Research in Astron. Astrophys. 2012 Vol. 12 No. 4, 453–464 http://www.raa-journal.org http://www.iop.org/journals/raa Research in Astronomy and Astrophysics Relative flux calibration for the Guoshoujing Telescope (LAMOST) * Yi-Han Song 1,2,3 , A-Li Luo 1,2,⋆ , Georges Comte 1,4 , Zhong-Rui Bai 1,2 , Jian-Nan Zhang 1,2 , Wei Du 1,2,3 , Hao-Tong Zhang 1,2 , Jian-Jun Chen 1,2 , Fang Zuo 1,2 and Yong-Heng Zhao 1,2 1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; lal@lamost.org; lal@nao.cas.cn 2 Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; 3 Graduate University of Chinese Academy of Sciences, Beijing 100049, China; 4 Observatoire Astronomique Marseille-Provence and Laboratoire d’Astrophysique de Marseille, F-13388 Marseille Cedex, France Received 2011 April 21; accepted 2011 May 12 Abstract This paper presents a relative flux calibration method for the Guoshoujing Telescope (LAMOST), which may be applied to connect a blue spectrum to a red spec- trum to build the whole spectrum across the total wavelength range (3700 ∼ 9000 ˚ A). In each spectrograph, we estimate the effective temperatures of selected stars using a grid of spectral line indices in the blue spectral range and a comparison with stel- lar atmosphere models. For each spectrograph, stars of types A and F are selected as pseudo-standard stars, and the theoretical spectra are used to calibrate both the blue (3700 ∼ 5900 ˚ A) and red spectrograph arms (5700 ∼ 9000 ˚ A). Then the spectral response function for these pseudo-standard stars could be used to correct the raw spectra provided by the other fibers of the spectrograph, after a fiber efficiency func- tion has been derived from twilight flat-field exposures. A key problem in this method is the fitting of a pseudo stellar continuum, so we also give a detailed description of this step. The method is tested by comparing a small sample of LAMOST spectra cal- ibrated in this way on stars also observed by the Sloan Digital Sky Survey. The result shows that the T eff estimation and relative flux calibration method are adequate. Key words: techniques: spectroscopic — calibration: methods:data analysis 1 INTRODUCTION The Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST, now called the Guoshoujing Telescope) is a 4-meter reflecting Schmidt telescope with a 5 degree field of view and 4000 fibers in the focal plane (Su et al. 1998). In the commissioning phase since 2009, the test observations identified many problems of data reduction that need to be solved. * Supported by the National Natural Science Foundation of China.