Phase II of the LAMOST-Kepler/K2 Survey. II. Time Domain of Medium-resolution Spectroscopic Observations from 2018 to 2023

The LAMOST-Kepler/K2 Medium-Resolution Spectroscopic Survey (LK-MRS) conducted time-domain (TD) medium-resolution spectroscopic observations of 20 LAMOST plates in the Kepler and K2 fields from 2018 to 2023, a phase designated as LK-MRS-I. A catalog of stellar parameters for a total of 36,588 stars, derived from the spectra collected during these 5 yr, including the effective temperature, the surface gravity, the metallicity, the α-element abundance, the radial velocity (RV), and vsini of the target stars, is released, together with the weighted averages and uncertainties. At a signal-to-noise ratio = 10, the measurement uncertainties are 120 K, 0.18 dex, 0.13 dex, 0.08 dex, 1.9 km s⁻¹, and 4.0 km s⁻¹ for the above parameters, respectively. Comparisons with the parameters provided by the APOGEE and GALAH surveys validate the effective temperature and surface gravity measurements, showing minor discrepancies in metallicity and α-element abundance values. We identified some peculiar star candidates, including 764 metal-poor stars, 174 very metal-poor stars, and 30 high-velocity stars. Moreover, we found 2333 stars whose RV seems to be variable. Using Kepler/K2 or TESS photometric data, we confirmed 371 periodic variable stars among the RV variable candidates and classified their variability types. LK-MRS-I provides spectroscopic data that is useful for studies of the Kepler and K2 fields. The LK-MRS project will continue collecting TD medium-resolution spectra for target stars during the third phase of LAMOST surveys, providing data to support further scientific research.