Study of 27 Polluted White Dwarfs Observed by LAMOST: Spectral Features, Ages, and Kinematics

We present a comprehensive spectral and kinematic analysis of 27 polluted white dwarfs selected from the catalog of polluted white dwarf candidates by \citep{2024MNRAS.527.4515B}. Using LAMOST DR9 and Gaia DR3 data, we derive the effective temperature ($T_{\mathrm{eff}}$), surface gravity ($\log g$), and radial velocity ($RV$), and measure the Ca\,\textsc{II}\,K line parameters, including equivalent width ($EW_{\mathrm{Ca\,II\,K}}$) and radial velocity ($RV_{\mathrm{Ca\,II\,K}}$). In addition, we estimate cooling ages and determine the three-dimensional Galactic kinematics and orbital parameters. Our results show that the majority of the targets lie above the pure-ISM expectation for the Ca\,\textsc{II}\,K line, suggesting that the line primarily originates from circumstellar material (CSM) rather than the interstellar medium (ISM). For DA-type white dwarfs in our sample, the Ca\,\textsc{II}\,K absorption is more prominent at lower effective temperatures and becomes significantly weaker toward higher temperatures, consistent with previous studies of metal-polluted white dwarfs. Additionally, DA stars show prominent $EW_{\mathrm{Ca\,II\,K}}$ values primarily in the cooling-age bin of $0.9$--$1.4\,\mathrm{Gyr}$, whereas DB stars are concentrated in the $\tau_{\mathrm{cool}} \lesssim 0.5\,\mathrm{Gyr}$ range, with a similar trend of first increasing and then decreasing $EW_{\mathrm{Ca\,II\,K}}$ with cooling age. Kinematic analysis reveals no significant differences between the Galactic populations of DA and DB white dwarfs. These findings indicate that metal pollution is common across different disk components of the Galaxy, with evidence for ongoing or recurrent evolution of white dwarf planetary systems within various Galactic structures.