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Introduction on Chinese 12m optical/infrared telescope (LOT)

Except for the spectroscopic survey telescope LAMOST, there are only two 2m class general purpose telescopes for precision observation in China (2.16m in Xinglong and 2.4m in Lijiang). Chinese astronomical community unanimously agrees that a 10m class large diameter general purpose optical/infrared telescope is urgently needed in China for a wide range of scientific research. The configuration for LOT with primary aperture 12m has been selected by Chinese government for the Thirteen-five-years plan in July, 2016. The concept design introduced here has been approved by Chinese astronomical community and Chinese Academy of Sciences in Dec. 2017, and submitted into the formal funding procedure of Chinese government. For quite a long time, China will very likely have only one 10m class telescope, therefore LOT should be a general-purpose telescope including multi-foci. The Nasmyth focus, prime focus, Cassegrain focus and coudé focus have been considered or reserved. Also, LOT will closely combine with the development of new technologies, such as AO, GLAO, fiber and instrument related new technologies, to make it has powerful capability for the frontier sciences. The four-mirror Nasmyth system, optimized according to the GLAO requirements, has a f-ratio about 14 and field of view 14 arecmin with excellent image quality. Some off-axis four-mirror Nasmyth optical systems are also presented in this paper. The primary focus system has a f-ratio 2 and 1.5degree field of view with 80% light energy encircled in 0.5 arecsec, which will let LOT complementary with the coming 30m-class telescopes. A double–layer Nasmyth platforms are proposed to accommodate more instruments, such as the wide field imaging spectrograph, broad band medium resolution spectrograph, high resolution spectrograph and multi-object fiber spectrographs and so on. Not all optical systems will be constructed in the same time, which will be in stages depending on the science and funding situation.