Seimei 3.8-m Telescope has been commissioned

The Seimei Telescope, a 3.8-m optical and infrared telescope located on the range of Mount Chikurinji in Okayama prefecture of Japan was commissioned in 2019. The Seimei Telescope project was started with the actual commencement of technical development in 2006. Seimei is a segmented-mirror telescope whose primary mirror consists of 18 petal-shaped segments on an ALT-AZ mounting. We will aim at diffraction-limited images with Seimei, by phasing the segments and employing adaptive optics in the future. The telescope tube has a light-weight homologous structure designed with a genetic algorithm. The total moving mass is only 18 000 kg including the two Nasmyth platforms; it can acquire anywhere on sky within 1 min. Current blind pointing accuracy is about 5 arcsec RMS above the altitude of 30 deg. Seimei is a Ritchey-Chretien telescope with two Nasmyth foci of focal ratio of f/6.0, and its optical design is based on that of the WIYN 3.5-m telescope on Kitt Peak, USA. Seimei is operated by Kyoto University with the help of National Astronomical Observatory of Japan (NAOJ). Half of the telescope time is used by Kyoto University, and the remaining time is open to the astronomical community; NAOJ is responsible for the management of the open-use time. Since 2019 February 28, open-use time observations have been made without any serious problems; 140 science night observations are planned for the semester 2021A (from January 4 to June 20, avoiding the Japanese rainy period), with a small amount of engineering time.