Sky subtraction for LAMOST

作     者：Zhong-Rui Bai Hao-Tong Zhang Hai-Long Yuan Guang-Wei Li Jian-Jun Chen Ya-Juan Lei Hui-Qin Yang Yi-Qiao Dong Gang Wang Yong-Heng Zhao 

作者机构：1 University of Chinese Academy of SciencesBeijing 100049China Key Lab for Optical AstronomyNational Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2017年第17卷第9期

页      面：25-38页

核心收录：

学科分类：0709[理学-地质学] 07[理学] 0708[理学-地球物理学] 070401[理学-天体物理] 0825[工学-航空宇航科学与技术] 0704[理学-天文学] 

基　　金：supported by the National Natural Science Foundation of China(NSFC)(Grant No.11503054) NSFC Key Program(Grant No.11333004) the National Key Basic Research Program of China(Program 973 Grant No.2014CB845700) The Guo Shou Jing Telescope(the Large sky Area Multi-Object fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of Sciences the project has been provided by the National Development and Reform Commission SDSS-Ⅲhas been provided by the Alfred P.Sloan Foundation the Participating Institutions,the National Science Foundation the U.S.Department of Energy Office of Science 

主　　题：techniques: spectroscopic -- methods data analysis -- instrumentation spectrographs 

摘      要：Sky subtraction is a key technique in data reduction of multi-fiber spectra. Knowledge of characteristics related to the instrument is necessary to determine the method adopted in sky subtraction. In this study, we describe the sky subtraction method designed for the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST） survey. The method has been integrated into the LAMOST 2D Pipeline v2.6 and applied to data from LAMOST DR3 and later. For LAMOST, calibration using sky emission lines is used to alleviate the position-dependent （and thus time-dependent） ,-~ 4% fiber throughput uncertainty and small wavelength instability （0.1/~） during observation. Sky subtraction using principal component analysis （PCA） further reduces 25% of the sky line residual from OH fines in the red part of LAMOST spectra after the master sky spectrum, which is derived from a B-spline fit of 20 sky fibers in each spectrograph. Using this approach, values are adjusted by a sky emission line and subtracted from each fiber. Further analysis shows that our wavelength calibration accuracy is about 4.5 km s-1, and the averages of residuals after sky subtraction are about 3% for sky emission lines and 3% for the continuum region. The relative sky subtraction residuals vary with moonlight background brightness, and can reach as low as 1.5% for regions that have sky emission lines during a dark night. Tests on F stars with both similar sky emission line strength and similar object continuum intensity show that the sky emission line residual of LAMOST is smaller than that of the SDSS survey.