Number and Distribution of Fiducial Fibers in a Spectroscopic Survey Telescope

Abstract

To date, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has been in operation for 12 yr. To improve the telescope's astronomical observation accuracy, the original open-loop fiber positioning system of LAMOST is in urgent need of upgrading. The upgrade plan is to install several fiber view cameras (FVCs) around primary mirror B to build a closed-loop feedback control system. The FVCs are 20 m from the focal surface. To reduce a series of errors when the cameras detect the positions of the optical fibers, we designed fiducial fibers on the focal surface to be fiducial points for the cameras. Increasing the number of fiducial fibers can improve the detection accuracy of the FVC system, but it will also certainly reduce the number of fiber positioners that can be used for observation. Therefore, the focus of this paper is how to achieve the quantity and distribution that meet the requirements of system detection. In this paper, we introduce the necessity of using fiducial fibers, propose a method for selecting their number and present several methods for assessing the uniformity of their distribution. Finally, we implement particle swarm optimization to find the best distribution of fiducial fibers.