A New Wavelength Calibration Method for LAMOST Based on Piecewise Fitting

The traditional methods of wavelength calibration for the LAM-OST (Large Area Multi-Object Fiber Spectroscopic Telescope) usually use a fifth-order polynomial to perform fitting and calibration in a broad wavelength range. Obviously, it is unable to reflect very well the local dispersion relations by using only one polynomial to fit the whole waveband. In order to reflect accurately the dispersion characteristics of local wavebands, a new wavelength calibration method based on piecewise fitting is proposed. In this method, the entire wavelength range is divided into several sub-bands according to certain principles, and a proper polynomial is used to perform fitting and calibration for each sub-band separately. Compared with the traditional methods of wave-length calibration, the experimental results show that this new method can get a more precise description of the dispersion characteristics of local wavebands. Therefore, the accuracy of wavelength calibration in the whole waveband will be further improved.