Highly Sensitive, Non-cryogenic NIR High-resolution Spectrograph, WINERED
Yuji Ikeda, Sohei Kondo, Shogo Otsubo, Satoshi Hamano, Chikako Yasui, Noriyuki Matsunaga, Hiroaki Sameshima, Tomohiro Yoshikawa, Kei Fukue, Kenshi Nakanishi, Takafumi Kawanishi, Ayaka Watase, T. Nakaoka, Akira Arai, Masaomi Kinoshita, Ayaka Kitano, Kazuki Nakamura, Akira Asano, Keiichi Takenaka, Taichi Murai, Hideyo Kawakita, Atsushi Minami, Natsuko Izumi, Ryō Yamamoto, Misaki Mizumoto, Daisuke Taniguchi, Takuji Tsujimoto
Abstract
Abstract WINERED is a novel near-infrared (NIR) high-resolution spectrograph (HRS) that pursues the highest possible sensitivity to realize high-precision spectroscopy in the NIR as in the optical wavelength range. WINERED covers 0.9–1.35 μ m ( z , Y , and J -bands) with three modes (Wide mode and two Hires modes) at the maximum spectral resolutions of R = 28,000 and R = 70,000. For fulfilling the objective, WINERED is designed with an unprecedentedly high instrument throughput (up to 50% at maximum including the quantum efficiency of the array) that is three times or more than other existing optical/NIR HRSs. This is mainly realized by a combination of non-white pupil and no fiber-fed configuration in optical design, the moderate (optimized) wavelength coverage, and the high-throughput gratings. Another prominent feature of WINERED is “warm” instrument despite for infrared (IR) observations. Such non-cryogenic (no cold stop) IR instrument finally became possible with the combination of custom-made thermal-cut filter of 10 −8 class, 1.7 μ m cutoff HAWAII-2RG array, and a cold baffle reducing the direct thermal radiation to the IR array into the solid angle of f /2. The thermal background is suppressed below 0.1 photons pixel −1 s −1 even in the wide band of 0.9–1.35 μ m under the environment of 290 K. WINERED had been installed to the 3.58 m New Technology Telescope at La Silla Observatory, ESO, since 2017. Even with the intermediate size telescope, WINERED was confirmed to provide a limiting magnitude (for SNR = 30 with 8 hr. integration time) of J = 16.4 mag for the Wide mode and J = 15.1 mag for the Hires mode, respectively, under the natural seeing conditions. These sensitivities are comparable to those for the existing NIR-HRSs attached to the 8–10 m class telescopes with AO. WINERED type spectrographs may become a critical not only for the currently on-going extremely large telescopes to reduce the developing cost and time but also for smaller telescopes to extend their lives with long programs.