Spectral Extraction Algorithm for LAMOST Two-dimensional Fiber-spectroscopic Images

This paper describes the method of spectral extraction to be used for the data processing of LAMOST's two-dimensional fiber-spectroscopic images. The effect of the selection of sampling points on the result of spectral extraction is analyzed. Based on the characteristics of Gaussian distribution functions and some experiments, the selection range of sampling points is defined, and the problem that some negative flux values appear in the result of spectral extraction is resolved. In addition, aiming at the problem that rather large errors exist in the result of spectral extraction under strong noise background, an improved extraction method based on the frequency-domain filtering is proposed. By using the FFT and low-pass filter, the sharp noises affecting the real fiber profiles are removed at first, before the normal spectral extraction is performed. Experiments and tests are made by using the simulative data provided by the data processing system of the LAMOST telescope, and the results indicate that the improved extraction method is feasible and effective.