Spectra Stacking for LAMOST Low SNR Spectra

LAMOST is an innovative active reflecting Schmidt telescope in combining a large aperture with a wide field of view, and releasing more than 5,000,000 spectra in DR3. A considerable part of the low SNR spectra are not released or measured parameters, some of these can improve the SNR by the method of spectra stacking. Firstly, targets are selected whose distances of latitude or longitude are less than a certain threshold value. Then, calculating direct distances of targets if distances are less than a certain threshold value, we can think that they are repeated observations of the target star. Finally, stacking observations of the target star if they have same results of wavelength calibration.