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Although red clump (RC) stars are easy to identify due to their stability ofluminosity and color, about 20-50% are actually red giant branch (RGB) stars inthe same location on the HR diagram. In this paper, a sample of 210,504 spectrafor 184 318 primary RC (PRC) stars from the LAMOST DR7 is identified, which hasa purity of higher than 90 percent. The RC and the RGB stars are successfullydistinguished through LAMOST spectra(R~1800 and SNR>10) by adopting the XGBoostensemble learning algorithm, and the secondary RC stars are also removed. TheSHapley Additive exPlanations (SHAP) value is used to explain the top featuresthat the XGBoost model selected. The features are around Fe5270, MgH & MgIb,Fe4957, Fe4207, Cr5208, and CN, which can successfully distinguish RGB and RCstars. The XGBoost is also used to estimate the ages and masses of PRC stars bytraining their spectra with Kepler labeled asteroseismic parameters. Theuncertainties of mass and age are 13 and 31 percent, respectively. Verifyingthe feature attribution model, we find the age-sensitive elements XGBoost getsare consistent with the literature. Distances of the PRC stars are derived by$K_{S}$ absolute magnitude calibrated by Gaia EDR3, which has an uncertainty ofabout 6 percent and shows the stars mainly locate at the Galactic disk. We alsotest the XGBoost with R$\sim$250, which is the resolution of the Chinese SpaceStation Telescope(CSST) under construction, it is still capable of findingsensitive features to distinguish RC and RGB.

Identification, mass and age of primary red clump stars from spectral features derived with the LAMOST DR7