared Camera (IRC) is one of the focal-plane instruments on board ASTRO-F(Japanese Infrared Astronomical satellite to be launched in 2004). IRC will make imaging and spectroscopy observations in the near-and mid-infrared regions. IRC comprises of three channels; NIR, MIR-S and MIR-L, which cover 2-5, 5-12, and 12-26μm, respectively. In this paper we report the optical performance of the NIR imaging mode at cryogenic temperatures with three filters; N2, N3, and N4, which cover the wavelength regions of 2-2.7, 2.7-3-7, and 3.7-5.05μm, respectively. The NIR channel consists of three Si and one Ge lenses with the infrared array (412 x 512 format of InSb) manufactured by Raytheon IRO. At cryogenic temperatures (～ 6K) we found slightly larger chromatic focal shifts than designed probably due to the uncertainty in low-temperature refractive indices of the lens materials. We obtained the modulation transfer function for each band by the knife-edge method and estimated the optical performance of the IRC with the telescope at cryogenic temperatures.