DZ White Dwarfs from HETDEX: New Identifications and Reclassifications

Abstract We present 18 DZ white dwarfs, identified by metal absorption features, most prominently the Ca ii H and K lines, from spectroscopic observations in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). Of these objects, 11 are newly spectroscopically confirmed through the detection of Ca ii H and K absorption in the HETDEX spectra ( R ∼ 750). The presence of Ca ii H and K absorption provides a direct spectroscopic signature of atmospheric metal pollution, which is generally interpreted as evidence for the accretion of planetary debris. By crossmatching the continuum-selected objects in the HETDEX Source Catalog with the Gaia eDR3 white dwarf catalog, we recovered 759 white dwarf candidates. Of these, all were visually inspected to account for potential metal-polluted white dwarfs that may fall below the high probability threshold ( P WD ≥ 0.75), resulting in 18 objects showing clear Ca ii H and K absorption. We determine their atmospheric parameters using an iterative fitting procedure that combines HETDEX spectroscopy with multiband photometry from the Galaxy Evolution Explorer (GALEX), Sloan Digital Sky Survey (SDSS), and Pan-STARRS, together with Gaia parallaxes. All 18 objects were misclassified by the automated spectral classifier, demonstrating that visual inspection remains essential for recovering cool, metal-polluted white dwarfs in large spectroscopic surveys. These results highlight the power of combining low-resolution spectroscopy with Gaia astrometry to expand the census of metal-polluted white dwarfs and identify systems for future follow-up studies of planetary debris around evolved stars.