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The low Resolution Spectrographs (LRSs)

The 16 low resolution spectrographs are the main survey instruments for LAMOST. These spectrographs have been put into operation and observation in Xinglong Observatory since late 2008. Each of the 16 low resolution spectrographs can accommodate 250 fibers. The spectrographs can obtain spectrums of 4000 celestial objects simultaneously via fibers of 3.3 arc second located in 5 degree field of view of the telescope. The wavelength range of each spectrograph is from 370nm to 900nm, and spectral resolution is 1000 or 5000 by using different gratings and changing cameras to different positions. The resolution of the spectrographs could be doubled by limiting the fiber slit entrance. The throughput of the spectrographs is better than 30%.

Each spectrograph is articulated to work in low or medium resolution mode. Table 1 and Table 2 list the resolution of each resolution mode.

The 16 spectrographs used in LAMOST are low-resolution mode with 2/3 slits. The spectral resolution is R=1500. In the future, one can change the spectral resolution by replacing gratings or slits.