System Design of Medium-spectral-resolution Multi-object Fiber-fed Spectrograph for the Wide Field Multiplexed Survey Telescope (MUST)

Abstract In recent years, the accelerated development of astronomy has created an urgent need for spectroscopic survey instruments with high speed and efficiency. The 6.5 m Wide Field Multiplexed Survey Telescope (MUST) proposed by Tsinghua University aims to address this need. In this paper, we present the medium spectral resolution multi-object fiber-fed spectrograph to meet the science requirement of the MUST project. The spectrograph, utilizing 92 mm × 92 mm large-size detectors, can accommodate 750 fibers with a core diameter of 150 μ m. The transmissive camera features an 18° large field of view and F/1.4 fast focal ratio and achieves 90% average throughput for each channel. The system exhibits excellent image quality, enabling simultaneous acquisition of the spectra from 750 fibers across wide wavebands (365 nm ∼ 550 nm, 520 nm ∼ 765 nm, and 735 nm ∼ 980 nm) with the spectral resolution of 3000, 4000, and 5000. The system design strategies, trade-off study, and system design can serve as references for other spectroscopic survey instruments.