A Study of the Pulsation Properties of 57 Non-Blazhko Ab-type RR Lyrae Stars with Homogeneous Metallicities from the LAMOST-Kepler/K2 Survey

Homogeneous metallicities and continuous high-precision light curves play key roles in studying the pulsation properties of RR Lyrae stars. By cross matching LAMOST DR6 with the Kepler and K2 fields, we have determined seven and 50 non-Blazhko RRab stars, respectively, that have homogeneous metallicities determined from low-resolution spectra of the LAMOST-Kepler/K2 survey. The Fourier decomposition method is applied to the light curves of these stars provided by the Kepler space-based telescope to determine the fundamental pulsation periods and parameters. The calculated amplitude ratios of R (21), R (31) and the phase differences of phi (21), phi (31) are consistent with the parameters of RRab stars in both globular clusters and the Large Magellanic Cloud. We find a linear relationship between the phase differences phi (21) and phi (31), which is in good agreement with the results in the literature. As far as the amplitude, we find that the amplitude of primary frequency A (1) and the total amplitude A (tot) follow either a cubic or linear relationship. For the rise time, we do not find its relevance with the period of the fundamental pulsation mode P-1, or A (tot) and phi (21). However, it might follow a linear relationship with R (31). Based on the homogeneous metallicities, we have derived a new calibration formula for the period-phi (31)-[Fe/H] relation, which agrees well with previous studies.