Wavefront sensing over a 20-arcmin field in the ULTIMATE-Subaru Ground Layer Adaptive Optics system

Abstract

The ULTIMATE Ground Layer Adaptive Optics (GLAO) system is part of ULTIMATE-Subaru, the next generation facility instrumentation project at the Subaru telescope in Hawaii. GLAO is led by the Subaru Telescope in collaboration with Tohoku University, Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), and the Australian National University (ANU). ANU is currently designing the Laser Guide Star Facility and the Wavefront Adaptor Flange with four Laser Guide Star wavefront sensors, and four Natural Guide Star wavefront sensors. The GLAO Wavefront Adaptor Flange will provide Adaptive Optics capability to the wide-field imager (WFI) instrument to be installed at the Subaru Cassegrain focus in 2027. Four Laser Guide Star wavefront sensors mounted over a fabricated steel structure enable the acquisition of LGS asterisms of up to 20 arcmin in diameter. Each WFS has been designed to also account for the telescope optical aberrations and the non-telecentricity. The NGS instance consists of four Natural Guide Star wavefront sensors for tip-tilt and focus measurement. In this paper, we present an overview of the GLAO Wavefront Adaptor Flange including the preliminary design for the opto-mechanical assembly of both LGS and NGS instances, and the mechanisms control system that enables fine acquisition of the guide stars over the wide patrol field of the GLAO system.