The correction of atmospheric dispersion in LAMOST *

Atmospheric refraction and dispersion affect the observational quality and efficiency of the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST). In this paper, by both ZEMAX simulation and numerical calculation, the atmospheric dispersion for LAMOST, which will be installed at the latitude 40°.4 and has a 20 m focal length and F5 focal ratio, are calculated for the 0.75 h before and after the transit time. Various types of dispersion prism to be used for correcting the atmospheric dispersion in LAMOST were calculated and analyzed, from which one was finally adopted. The secondary spectrum of the dispersion prism, the residual dispersion during tracking of the telescope and the installation errors of the dispersion prism are investigated.